Detailed electrophysiologic evaluation of the sinus node and atrium was undertaken in 26 patients. Half had bi- or trifascicular conduction disease (BTD) and the others had a narrow QRS (non-BTD). BTD and non-BTD groups were comparable with respect to age, sex and incidence of coronary artery disease (CAD). One or more electrophysiologic abnormalities of the sinus node or atrium were found in nine of 13 BTD patients (more than one abnormality was present in five) and a single isolated abnormality was seen in one of 13 non-BTD patients (p < 0.01). PA interval (41 ± 3 vs 28 ± 3 msec), sinus node recovery time (1289 ± 76 vs 988 ± 44 msec), corrected sinus node recovery time (369 ± 62 vs 221 ± 35 msec), atrial effective (253 ± 14 vs 205 ± 11 msec) and functional (324 ± 15 vs 272 ± 9 msec) refractory periods were significantly longer in BTD than in non-BTD patients (p < 0.05). These differences were greatest when CAD patients were excluded and primary BTD patients (BTD without other evident cardiovascular disease) were compared with controls (narrow QRS without CAD). Sinoatrial conduction time was significantly longer in primary BTD patients (126 ± 11 msec) than it was in controls (82 8 msec).
We conclude that electrophysiologic abnormalities of the sinus node and atrium are extremely common in patients with BTD, particularly primary BTD, and may cause symptomatic dysrhythmias.