Patient preparation
Patients should be studied in the postabsorptive state and after beta blockers or other antiarrhythmic agents have been discontinued for at least 5 days. Amiodarone should be withdrawn at least 2 months before the procedure if feasible. A transesophageal echocardiogram is recommended to exclude intracardiac thrombi in patients with atrial fibrillation (AF) or atrial flutter and is particularly important in such patients who have not been therapeutically anticoagulated for at least 3 to 4 weeks.
In most cases a diagnostic electrophysiology study (EPS) can be performed without sedation, but conscious sedation is appropriate when needed to attenuate anxiety. Intravenous sedation now can be proceduralist (or operator) directed and nurse administered (i.e., the PDNA model). , An abundance of observational studies have indicated that sedation does not significantly affect basic electrophysiologic properties or inducibility of supraventricular tachycardia (SVT), with the possible exception of automatic atrial tachycardia. , For clinical purposes, this is true not only for the opiate-benzodiazepine combination but even for propofol, despite its dose-related depression of the sinus node and His-Purkinje conduction. The opiate-benzodiazepine combination is safer than propofol but does not necessarily comprise only midazolam and fentanyl. Emulsified diazepam offers a less expensive alternative to midazolam and avoids the irritating effects of intravenously administered diazepam. Morphine or diamorphine (available in the United Kingdom), which lacks the emetic effects of morphine, are alternatives to fentanyl. An initial dose of 5 mg diazepam, followed by 5 mg diamorphine if needed, is usually adequate. However, individual drug and dosing choices depend on drug availability and legal environments in different countries and on the experience of the medical personnel. Dexmedetomidine, an α 2 -adrenergic agonist, is an emerging, attractive sedative because of its short half-life and lack of respiratory depression, although it has been associated with cardiac conduction abnormalities and hypotension.
Femoral vein puncture
The femoral veins can be used for insertion of all electrode catheters, including the coronary sinus (CS). Some operators prefer to use the internal jugular vein for the CS catheter. Local anesthesia is administered, and the femoral vein is cannulated. The vein lies just medial to the artery below the inguinal ligament. Many laboratories now require femoral vein cannulation under ultrasound guidance. If this is not feasible, access is accomplished by feeling the femoral artery pulse on the groin crease and puncturing at a point 2 cm medial to and 1 cm higher than the point of maximal impulse. A syringe half filled with heparinized flush solution is attached to the hub of a 18-gauge needle, which is advanced under negative pressure by withdrawing gently on the syringe, at a 45-degree angle from the skin surface. The needle is advanced while gentle aspiration is maintained on the syringe. If the need is inserted quickly, it may penetrate the front and back walls of the vein, reaching the pubic ramus. In this case the needle should be withdrawn slowly back into the vein lumen while maintaining suction. If the femoral artery is inadvertently punctured, the vein puncture is reattempted after 5 minutes of compression on the arterial puncture site.
Jugular vein puncture
If the femoral veins are inaccessible or not unsuitable, the internal jugular vein may be used. This is accomplished either by puncturing the vein 2 cm lateral to the carotid pulse in the neck, usually under ultrasound guidance, or by puncturing between the two heads of the sternocleidomastoid muscle that insert into the sternum and clavicle. The needle pierces the skin at the apex of the triangle formed by the two heads of the sternocleidomastoid muscle and is directed inferiorly and posteriorly at a 30-degree angle to the skin. It is important to keep the needle parallel to the midline to avoid the carotid artery. The former approach avoids the risk of pneumothorax at the expense of inadvertent puncture of the carotid artery. In this case 5 minutes of compression of the carotid artery puncture site artery is usually sufficient for hemostasis.
Transseptal puncture
Transseptal access is obtained usually from the right femoral vein by using anatomic landmarks or transesophageal or intracardiac echocardiography. When echocardiographic assistance is not available, anatomic landmarks may be used. The transseptal sheath with the needle inside it, without protruding, is withdrawn from the superior vena cava on the atrial septum until it drops into the foramen ovale. Ideally, tenting of the fossa ovalis is confirmed by the ultrasound image or by contrast injection, after which the needle is advanced into the left atrium, ideally with continuous pressure monitoring. If the needle puncture is made through the fossa ovalis or its limbus (the “true” interatrial septum), the needle will always enter the left atrium (LA). However, if the needle is advanced through another part of the septum, entrance into the pericardial space or aorta is likely. A too anterior puncture risks entrance into the aorta, whereas a puncture that is too posterior risks entry into the pericardial space. If the needle inadvertently punctures the aorta, it usually can be simply withdrawn without adverse effects, unless the dilator and sheath have been advanced over the needle and into the aorta.
