Reflex regulation of atrioventricular conduction.

We evaluated the time course of baroreflex modulation of atrioventricular (AV) nodal conduction in anesthetized dogs (n = 28). Beat-by-beat changes in heart rate (HR) and AV interval (AVI) evoked by transient alterations in arterial pressure (AP) were recorded in the intact state, after vagotomy, and following stellectomy. Under each experimental condition, alterations in AP induced parallel changes in HR and AVI with maximum HR and AVI responses occurring simultaneously. In three animals, AP alterations elicited pacemaker shifts that markedly altered AVI. Reflex changes in AVI were also examined during atrial pacing. When pacing at a low (120 beats/min) versus a high (190 beats/min) level of heart rate, reductions in AP decreased AVI to a significantly lower absolute value in the intact state, after vagotomy, and following stellectomy. However, under each experimental condition, decreases in AP elicited marked changes in AVI at either level of pacing. We conclude that baroreflex-induced changes in sympathetic and parasympathetic activity influence the sinoatrial and AV nodes simultaneously, predominate over the effects of changes in HR at the AV node, and may induce pacemaker shifts that influence the measurement of AVI.