Abstract
Invasive electrophysiological (EP) testing involves recording a portion of cardiac electrical activity and programmed cardiac electrical stimulation via multipolar catheter electrodes positioned percutaneously strategically at various locations within the cardiac chambers. Electrode catheters come in different sizes and shapes. A variety of multipolar electrode catheters have been developed to facilitate placement of the catheter in the desired place and to fulfill various recording requirements.
Cardiac electrograms are generated by the potential (voltage) differences recorded at two electrodes during the cardiac cycle. Recorded unipolar and bipolar intracardiac electrograms can provide three important pieces of information: (1) the local activation time (i.e., the time of activation of the myocardium immediately adjacent to the recording electrode relative to a reference), (2) the direction of propagation of electrical activation within the field of view of the recording electrode, and (3) the complexity of myocardial activation within the field of view of the recording electrode. Programmed cardiac electrical stimulation provides a method for evaluation of the functional properties of the cardiac tissue and of the means of induction of different arrhythmias. EP testing is used predominantly in patients with suspected or documented cardiac arrhythmias when the precise EP diagnosis is required for management decisions or when catheter ablation is planned. Additionally, EP testing is of value in selected groups of patients for risk stratification of life-threatening arrhythmias.
Keywords
electrophysiological testing, intracardiac electrograms, programmed electrical stimulation, electrode catheters, conduction velocity, refractoriness
Outline
Indications, 81
Periprocedural Management, 81
Preprocedure Evaluation, 81
Consent, 81
Procedural Sedation, 82
Oxygen and Carbon Dioxide Monitoring, 83
Blood Pressure Monitoring, 83
Defibrillator Pads, 83
Urinary Problems, 83
Antiarrhythmic Drugs, 83
Anticoagulation, 83
Catheterization Techniques, 84
Electrode Catheters, 84
Catheter Positioning, 84
Transcaval Approach, 85
Transaortic Approach, 87
Transseptal Approach, 87
Subxiphoid Epicardial Approach, 95
Signal Acquisition and Processing, 101
Analog Versus Digital Recordings, 101
Signal Amplification, 101
Signal Clipping, 101
Signal Filtering, 102
Intracardiac Electrograms, 103
Unipolar Recordings, 103
Bipolar Recordings, 104
Timing of Local Events, 105
Choices of Surface and Intracardiac Signals, 105
Baseline Intervals, 107
P Wave–Atrial Interval, 107
Interatrial Conduction, 108
Atrial–His Bundle Interval, 109
His Potential, 109
His Bundle–Ventricular Interval, 109
Programmed Electrical Stimulation, 109
Atrial Stimulation, 112
Technical Aspects, 112
Normal Response to Rate-Incremental Atrial Pacing, 112
Normal Response to Atrial Premature Stimulation, 114
Repetitive Atrial Responses, 115
Ventricular Stimulation, 115
Technical Aspects, 115
Normal Response to Rate-Incremental Ventricular Pacing, 117
Normal Response to Ventricular Premature Stimulation, 117
Repetitive Ventricular Responses, 118
Miscellaneous Electrophysiological Phenomena, 120
Complications of Electrophysiological Testing, 122
Risks and Complications, 122
Iatrogenic Problems Encountered During Electrophysiological Testing, 123
Indications
Invasive electrophysiological (EP) testing involves recording a portion of cardiac electrical activity and programmed cardiac electrical stimulation via multipolar catheter electrodes positioned percutaneously strategically at various locations within the cardiac chambers. EP testing is used predominantly in patients with suspected or documented cardiac arrhythmias when the precise EP diagnosis is required for management decisions or when catheter ablation is planned. In addition, EP testing is of value in selected groups of patients for risk stratification of life-threatening arrhythmias. The role of EP testing in specific cardiac electrical and structural cardiac diseases is discussed in subsequent chapters.
Periprocedural Management
Preprocedure Evaluation
Heart failure, myocardial ischemia, and electrolyte abnormalities should be treated and adequately controlled before any invasive EP testing is undertaken. Patients with critical aortic stenosis, severe hypertrophic cardiomyopathy, left main or severe three-vessel coronary artery disease, or decompensated heart failure are at higher than average risk of complications. Induction of sustained tachyarrhythmias in these patients can cause rapid and severe hemodynamic deterioration. In addition, assessment of the risks for sedation and anesthesia must be performed prior to the procedure.
Consent
Patients generally are not as familiar with EP procedures as they are with other invasive cardiac procedures such as coronary angiography. Therefore patient education is an essential part of the procedure, and is best delivered in the outpatient setting before the procedure day. The patient should be informed about the value of the EP study, its risks, and the expected outcome. Patients should also have a realistic idea of the benefit that they can derive from undergoing EP studies, including the possibility that the study result can yield negative or equivocal results.
Obtaining an informed consent is an integral part of the procedure and is not only a legal requirement but also an ethical obligation. The discussion should take place out of the procedure room and be in a language that the patient adequately understands. Common risks, even if not considered serious, should be discussed, as should serious risks that are potentially life threatening, even if exceedingly rare. All aspects of the procedure that can be reasonably anticipated should be included in the discussion. Patients should be given ample opportunity to discuss their concerns about the procedure and to have their questions answered satisfactorily.
Procedural Sedation
Some degree of sedation is required in most patients undergoing invasive EP procedures to relieve anxiety, discomfort, and pain. Also, sedation is often necessary to prevent patient movements during long and potentially painful procedures. Patient movement can expose the patient to potential risk during transseptal puncture, pericardial access, or catheter dislocation during ablation in close proximity to critical structures. In addition, large shifts in reconstructed geometry on the electroanatomical map resulting from patient movement can hinder mapping and ablation efforts.
Sedation and anesthetic practices vary dramatically among different institution and operators. There is variation in the selection of patients for sedation or general anesthesia, the personnel administering sedation, the agents employed, and the technique for monitoring sedation.
Several patient factors warrant consultation with an anesthesiologist, such as increased risk for airway obstruction or difficult mask ventilation (e.g., obesity, obstructive sleep apnea, anatomical factors) and high risk for sedation complications (e.g., pulmonary disease, heart failure, hemodynamic instability, psychiatric or neuromuscular disorders, previous problems with anesthesia or sedation, and medication or substance use that complicates the administration of sedative agents, such as chronic opioid or benzodiazepine use, alcohol abuse).
Types of Anesthesia
The anesthetic plan must be individually tailored, depending on the nature of procedure, patient characteristics, hospital resources, patient preference, and anesthesia skill/training of the EP team. Furthermore, changes in the level of sedation and in the type of drugs used can be necessary during the course of the procedure and must be aligned with the needs of the interventional procedures. For example, the optimal degree of anesthesia may vary from minimal (during induction of arrhythmias) to deep (during painful ablation or electrical cardioversion). Also, the anesthesiologist should be asked to avoid or minimize nondepolarizing muscle relaxants when the evaluation of phrenic nerve function is required during ablation. Therefore close communication and collaboration between the electrophysiologists and anesthesia providers are crucial to perform EP procedures safely and successfully.
One of following anesthesia techniques or their combinations may be used: (1) local anesthesia at the site of vascular access; (2) conscious (moderate) sedation with intravenous (IV) sedatives; (3) deep sedation with IV sedatives; and (4) general anesthesia.
Local anesthesia.
Infiltration of the site of vascular access with local anesthetics is commonly used. Lidocaine is the local anesthetic of choice given its fast onset of action and safety profile. Bupivacaine offers longer periods of analgesia after procedure completion, but it is not preferred due to its cardiac toxicity. Local anesthesia may be preferred to IV sedation when arrhythmia induction is expected to be adversely affected by sedation (e.g., automatic or triggered-activity tachycardias). This approach requires a well-informed and cooperative patient who can cope with lying still during the procedure. Of note, injecting large amounts of lidocaine can result in systemic levels that might affect arrhythmia induction.
Conscious sedation.
Mild to moderate conscious sedation, in conjunction with local anesthesia, is utilized in most EP procedures. The combination of a benzodiazepine and a narcotic are typically used to provide analgesia, sedation, and amnesia. Midazolam and fentanyl are preferred because of their rapid onset, titratability, reversibility, and very wide therapeutic window.
