|7||Epicardial Access for Left Atrial Appendage Occlusion: Techniques and Challenges|
|Sharan Prakash Sharma, MD; Mohit K. Turagam, MD; Dhanunjaya Lakkireddy, MD|
Percutaneous epicardial access was first described by Sosa and coworkers in 1996 for the management of recurrent ventricular tachycardia from an epicardial substrate in Chagas cardiomyopathy.1 Since then, this approach has expanded for the management of various cardiac arrhythmias, including atrial fibrillation, atrial tachycardia, accessory pathways and ventricular tachycardias especially after a failed endocardial ablation.2–5 Due to its unique capability to access the left sided-cardiac structures by this approach several novel innovations such as left atrial appendage (LAA) ligation, epicardial lead implantation and drug-delivery techniques are currently being studied.6
Percutaneous epicardial LAA ligation using the LARIAT system (SentreHEART, Inc., Redwood City, CA) is one such technique that has emerged in the past decade for stroke prevention and reducing AF burden. The LARIAT utilizes the anterior pericardial puncture to deliver the preformed suture through the epicardial delivery snare that aligns with the magnet-tipped wire endocardially via transeptal access. While performing the LARIAT procedure, there are several anatomical challenges and pericardial anomalies that needs careful consideration from an interventional electrophysiologists’ perspective.
ANATOMICAL CONSIDERATIONS AND PREPROCEDURAL PLANNING
The pericardium is a fibrous sac that surrounds the heart and is attached to the walls of the great vessels and the diaphragm. It consists of two layers: the visceral pericardium and the parietal pericardium. The visceral pericardium is adherent to the epicardial surface of the heart. The parietal pericardium (0.8–2.5 mm thick) consists of an outer fibrous layer and an inner serosal layer, which is the reflection of the visceral pericardium. The potential space between the parietal and the visceral pericardium is called pericardial space and normally contains 15–50 mL of serous fluid. The visceral pericardium continues posteriorly to form the transverse sinus and the oblique sinus. The transverse sinus is bounded by the aorta and the pulmonary artery anteriorly and the superior vena cava posteriorly, while the oblique sinus bounded by the inferior vena cava and the right and left pulmonary veins.
While performing LAA ligation, it is critical to have a thorough understanding of the cardiac structures surrounding the LAA in order to access the pericardium at the optimal anterior location. Otherwise, it would be impossible to gain access to the LAA by negotiating the cardiac structures that lie in between the puncture site and the LAA. A preprocedural cardiac computed tomography (CT) is invaluable for careful planning of the procedure including the epicardial access route. Figure 7.1 demonstrates the ideal trajectory of the pericardial puncture and access to the LAA. The angle between the needle and the chest wall determines the site of the ventricle accessed; a steeper (less acute angle) tends to access the posterior right ventricle, while a less steep angle (more acute angle) tends to access the anterior right ventricle.
Once pericardial access is obtained, the catheter must negotiate the adjoining blood vessels that lie in close vicinity to the LAA. Figure 7.2 demonstrates the relationship of the various blood vessels in relationship with the LAA.
Figure 7.1 CT roadmap showing orientation of important structures and preferred angle of approach.
Figure 7.2 Anatomical relationship of left atrial appendage with various vascular structure. Panel A: LAA relationship with pulmonary artery, pulmonary vein, and coronary artery. From Shahoud JS, Tivakaran VS. Cardiac Dominance. [Updated 2020 Feb 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: www.ncbi.nlm.nih.gov/books/NBK537207/ Panel B: The pulmonary artery is shown lying in front of LAA; epicardial exclusion should be avoided in such instance. Panels C and D: The course of superior epigastric artery and left internal mammary artery (blue arrow) are shown. The movement of the needle must be tailored to avoid injury to these vessels.
The pulmonary artery is typically located superior and medial to the LAA, but anatomic variations in pulmonary artery in relation to LAA have been described. In addition, the internal mammary artery courses vertically and parallel to the sternal border, giving off perforating vessels to the chest wall. The internal mammary artery bifurcates into the superior epigastric artery and the musculophrenic artery around the sixth intercostal space. Inferior to the bifurcation, the distance between the inferior mammary artery and the sternum and the xiphoid is the maximum pericardial access at that location that can minimize collateral damage.
