Atrial, His bundle (H), and ventricular electrograms were recorded by an electrode catheter in unanesthetized man. Conduction time through the atrioventricular (A-V) conduction system was subdivided into A-V nodal (A-H interval) and ventricular specialized conduction system (H-V interval). The right atrium was driven at a constant rate and the pattern of A-V conduction of premature atrial test impulses was determined as they occurred progressively earlier in the cardiac cycle. In the type 1 response, conduction delay and block were limited to the A-V node only. The type 2 response was characterized by progressive conduction delay in both the A-V node and ventricular specialized conduction system with block occurring in several instances in the latter. In the type 3 response there was also a progressive delay in A-V nodal conduction time, and a sudden marked delay in conduction in the ventricular specialized conduction system. Conduction block occurred distal to the His bundle depolarization. The relevance of conduction delay and block in the different regions of the A-V conduction system to the full recovery time and the relative, functional, and effective refractory periods of A-V conduction are indicated.
ADDITIONAL KEY WORDS premature atrial impulses functional refractory period effective refractory periodHis bundle electrogram conduction block conduction delay full recovery time relative refractory period • Conduction of impulses from the atria to the ventricles involves propagation through a series of elements known as the atrioventricular (A-V) conduction system. This system includes the A-V node and the ventricular specialized conduction system (VSCS), which includes the bundle of His, the bundle branches and peripheral Purkinje network (1).Previous investigations in dogs have shown some of the physiological properties of A-V conduction by studying the propagation of premature atrial impulses (2-5). The characteristic types of A-V delay differed in different
Overall, ACE and FCH PET/CT showed excellent concordance, on both a per-lesion and a per-patient basis, suggesting that both tracers perform equally for recurrent prostate cancer staging.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.