The influence of the parasympathetic nervous system on atrioventricular conduction

Abstract

The parasympathetic nervous system plays a significant role in the normal process of AV excitation. The AV node is innervated richly by vagal fibers. Even relatively low levels of brief or sustained vagal stimulation may alter AV conduction profoundly. However, the effect of autonomic activity on the overall AV conduction process is not dependent solely on the direct response of the AV node to neural activity. Neural activity also has appreciable effects on cardiac rate, pacemaker location, and atrial activation patterns. Furthermore, neurally induced changes in the action potential from higher AV nodal regions can markedly alter the conduction time through the lower elements of the conducting system. Each of these indirect responses also has an effect on AV conduction time, some in a direction just opposite to those of the direct neural influences. The overall effect of vagal activity on AV conduction, then, is the summated resultant of the direct and the many indirect effects. There will undoubtedly be a much better definition in the future of the neural effects on discrete elements of the AV conduction system and of the interactions among the various elements. Perhaps such work will lead to an enhanced understanding of the functional significance of discrete bursts of vagal activity in a cardiac cycle and of the role of the autonomic nervous system in the genesis of arrhythmias. These areas have not received sufficient attention.