It is important to recognize that sedation and general anesthesia are part of a continuum, and there is a danger of patients unintentionally slipping into anesthesia with the loss of spontaneous ventilation, requiring immediate airway intervention. The transition from moderate to deeper levels of sedation can occur suddenly and unexpectedly. In fact, oversedation, loss of airway, necessity of airway intervention, or conversion to general anesthesia is reported to occur in 40% of non–general anesthesia EP procedures. Therefore even when mild to moderate levels of sedation are targeted with only benzodiazepine and narcotics, the electrophysiologist and EP staff performing the procedure must be knowledgeable and trained to promptly recognize and treat sedation-related adverse events in the absence of a specialist anesthesiologist. Hence, some operators prefer to have anesthesia providers (anesthesiologists or nurse anesthetists working with anesthesiologists) provide monitored anesthesia care (MAC) during such procedures, especially given the fact that an unplanned need for deep sedation (e.g., for electrical cardioversion of induced atrial fibrillation [AF] or ventricular tachycardia [VT]) or unpredicted complications (e.g., cardiac perforation, worsening heart failure) not infrequently arise during the course of the procedure. The latter approach allows the electrophysiologist to focus solely on the technical aspects of the procedure and share the responsibility for the patient with the anesthesia care team. The decision to involve an anesthesiologist ideally should be made before the start of the procedure. The practice of calling the anesthesia team only as needed during the course of the procedure to provide deeper levels of sedation or to rescue a deteriorating patient or manage airway emergencies is suboptimal for patient care and is not recommended.
Deep sedation.
Deep levels of sedation can be required for longer procedures, such as for AF or VT ablation, and during electrical cardioversion. Deep sedation is administered under the supervision of an anesthesiologist. Although the combination of midazolam and fentanyl is commonly utilized, the use of propofol for cardiac procedures has recently been reported in several large series. Propofol has rapid onset and offset of action and an excellent safety profile; however, it also has profound respiratory depressant actions as well as vasodilatory and myocardial depressant effects, which can cause hypotension, particularly when used with other anesthetics. Propofol offers significant advantages over benzodiazepines, including more rapid induction, better acute intraprocedural control of sedation level, and more rapid recovery. Continuous infusions of IV sedatives are preferred to repeated boluses to avoid waxing and waning levels of consciousness.
Other options include a low dose of ketamine or etomidate. Ketamine has minimal respiratory and stimulatory effects on blood pressure and heart rate, a significant advantage in patients with preexisting hypotension or bradycardia. Etomidate also has a stable hemodynamic profile but a high incidence of transient myoclonus and nausea.
When deep sedation is required for only a brief period (e.g., for direct current cardioversion), IV anesthetics (such as methohexital, propofol, or etomidate) may be considered.
General anesthesia.
General anesthesia has increasingly been used for complex EP procedures. Advantages of general anesthesia include optimal airway management, pain control, and patient immobilization, as well as enhanced tolerance of esophageal temperature probes. However, this requires the additional expense and time of a dedicated anesthetic team in the laboratory, and turn around between patients is prolonged by induction of anesthesia and recovery. In addition, the use of general anesthesia is associated with an increased risk of trauma during intubation and esophageal complications, as well as the delay in recognition of and intervention for thromboembolic complications. Furthermore, general anesthetics can suppress inducibility of various arrhythmias or render them hemodynamically unstable by the abolition of sympathetic tone for compensatory vasoconstriction.
Propofol or etomidate is commonly used for induction. Midazolam is often administered to patients upon arrival in EP laboratory for its anxiolytic and amnesic effects. Rocuronium is a preferred muscle relaxant to facilitate the intubation. Anesthesia is usually maintained by an inhalation agent (nitrous oxide, isoflurane, sevoflurane, or desflurane), combined with IV narcotics. Importantly, if there is concern about phrenic nerve stimulation or injury, the anesthesiologist should be asked to avoid or minimize nondepolarizing muscle relaxants to verify the preservation of diaphragmatic function.
Jet Ventilation
Using high-frequency ventilation during general anesthesia decreases the regular chest wall motion associated with standard mechanical ventilation, thus minimizing respiration-related cardiac movement. Recent data suggest that the use of jet ventilation in the EP laboratory can enhance catheter stability during mapping and ablation and potentially improve the efficacy and safety of the ablation procedure, especially when a stable field needs to be established.
On the other hand, several disadvantages of high-frequency jet ventilation have been reported, including the lack of airtight sealing of airway to decrease secretions, the inability to use inhaled anesthesia, and the difficult measurement of resulting ventilator parameters and efficiency of gas exchange. Furthermore, the risk of barotrauma (e.g., volutrauma, pneumothorax, mediastinal emphysema) is increased, especially in patients with chronic obstructive pulmonary disease. Mucosal damage, especially necrotizing tracheobronchitis, has been reported, and can be prevented by adequate humidification of the ventilator circuit.
Electrophysiological Effects of Anesthetic Medications
The exact influences anesthetics have on cardiac EP in the clinical setting are not entirely certain. In general, sedation of any kind decreases endogenous catecholamine release, potentially suppressing arrhythmic activity, which can impede the mapping and ablation procedure. Nonetheless, some anesthetics (e.g., ketamine) induce sympathetic stimulation, which can potentially facilitate or induce arrhythmias.
Benzodiazepines reduce blood pressure by decreasing peripheral vascular resistance leading to reflex tachycardia. Opioids, especially at high doses, have a central vagotonic effect with resultant bradycardia. Propofol can trigger vagally mediated bradycardia and inhibit spontaneous ventricular arrhythmias.
Inhalational anesthetics enhance automaticity of latent atrial pacemakers relative to the sinus node, promoting ectopic atrial rhythms and wandering atrial pacemakers. In addition, these agents demonstrate varying effects on the atrioventricular node (AVN) and His-Purkinje system (HPS). Isoflurane prolongs the atrial refractory period and delays ventricular repolarization, but the clinical significance of these effects appears minimal.
Neuromuscular relaxants modulate autonomic tone; some agents can precipitate vasodilatation and reflex tachycardia while others can cause bradycardia, particularly if used in combination with other vagotonic drugs. Ketamine can increase heart rate and blood pressure by increasing central sympathetic outflow. Also, ketamine is a direct myocardial depressant.
Oxygen and Carbon Dioxide Monitoring
Continuous pulse-oximetry to monitor oxygen saturation is mandatory. Supplemental oxygen is generally administered to help prevent arterial desaturation and to increase the margin of safety during sedation. End-tidal CO 2 monitoring (capnography) is a noninvasive method for monitoring respiratory rate and pattern and can help detect airway obstruction and hypoventilation, and is recommended during cases involving moderate and deep sedation and general anesthesia. Monitoring oxygen saturation alone can be misleading, especially in patients receiving supplemental oxygen. The elevated baseline arterial oxygen concentration allows a longer period of apnea to ensue before arterial desaturation falls low enough to prompt airway intervention. Capnography, on the other hand, provides instantaneous information about ventilation, perfusion, and metabolism.
Blood Pressure Monitoring
Accurate monitoring of blood pressure is vital. Noninvasive automated cuff blood pressure devices are usually adequate in most EP procedures performed under minimal or moderate sedation. Invasive arterial pressure monitoring should be considered for unstable patients, those with severely compromised cardiac function, when periods of deep sedation are expected or planned, and during procedures with higher risk of complications with serious hemodynamic consequences (e.g., procedures involving transseptal left atrium [LA] access, scar-related VT ablation).
Defibrillator Pads
A functioning cardioverter-defibrillator should be available at the patient’s side throughout the EP study. Using preapplied adhesive defibrillator pads is preferred to avoid disrupting the sterile field in the event that electrical defibrillation or cardioversion is needed during the procedure. Biphasic devices are more effective than devices with monophasic waveforms.
Urinary Problems
Urinary retention can occur during lengthy EP procedures, particularly in combination with sedation, fluid administration, and tachycardia-related diuresis. When such situations are anticipated, it is useful to insert a urinary drainage catheter before the procedure.
Antiarrhythmic Drugs
Antiarrhythmic drugs are usually, but not always, stopped for at least five half-lives prior to EP testing. In selected cases, antiarrhythmic drugs can be continued if an arrhythmic event occurred while the patient was taking a specific agent.
Anticoagulation
Therapeutic levels of oral anticoagulation for 4 weeks before the procedure or transesophageal echocardiography (TEE) (to exclude the presence of intracardiac thrombus) are required before studying patients who have persistent AF and atrial flutter (AFL) who may have sinus rhythm restored intentionally or inadvertently (i.e., cardioversion of VT).
Periprocedural anticoagulation for catheter ablation of persistent AFL or AF is necessary to minimize thromboembolic stroke risk; LA stunning and increased spontaneous echo contrast within the LA can occur following cardioversion or ablation of these arrhythmias. Similarly, patients with a mechanical valvular prosthesis require uninterrupted anticoagulation.
