The relative risk of spontaneous complete atrioventricular block in elderly patients with impaired intra-ventricular conduction.

We reviewed 144 consecutive patients with symptomatic high grade atrioventricular block. Cases due to congenital heart disease, acute myocardial infarction, cardiac surgery or digitalis toxicity were excluded. Of the remaining, we chose 71 patients in whom atrioventricular conduction was observed either intermittently during complete heart block (CHB) or in electrocardiograms taken within two years prior to documentation of CHB. The mean age was 69 years, with the peak incidence in the seventh decade in 43 men and eight decade in 28 women. Bundle branch block (BBB) was present in 76% of patients as follows: 47% had right BBB (20% with normal QRS axis, 20% with left axis deviation and 7% with right axis deviation), 17% had left BBB (11% with normal QRS axis and 6% with left axis deviation) and 12% had either alternating BBB, right BBB with alternating axis deviation or atypical BBB. "Trifascicular block" patterns accounted for 21% of the total group of CHB. We also studied the prevalence of various patterns of BBB in a group of 2000 random hospital patients of comparable age and sex exclusive of those with acute myocardial infarction and heart surgery. The risk of CHB for the various patterns of BBB was calculated relative to normal intraventricular conduction. All patterns of BBB carried a considerably increased relative risk of CHB, (P smaller than .01). The relative risk was highest for RBBB with left axis deviation and lowest for LBBB with normal or left axis deviation. In the men, 74% had QRS patterns of "bifascicular" or "trifascicular" block during atrioventricular conduction. By contrast, 71% women had atrioventricular beats showing either no BBB or right BBB with normal QRS axis. QRS pattern during CHB was unchanged from that during atrioventricular conduction in 52% if cases (rabge 38%-76% with different QRS patterns) suggesting idiojunctional pacemaker. CHB in these cases was thought to be due probably to coexistent disease in the AV node or His bundle. Although the concept of uni-, bi- and trifascicular block patterns has been useful in identifying patients at greater risk of CHB, the predictability of the electrocardiogram has obvious limitations, particularly in women.