Prognostic value of infranodal conduction time in patients with chronic bundle branch block.

His bundle recordings were obtained in 121 patients with chronic bundle branch block and the patients were followed for a mean period of 18 months. Seventy-nine patients had an infranodal conduction time (H-Q) less than 70 msec while 42 had H-Q greater than or equal to 70 msec. There was no significant difference in mean age, smoking history, diabetes, syncope, dizziness, blood pressure, and serum cholesterol or triglyceride levels between the two groups. There was a significantly greater incidence of progresssion to second degree or third degree atrioventricular block (9/42, 21%), and of severe congestive heart failure (16/42, 38%) in patients with H-Q greater than or equal to 70 compared with those with H-Q less than 70 (1/79, 1.3%; and 13/79, 16%, respectively). The risk of sudden death was significantly greater only in the group with H-Q greater than or equal to 70 and severe congestive heart failure. There was no correlation between the presence of first degree atrioventricular block and/or any particular type of bundle branch block pattern with sudden death and/or progression to second degree or third degree atrioventricular block. Analysis of the surface electrocardiogram is only of limited value in predicting high risk patients with chronic bundle branch block. Electrophysiologic studies are of greatest value in patients with bundle branch block with transient neurologic symptoms in whom no cause for the symptoms is evident.