Two patients with a history of paroxysmal supraventricular tachycardia were analysed by His bundle and intra-atrial recordings. The electrocardiogram showed sinus bradycardia in I patient and sinus bradycardia with sino-atrial Wenckebach in the other. The conduction times through the A V node and His Purkinje system were normal in both cases. The intra-atrial conduction time was slightly prolonged (55 msec) in one and normal (40 msec) in the other during normal sinus rhythm. In both cases with atrial pacing from high right atrium, the conduction time from the pacing impulse (PI) to atrial activation in the area of the AVjunction (PI-A) progressively lengthened with increase in atrial pacing rate and finally classical second-degree Wenckebach type of block was manifested at cycle lengths of 460 and 465 msec. The pacing impulse to QRS interval (PI-R) showed a progressive increase before the blocked stimulus. The lengthening of the PI-R interval was due to progressive increase in the intra-atrial (PI-A) conduction time. In the dropped beats, the pacing impulse was notfollowed by an A deflection. This observation indicated Type I block within the atrium. Similarly, during induced premature atrial beats, the PI-A time progressively lengthened as the coupling interval was shortened. These findings were reproducible and were seen despite a fourfold increase in stimulus strength and changes in electrodes and site of stimulation along the lateral right atrial border. This study (I) shows second-degree Wenckebach block within the atrium; (2) supports the existence of sinoatrial Wenckebach; and (3) suggests the atrium as another possible site for re-entry and a cause for supraventricular tachycardia because of the degree of delay and block exhibited within the atrium.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine