Effect of lidocaine on escape rate in patients with complete atrioventricular block: B. Proximal His bundle block.

Lidocaine was administered intravenously (a loading dose of 1.5 mg/kg body weight followed by a 3 mg/min infusion) to 10 patients with complete atrioventricular (A-V) block proximal to the His bundle and A-V junctional escape rhythm. A-V block was not due to an acute myocardial infarction in seven patients (group I) and was due to an acute inferior wall infarction in three patients (group II). Lidocaine had either no or only a slight depressant effect on the rate of the escape pacemaker in patients in group I but caused severe bradycardia or asystole in two of three patients in group II. Lidocaine had no consistent effect on the atrial rate and did not change the QRS duration and H-V intervals in any patient. These observations are consistent with the results of animal studies that showed that lidocaine selectively depressed conduction in ischemic or depolarized myocardium. The findings also suggest that the use of lidocaine without prior insertion of a pacemaker is unsafe in patients with acute myocardial infarction and complete A-V block proximal to the His bundle.