How to Perform Endocardial/Epicardial Ventricular Tachycardia Ablation
Jorge Romero, MD; J. David Burkhardt, MD; Carola Gianni, MD, PhD; Matthew Dare, CEPS; Pasquale Santangeli, MD, PhD; Andrea Natale, MD; Luigi Di Biase, MD, PhD
Catheter ablation (CA) therapy for scar-related ventricular tachycardia (VT) has advanced significantly advanced in the last decade. Mapping techniques such as substrate mapping, pace mapping, and entrainment mapping, as well as improvements in ablation technology such as irrigated radiofrequency (RF) ablation have improved the success rates in VT ablation, making this therapy a viable option in drug-refractory patients.1–7 Recent innovations include the technique of epicardial ablation via a minimally invasive subxiphoid approach using different needles (Tuohy needle, micropuncture needle and EpiAccess needle).8–10 This technique allows ablation on the outer surface of the heart, which may be the focus of some ventricular arrhythmias (VA). This area may not be accessible by even the deepest endocardial ablation lesions.
History and Exam
Prior to the ablation procedure, it is important to obtain a detailed history, including any history of prior cardiac surgeries, pericarditis, and device implantation. If the patient has had pericarditis, previous coronary artery bypass grafting (CABG), or other cardiac surgery, subxiphoid access to the pericardial space may be challenging. In such cases, the parietal pericardium may attach to the epicardial surface, not allowing free access to the pericardial space. Occasionally, catheters can be introduced, but manual techniques are required to break through fibrotic areas.11,12 This process can be difficult and bloody. In most cases of patients who have had coronary artery bypass surgery and who need epicardial ablation, a surgical approach can be tailored to the region of interest. A subxiphoid window or a limited anterior thoracotomy can be performed in the electrophysiology laboratory;13 although, in most of these cases, an open-chest procedure with a cardiac surgeon is likely the best approach.
During the physical examination, one should focus on the shape of the chest, xiphoid process, and abdominal contents near this area. During insertion of the needle for epicardial access, abdominal contents can be injured. This is especially problematic in patients with splenomegaly or hepatomegaly, as these structures may lie in the preferred area for needle insertion.
If the patient has an implantable cardioverter-defibrillator (ICD) implanted, this provides valuable information, which can be used for procedural planning. The ICD should be interrogated. The cycle lengths (CLs) of the clinical VTs should be noted. Also, the morphology of the tachycardia on the right ventricular (RV) lead and other available electrograms (EGMs) should be saved. If the rhythms are pace terminable, then the scheme should also be saved for the procedure. This information can be used to determine if the induced arrhythmias at the time of electrophysiology study are clinically relevant.
It is also important to ensure that the patient is not better served by a simultaneous surgical procedure. A transthoracic echocardiogram (TTE) and a myocardial stress test should be updated. If the patient requires CABG or valvular repair, then ablation can be performed at the time of the surgical procedure.
A 12-lead ECG during VT is invaluable. This yields localization and CL information. If not in tachycardia, the location of previous myocardial infarctions as assessed by the ECG and cardiac imaging (more commonly, a TTE) may suggest potential locations. The echocardiogram may also show the presence of non-laminated left ventricular thrombus that may necessitate the delay of any procedure. Although not necessary, cardiac CT or MRI may be useful in determining areas of scar and can be imported into the electro-anatomic mapping system.
If patients are on anticoagulation with warfarin, this is usually stopped 5 days prior to the procedure if epicardial access is anticipated. If the patient is on any of the new oral anticoagulants (NOACs) (i.e., rivaroxaban, apixaban) these are stopped the day before the procedure. If possible, antiarrhythmic drugs are held for 5 half-lives. If the patients are concerned or having frequent episodes, they may be admitted to the hospital for observation while the medications are being washed out. Some patients are already hospitalized for VT storms or frequent ICD shocks and are usually on intravenous antiarrhythmic medications preferably with short half-lives such as lidocaine, which are held a few hours prior to the procedure, enough to allow complete drug wash-out.
As for preprocedural blood work, a basic metabolic profile along with a complete blood count (including hemoglobin levels and platelet counts) and coagulation are obtained.
Most patients undergoing ablation for VT are sedated with moderate to deep sedation, usually using propofol. Some patients need to be more responsive to fully awake to induce the target arrhythmia. Also, the blood pressure tends to be higher when patients are not under general anesthesia, and this might help in cases where VT is induced to be mapped. It is important to have an anesthesiologist who is familiar with ablation and cardiovascular drugs for such procedures. Some anesthetics, such as fentanyl, have antiarrhythmic properties and should be avoided. Occasionally, vasopressor medications are required to support the blood pressure when performing activation mapping during tachycardia. Of course, the anesthesiologist must also be comfortable and understand that VT mapping may require long periods of sustained tachycardia. They are also important in recognizing complications early.
Most patients have a urinary catheter placed after anesthesia is started, anticipating fluid overload. If the patient has an ICD, it is interrogated and reprogrammed to turn detections off. If possible, ventricular pacing is minimized to allow for any substrate map to be acquired during natively conducted sinus rhythm. The EGMs, morphologies, and CLs of the clinical VTs are noted. Paper printouts of the EGM morphologies are obtained for review during tachycardia induction. In general, a person is assigned to manage the implanted device during the procedure for pacing, internal cardioversion, or defibrillation.
The patient is prepped from the carotid notch to the groin bilaterally. Under ultrasound guidance, arterial and venous access are obtained. Unless there is a contraindication (presence of an aortic mechanical valve, severe aortic stenosis, significant aortic atherosclerosis, or aortic aneurysms) both a retrograde aortic and transseptal approach are used. For the retrograde aortic approach, 1 arterial access is obtained in the right femoral artery, where an 8-Fr short sheath is used for passing the mapping/ablation catheter and arterial pressure monitoring. If the ileofemoral system is tortuous, a long stainless steel 24-cm sheath is used. In addition, 2 venous accesses are obtained, 1 for the ablation/mapping catheter and 1 for the intracardiac ultrasound (ICE) catheter. All sheaths are flushed with heparinized saline, and the arterial sheath is connected to pressure monitoring. One of the central venous sheaths is connected to an IV pump for delivery of medications. The ICE catheter is placed into the RA and in the RV across the tricuspid valve to obtain view a long-axis view of the LV. This view shows any pericardial effusion, LV myocardium as well as the mitral apparatus (Figure 48.1).
At this point, epicardial access is the next step in all patients with anticipated epicardial substrate. This commonly includes patients with arrhythmogenic right ventricular cardiomyopathy (ARVC), Brugada syndrome, presence of mid-myocardial or subepicardial scar on imaging, VT morphology suggestive of an epicardial exit, or those undergoing a redo procedure for both nonischemic and ischemic cardiomyopathy (NICM and ICM).
A towel is placed over the femoral sheaths. The equipment needed for this includes a 7-cm 17-G epidural Tuohy needle, contrast dye, a 180-cm 0.032-inch diameter wire, a short 8-Fr introducer, and a 24-cm stainless steel sheath.15 Fluoroscopic settings for this stage of the procedure are adjusted to obtain maximum definition (e.g., 15 frames per second). The fluoroscope is placed into the LAO 18° position. In this view the needle should not violate the left or right side of the spine. The operator palpates the xiphoid process and plans to puncture slightly to the patient’s left and about 2 cm inferior. This area is infiltrated with lidocaine. It is preferable that the patient is anesthetized so only shallow slow breathing is seen, or else deep breathing can pull the heart downward. The needle is placed on top of the chest under fluoroscopy to the level of the cardiac border to approximate the distance needed once inside the patient. A small skin incision (around 5 mm) is often made before needle insertion to maximize tactile sensitivity. To decrease the risk of RV perforation, the bevel of the needle should point away from the cardiac border, i.e., upward when accessing the pericardial space with an anterior approach (targeting the anterior wall) and downward with a posterior approach (targeting the inferior wall). When entering the skin, the needle is angled superficially at about 20° to the horizontal plane and superiorly aiming to the left shoulder. Once over the dome of the diaphragm (i.e., needle behind sternum), the needle can be angled slightly further, depending on the type of epicardial access approach (around 30° for an anterior approach, and 45° for a posterior approach). The needle should advance smoothly. Once any resistance or cardiac pulsation is felt, or the needle tip is at the cardiac border, the stylet is removed from the needle, and contrast is attached. A small amount (< 0.5 cm3) of contrast is infused. If one is near the pericardium, tenting is seen. The needle should be advanced until it pops through this tented area. A