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The Emerging Indications for Epicardial Access During Catheter Ablation
Endocardial catheter-based ablation has revolutionized the field of cardiac electrophysiology to a therapeutic subspecialty. Over the last decade, it has become apparent an epicardial approach is needed to successfully ablate certain arrhythmias. Additionally, the use of epicardial access has been used to make endocardial ablation safer by adding techniques to protect nearby vital structures. The objective of this article is to review the procedure of percutaneous epicardial puncture and the indications for epicardial ablation for ventricular tachycardia, atrial fibrillation, and supraventricular tachycardia.
Percutaneous Epicardial Puncture
Sosa et al1,2 initially described percutaneous epicardial access and catheter ablation to guide the treatment of ventricular tachycardia (VT). In the roughly 15 years since this initial description, the mainstay of the procedure remains the same. In summary, we perform the procedure with the patient usually under general anesthesia, because of the higher risk of right ventricular puncture and as puncture of the epicardial surface is generally painful for patients under conscious sedation. Next, we place the appropriate endocardial mapping catheters via a femoral and/or intrajugular approach prior to the start of epicardial puncture. The pericardial space is reached using a Tuohy needle as the tip of this needle is shaped to reach a virtual space. The needle is a 17-gauge caliber and is available in either 3.875 inches or 5 inches in length. We generally start with the shorter length needle, and change to the longer needle if the pericardial space is not accessible. Before the puncture is made, a small vertical incision is made to the left of the subxiphoid process. We puncture the skin and subcutaneous tissue at a 45-degree angle pointing toward the left shoulder. Once beyond the initial subcutaneous tissue, the needle is then advanced with the guidance of fluoroscopy. We use biplane fluoroscopy with an LAO projection of 40 to 45 degrees and an RAO projection of 30 to 35 degrees. The needle is then slowly advanced toward the cardiac border. Periodically, small amounts of contracts can be injected to ascertain if one is still in the subdiaphragmatic space or elsewhere. It is important to use contrast sparingly as excess contrast will opacify the region of interest, making further needle movement difficult to visualize. Once the cardiac pulsation is felt, the needle advancement should be slowed. Another advantage of general anesthesia is that respirations can be held to assist in pericardial puncture. With slight forward movement, the needle will puncture the pericardium. Once in the pericardial space, contrast can be injected to confirm the location, and a guidewire is then advanced (Figure 1). The guidewire should track along the cardiac border in the LAO view, and may enter the transverse sinus, confirming it is located in the pericardial space. Before placement of a pericardial sheath, we place a 5F dilator over the guidewire and inject 5-10cc of contrast and document a pericardiogram. This further confirms access to the pericardial space as well as the location of any adhesions that may be present. Next, a long guidewire is then placed through the dilator and a long sheath (usually St. Jude Medical’s SL0 sheath) is advanced into the pericardial space. An ablation or mapping catheter can then be placed through the sheath to access the epicardial surface. During the procedure, careful monitoring via the sheath is essential to ensure there are no bleeding complications.
Ventricular Tachycardia
In 15-30% of patients undergoing VT ablation, epicardial mapping is required for locating successful ablation sites.3,4 Patient subsets that may benefit from epicardial mapping include patients with a VT suggestive of an epicardial exit based on EKG criteria5 such as a maximal deflection index of >0.55, a pseudodelta of >34ms and/or previously failed endocardial ablation. This primarily includes patients with either non-ischemic cardiomyopathy (Figure 2),6 prior inferior infarction,7 chagasic heart disease,8 arrhythmogenic right ventricular dysplasia,9 and occasionally epicardial premature ventricular contractions.10 Once epicardial access is obtained for ventricular tachycardia ablation, multiple options are available with regard to mapping. Epicardial left ventricular access is usually obtained via a transseptal approach; double transseptal access allows for both a mapping catheter (we occasionally use a duodecapolar) and an ablation catheter. Our center’s general approach is to obtain a detailed voltage map of the endocardial and epicardial substrate of interest. Additionally, isolated late potentials and/or fractionated potentials are sought.11 If a clinical VT is targeted, then entrainment mapping and/or pacemapping are performed at sites of late potentials and/or border zone of areas of interest. Frequently, the epicardial sites are compared to corresponding endocardial regions which can aid in determining the ideal site for ablation. Once epicardial mapping and/or ablation is completed, our center’s practice is to administered steroids to the pericardial space. Usually, the dose administered is 120mg of methylprednisolone. This is done after all pericardial blood or fluid (frequently saline from an irrigated catheter) has been drained from the pericardial space. If bleeding is noted at the end of the procedure, a soft-tipped pigtail catheter is placed in the pericardial space for drainage and monitoring. When this occurs, it is usually due to anticoagulation delivered for simultaneous endocardial mapping, and frequently any pericardial bleeding subsides in the subsequent 12-24 hours after the procedure.
