LAUSR

The coronary sinus venous system (CVS) has played a multifaceted role in cardiac electrophysiology. The primary utility of this structure has been for positioning pacing electrodes in its various branches to facilitate cardiac resynchronization therapy. However, its unique epicardial location has allowed it to also serve as a vantage point in the mapping and ablation of various cardiac arrhythmias but especially idiopathic focal ventricular tachycardias. One of the first comprehensive series that showed the utility of mapping and ablating ventricular arrhythmias (VAs) within the CVS was the paper by Daniels et al. [1] In that study, the authors identified ECG features of VAs that were successfully targeted from within the CVS. Since that publication there has been a growing body of literature reporting approaches and outcomes of catheter ablation of VAs from the CVS [2,3]. The early enthusiasm with mapping and ablation of VAs from CVS has been tempered by recognition of various limitations associated with this approach. Those include, 1) anatomic constraints of the CVS and its various branches which may not always travel through locations that require mapping, 2) diminishing dimensions of distal CVS branches that may not permit mapping with standard catheters, 3) delivering adequate radio-frequency (RF) energy within the narrow confines of the CVS, 4) proximity of CVS to critical structures, especially major coronary arteries, etc. [2e4] The electrophysiology community has responded to these challenges by improving the tools at their disposable. In particular, the advent of deflectable sheaths and smaller caliber multi-polar catheters have improved our ability to navigate andmap the distal aspects of CVS [2e4]. Also, the irrigated and cooled tip catheter platforms can facilitate better lesion creation. It is also being increasingly recognized that mapping within the CVS may serve to identify the arrhythmia site of origin (SOO) which can then be more effectively targeted from adjacent cardiac locations (cusp and outflow tract region) that permit better RF energy delivery [2,3]. Thus the CVS remains an important area for mapping and ablation of VAs and electrophysiologist continue to report their experience in working within this