Comparative study on atrial functional refractory period and atrioventricular nodal effective refractory period in the dog

In order to observe further electrophysiologic characteristics of atrioventricular (AV) conduction,We compared atrial functional refractory peroid (AFRP) and atrioventricular nodal effective refractory period (AVNERP) in 8 dogs. AV condution was assessed by atrial extrastimulus technique using at least two basic cycle lengths. The electophysiologic parameters were recorded before and after administering intravenous Metoprolol to block the β receptor in the heart, and plotted into the AV conduction curve. As a result,the AVNERP could not be measured in any dog. AV conduction curve showed significant changes before and after the administration of Metoprolol at equivalent basic cycle length,AFRP also showed significant prolongation. It domonstrated that the refractory periods of cardiac conduction are obvious difference in different species. The properties that AVNERP is permanently shorter than AFRP in the dog may be functional manifestation of its physiologic characteristics.