Left Atrial Appendage (LAA)/Ligament of Marshall
As previously discussed, patients with advanced AF have more non-pulmonary vein triggers, such as the posterior wall, and this can also include the LAA and Ligament of Marshall (LOM).38 Excluding the LAA at the time of the hybrid epicardial ablation stage can address a site of AF triggers through electrical isolation as well eliminating a predominant site of thrombus in AF.39 The addition of LAA exclusion is often performed in hybrid thoracoscopic ablation, which is the subject of several clinical trials (NCT01246466; NCT02695277; NCT02441738). The LAA exclusion technique involves epicardial clip exclusion of the LAA by a simultaneous left thoracoscopic approach.39 In the absence of randomized controlled trial data evaluating the effectiveness and safety of Hybrid Convergent with LAA exclusion, multi-disciplinary care teams are using the available evidence and determining patient selection for whom they feel the benefit-risk profile is acceptable to proceed with this approach.40 In a study over 6 years, 139 patients with persistent AF and no history of prior ablation underwent a Hybrid convergent procedure. In April 2016, LAA exclusion was added to the study procedures. Of the 139 patients, 59 had only Hybrid ablation and 64 had the concomitant Hybrid ablation with LAA exclusion. Both groups were similar with respect to age and gender as well as BMI, which was elevated in both groups (>32). In the Hybrid plus LAA clip group, the patients appeared to have a longer time since AF diagnosis although not statistically significant (mean of 6.4 years vs 4.6 years; p=0.15). Other baseline data and comorbidities were similar between the groups. The Hybrid plus LAA exclusion group had a greater freedom from AF recurrent compared to Hybrid ablation only group (77% vs 58%; p=0.04).41
Initially described by British surgeon John Marshal in the 1800s, the LOM and Vein of Marshall (VOM) are remnants of the embryonic left superior vena cava with the VOM enclosed within the LOM.42,43The cluster of nerve cells known as the autonomic ganglionated plexi are found in abundance in the epicardial fat, embedded along the Ligament of Marshall, near the pulmonary vein-left atrial junctions. This composition of the epicardial fat stimulates triggers, enabling the perpetuation of AF.44If the ablation procedure is expanded to include targeting the GP specifically located in the LOM in addition to PVI, this may improve the success rates in patients with paroxysmal as well as persistent AF.45 These ganglionated plexi are also implicated in left atrial remodeling and substrate changes, commonly found in more progressive forms of AF.46 In a study examining the effect of ethanol infusion added to the VOM during catheter ablation in persistent and long-standing persistent AF, patients receiving the combined catheter and VOM ethanol infusion had higher rates of freedom from AF vs the catheter only group (49.2% vs 38%; p=0.04). Due to the LOM harboring the source of AF and AT triggers, targeting this anatomical region rich with theses ganglionated plexi during epicardial ablation along with LAA exclusion is of increasing interest.47