A perception of increased bleeding risks of invasive procedures in patients taking therapeutic doses of oral anticoagulants led many operators to adopt a “bridging” strategy of conversion to enoxaparin to allow ablation and subsequent hemostasis to be performed during a pause in anticoagulation. An alternative strategy of uninterrupted oral anticoagulation during these procedures was found to be safe and feasible and more cost-effective for ablation of typical AFL or AF, without increasing hemorrhagic complications. This anticoagulation strategy can potentially be used routinely for EP studies and ablation of other arrhythmias when interruption of anticoagulation poses a significant risk.
Anticoagulation with heparin (or bivalirudin in patients allergic to heparin) is necessary for all left heart procedures, even in patients on uninterrupted oral anticoagulation. For right heart procedures, there is no evidence favoring routine use of anticoagulation, unless in individual patients at particularly high risk for thromboembolism.
Catheterization Techniques
Electrode Catheters
Electrode catheters are used during EP testing for recording and pacing. These catheters consist of insulated wires; at the distal tip of the catheter, each wire is attached to an electrode, which is exposed to the intracardiac surface. At the proximal end of the catheter, each wire is attached to a plug, which can be connected to an external recording device. Electrode catheters are generally made of woven Dacron or newer synthetic materials, such as polyurethane. The Dacron catheters have the advantage of stiffness, which helps maintain catheter shape with enough softness at body temperature to allow formation of loops. Catheters made of synthetic materials cannot be easily manipulated and change shape within the body, but they are less expensive and can be made smaller. Some manufacturers use braided metal strands to enhance torque control.
Electrode catheters come in different sizes (3 to 8 Fr). In adults, sizes 5, 6, and 7 Fr catheters are the most commonly used. Recordings derived from electrodes can be unipolar (one pole) or bipolar (two poles). The electrodes are typically 1 to 2 mm in length. The interelectrode distance can range from 1 to 10 mm or more; catheters with a 2- or 5-mm interelectrode distance are most commonly used.
Many multipolar electrode catheters have been developed to facilitate placement of the catheter in the desired place and to fulfill various recording requirements. Bipolar or quadripolar electrode catheters are used to record and pace from specific sites of interest within the atria or ventricles. These catheters come with a variety of preformed distal curve shapes and sizes ( eFig. 4.1 ). Multipolar recording electrode catheters are placed within the coronary sinus (CS) or along the crista terminalis in the right atrium (RA). The Halo catheter is a multipolar catheter used to map atrial electrical activity around the tricuspid annulus during atrial tachycardias, as well as for locating right-sided bypass tracts (BTs) ( Fig. 4.1 ). A multipolar catheter with a distal ring configuration is used to record electrical activity from the pulmonary veins (PVs) ( Fig. 4.2 ). The star-shaped multielectrode PentaRay is a 7 Fr steerable catheter with 20 electrodes distributed over 5 soft, radiating spines, allowing for rapid and high-density mapping (see Fig. 4.2 ). Basket catheters capable of conforming to the chamber size and shape have also been used for mapping atrial and ventricular arrhythmias ( Fig. 4.3 ). Special catheters are also used to record LA and left ventricular (LV) epicardial activity from the CS branches.
Catheters can have a fixed or deflectable tip. Steerable catheters allow deflection of the tip of the catheter in one or two directions in a single plane; some of these catheters have asymmetrical bidirectional deflectable curves ( eFig. 4.2 ).
Ablation catheters have tip electrodes that are conventionally 4 mm long and are available in sizes up to 10 mm in length ( eFig. 4.3 ). The larger tip electrodes on ablation catheters reduce the resolution of a map obtained using recordings from the distal pair of electrodes.
Catheter Positioning
The percutaneous technique is used almost exclusively. RA, His bundle (HB), and right ventricular (RV) electrograms are most commonly recorded using catheters inserted via a femoral vein. Some other areas (e.g., the CS) are more easily reached through the superior vena cava (SVC), although the femoral approach can be adequate in most cases. Insertion sites can also include the internal jugular and subclavian veins. Femoral arterial access can be required for mapping of the LV or mitral annulus or for invasive blood pressure monitoring. Occasionally, an epicardial approach is required to map and ablate certain VTs and BTs as well as the sinus node. For this purpose, the epicardial surface is accessed via the CS and its branches or percutaneously (subxiphoid puncture).
Fluoroscopy is conventionally used to guide intracardiac positioning of the catheters. It is important to remember that catheters can be withdrawn without fluoroscopy (an exception being when permanent pacemaker or implantable cardioverter-defibrillator [ICD] leads are in place), but they should always be advanced under fluoroscopic guidance. More recently, newer navigation systems have been tested to guide catheter positioning in an effort to limit radiation exposure ( see Chapter 6 ).
Transcaval Approach
The modified Seldinger technique is used to obtain multiple venous accesses. The femoral approach is most common, but the subclavian, internal jugular, or brachial approaches may be used, most often for the placement of a catheter in the CS.
Ultrasound guidance is recommended for cannulation of the internal jugular veins. Recent studies have also shown potential benefit of ultrasound-guidance for femoral vein puncture in reducing vascular complications, particularly in the setting of anticoagulation. Ultrasound imaging allows direct visualization of peripheral arterial and venous anatomy and assessment of variations in the spatial relationship between the common femoral vein and the adjacent common femoral artery.
The femoral access should be avoided in patients with any of the following: known or suspected femoral vein or inferior vena cava (IVC) thrombosis, active lower extremity thrombophlebitis or postphlebitic syndrome, groin infection, bilateral leg amputation, extreme obesity, or severe peripheral vascular disease resulting in nonpalpable femoral arterial pulse. IVC umbrella filters are not necessarily a contraindication to the femoral approach.
Typically, the RA, HB, and RV catheters are introduced via the femoral veins. It is advisable to use the left femoral vein for diagnostic EP catheters and to save the right femoral vein for potential ablation or mapping catheter placement, which then would be easier to manipulate because it would be on the side closer to the operator. Multiple venous punctures and single vascular sheaths may be used for the different catheters. Alternatively, a single triport 12 Fr sheath can be used to introduce up to three EP catheters (usually the RA, HB, and RV catheters). The CS catheter is frequently introduced via the right internal jugular or subclavian vein, but also via the femoral approach.
Right Atrial Catheter
A fixed-tip, 5 or 6 Fr quadripolar electrode catheter is typically used. The RA may be entered from the IVC or SVC. The femoral veins are the usual entry sites. Most commonly, stimulation and recording from the RA is performed by placing the RA catheter tip at the high posterolateral wall at the SVC-RA junction in the region of the sinus node or in the RA appendage ( Fig. 4.4 ).
Right Ventricular Catheter
A fixed-tip, 5 or 6 Fr quadripolar electrode catheter is typically used. All sites in the RV are accessible from any venous approach. The RV apex is most commonly chosen for stimulation and recording because of stability and reproducibility (see Fig. 4.4 ).
His Bundle Catheter
A fixed- or deflectable-tip, 6 Fr quadripolar electrode catheter is typically used. The catheter is passed via the femoral vein into the RA and across the tricuspid annulus until it is clearly in the RV (under fluoroscopic monitoring, using the right anterior oblique [RAO] view) (see Fig. 4.4 ). It is then withdrawn across the tricuspid orifice while maintaining a slight clockwise torque for good contact with the septum until a His potential is recorded. Initially, a large ventricular electrogram can be observed; then, as the catheter is withdrawn, the right bundle (RB) potential can appear (manifesting as a narrow spike less than 30 milliseconds before the ventricular electrogram). When the catheter is further withdrawn, the atrial electrogram appears and grows larger. The His potential usually appears once the atrial and ventricular electrograms are approximately equal in size and is manifest as a biphasic or triphasic deflection interposed between the local atrial and ventricular electrograms. If the first pass was unsuccessful, the catheter should be passed again into the RV and withdrawn with a slightly different rotation. If, after several attempts, a His potential cannot be recorded using a fixed-tip catheter, the catheter should be withdrawn and reshaped, or it may be exchanged with a deflectable-tip catheter. Once the catheter is in place, a stable recording can usually be obtained. Occasionally, continued clockwise torque on the catheter shaft is required to obtain a stable HB recording, which can be accomplished by looping the catheter shaft remaining outside the body and fixing the loop by placing a couple of towels on it, or by twisting the connection cable in the opposite direction so that it maintains a gentle torque on the catheter.
