Persistent Left Superior Vena Cava (PLSVC) and the Vein of
Marshall (VOM)
PLSVC occurs when the left superior cardinal vein fails to regress to
the VOM, as should normally occur (110). A recent study described the
possible arrhythmogenic role of PLSVC (111). Data on the use of
cryotherapy for isolation of SVC (112) and PLSVC (113,114) has been
limited to a few cases but appears to be an attainable alternative.
The VOM is a vestigial fold, which marks the site of the embryological
left SVC. This structure has been particularly important in the setting
of atrial tachycardias and AFL post-AF ablation (115). In most cases,
the VOM triggers can be detected by direct cannulation of the CS with a
multipolar catheter. Direct ethanol injection into the VOM has been
described, as it allows for specific ablation of the vascular structure,
its intrinsic electrical activity, the mitral isthmus, the neighboring
myocardium, associated PV connections, and parasympathetic innervation
(116). Chugh et al. (117) reported 56 cases in which the VOM was a
therapeutic target based on pacing data. The mapping was suggestive of
VOM-mediated LA–PVs connections, or VOM-mediated macro-reentrant
circuits, or focal tachycardias. The RCT VOM Ethanol Infusion for
Persistent Atrial Fibrillation (VENUS)has shown improved freedom from
AT/AF with additional VOM ethanol infusion in patients undergoing their
first CA (118). However, in patients undergoing redo ablation, addition
of VOM EI did not improve outcomes(119). Interestingly as described
before, adjunctive VOM EI with linear ablation had favorable outcomes in
PersAF(33). (Figure 12)