Effects of Glucagon on Atrioventricular Conduction and Ventricular Automaticity in Dogs

Abstract

The effects of glucagon, 50 µ/kg, on atrioventricular (A-V) conduction and ventricular automaticity were studied in 14 dogs. Atrial pacing was used to control the heart rate. The His bundle electrogram was recorded, and the interval from the pacing impulse (P) to the His bundle spike (H), the P-H interval, was used as a measure of A-V conduction. Ventricular automaticity was estimated in four dogs by recording vagal escape time and idioventricular rate after 60 seconds of continuous vagal stimulation. In three dogs with experimentally produced, complete heart block the effect of glucagon on idioventricular rate was estimated. When the heart rate was 250/minute, glucagon decreased the P-H interval by 30 ± 3%, from 126 ± 5 to 85 ± 5 msec (P < 0.01). When the heart rate was 310/minute, eight dogs demonstrated second-degree A-V block before glucagon; after glucagon, seven of the eight showed 1:1 A-V conduction. Glucagon increased heart rate by 38 ± 3.5%, from 148 ± 6.6 to 205 ± 8 beats/min (P<0.01). Propranolol, 2 mg/kg, did not block these effects on rate and A-V conduction. The vagal escape time and idioventricular rate with vagal stimulation and idioventricular rate in complete heart block did not change significantly after glucagon. Since glucagon profoundly increased the speed of A-V conduction without increasing ventricular automaticity, it may be useful in the treatment of A-V block especially in the presence of propranolol.