New insights into the management of myocardial ischemia

Episodes of ST depression are closely related to transient decreases in regional myocardial perfusion during physical or mental stress. At the on-set of these events, there is transient constriction of atherosclerotic stenoses, with an increase in myocardial demand as reflected by increases in heart rate and blood pressure. Recent research has shown that normal epicardial coronary arteries respond to these provocations and to increasing blood flow with progressive vasodilation. In contrast, atherosclerotic vessels lose this ability to dilate and may show paradoxical constriction. This abnormal constriction parallels the response of the arteries to acetylcholine, which can be used to assess the ability of the coronary endothelium to regulate vasodilation. The loss of endothelium-dependent vasodilation appears to be an important functional manifestation of coronary atherosclerosis and a potential triggering mechanism for transient ischemia. Dysfunctional endothelium may also result in a procoagulant surface, with cell adherence and local thrombus formation. Restoration of normal endothelial function is likely to emerge as an important therapeutic objective in the management of myocardial ischemia and coronary atherosclerosis.