During redo ablation procedures, scarring at the previous transseptal site can make the puncture more difficult. This might be overcome by changing the needle curve from a small curve to a large curve design with an extra-sharp tip. In the presence of a dilated left atrium, atrial angiography using a modification of the initial method described by Inoue for percutaneous mitral commissurotomy may be of help ( Fig. 4.1 ). When a difficult transseptal puncture is anticipated, intracardiac echocardiography has been shown to significantly reduce the rate of hemopericardium and tamponade ( Fig. 4.2 ).
After penetration of the septum, a pressure line is connected to the needle to ensure recording of left atrial pressure. Alternatively, a small-gauge wire with a J curve (e.g., SafeSept) is advanced past the tip of the needle and positioned within a left pulmonary vein to confirm that the needle is in the left atrium ( Fig. 4.3 ). If this is confirmed, the sheath and the needle are gently pushed forward, the needle is withdrawn, and a long J-curve guidewire is inserted and positioned with a left pulmonary vein to allow safe passage of the sheath into the left atrium. The SafeSept is particularly useful in the case of a redundant membrane that results in a higher risk of perforation of the posterior wall or left atrial appendage when the needle in pushed and suddenly jumps into the LA. If the foramen ovale is thick or the procedure is truly necessary in patients with an atrial patch, the extra-sharp BRK-1 transseptal needle with intracardiac echocardiographic guidance and SafeSept wire, or radiofrequency-assisted puncture, may be helpful.
The sheath should receive a continuous infusion of heparinized saline to prevent thrombi and air emboli. Diagnostic or ablation catheters can then safely be introduced into the left atrium after heparinization. The target activated clotting time (ACT) depends on the nature of the procedure. Ablation of a left-sided accessory pathway usually requires no more than a single heparin bolus of 3000 to 5000 units of heparin. For AF ablation procedures, most operators prefer a heparin bolus and continuous infusion to rapidly attain and maintain an ACT of 350 ms.
The most common complication of transseptal puncture is cardiac tamponade, with an average incidence of approximately 1%. It is usually treated by pericardiocentesis and drainage for 24 to 72 hours, even in anticoagulated patients. Surgical drainage and repair of the puncture site sometimes are necessary. Advanced age, female sex, and AF ablation are risk factors for pericardial tamponade. ,
Epicardial access
Percutaneous epicardial access is increasingly being performed to facilitate catheter ablation of ventricular tachycardias (VTs) with epicardial circuits, difficult cases of idiopathic VTs, and, rarely, focal atrial tachycardia and accessory pathways that cannot be successfully targeted endocardially. It consists of two layers: the visceral pericardium or epicardium, a serous layer that is adjacent to the heart and proximal great vessels; and the parietal pericardium, which is formed by the outer fibrous sac and the continuation of the visceral pericardium as it reflects back near the origin of the great vessels to form the inner layer of the parietal pericardium. The visceral and parietal layers are separated by the pericardial cavity, which in healthy people contains 15 to 50 mL of serous physiologic fluid. The thickness of the parietal pericardium varies from 0.8 to 2.5 mm. Partial left (70%) or right (17%) pericardial absence may occur in 0.0001% of patients. , Thus cardiac magnetic resonance imaging or cardiac computed tomography (CT) is always recommended before undertaking the procedure. Furthermore, pericardial access is limited by pericardial sinuses and recesses around the veins and great arteries and may not be feasible in patients with prior open heart surgery.
Anticoagulation should be discontinued or reversed before the procedure, although in experienced centers epicardial ablation may be performed on anticoagulation to allow simultaneous endocardial ablation.
The starting place for entrance into the skin is approximately 1 cm below the subxiphoid process for an anterior approach and right under the rib margin adjacent to the xyphoid for a posterior approach ( Figs. 4.4 , 4.5 , and 4.6 ). For pericardial access, an anterior approach or a posterior approach can be used. The anterior approach allows easier access to the anterior surface of the heart and ventricles and is safer than the posterior. It is associated with an increased risk for puncture of the superior epigastric artery or left internal mammary artery, and in certain situations (i.e., history of cardiac surgery and/or anterior sternotomy), a posterior puncture approach is preferred. The posterior approach allows easier access to the inferior ventricular walls and posterior LA walls but has the potential for causing intraabdominal bleeding through an inadvertent puncture of the diaphragm and the subdiaphragmatic structures. If the patient has had previous epicardial ablation with potential pericardial adhesions, a surgical pericardial window is preferable. Prior coronary artery bypass surgery is a relative contraindication for epicardial ablation unless coronary anatomy is well defined and access to the VT circuit on the opposite side of the heart is possible. Prior cardiac valvular surgery is also a relative contraindication given the potential for significant adhesions that limit access and, even if obtained, limit the ability to map freely.