When the access is from the SVC, it is more difficult to record the His potential because the catheter does not lie across the superior margin of the tricuspid annulus. In this case, a deflectable-tip catheter is typically used, advanced into the RV, positioned near the HB region by deflecting the tip superiorly to form a J shape, and then withdrawing the catheter so that it lies across the superior margin of the tricuspid annulus. Alternatively, the catheter can be looped in the RA (“figure-of-6” position); then the body of the loop is advanced into the RV so that the tip of the catheter is pointing toward the RA and lying on the septal aspect of the RA. Gently withdrawing the catheter can increase the size of the loop and allow the catheter tip to rest on the HB location.
Recording of the HB electrogram can also be obtained via the retrograde arterial approach. Using this approach, the catheter tip is positioned in the noncoronary sinus of Valsalva (just above the aortic valve) or in the left ventricular outflow tract (LVOT), along the interventricular septum (just below the aortic valve).
Coronary Sinus Catheter
A femoral, internal jugular, or subclavian vein can be used to access the CS. It is easier to cannulate the CS using the right internal jugular or left subclavian vein versus the femoral vein because the CS valve is oriented anterosuperiorly and, when prominent, can prevent easy access to the CS from the femoral venous approach. A fixed-tip, 6 Fr decapolar electrode catheter is typically used for access from the SVC, whereas a deflectable-tip catheter is preferred for CS access from the femoral veins.
The standardized RAO and left anterior oblique (LAO) fluoroscopic views are used to guide placement of catheters in the CS. Although the CS cannot be directly visualized with standard fluoroscopy, the epicardial fat found in the posteroseptal space just posterior to the CS ostium (os) can be visualized as a characteristic radiolucency on cine fluoroscopy in the RAO projection, where the cardiac and diaphragmatic silhouettes meet.
When cannulating the CS from the SVC approach, the LAO view is used, the catheter tip is directed to the left of the patient, and the catheter is advanced with some clockwise torque to engage the CS os; electrodes should resemble rectangles rather than ovals when the catheter tip is properly oriented to advance into the CS. Once the CS os is engaged, the catheter is further advanced gently into the CS, so that the most proximal electrodes lie at the CS os (see Fig. 4.4 ).
During cannulation of the CS from the IVC approach, the tip of the catheter is first placed into the RV, in the RAO fluoroscopy view, and flexed downward toward the RV inferior wall. Subsequently, the catheter is withdrawn until it lies at the inferoseptal aspect of the tricuspid annulus. In the LAO or RAO view, the catheter is then withdrawn gently with clockwise rotation until the tip of the catheter drops into the CS os. Afterward, the catheter is advanced into the CS concomitantly with gradual release of the catheter curve ( Fig. 4.5 ). Alternatively, the tip of the catheter is directed toward the posterolateral RA wall and advanced with a tight curve to form a loop in the RA, in the LAO view, with the tip directed toward the inferomedial RA. The tip is then advanced with gentle up-down, right-left manipulation using the LAO and RAO views to cannulate the CS. In the RAO view, the atrioventricular (AV) fat pad (containing the CS) appears as more radiolucent than surrounding heart tissue.
When attempting CS cannulation, the catheter can enter the RV, and premature ventricular complexes (PVCs) or VT can be observed. Catheter position in the right ventricular outflow tract (RVOT) can be misleading and simulate a CS position. Confirming appropriate catheter positioning in the CS can be achieved by fluoroscopy and recorded electrograms. In the LAO view, further advancement in the CS directs the catheter toward the left heart border, where it curves toward the left shoulder. Conversely, advancement of a catheter lying in the RVOT leads to an upward direction of the catheter toward the pulmonary artery. In the RAO view, the CS catheter is directed posteriorly, posterior to the AV sulcus, whereas the RVOT position is directed anteriorly. Recording from the CS catheter shows simultaneous atrial and ventricular electrograms, with the atrial electrogram falling in the later part of the P wave, whereas a catheter lying in the RVOT records only a ventricular electrogram. The catheter can also pass into the LA via a patent foramen ovale, in which case it takes a straight course toward the left shoulder, and all recordings are atrial.
If used, the CS catheter should be placed first because its positioning can be impeded by the presence of other catheters. It is also recommended that the CS catheter sheath be sutured to the skin to prevent displacement of the catheter during the course of the EP study.
Transaortic Approach
This approach is generally used for mapping the LV and mitral annulus (for VT and left-sided BTs). The right femoral artery is most commonly used. The mapping-ablation catheter is passed to the descending aorta. If any resistance to catheter advancement occurs, it should not be forced; the tip can be withdrawn a few centimeters, deflected and torqued slightly, and another attempt made at advancing it. If several attempts do not allow access to the descending aorta, this approach should be abandoned, since even if one is able to manipulate the catheter through tortuous vessels, torque control of the tip within the LV is likely to be severely restricted. A solution is use of a long vascular sheath; the catheter is removed from the short sheath, and a long guidewire placed in it to ascertain if it passes smoothly into the distal aorta. If so, a long sheath can be advanced over the guidewire and the catheter can then be safely passed through the sheath into the aorta. If access to the aorta via the right femoral artery is impossible or unsafe, the left femoral artery can be used.
Once the catheter tip is in the central aorta, movement proximally toward the heart is usually relatively smooth (although side branches and atheromas can be encountered). In this position, a tight J curve is formed with the catheter tip before passage to the aortic root to minimize catheter manipulation in the arch. In a 30-degree RAO view, the curved catheter is advanced through the aortic valve with the J curve opening to the right, so the catheter passes into the LV oriented anterolaterally ( eFig. 4.4 ). The straight catheter tip must never be used to cross the aortic valve because of the risk of leaflet damage or perforation and also because the catheter tip can slip into the left or right coronary artery or a coronary bypass graft, thus mimicking entry to the LV and causing damage to these structures.
In addition to facilitating catheter passage through a tortuous iliac artery, the use of a long sheath (e.g., SL0 or SL1; 81 cm; St. Jude Medical, St. Paul, MN, United States), with the tip of the sheath placed through the aortic valve into the LV, can provide added catheter stability and limit catheter dislodgement out of the LV.
Anticoagulation with IV heparin should be started once the LV is accessed or before, to maintain the activated clotting time (ACT) between 250 and 350 seconds.
Transseptal Approach
The atrial transseptal atrial approach is utilized for mapping and ablation in the LA and has also been increasingly used for accessing the LV. A search for a patent foramen ovale, which is present in 15% to 20% of normal subjects, is initially performed by probing the septum from the inferior approach. If no opening is found, atrial septal puncture is performed. Several approaches have been described to achieve a safe and successful transseptal puncture. The challenge for a successful atrial septal puncture is positioning the Brockenbrough needle at the thinnest aspect of the atrial septum, the membranous fossa ovalis, guided by fluoroscopy or intracardiac echocardiography (ICE).
Anatomical Considerations
Knowledge of septal anatomy and its relationship with adjacent structures is essential to ensure safe and effective access to the LA. Many apparent atrial septal structures are not truly septal. The true interatrial septum is limited to the floor of the fossa ovalis (primary septum), the flap valve, and the anteroinferior rim of the fossa. Therefore the floor of the fossa (with an average diameter of 18.5 ± 6.9 mm [vertically] and 10.0 ± 2.4 mm [horizontally] and 1 to 3 mm in thickness) is the target for atrial septal crossing ( Fig. 4.6 ). The area between the superior border of the fossa and the mouth of the SVC is an infolding of the atrial musculature filled with adipose tissue (corresponding to the pericardial transverse sinus and the anterosuperior interatrial groove). Although this area is often described incorrectly as the “septum secundum,” it is not really a true septum, and puncture in this region would lead to exiting the heart. The infolded groove ends at the superior margin (superior rim) of the fossa ovalis. The anteroinferior muscular buttress anchors the primary septum to the muscular ventricular septum and attaches to the central fibrous body (which is composed of the right fibrous trigone and the AV portion of the membranous septum) just beneath the noncoronary aortic sinus. Anterior and superior to the fossa ovalis, the RA wall overlies the aortic root. Advancing the transseptal needle in this area can puncture the aorta.
Understanding the attitudinal anatomical relationships of the atrial septum and adjacent structures as well as the fluoroscopic anatomy based on conventional landmarks is critical for a safe and successful transseptal puncture procedure. When the heart is viewed in an attitudinally correct orientation (as it lies within the chest), the RA lies rightward and anterior, while the LA lies posterior, leftward, and slightly superior in relation to the RA. The aortic root runs along the anterior aspect of the interatrial septum ( Fig. 4.7 ). The fossa ovalis is located inferior and posterior relative to the noncoronary aortic sinus, and posterior to the triangle of Koch. The plane of the interatrial septum is slanted from left anterior to right posterior, with a mean orientation of 37 degrees, but can vary from 19 to 53 degrees. The orientation of the atrial septum orientation was found to strongly correlate with the direction of the CS, despite a wide range of variability in our patient population. Hence, typically the interatrial septum is almost perpendicular to the plane of the screen in the LAO 50- to 60-degree projection angle, and horizontal in the RAO 30- to 40-degree projection angle. However, adjustment of the RAO and LAO projection angles can be required to account for rotation of the interatrial septum observed in some patients. This can be facilitated by aligning the RAO projection to an angle where the proximal part of CS catheter lies perpendicular to the screen or a His recording catheter is pointing directly toward the screen.
Anticoagulation
Anticoagulation is essential for prevention of thromboembolism during any left-sided heart catheterization. Current recommendations advocate that IV heparin bolus be administered immediately after or, preferably, just before puncturing the atrial septum, followed by intermittent boluses or continuous heparin infusion to maintain an elevated ACT (300 to 400 seconds), even in patients on uninterrupted therapeutic doses of oral anticoagulation. However, recent evidence found that unfractionated heparin displays unexpected slow anticoagulation kinetics in a significant proportion of patients for up to 20 minutes after infusion (reflected in ACTs less than 300 seconds). Hence, some investigators have suggested administering IV heparin at least 10 minutes before transseptal puncture and assessing ACT at 10 minutes with an additional unfractionated heparin infusion in patients with subtherapeutic ACT.
Fluoroscopy-Guided Transseptal Catheterization
Equipment required for atrial septal puncture includes the following: an 8 Fr transseptal sheath for LA cannulation (e.g., SR0, SL series, Mullins, or Agilis NxT Steerable sheath, St. Jude Medical, Minnetonka, MN, United States), a 0.032-inch J guidewire, a Brockenbrough needle (e.g., BRK, St. Jude Medical), and a 190-cm, 0.014-inch guidewire. The transseptal sheaths and Brockenbrough needles are available in two different lengths; it is important to ensure that the length of needle matches that of the sheath.
Venous access is obtained via the femoral vein, preferably the right femoral vein because it is closer to the operator. The sheath, dilator, and guidewires are flushed with heparinized saline. The transseptal sheath-dilator assembly is advanced over a 0.032-inch J guidewire under fluoroscopy guidance into the SVC (to the level of the tracheal carina). The guidewire is then withdrawn, thus leaving the sheath and its dilator locked in place. The dilator within the sheath is flushed and attached to a syringe to avoid introduction of air into the RA.
Attention is then directed to preparing the transseptal needle. The Brockenbrough needle comes prepackaged with an inner stylet, which may be left in place to protect it as it is advanced within the sheath. Alternatively, the inner stylet may be removed and the needle connected to a pressure transducer line (pressure monitoring through the Brockenbrough needle will be required during the transseptal puncture); continuous flushing through the Brockenbrough needle is used while advancing the needle into the dilator. A third approach, when the use of contrast injection is planned, is to attach the Brockenbrough needle to a standard three-way stopcock via a freely rotating adapter. A 10-mL syringe filled with radiopaque contrast is attached to the other end of the stopcock while a pressure transducer line is attached to the third stopcock valve for continuous pressure monitoring. The entire apparatus should be vigorously flushed to ensure that no air bubbles are present within the circuit.
Before making an attempt at puncturing the atrial septum, it is important to ensure that all equipment is working properly, especially the pressure transducer attached to the needle. If this detail is not attended to prior to the septal puncture attempt, it becomes difficult to interpret a flat pressure tracing when the needle tip is supposedly in the LA cavity. This may mean the needle is in fact in the LA but the stopcock on the pressure tubing is turned incorrectly, or that the wrong tubing was connected to the needle hub, or that the needle tip is not in the LA. Assuring that the pressure system is working properly by “flicking” the needle shaft and seeing its corresponding pressure reverberation waveform obviates uncertainty as to whether the connections are correct. In addition, taking note of baseline blood pressure and appearance of the left heart border on fluoroscopy are important for reference; unanticipated decreases in blood pressure or decreased motion of the left heart border, compared to baseline, may be early clues to a developing pericardial effusion.
Engaging the fossa ovalis.
The Brockenbrough needle is advanced into the dilator until the needle tip is within 1 to 2 cm of the dilator tip. The needle tip must be kept within the dilator at all times, except during actual septal puncture. This can be ensured by holding the sheath-dilator assembly by the left hand, and holding the needle by the right hand, while minding a safe distance of the proximal needle hub from the dilator. The curves of the dilator, sheath, and needle (as indicated by the side port of the sheath and the pointer on the proximal hub of the needle) should be aligned so that they are all in agreement and not contradicting each other. The sheath, dilator, and needle assembly is then rotated leftward and posteriorly (usually with the Brockenbrough needle arrow pointing at the 3 to 6 o’clock position relative to its shaft) and retracted caudally as a single unit (while maintaining the relative positions of its components) to engage the tip of the dilator into the fossa ovalis. Under fluoroscopy monitoring (30-degree LAO view), the dilator tip moves slightly leftward on entering the RA and then leftward again while descending below the aortic root. A third abrupt leftward movement (“jump”) below the aortic root indicates passage over the limbus into the fossa ovalis ( Fig. 4.8 ). This jump generally occurs at the level of the HB region (marked by an EP catheter recording the HB potential). If the sheath and dilator assembly is pulled back farther than intended (i.e., below the level of the fossa and HB region), the needle should be withdrawn and the guidewire placed through the dilator into the SVC. The sheath and dilator assembly is then advanced over the guidewire into the SVC and repositioning attempted, as described earlier. The sheath and dilator assembly should never be advanced without the guidewire at any point during the procedure.
Confirming position at the fossa ovalis.
Several fluoroscopic markers are used to confirm the position of the dilator tip at the fossa ovalis. As noted, an abrupt leftward movement (jump) of the dilator tip below the aortic knob is observed (in the LAO view) as the tip passes under the muscular atrial septum onto the fossa ovalis. In addition, the posterior extent of the aortic root can be marked by a pigtail catheter positioned through the femoral artery in the noncoronary cusp or by the HB catheter (recording a stable proximal HB potential), which lies at the level of the fibrous trigone opposite and caudal to the noncoronary aortic cusp. When the dilator tip lies against the fossa ovalis, it is directed posteroinferiorly to the proximal HB electrode (or pigtail catheter) in the RAO view and to the left of the proximal HB electrode (or pigtail catheter) in the LAO view (see Fig. 4.8 ). Another method that can be used to ensure that the tip is against the fossa ovalis is injection of 3 to 5 mL of radiopaque contrast through the Brockenbrough needle to visualize the interatrial septum. The contrast stains the fossa and the needle tip then can be seen tenting the fossa ovalis membrane with small movements of the entire transseptal apparatus. Typically, septal staining remains visible after contrast injection, which allows for real-time septal visualization while monitoring the pressure during transseptal puncture.
Puncturing the septum.
Once the position of the dilator tip is confirmed at the fossa ovalis, the sheath-dilator-needle assembly is pushed slightly against the interatrial septum, and the needle is then briskly advanced to protrude outside the dilator in the LAO view during continuous pressure monitoring. If excessive force is applied without a palpable “pop” to the fossa, then the Brockenbrough needle likely is not in proper position. Occasionally, pushing the sheath-dilator-needle assembly against the fossa ovalis results in sliding of the whole assembly up the interatrial septum rather than tenting of the fossa ovalis. Increasing the “reach” of the transseptal needle tip by curving the shaft 15 to 20 back from the tip (achieved by manual adjustment) or of the sheath (when a deflectable transseptal sheath is utilized) can help mitigate this problem.
Confirming position in the LA.
After passage through the fossa ovale and before advancing the dilator and sheath, an intraatrial position of the needle tip within the LA, rather than the ascending aorta or posteriorly into the pericardial space, needs to be confirmed. Recording an LA pressure waveform from the needle tip confirms an intraatrial location ( Fig. 4.9 ). An arterial pressure waveform indicates intraaortic position of the needle. Absence of a pressure wave recording can indicate needle passage into the pericardial space or sliding up and not puncturing through the atrial septum. A second method is injection of contrast through the needle to assess the position of the needle tip. Opacification of the LA (rather than the pericardium or the aorta) verifies the successful transseptal access. Alternatively, passing a 0.014-inch floppy guidewire through the Brockenbrough needle into a left-sided PV (beyond the cardiac silhouette in the LAO fluoroscopy view) helps verify that needle tip position is within the LA. If the guidewire cannot be advanced beyond the fluoroscopic border of the heart, atrial free-wall puncture with pericardial needle location should be suspected. In addition, aortic puncture should be suspected if the guidewire seems to follow the course of the aorta. In these situations, contrast should be injected to assess the position of the Brockenbrough needle before advancing the transseptal dilator. Sometimes, the guidewire enters the LA appendage rather than a PV; in this setting, a clockwise torque of the sheath and dilator assembly can help direct the guidewire posteriorly toward the ostium of the left superior or left inferior PV.
Once the position of the needle tip is confirmed to be in the LA, both the sheath and dilator are advanced as a single unit over the needle by using one hand while fixing the Brockenbrough needle in position with the other hand (to prevent any further advancement of the needle). Preferably, the sheath-dilator assembly is advanced into the LA over a guidewire placed distally into a left-sided PV, which helps direct the path of the assembly as it enters the LA and minimize the risk of inadvertent puncture of the LA free wall, especially in the presence of an elastic or redundant septum that can suddenly release, resulting in a significant forward lurch of the dilator and sheath. Once the dilator tip is advanced into the LA over the needle tip, the needle and dilator are firmly stabilized as a unit—to prevent any further advancement or withdrawal of the needle and dilator—and the sheath is advanced over the dilator into the LA. It is important to keep the needle across the septum at this time to facilitate advancement of the sheath through the puncture site. In some cases, the septum is very stiff (after prior transseptal procedures, especially) and attempts to advance the sheath into the LA result in bowing of the assembly in the RA, risking “backing out” of the dilator from the LA. In such cases, rotating the entire apparatus such that the dilator points toward the head or right superior PV can facilitate passage of the sheath through the septum, since the pushing force administered along the long axis of the assembly is now transmitted in line with the intended direction of the sheath tip (as opposed to pushing from the groin and hoping the sheath advances more sideways, toward the left shoulder). Once the transseptal sheath tip is within the LA, the dilator and needle are withdrawn slowly during continuous flushing through the needle or while suction is maintained through a syringe placed on the sheath side port to minimize the risk of air embolism and while fixing the sheath with the other hand to prevent dislodgment outside the LA. The sheath should be aspirated until blood appears without further bubbles; this usually requires aspiration of approximately 5 mL and sometimes “flicking” the sheath hub with a finger is needed to dislodge trapped air. The sheath is then flushed with heparinized saline at a flow rate of 3 mL/min during the entire procedure.
The mapping-ablation catheter is advanced through the sheath into the LA. This is safely done by advancing the catheter tip to the tip of the sheath, and while holding the catheter steady, withdrawing the sheath slightly over the catheter, exposing about 2 cm of the catheter tip. In so doing, one ensures that the catheter (stiffened by being inside the sheath) does not perforate the atrial wall. Flexing the catheter tip and applying clockwise and counterclockwise torque to the sheath help confirm free movement of the catheter tip within the LA, rather than possibly in the pericardium. It is important to recognize that merely recording atrial electrograms does not confirm an LA catheter location because an LA recording can be obtained from the epicardial surface of the LA, from the RA, or even the aortic root.
Second transseptal puncture.
When two transseptal accesses are required, the second access can be obtained through a separate transseptal puncture performed in a fashion similar to that described for the first puncture. Alternatively, the first transseptal puncture can be used for the second sheath. This technique entails passing a guidewire or thin catheter through the first transseptal sheath into the LA, preferably into the left inferior or superior PV, and then the sheath is pulled back into the RA. Subsequently, a deflectable tip catheter is used through the second transseptal sheath to interrogate the fossa ovalis and to try to access the LA through the initial puncture site. Once this is accomplished, the first sheath is advanced back into the LA, and the guidewire is replaced with the mapping catheter. It is also possible to advance two guidewires through the first transseptal sheath into the LA (preferably into the left inferior or superior PV). The sheath is then pulled out, and a separate transseptal sheath is advanced over each of the two guidewires. This requires both sheaths to go through the same femoral puncture site, which can increase bleeding in the presence of significant anticoagulation.
Intracardiac Echocardiography–Guided Transseptal Catheterization
Although fluoroscopy provides sufficient information to allow safe transseptal puncture in most cases, variations in septal anatomy, atrial or aortic root dilation, the need for multiple punctures, and the desired ability to direct the catheter to specific locations within the LA can make fluoroscopy inadequate for complex LA ablation procedures. Intraoperative TEE allows identification of the fossa ovalis and its relation to surrounding structures and provides real-time evaluation of the atrial septal puncture procedure, with demonstration of tenting of the fossa prior to entry into the LA and visualization of the sheath advancing across the septum. However, the usefulness of TEE is limited by the fact that the probe obstructs the fluoroscopic field, and it is impractical in the unanesthetized patient. ICE, which provides similar information on septal anatomy, can be used for the conscious patient and does not impede fluoroscopy.
The intent of ICE-guided transseptal catheterization is to image intracardiac anatomy and identify the exact position of the distal aspect of the transseptal dilator along the atrial septum—in particular, to assess for tenting of the fossa ovalis with the dilator tip.
Two types of ICE imaging systems are currently available: the electronic phased-array ultrasound catheter and the mechanical ultrasound catheter. The phased-array ultrasound catheter sector imaging system (AcuNav, Siemens Medical Solutions, Malvern, PA, United States) uses an 8 or 10 Fr catheter that has a forward-facing 64-element vector phased-array transducer scanning in the longitudinal plane. The catheter has a four-way steerable tip (160 degree anteroposterior or left-right deflections). The catheter images a sector field oriented in the plane of the catheter. The mechanical ultrasound catheter radial imaging system (Ultra ICE, EP Technologies, Boston Scientific, San Jose, CA, United States) uses a 9-MHz catheter-based ultrasound transducer contained within a 9 Fr (110-cm length) catheter shaft. It has a single rotating crystal ultrasound transducer that images circumferentially for 360 degrees in the horizontal plane. The catheter is not freely deflectable.
When using the mechanical radial ICE imaging system, a 9 Fr sheath (preferably a long, preshaped sheath) for the ICE catheter is advanced via a femoral venous access. To enhance image quality, all air must be eliminated from the distal tip of the ICE catheter by flushing vigorously with 5 to 10 mL of sterile water. The catheter then is connected to the ultrasound console and advanced until the tip of the rotary ICE catheter images the fossa ovalis. Satisfactory imaging of the fossa ovalis for guiding transseptal puncture is viewed from the mid-RA ( Fig. 4.10 ).
The AcuNav ICE catheter is introduced under fluoroscopy guidance through a 23-cm femoral venous sheath. Once the catheter is advanced into the mid-RA with the catheter tension controls in neutral position (the ultrasound transducer oriented anteriorly and to the left), the RA, tricuspid valve, and RV are viewed. This is called the home view ( Fig. 4.11A ). Gradual clockwise rotation of a straight catheter from the home view allows sequential visualization of the aortic root and the pulmonary artery (see Fig. 4.11B ), followed by the CS, the mitral valve, the LA appendage orifice, and a cross-sectional view of the fossa ovalis (see Fig. 4.11C and D ). The mitral valve and interatrial septum are usually seen in the same plane as the LA appendage. Posterior deflection or right-left steering of the imaging tip in the RA, or both, is occasionally required to optimize visualization of the fossa ovalis; the tension knob (lock function) can then be used to hold the catheter tip in position. Further clockwise rotation beyond this location demonstrates images of the left PV ostia (see Fig. 4.11E ). The optimal ICE image to guide transseptal puncture demonstrates adequate space beyond the interatrial septum on the LA side and clearly identifies adjacent structures, but it does not include the aortic root because it would be too anterior for the interatrial septum to be punctured safely. In patients with an enlarged LA, a cross-sectional view that includes the LA appendage is also optimal if adequate space exists beyond the atrial septum on the LA side.
The sheath-dilator-needle assembly is introduced into the RA, and the dilator tip is positioned against the fossa ovalis, as described earlier. Before advancing the Brockenbrough needle, continuous ICE imaging should direct further adjustments in the dilator tip position until ICE confirms that the tip is in intimate contact with the middle of the fossa, confirms proper lateral movement of the dilator toward the fossa, and excludes inadvertent superior displacement toward the muscular septum and aortic valve. With further advancement of the dilator, ICE demonstrates tenting of the fossa ( Figs. 4.10 and 4.12 ). If the distance from the tented fossa to the LA free wall is small, minor adjustments in the dilator tip position can be made to maximize the space. The Brockenbrough needle is then advanced. With successful transseptal puncture, a palpable pop is felt, and sudden collapse of the tented fossa is observed (see Fig. 4.12 ). Advancement of the needle is then immediately stopped. Saline infusion through the needle is visualized on ICE as microbubbles in the LA, thus confirming successful septal puncture. With no change in position of the Brockenbrough needle, the transseptal dilator and sheath are advanced over the guidewire into the LA, as described earlier.
