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 postulated to explain this phenomenon. One is incomplete atrio-ventricular block; another is atrio-ventricular synchronization and accrochage (Marriott, 1956; Schubart, Marriott, and Gorten, 1958; Ettinger, 1965). A third possibility rarely considered is unidirectional block in the atrio-ventricular 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 investigated by similar techniques. Gubbay and Mora (1964) have previously reported a patient with complete 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 ventriculoatrial conduction in complete heart block.