palpable “pop” may be felt. After popping through, more contrast is infused that should layer around the heart (Figure 48.2; Video 48.1). If one is not in the correct area, contrast will simply diffuse into the tissue. If the needle has punctured the heart, the contrast will swiftly move away and bubbles can be observed flowing across the RV on ICE. Usually PVCs are seen during advancement in the latter situation. In this case, the needle should be withdrawn into the pericardial space if felt to be intracardiac. Occasionally, a tenting is seen when the diaphragm is punctured. The pericardial surface is just past this location. Once the needle is confirmed to be in the pericardial space, the guidewire is advanced through the needle. During this process, the needle can be pushed out due to breathing. Slight advancement will re-engage the space. The wire should advance easily. A very long segment of wire should be advanced into the space so that large loops are seen around the heart. These loops should cross multiple chambers, confirming epicardial location (Figure 48.3; Video 48.2); in addition, it is also important to ensure that no wire is observed on ICE in the RV. A sheath should not be inserted over the wire unless it is seen crossing multiple chambers. At this point, the needle is removed, and the sheath is placed over the wire into the space. If difficulty is met at the cardiac border due to a sharp angle, a short 7-Fr dilator may be inserted first. Once the sheath is inserted well into the space, the dilator and wire are removed. The side arm of the sheath is aspirated, and any fluid removed is examined for blood content (Figure 48.4; Video 48.3). Some blood may be expected, but it is usually dilute. All fluid removed from the space is tabulated, as well as any fluid infused from the ablation catheter. The ICE catheter is used to monitor for pericardial effusion. The side arm is aspirated every 20 minutes or more frequently during ablation.
Due to the substantial incidence of pericardial bleeding due primarily to inadvertent RV free wall puncture, which may be severe enough to require surgical repair, large efforts have been made to develop different techniques that might improve procedural safety, using different access needles, multimodality image integration and assessment of changes in pressure frequency to recognize pericardial entry, with encouraging results from small series.10,16–21 Epicardial access can be attempted with a long 21-G micropuncture needle, as inadvertent cardiac or vascular puncture with this needle is less likely to result in significant bleeding.22 Nonetheless, due to small needle caliber, it is challenging to manipulate the needle under the sternum because it tends to flex over the course of insertion, and tactile feedback is limited. Alternatively, a “needle-in-needle” technique can be used.10 After subxiphoid insertion of a 7-cm 18-G needle is made through superficial tissue just before the cardiac silhouette, a 21-G micropuncture needle is inserted through the 18-G needle. The micropuncture needle alone is used to enter the pericardial space with the aid of contrast, fluoroscopy, and tactile sensation of entry into the pericardial space while maintaining the position of the 18-G needle steady. A 190-cm 0.018-in guidewire with a floppy tip is advanced through the 21-G needle. After confirmation that the wire is in the pericardial space (demonstrating on fluoroscopy that the wire crosses multiple cardiac chambers and hugs the border of the lateral left cardiac silhouette in the LAO projection) both needles are removed, and a micropuncture dilator is advanced into the pericardial space over the 0.018-in guidewire and then exchanged for a 6-Fr or 8-Fr dilator; confirmation of pericardial entry is again obtained with contrast and/or fluid aspiration. Finally, the 0.018-in guidewire is exchanged for a floppy-tip 0.035-inch guidewire that is used to advance the long steerable sheath as described above. There are disadvantages of the needle-in-needle technique. First, the tactile sensation of pericardial entry (the “give”) is still not well appreciated with the needle-in-needle technique, so reliance on contrast injection is mandatory to confirm pericardial access. Likewise, the classic tenting of the different layers of tissue prior to getting access into the pericardial space is usually absent. Another alternative is using the EpiAccess system, which comprises of an access needle with a pressure frequency fiber optic sensor housed within a stainless-steel tube welded inside the lumen of the cannula. The pressure/frequency data recorded by the sensor is displayed real-time, which provides additional guidance for pericardial access (Figure 48.2). EpiAccess uses a needle designed with a luer hub and a 2-mm stainless steel cannula with a tip that is very similar in shape and size to a Tuohy Needle. When the needle is advanced into the pericardial space, the pressure oscillates between +5 to –5 mm Hg. More importantly, when the needle is in proximity to the RV wall or inside the RV cavity, the tip needle tracing will display significantly higher pressures, oscillating between +20 and –20 mm Hg (Figure 48.5).