A study of atrioventricular conduction in man using premature atrial stimulation and His bundle recordings

In 20 subjects the effects of controlled premature atrial stimulation on atrioventricular conduction was studied using an electrode catheter technic for recording electrical activity of specialized conducting fibers. The least common type of response observed was that in which A-V conduction delay was limited only to the A-V nodal region (type A). This type of response was obtained whenever the conduction delay in the A-V nodal region increased in direct proportion to the prematurity of a propagated atrial impulse. It was characterized by a progressive prolongation in the P-H interval with ultimate failure of conduction occurring proximal to the His bundle. In type B response, conduction delay occurred in both the A-V nodal and His-Purkinje systems. The recording of a characteristic A-V nodal potential permitted the localization of A-V nodal delay to the N-H interval.

Effects of glucagon on atrioventricular conduction and ventricular automaticity in dogs

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.