For epicardial LAA closure, the needle is advanced towards the one o’clock position in the left anterior oblique view, so that it lies lateral to the pulmonary artery (Figure 7.3). In addition, inferior access, or apical access, creates a secondary curve in the soft tip and device that negatively affects the control of the LARIAT. Hence, coming into the right ventricle at a more shallow angle reduces the likelihood of perforations or over advancement of the device, as shown in Figure 7.4. The left circumflex coronary artery is the other important structure that courses in the atrioventricular groove and lies at the ostium of the LAA. Coronary angiography may be required during the procedure in the setting of diffuse precordial ST elevation, ventricular arrhythmias, or hemodynamic instability. The proximity of the left phrenic nerve needs careful consideration as it runs over the aortic arch and the pulmonary trunk anterior to the LAA and then passes anterolateral as it courses along the left ventricle.
Figure 7.3 A good approach has catheter tip aiming right down the center of LAA in the left anterior oblique view.
Figure 7.4 A shallow epicardial access reduces the likelihood of right ventricle perforations.
PERICARDIAL ACCESS TECHNIQUE
All anticoagulants, including antithrombotics, are discontinued before obtaining epicardial access. The pericardial space is most commonly accessed by subxiphoid approach. The entry point is 1 to 2 inches below the tip of the xiphoid parallel to the sternum with the needle aiming toward the left midclavicular region. For left atrial appendage occlusion (LAAC), an anterior pericardial approach is the preferred route. The precise entry point and the direction of the needle are crucial components of gaining successful pericardial access. For anterior puncture, the needle should be no more than 15–30 degrees off the skin surface. Several epicardial access techniques have been described (Table 7.1). Two needles are commonly used: the conventional Sosa approach uses a 17-gauge blunt-tipped epidural needle (Tuohy), whereas the micropuncture “needle-in-needle” technique most commonly used in the clinical setting involves insertion of a short 18-gauge needle through which a long 21-gauge micropuncture needle is inserted. Sometimes the 21-gauge micropuncture needle can be used directly without the need for another large-bore needle in thin patients where the support of the outer large-bore needle might not be necessary. The needle is directed toward the cardiac silhouette at one o’clock position under fluoroscopic guidance in the anteroposterior and lateral views. The left lateral view helps identify the distance between the pericardial space and the retrosternal space. Needle movement must be coordinated with diaphragmatic movements with slow injection of contrast. When the needle touches fibrous pericardium, cardiac pulsation can be palpable. Tenting the pericardial sac by tightly holding the needle for a few respiratory cycles can puncture the pericardial sac. On the other hand, the needle can be advanced while the patient is under apnea using cardiac pulsations (Figure 7.5, Panels A and B). Penetration of the fibrous pericardium is associated with a palpable “give-in” that can be especially noticed with the 18-gauge needle. After confirming the correct position of the needle in pericardial space, a 0.35-inch guidewire is introduced in the pericardial space through the needle (Figure 7.5, Panel C). The guidewire is also monitored with fluoroscopy to make sure it remains within the cardiac silhouette. In difficult cases, maneuvers such as creating a less acute angle on the needle, rotating the needle tip, or inserting a stylet can be performed under careful fluoroscopy guidance. Once the location of the needle is confirmed, a transseptal access is performed. If the wire goes outside the cardiac silhouette it represents either an right ventricle puncture or a pleural puncture. After transseptal access is secured in place, the epicardial puncture site is then sequentially dilated over the guidewire for placement of the 14-Fr soft-tipped epicardial guide cannula. The 0.035-inch epicardial magnet-tipped guidewire is then placed through to achieve an end-to-end magnetic union with the endocardial guide-wire (Figure 7.6). The LARIAT snare is advanced over the epicardial magnet-tipped wire and positioned over the proximal part of the LAA, guided by endocardial catheter that is advanced by transseptal approach. Once properly positioned, the snare is closed.
Table 7.1 Comparison of Different Epicardial Access Techniques
aGunda S, Reddy M, Pillarisetti J, et al. Differences in complication rates between large bore needle and a long micropuncture needle during epicardial access: Time to change clinical practice? Clrc Arrhythm Electrophysiol. 2015;8:890-895.
bDi Biase t, Burkhardt JD, Reddy V, et al. Initial international multicenter human experience with a novel epicardial access needle embedded with a real-time pressure/frequency monitoring to facilitate epicardial access: Feasibility and safety. Heart Rhythm 2017;14:981-988.
cGreenbaum AB, Rogers T, Paone G, et al. Intentional right atrial exit and carbon dioxide insufflation to facilitate subxiphoid needle entry into the empty pericardial space: first human experience. JACC Clin Electrophysiol.