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Persistence of a left sided superior vena cava (SVC) is the most common thoracic venous congenital anomaly. It results from obliteration of the proximal part of the right anterior and the right common cardinal veins. The left anterior cardinal vein persists, forming a left sided vena cava which drains into the coronary sinus.
A 38 year old woman with a history of idiopathic dilated cardiomyopathy and left bundle branch block underwent placement of a biventricular pacemaker. She was not previously known to have a left sided SVC which only became apparent when, after cannulation of the left subclavian vein, the guidewire passed along the left side of the mediastinum. The image shows a postero-anterior film of the implanted device and leads.
The presence of a left sided SVC is appreciated. The three leads enter the venous circulation via the left subclavian vein and pass through the left sided superior vena cava and the dilated coronary sinus to enter the right atrium (a), right ventricle (b), and a posterolateral tributary of the coronary sinus (c).
A persistent left sided SVC poses technical challenges in the placement of the left ventricular pacing lead as the usefulness of coronary sinus venography is limited by inability to occlude the relatively large vein. The condition of this patient improved following device implantation and she remains well and pacing thresholds are stable at one year follow up.