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 plotted against the atrial interval (AA‐recovery curve) or His‐atrial interval (HA‐recovery curve). This study characterizes these differences in the context of controlled changes of nodal functional properties, determines their functional significance, and tests the hypothesis that they 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 preparations under various steady‐state and transient conditions were plotted as a function of the corresponding HA and AA intervals, as well as the AA interval corrected for the last conduction time. Under all conditions, the corrected AA‐recovery curve was indistinguishable in shape from the HA‐recovery curve, and as such reflected similar underlying nodal functional properties. Moreover, a selective increase in the last conduction time, induced in the absence of time‐dependent effects associated with the functional property of fatigue, shifted the AA‐recovery but not the HA‐recovery curve upward with respect to the control curve. Conclusion: The last conduction time accounts entirely for differences between AA‐recovery and HA‐recovery curves that otherwise reflect the same underlying nodal functional state. Thus, a consistent assessment of rate‐dependent changes in nodal function can be achieved with either measure of recovery time.