Effects of autonomic nerve stimulation, asynchrony, and load on dP/dtmax and on dP/dtmin

We studied asynchronous depolarization effects on mechanical responses to autonomic nerve stimulation (ANS) in 21 dogs with AV nodal block. In 11 of these dogs, we kept mean aortic pressure (AoP) at 85 mmHg and paced the hearts at 120 beats/min. We paced, in random order, either the LV apex or the RV anterior or lateral wall to increase the asynchrony of ventricular contraction and relaxation. During pacing at each site, we determined maximum rate of LVP rise (dP/dtmax) and fall (dP/dtmin) before and during stimulation of cardiac sympathetic and vagal nerves and during combined nerve stimulation. Changing the pacing site from LV to RV decreased dP/dtmax and also dP/dtmin (P less than 0.001); the decrease was most pronounced when we shifted pacing from LV apex to RV anterior wall. Sympathetic stimulation increased (P less than 0.0001) and vagal stimulation decreased (P less than 0.001) dP/dtmax and dP/dtmin during pacing at each site. Effect of vagal stimulation was substantially enhanced during concomitant sympathetic stimulation. However, the magnitude of changes in dP/dtmax and also in dP/dtmin due to nerve stimulations during pacing at each ventricular site was similar. In 10 additional dog experiments, we also varied AoP from a mean value of 74 to 113 mmHg during pacing at each site. An increase in AoP augmented dP/dtmax by a mean value of 582 mmHg/s and increased dP/dtmin by a mean value of 617 mmHg/s (both P less than 0.0001). Sympathetic stimulation increased, whereas vagal stimulation decreased, dP/dtmax and dP/dtmin at each afterload (P less than 0.001).