Alternative Methods for Difficult Transseptal Catheterization
In some cases, the conventional approach using a Brockenbrough needle sheath fails to pierce the septum because of the presence of a small fossa area, a thick interatrial septum, fibrosis and scarring of the septum from previous interventions, or an aneurysmal septum with excessive laxity. Applying excessive force to the needle-dilator-sheath assembly against a resistant septum (which can be seen as bending and buckling of the assembly in the RA) can lead to building pressure of the needle tip on the septum, which can potentially lead to an uncontrolled sudden jump of the assembly once across the fossa ovalis, thus perforating the opposing lateral LA wall. Similarly, excessive tenting of the interatrial septum (beyond halfway into the LA) can bring it in close proximity to the lateral LA wall, so that the needle can potentially puncture the lateral LA wall once across the septum. Some of these difficulties can be overcome by manual reshaping of the curvature of the Brockenbrough needle tip, applying slight rotation on the needle and sheath assembly to puncture a different point on the fossa ovalis, or using a sharper transseptal needle type (BRK-1 extra sharp).
Other tools designed specifically for transseptal puncture, including the SafeSept Transseptal Guidewire and the radiofrequency (RF)-powered needle, can help minimize pressure application to the needle as it crosses the septum and tenting of the septum, which can potentially reduce the chances of sudden advancement through the lateral LA as the needle crosses the septum.
SafeSept Transseptal Guidewire.
The SafeSept Transseptal Guidewire (Pressure Products, San Pedro, CA, United States) is a 135-cm long, 0.014-inch diameter nitinol guidewire, tipped with a flexible J -curve needle specifically designed for transseptal puncture. Once the sheath-dilator-needle assembly is appropriately positioned at the fossa, and tenting of the fossa is seen on ICE, the SafeSept guidewire is advanced through the Brockenbrough needle to puncture the floor of the fossa with minimal force. The flexible J -curve needle then forms a loop ( J curve) in the LA once it crosses the septum and is exposed out of the dilator, rendering it incapable of further tissue penetration. The transseptal needle, dilator and sheath are then sequentially advanced over the SafeSept wire into the LA.
A second iteration of this technique uses a 150-cm long, 0.032-inch diameter nitinol guidewire (SafeSept Needle Free Transseptal Guidewire) with a very sharp tip specifically designed to easily perforate and cross the fossa ovalis in conjunction with a transseptal sheath and dilator, but without the need for a transseptal needle. When the tip of the introducer has reached the fossa ovalis and tenting is seen on ICE, the guidewire is advanced, tapping on the interatrial septum until it pushes through the septum into the LA. Once across the septum, unsupported by the dilator and sheath, the tip of the guidewire assumes a J shape, rendering it incapable of further tissue penetration. The wire is then advanced into the left superior PV under fluoroscopic guidance, and the transseptal sheath-dilator assembly is advanced over the guidewire into the LA. A limitation of this technique, when compared to the Brockenbrough needle, is the lack of an open lumen to easily inject contrast or measure pressure.
RF-powered needle.
A specialized, electrically insulated RF-powered needle (Baylis Medical Company, Montreal, Canada) has been developed to facilitate transseptal puncture. The needle is connected to a proprietary RF generator (RFP-100 RF Puncture Generator, Baylis Medical), which delivers RF energy to the blunt, closed tip of the needle positioned at the atrial septum. Once septal tenting is visualized on ICE, RF energy is applied at 10 W for 2 seconds (unipolar mode). The RF perforation generators apply a high-voltage/low-power RF current from a small surface area of the embedded needle tip for short bursts, resulting in a high-energy electric field and an almost instantaneous temperature rise to 100°C, leading to steam popping and septal perforation with minimal collateral tissue damage (similar to the cut-mode of a surgical electrocautery unit). This can facilitate needle passage through atrial muscle with minimal—or at least reduced—mechanical pressure. This in contrast to conventional RF generators, which deliver a higher power with a lower voltage and impedance range for longer periods of time, with resulting thermal destruction of the local tissue around the needle tip, rather than perforation. The needle is also equipped with two distal side ports for measuring pressure and injecting contrast and fluids. The blunt tip of the RF needle offers an additional benefit. In contrast to the standard transseptal needle, advancing the blunt-tipped RF needle through the dilator is not associated with shaving off pieces of plastic from the inside of the dilator, which can potentially enter the patient’s vascular system.
Other techniques to facilitate transseptal puncture include the application of pulses of electrosurgical cautery or RF energy to the proximal end of the Brockenbrough needle. Once the position of the dilator tip is confirmed at the fossa ovalis (under ICE guidance), the needle is advanced beyond the tip of the dilator in contact with the septum until resistance is met. RF energy (5 to 30 W for 1 to 11 seconds) can be applied through a conventional ablation catheter electrode brought manually in contact with the proximal hub of the transseptal needle. Typically, the fossa is punctured almost instantaneously (within 1 to 2 seconds) following RF application. Alternatively, electrosurgical cautery (set to 15 to 20 W for a 1- to 2-second pulse of cut-mode cautery) is applied to the proximal hub of the needle as its tip is advanced out of the dilator. Importantly, the cautery should be initiated on the needle handle prior to pushing the needle tip beyond the dilator tip to help minimize the power needed to puncture the septum, and it should be stopped as soon as the needle is pushed out fully.
A potential disadvantage of using RF-assisted transseptal puncture is that it is more traumatic at the puncture site than a standard needle, and it is possible that the transseptal puncture site is less likely to close spontaneously after the procedure. Similarly, inadvertent cardiac perforation occurring in the setting of powered needles can potentially be associated with serious consequences. This is of a lesser concern when using the RF-powered Baylis needle, since it results in less tissue damage than that when applying electrosurgical cautery or standard RF energy to the Brockenbrough needle. Whether RF is more likely to cause a thrombus at the puncture site compared with a standard needle is unknown.
Another potential complication of applying electrocautery or RF energy to a standard open-ended Brockenbrough needle is coring (entrapment of a small plug) of septal atrial tissue into the tip of the open-ended Brockenbrough needle, which can lead to systemic embolization. In contrast, the Baylis needle is specifically designed with side holes, rather than an end-hole, to prevent coring.
Transseptal Puncture in the Presence of Atrial Septal Defect Repair
Transseptal catheterization is feasible and safe in most patients with prior surgical repair of an atrial septal defect or a patent foramen ovale. Nonetheless, because of the altered anatomical landmarks after repair, fluoroscopic guidance for transseptal puncture is not as reliable, and the procedure can be challenging. In these patients, an understanding of the method of repair and utilization of ICE guidance are essential.
In patients with a septal stitch or pericardial or Dacron patch, puncture can be achieved through the thickened septum or the patch. However, transseptal access is typically not achievable through a Gore-Tex patch (W.L. Gore & Associates, Flagstaff, AZ, United States) because of its resistant texture; instead, puncture can be performed directly through neighboring native interatrial tissue. However, when the patch is wide, sufficient free septal tissue for transseptal puncture may not be available, in which setting transseptal access to the LA may not be feasible.
In patients with atrial septal defect closure devices, puncture is preferably performed at the portion of the septum located inferior and posterior to the closure device and not through the device itself ( eFig. 4.5 ). When areas of native septum are not available for transseptal access, recent reports described successful LA access through a direct puncture of the closure device.
Complications of Atrial Transseptal Puncture
Injury to cardiac and extracardiac structures is the most feared complication. Because of its stiffness and large caliber, the transseptal dilator should never be advanced until the position of the Brockenbrough needle is confirmed with confidence. Advancing the dilator into an improper location, such as the aortic root, can be fatal. Therefore many operators recommend the use of ICE-guided transseptal puncture, especially for patients with normal LA chamber size.
Cardiac perforation.
Cardiac perforation, hemopericardium, and cardiac tamponade can result from puncturing the atrial wall outside the region of the fossa ovalis. In addition, perforation of the opposing posterior or lateral LA wall can occur once the transseptal assembly crosses the atrial septum, especially in the setting of excessive stiffness of the septum. Similarly, excessive tenting of the interatrial septum (beyond halfway into the LA) can bring it in close proximity to the lateral LA wall, so that the needle can potentially puncture the lateral LA wall once across the septum. It is possible to puncture the RA free wall above the fossa and continue forward with the apparatus, puncturing back into the LA. In such a situation, sheath and catheter will be in the LA, but having achieved that position by exiting the heart and reentering it. This may not be noticed immediately, as the sheath may effectively occlude the holes it has traversed in the atrial walls, but will become evident when sheaths are withdrawn at the end of the procedure, leaving a hole in each atrium.
