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In five patients treated with external pacemaker for complete heart block, the adaptation of left ventricular volume to sudden changes in ventricular rate has been analysed on a beat-to-beat basis, by one-plane cineangiocardiography and simultaneous aortic pressure recordings. The results are unambiguous and show: (1) When heart rate is changed above a certain lower limit left ventricular stroke volume varies inversely with heart rate. (2) The changes in stroke volume are brought about by changes in left ventricular end-diastolic volume proportionate to the duration of mechanical diastole and filling energy. The end-systolic volume is unchanged. (3) Left ventricular end-diastolic volume and stroke volume adapt, on a beat-to-beat basis, to changes in heart rate. (4) There is a lower border-frequency at which the ventricular end-diastolic volume is maximal. Below this frequency, a further increase in length of diastole does not increase the stroke volume.
Karlöf et al. (Tue,) studied this question.