Inappropriate shock during left ventricular threshold measurement in a patient with coexisting ICD and a biventricular pacemaker.

Cardiac resynchronization therapy (CRT) using coronary sinus (CS) leads for biventricular stimulation is an established method for the therapy of congestive heart failure (CHF) in the case of inter- or intraventricular conduction delays. There are some patients having two separate devices: an ICD and a biventricular pacemaker. This case report describes an unusual interaction of these systems: an inappropriate VVI defibrillator shock during left ventricular threshold measurement in a biventricular pacemaker implanted on the other side.