Hemodynamic determinants of exercise ST-segment depression in coronary patients

Eight patients with coronary heart disease were studied during two periods of exercise separated by 30 min of rest; workload was increased in a stepwise fashion every minute of exercise up to a level that produced limiting symptoms of angina, fatigue, or dyspnea. The magnitude of ST-segment depression and the central aortic pressure were measured during exercise and recovery periods, and myocardial oxygen requirements were estimated by the pressure-time index (systolic aortic pressure x heart rate x ejection time). Seven of the eight patients exhibited a close relationship (r ranged from 0.74 to 0.98) between magnitude of exercise ST-segment depression and indices expressing myocardial oxygen requirements; heart rate, blood pressure, and ejection time were also related to magnitude of exercise ST-segment depression. These relationships were reproducible during two consecutive exercises. Like onset of angina, magnitude of exercise ST-segment depression is usually related to hemodynamic factors influencing myocardial oxygen needs. Consequently, comparisons of exercise-induced ST depression before and after therapy (drugs, physical training, and surgery) are valid only if ECG findings are compared at the same level of myocardial oxygen requirements. In contrast, absence of such a relationship during recovery suggests an important difference in mechanisms of the post-exercise electrocardiogram.