Electrophysiologic studies in patients with bundle branch block.

A total of 401 patients with chronic bundle branch block underwent electrophysiologic studies and were followed for a mean of approximately 30 months. Patients with an infranodal conduction time (H-Q) greater than or equal to 70 ms had a significantly higher incidence of progression to spontaneous second-degree or third-degree atrioventricular (AV) block (12%) compared with those with H-Q less than 70 ms (3.5%). The incidence of AV block was 25% for those with H-Q greater than or equal to 100 ms. Although the incidences of all deaths and cardiac deaths were higher for the H-Q greater than or equal to 70 ms group, there was no statistically significant difference in the incidence of sudden deaths in the two groups. A subgroup of 77 patients underwent prophylactic pacemaker insertion based on the presence of transient neurologic symptoms and/or a prolonged H-Q interval. We found no significant difference in the incidence of relief of symptoms or incidence of cardiac or sudden deaths between paced and unpaced groups. A subgroup of 25 patients with syncope underwent ventricular stimulation studies and ventricular tachycardia was induced in 14. We conclude that a markedly prolonged H-Q interval (greater than or equal to 100 ms) may be of value in detection of spontaneous AV block. Prophylactic pacing is of no value in either relief of symptoms or prolongation of life. Complete electrophysiologic studies, including ventricular stimulation studies, are indicated for patients with bundle branch block and syncope.