Retrograde conduction in complete heart block.

In complete heart block, absolute independence between atrial and ventricular activity does not always occur. Several mechanisms may be postu-lated to explain this phenomenon. One is incom-plete atrio-ventricular block; another is atrio-ven-tricular synchronization and accrochage (Marriott, 1956; Schubart, Marriott, and Gorten, 1958; Ettinger, 1965). A third possibility rarely con-sidered is unidirectional block in the atrio-ven-tricular conduction system, that is, forward block may exist in complete atrio-ventricular block but retrograde ventriculo-atrial conduction may be preserved. The purpose of this report is to present relevant data in 7 patients with complete heart block studied with bipolar catheter electrodes in both right atrium and right ventricle. An eighth patient with 2: 1 atrio-ventricular block was investi-gated by similar techniques. Gubbay and Mora (1964) have previously reported a patient with com-plete heart block in whom right ventricular pacing resulted in retrograde ventriculo-atrial conduction, with suppression of the sinus node by raising the rate of the ventricular stimulus. Fusion P waves were also observed. Unlike our cases, retrograde conduction and retrograde P waves were evident in the control electrocardiogram before institution of ventricular pacing. Winternitz and Langendorf (1944) have also described retrograde ventriculo-atrial conduction in complete heart block. SUBJECTS AND METHODS Seven patients with complete heart block and idio-ventricular rhythm and one with 2: 1 block were studied, whose ages ranged from 62-76 years. In five, the cause was arteriosclerotic heart disease, and in three, it was heart disease of undetermined etiology. A 3-5 bipolar cathetert was passed to the right ven-