Technical failure to perform cardiac resynchronization therapy: use of cardiac magnetic resonance imaging techniques to clarify a left-sided superior vena cava and coronary sinus morphology.

The most common reason for failure to implant a left ventricular lead to deliver cardiac resynchronization therapy is the presence of unfavourable coronary venous anatomy. The present report illustrates the use of cardiac magnetic resonance imaging to delineate the anatomy of a left-sided superior vena cava in two patients in whom permanent cardiac pacing was unattainable.