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Elucidation of physiologic lengthening of left ventricular ejection time during early upright exercise
Insights
Early exercise causes a surprising increase in left ventricular ejection time (LVET) despite rising heart rate (HR). This initial LVET lengthening is a physiological response, not indicative of cardiac issues.
Area of Science:
- Cardiology
- Exercise Physiology
Background:
- The relationship between heart rate (HR) and left ventricular ejection time (LVET) during exercise is complex.
- Previous assumptions suggested LVET should shorten as HR increases during early exercise.
Purpose of the Study:
- To investigate the dynamic changes in LVET in response to early exercise.
- To determine if patients with chest pain exhibit altered LVET responses during exercise.
Main Methods:
- Studied 30 patients with chest pain during a graded exercise test.
- Measured HR and LVET at rest, 1 minute, and 4 minutes of exercise.
Main Results:
- Instead of shortening, LVET significantly increased (p < 0.001) at 1 minute of exercise as HR rose.
- LVET subsequently decreased by 4 minutes, approaching baseline levels.
- No difference in LVET response was observed between exercise-positive and exercise-negative patients.
Conclusions:
- Early exercise elicits a paradoxical lengthening of LVET, contrary to predictions based on HR changes alone.
- This phenomenon is attributed to transiently disproportionate changes in stroke volume and ejection rate.
- The observed LVET response is a physiological adaptation rather than a sign of cardiac pathology.
Abstract:
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 leads to 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 less than 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 greater than or equal to 1 mm) and exercise-negative patients, also supports this initial paradoxical lengthening in LVET as a physiologic response.