ECHO-DOPPLER EVALUATION OF THE EFFECTS OF HEART-RATE INCREMENTS ON LEFT ATRIAL PUMP FUNCTION IN NORMAL HUMAN-SUBJECTS

It is commonly believed that the atrial contribution to left ventricular filling increases during heart rate increments. However, the relative contribution of the pump function (atrial systole) and of the passive role (diastasis and reservoir) of the atrium to end-diastolic left ventricular filling is not well known. In order to investigate this problem, we performed a two-dimensional echo-Doppler study during right atrial pacing. Transmitral flow velocity curves were obtained by means of pulsed Doppler. Pacing was performed (1) at the lowest heart rate at which it was possible to obtain a stable capture of the atria, (2) at the heart rate at which the early and late Doppler filling waves almost completely overlapped. In both stages pacing was interrupted for a few seconds to obtain some post-pacing beats. Doppler tracings recorded at rest, during pacing and in the immediate post-pacing beats were analysed to obtain well-known parameters of atrial contribution: atrial peak flow velocity, early to atrial peak flow velocity ratio, and time-velocity integral of the atrial wave. Furthermore, in order to distinguish end-diastolic passive flow from the active contribution of atrial systole to filling, we superimposed the envelope of the last Doppler curve obtained during atrial pacing over the envelope of the first post-pacing curve. In this way the area of the atrial wave of the paced beat was divided by the mid-diastolic part of the post-pacing one into two areas, the integrals of which correspond to the active and passive atrial contribution respectively. At higher heart rates we observed that: (1) atrial peak flow velocity remains unchanged; (2) the ratio of early to atrial peak flow velocity decreases significantly; (3) atrial contribution to filling, evaluated as the overall atrial wave integral, increases significantly; (4) the active atrial contribution does not increase, which means that the increase in atrial wave integral is totally due to the increment in the end-diastolic passive flow. We conclude that: (1) the active contribution of the atrial systole to left ventricular filling does not increase during tachycardia; (2) the parameters commonly used to evaluate atrial contribution to filling (early to atrial peak flow velocity ratio and atrial integral) can cause an overestimation as they cannot distinguish between active and passive end-diastolic flow; (3) the relative importance of these two components mainly depends on heart rate and must be considered carefully in various clinical and experimental conditions. © 1991 The European Society of Cardiology.