Intermittent bundle-branch block in patients with accessory atrio-His or atrio-AV nodal pathways. Variants of the Lown-Ganong-Levine syndrome.

Intracardiac electrophysiological studies were performed in two patients with a documented history of repetitive supraventricular tachyarrhythmias. Case 1, with short PR interval and narrow QRS complexes had a short AH interval and intermittent right bundle-branch block. Thus the short PR wide QRS syndrome is not always a result of the Wolff-Parkinson-White syndrome but can also be seen in the Lown-Ganong-Levine syndrome coexisting with bundle-branch block. Case 2, with normal PR and AH at the lower limits of normal, showed the dual pathway response to atrial pacing that can occur in patients with Lown-Ganong-Levine syndrome. He also had tachycardia-dependent right bundle-branch block and left posterior hemiblock. Therefore, neither the short PR interval nor the narrow QRS complexes characterized these forms of pre-excitation. The constant features were, from the clinical viewpoint, the occurrence of repetitive supraventricular tachyarrhythmias, and electrophysiologically the abnormal response to atrial stimulation.