Atrial Fibrillation
In 1998, Haissaguerre et al described the initiation of atrial fibrillation from ectopic foci from within the pulmonary veins.12 This seminal paper led to the development of catheter ablation of atrial fibrillation. In subsequent years, two findings have led to the investigation of the epicardial approach for ablation of atrial fibrillation ablation. There is growing evidence that the endocardial and epicardial activation wavefronts and response to endocardial catheter ablation may differ. Additionally, epicardial connections between the pulmonary veins and the left atrium have been described.13 In this patient cohort, roughly 20% of patients had evidence of epicardial connection between ipsilateral pulmonary veins and/or the body of the left atrium. This implies that even a perfect endocardial pulmonary venous isolation (wide area circumferential or ostial isolation) may not fully electrically isolate the pulmonary venous muscle sleeves. Hence, epicardial access and ablation may provide higher success rates in these patients. Additionally, the autonomic nervous system is now strongly implicated in the development of atrial fibrillation. The four predominant left atrial ganglionated plexi (GP) are located along the roof of the left atrium near the left upper pulmonary vein, two inferior GP are usually found inferior to the left and right inferior veins, and a GP is usually noted anterior to the right upper pulmonary vein.14 These GP are located epicardially in the surrounding fat pads adjacent to the left atrium. Further, clinical evidence suggests that endocardial ablation in these areas improves the outcomes in patients undergoing atrial fibrillation ablation;14 therefore, epicardial ablation may further improve patient outcomes for a subset of patients. In addition to the potential for epicardial ablation, entry to the epicardial space allows access to vital structures near the left atrium, whose location may limit endocardial catheter ablation for atrial fibrillation. First, the esophagus frequently abuts the left atrium, and extensive endocardial ablation in the posterior left atrium may lead to atrio-esophageal fistula formation resulting in stroke or death. Furthermore, the right phrenic nerve is in close proximity to the right upper pulmonary vein. In our institution, we pace at high output from a circular multipolar catheter to ensure no evidence of phrenic capture prior to isolation of the right sided pulmonary veins. The left phrenic nerve usually does not present a problem during ablation within the left atrium unless near the left atrial appendage,15 but its course is near the posterolateral LV and therefore can minimize the amount of ablation that can be performed during epicardial catheter ablation for ventricular tachycardia. Recent reports have suggested epicardial access may provide a greater safety margin for ablation in the region of these vitals structures. Nakahara et al16 from our institution described the use of an intrapericardial balloon placement to prevent esophageal injury in a porcine model. Further, Buch et al17 described the use of an intrapericardial balloon to displace the left phrenic nerve during epicardial ablation for ventricular tachycardia. Recent reports have also suggested other modalities besides balloon placement to allow safer epicardial and/or endocardial ablation. Di Biase et al18 attempted to compare the use of pericardial air and/or saline versus balloon placement in 8 patients requiring epicardial ablation near the phrenic nerve. In this series of patients, the combination of air and saline was more efficacious than either saline or air alone or balloon placement. These recent reports suggest that percutaneous epicardial access may be needed in a subset of patients to facilitate more extensive and safer catheter ablation.
Supraventricular Tachycardia
Although relatively rare, ablation of supraventricular tachycardia (SVT) may require the need for epicardial access. This scenario is most prevalent with accessory pathway ablation. Valderrabano et al19 in 2004 described the experience of simultaneous endocardial and epicardial mapping in 8 patients with accessory pathway mediated tachycardia from our institution. Epicardial mapping-guided ablation was required in 3 of 8 patients with prior unsuccessful catheter ablation. These results were similar to a prior report noting 5 of 10 patients with accessory pathways requiring epicardial access were successfully ablated epicardially.20 Additionally, iatrogenic atrio-ventricular connections have been noted in the pediatric population from prior surgery that potentially require epicardial mapping and ablation.21 Finally, as mentioned previously, the right phrenic nerve courses near the anterolateral SVC and then along the right atrium. Rarely, patients with right atrial tachycardias emanating near the crista terminalis cannot be safely be treated with ablation due to phrenic nerve proximity. Lee et al22 described the use of intrapericardial balloon protection to facilitate ablation of these tachycardias in the region of the right phrenic nerve.
Future Directions
Despite the growing indications for epicardial access and catheter ablation in patients with cardiac arrhythmias, much is still unknown. The role of epicardial mapping and ablation in patients with ventricular arrhythmias is now becoming more clearly defined. The first line use of epicardial access in the ablation of patients with atrial fibrillation needs to be studied prospectively. Finally, new technologies may use the epicardial space for left ventricular lead placement as well as occlusion of the left atrial appendage23 to reduce stroke risk in atrial fibrillation.
Conclusions
There is a growing indication and need for percutaneous epicardial access to aid in the safety and efficacy of catheter ablation in patients with various cardiac arrhythmias. Future technologies may continue to expand the current indications for epicardial access, warranting the invasive electrophysiologist to become well versed in this approach.
References
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