Does increasing heart rate via right atrial pacing affect left ventricular performance and myocardial contractility in conscious dogs?
In conscious dogs, myocardial contractility (LV dP/dt max) remains unaffected by changes in heart rate within the physiologic range (90-190 beats/min), despite reductions in stroke volume and end-diastolic volume.
An increase in heart rate produced in 12 conscious dogs by right atrial pacing resulted in a fall of end-diastolic volume, stroke volume, stroke work and end-diastolic pressure. Stroke power and the maximum rate of increase of left ventricular pressure (LV dP/dt max) were affected only slightly. Sudden large changes of rate produced transient changes in LV dP/dt max typical of the positive and negative inotropic effects of activation, but steady-state LV dP/dt max was not affected; these effects persisted after autonomic blockade with propranolol and atropine. Postural changes produced no change in LV dP/dt max even after autonomic blockade. We conclude that in this preparation, the interval-strength relationship has a plateau at the physiologic range of heart rate, i.e., myocardial contractility is unaffected by change in heart rate over the range 90 to 190 beats/min.
Noble et al. (Sat,) studied this question.
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