Influence of incremental changes in heart rate on mitral flow velocity: Assessment in lightly sedated, conscious dogs

AbstractTo determine the effect of increasing heart rate on mitral flow velocity variables, the time constant of left ventricular isovolumic relaxation and the transmitral pressure gradient, 16 lightly sedated, conscious dogs were studied with Doppler echccardiography during incremental right atrial pacing (n = 16) or the administration of atropine (n = 8) or isoproterenol (n = 8).With increasing heart rate, similar changes were seen with all three interventions and included: 1) mitral flow velocity in early diastole and the early diastolic transmilral pressure gradient either changed minimally or did not change; 2) mitral flow velocity at the start of and as a result of atrial contraction progressively increased; 3) the “absolute” increase in mitral flow velocity and transmitral pressure gradient at atrial contraction demonstrated a biphasic response, initially decreasing as heart rate increased, but then increasing again when atrial contraction occurred in close proximity (