A 76 year old man with dilated ischaemic cardiomyopathy, severe left ventricular dysfunction, and left bundle branch block was admitted for implantation of a biventricular internal cardioverter-defibrillator. The procedure was performed via the left subclavian approach and pacing leads were implanted into the right atrium and right ventricle. Coronary sinus (CS) angiography was then carried out to identify a suitable target vein for the left ventricular lead. Initial angiography (left anterior oblique (LAO) 10 projection) suggested that the CS was occluded with a small venous tributary (panel A, double arrow) leading up to the left subclavian vein. Further contrast injections into the CS, however, demonstrated that the CS was widely patent (panel B) with an excellent posterolateral (PL) vein arising from the main CS body. The initial stump was identified as the vein of Marshall (VM), the remnants of the left cardinal vein that may give rise to a persistent left superior vena cava. While these are well documented, a patent vein of Marshall is extremely unusual. On this occasion the guide catheter sat preferentially within this channel and gave the appearance of a CS which was unfavourable for lead placement. It was only after further manipulation of the guide catheter and contrast injections that the true anatomy of the CS was revealed.

We feel this is an important anatomical variant to be demonstrated, as an increasing number of CS angiograms are performed because of biventricular device implants. This may help the unsuspecting cardiologist who may encounter this anomaly and initially conclude that the CS is unfavourable for pacing.