Objective: To study the relationship between isometric exercise and myocardial ischemia in patients with coronary artery disease (CAD).
Methods: Twenty CAD patients and 10 normal subjects were included in our study. All subjects performed maximal brief isometric exercise (BIE), maximal sustained isometric exercise (SIE) and dynamic exercise (DE). Hemodynamic parameters and cardiac function were measured by Echo-Doppler technique. To avoid influence of different baseline values, increment (delta%) of exercise response was used as parameter for significant analysis: delta% = (exercise values - baseline values)/baseline values x 100%.
Results: Positive exercise testing (PET) showed no evidence of myocardial ischemia during BIE and SIE even though their rates of perceived exertion (RPE) were similar to DE. delta% heart rate (HR) and delta% rate pressure product (RPP) were higher during DE than during SIE and BIE in negative exercise testing (NET) and normal controls (NOR) (P < 0.01), except PET during DE and SIE; delta% systolic blood pressure (SBP) was higher during DE than during BIE in NOR (P < 0.01). delta% SBP in NOR and NET during SIE was higher than during BIE (P < 0.05). delta% diastolic blood pressure (DBP) was the highest during SIE among exercises in all gropus (P < 0.05). There were no significant inter-group differences of delta% HR, delta% SBP, delta% DBP and delta% RPP during SIE, BIE and DE, except that delta% SBP during SIE was higher in NET than in NOR and PET (P < 0.05). In NOR, delta% ejection fraction (EF), delta% fractional shortening of the minor-semi axis (SF), delta% cardiac output (CO), delta% E/A was higher during DE than during SIE and BIE (P < 0.01). delta% stroke volume (SV) was similar during DE, SIE and BIE. There were no significant differences in delta% EF, delta% SF, delta% CO, delta% SV and delta% E/A during DE, SIE and BIE in both NET and PET, except lower delta% CO in NET during SIE and BIE than DE (P < 0.01). There were no inter-group differences in delta% EF, delta% SF, delta% CO and delta% E/A, except that delta% E/A was higher during SIE in NET than PET (P < 0.01). During DE, NOR and NET had higher delta% SV, delta% SF, delta% CO and delta% E/A than PET (P < 0.05).
Conclusions: The incidence of myocardial ischemia in CAD patients was lower during isometric exercise than dynamic exercise at similar perceived exertion levels. Isometric exercise might protect the myocardium from ischemia through high coronary artery perfusion pressure and long perfusion duration. We suggest that application of isometric exercise in a cardiac rehabilitation program may have reasonable physiological background.