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)