It is important to recognize that successful atrial septal puncture is a painless procedure for the patient. If the patient experiences significant discomfort, careful assessment should be made of the catheter and sheath locations (pericardial space, aorta).
Prompt recognition and management of cardiac perforation are critical to prevent the development of cardiac tamponade. Assessment of the cardiac silhouette fluoroscopically can provide the first clue, especially if a careful assessment was made at baseline. Decreased excursion of the lateral heart border on fluoroscopy in the LAO projection, indicating accumulating pericardial effusion, usually can be seen well before a decrease in blood pressure and prior to progression to cardiac tamponade. It is reasonable to obtain a baseline LAO cine image at the outset of a procedure to serve as a reference for comparison during the procedure, followed by intermittent evaluation of the same fluoroscopic projection during the procedure. Similarly, when ICE is utilized to guide transseptal puncture, it can be used to obtain baseline images of the LV and pericardial space before transseptal puncture and then monitor for the development of pericardial effusion afterwards. Importantly, bleeding into the pericardial space may develop only after the transseptal sheath has been removed. This may occur especially when the transseptal puncture is performed too superiorly or posteriorly, crossing the pericardial space (the anterosuperior interatrial groove) before entering the LA, as noted above.
The management of pericardial effusion is largely determined by its relative size and hemodynamic effect. Trivial pericardial effusions, if recognized early during the procedure, should be monitored continuously but do not warrant termination of the procedure. For larger effusions, the procedure should be terminated and anticoagulation, if administered, should be reversed. Protamine is used to reverse the effects of heparin, and activated factor VII, fresh frozen plasma, and vitamin K can be used in patients with therapeutic anticoagulation with warfarin. Immediate pericardiocentesis is required for large, rapidly expanding, or hemodynamically significant effusions.
Aortic puncture.
When the aorta is advertently punctured by the Brockenbrough needle—an arterial waveform is recorded from the needle tip and dye injected through the needle is carried away from the heart—the needle should be withdrawn back into the dilator. If only the needle enters the aorta and this is recognized before advancing the dilator and sheath, the needle can be withdrawn and the patient monitored for stability of vital signs and with echocardiography. The procedure can usually be continued if there is no accumulation of pericardial fluid after 15 to 30 minutes of monitoring. Advancing the dilator and sheath assembly into the aorta can lead to catastrophic consequences. If the dilator and sheath have been advanced into the aortic root before the error is recognized, it is imperative that the sheath not be removed immediately, as this can result in immediate and perhaps irretrievable hemodynamic collapse due to intractable bleeding into the pericardial space. Once surgical intervention is readily available, and after reversal of anticoagulation, it may be feasible to pull the sheath back, leaving a wire in the aorta. Under careful hemodynamic and echocardiographic observation, this wire may be also pulled back 30 minutes later. In general, the need for closing device or open heart surgery is rare.
Systemic embolism.
Another potential complication is embolism of thrombus or air. To avoid air embolism, catheters must be advanced and withdrawn slowly so as not to introduce air into the assembly. Sheaths must be aspirated with a syringe on a stopcock to the amount of their volume (e.g., an 8 Fr sheath contains 5 mL when filled) to remove any retained air each time a catheter is removed and prior to reintroduction. Thromboembolic complications can be avoided by flushing all sheaths and guidewire with heparinized saline and maintaining the ACT at longer than 300 seconds. In addition, a guidewire should not be left in the LA for more than 1 minute, especially if no systemic heparin has been administered. As noted earlier, administration of heparin before, rather than after, the atrial septal puncture can also help reduce thromboembolism. Importantly, the presence of an LA thrombus is an absolute contraindication for transseptal catheterization.
Occasionally, ST segment elevation in the inferior electrocardiogram (ECG) leads (with or without transient bradycardia or AV block) can occur following transseptal catheterization, potentially secondary to air embolism in coronary arteries, although a Bezold-Jarisch–like reflex mechanism can also be implicated.
Interatrial shunt.
Iatrogenic atrial septal defects have been described in up to 20% to 30% of patients following transseptal atrial interventions, though about two thirds of these disappear with the first 12 months of follow-up. Predictors of developing a persistent iatrogenic atrial septal defect include the size of the transseptal sheath, LA pressure, RV systolic pressure, and the presence of severe mitral or tricuspid regurgitation. The location of the transseptal puncture (fossa ovalis vs. inferior limbus), the use of RF-powered transseptal needles, and the anatomy of the interatrial septum (e.g., aneurysmal septum) have been suggested to predict a higher risk for the development of persistent iatrogenic atrial septal defects. The clinical significance of persistent iatrogenic atrial septal defects is not clear, but can potentially result in hemodynamically significant interatrial shunts in some patients.
Subxiphoid Epicardial Approach
Coronary veins can be used to perform epicardial mapping, but manipulation of the mapping catheter is limited by the anatomical distribution of these vessels. In contrast, the subxiphoid percutaneous approach to the epicardial space allows for unrestricted mapping of wide areas of the epicardial surfaces of the ventricles and most part of the epicardial atria surface. Percutaneous epicardial access has become an increasingly important tool for mapping and ablation of complex ventricular arrhythmias and for LA appendage exclusion using an epicardial ligation system like the Lariat device. More recently, investigators have applied the technique to manage supraventricular arrhythmias, including inappropriate sinus tachycardia, AT arising from the LA appendage, BTs, and AF.
Anatomical Considerations
The pericardium is a double-walled sac that contains the heart and the roots of the great arteries, SVC, and PVs. By separating the heart from its surroundings—the descending aorta, lungs, diaphragm, esophagus, trachea, and tracheobronchial lymph nodes—the pericardial space allows complete freedom of cardiac motion within this sac.
The pericardium consists of two sacs intimately connected with one another: an outer fibrous envelope (the fibrous pericardium) and an inner serous sac (the serous pericardium). The fibrous pericardium (0.8 to 2.5 mm in thickness) consists of fibrous tissue and forms a flask-shaped bag, the neck of which is closed by its fusion with the adventitia of the great vessels, while its base is attached by loose fibroareolar tissue to the central tendon and to the muscular fibers of the left side of the diaphragm. The fibrous pericardium is also attached to the posterior sternal surface by superior and inferior sternopericardial ligaments. These attachments are essential to maintain the normal cardiac position in relation to the surrounding structures, to restrict the volume of the thin-walled cardiac chambers (RA and ventricle), and also to serve as direct protection against injuries.
The serous pericardium is a delicate membrane that lies within the fibrous pericardium and lines its walls; it is composed of two layers: the parietal pericardium and the visceral pericardium. The parietal pericardium is fused to and inseparable from the fibrous pericardium. On the other hand, the visceral pericardium, which is composed of a single layer of mesothelial cells, is part of the epicardium (i.e., the layer immediately outside of the myocardium) and covers the heart and the great vessels except for a small area on the posterior wall of the atria. The visceral layer extends to the beginning of the great vessels, and is reflected from the heart onto the parietal layer of the serous pericardium along the great vessels in tube-like extensions. This happens at two areas: where the aorta and pulmonary trunk leave the heart and where the SVC, IVC, and PVs enter the heart.
The pericardial cavity or sac is a continuous virtual space that lies between the parietal and visceral layers of serous pericardium. The heart invaginates the wall of the serous sac from above and behind, and practically obliterates its cavity, the space being merely a potential one. The pericardial sac normally contains 20 to 40 mL of clear fluid that occupies the virtual space between the two layers and serves as a lubricant.
The lateral surfaces of the heart are predominantly covered by the lungs, prohibiting a direct percutaneous access to the pericardial space. The anterior borders of the lungs extend vertically downward along the midsternal line. The right lung anterior border curves laterally and downward at the level of the sixth costal cartilage on the right side. On the left side, however, the anterior border of the lung diverges laterally at an earlier point (at the level of the fourth costal cartilage), forming the cardiac notch, and reaches the parasternal line at the fifth costal cartilage (about 1 inch from the sternal border) before turning medially and downward (as the lingula) to the sixth sternocostal junction ( eFig. 4.6 ). Thus, the subxiphoid region offers a window for direct pericardial access without traversing the lungs. Nonetheless, even with the subxiphoid approach, a needle angulated too far in the lateral direction can potentially puncture the left lung and result in pneumothorax.
