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