Silent obstruction of SVC with collateral circulation after cardioverter defibrillator implantation.

A 47-year-old woman with dilated cardiomyopathy underwent a single-chamber implantable cardioverter defibrillator (ICD) implantation for sustained ventricular tachycardia 10 years previously. Because bradycardia became clinically evident with beta-blocker therapy for heart failure, we attempted an upgrade from a single-chamber to dual-chamber ICD for physiological pacing. Venography revealed complete obstruction of the superior vena cava (SVC) with a collateral route through a huge azygous vein (Pictures A, B, C). SVC syndrome caused by pacemaker leads is only occasionally seen and its incidence has been estimated to be less than 1 in 1,000 pacemaker patients. The azygous vein is fre-