Effect of ventricular extrasystoles on idioventricular rhythm in patients with complete heart block.

Idioventricular rate, QRS width, site of block and responses to premature ventricular stimulation were studied in 23 patients with chronic complete heart block in an attempt to distinguish patients liable to syncopal attacks. Seven patients were asymptomatic, five gave a history of presyncope and 11 of syncope. Although the mean idioventricular rate of the nine patients in the narrow QRS group (39.7 per min) was significantly faster than that of the 14 patients in the wide QRS group (35.3 per min; P less than 0.05), the rate did not distinguish symptomatic patients within either the narrow or the wide QRS groups. His bundle studies of the site of block and the effect of single and paired right ventricular stimulation upon idioventricular rhythm were also unhelpful. The response of the return cycle to increasingly premature ventricular extrasystoles, however, proved more complex than was anticipated.