RELATIONSHIP BETWEEN DIFFERENT RECOVERY CURVES REPRESENTING RATE-DEPENDENT AV NODAL FUNCTION IN RABBIT HEART

Nodal Function and Recovery Measures. Introduction: The rate-dependent changes in atrioventricular (AV) nodal conduction time show different characteristics depending upon whether the conduction times are plott ed against the atrial interval (AA-recovery curve) or His-atrial inter val (HA-recovery curve). This study characterizes these differences in the contest of controlled changes of nodal functional properties, det ermines their functional significance, and tests the hypothesis that t hey are related solely to the nodal conduction time of the last beat ( last conduction time) before the premature beat. Methods and Results: Premature nodal conduction times obtained in isolated rabbit heart pre parations under various steady-state and transient conditions were plo tted as a function of the corresponding HA and AA intervals, as well a s the AA interval corrected for the last conduction time. Under all co nditions, the corrected AA-recovery curve was indistinguishable in sha pe from the HA-recovery curve, and as such reflected similar underlyin g nodal functional properties. Moreover, a selective increase in the l ast conduction time, induced in the absence of time-dependent effects associated with the functional property of fatigue, shifted the AA-rec overy but not the HA-recovery curve upward with respect to the control curve. Conclusion: The last conduction time accounts entirely for dif ferences between AA-recovery and HA-recovery curves that otherwise ref lect the same underlying nodal functional state. Thus, a consistent as sessment of rate-dependent changes in nodal function can be achieved w ith either measure of recovery time.