Elucidation of physiologic lengthening of left ventricular ejection time during early upright exercise

To elucidate the relationship between heart rate (HR) and left ventricular ejection time (LVET) during early exercise, 30 patients with chest pain were studied at 1 (1′) and 4 minutes (4′). Mean results for control → 1′ exercise: HR 79 to 105 beats per minute, LVET 247 to 260 msec. Thus instead of shortening as predicted by the HR change at 1′ of exercise, LVET rose significantly (p < 0.001). Subsequently LVET fell as HR continued rising, and by 4′ had fallen toward control level. This phenomenon is comparable to the paradoxical decline in LVET as HR decreases early post-exercise and is comparably explained by transiently disproportionate change in determinants of LVET, stroke volume, and ejection rate. Absence of difference in response of exercise-positive (ST depression ≥ 1 mm) and exercise-negative patients, also supports this initial paradoxical lengthening in LVET as a physiologic response.