Physiology and Pathology of Coronary Microcirculation

The heart is a unique organ in many respects since its activity is mandatory to sustain life. The heart’s circulatory system and coronary flow regulation are highly adapted to the vital role of the heart in sustaining life and to everyday physiological challenges.

Understanding coronary physiology is key for treating patients with ischemic heart disease in general, and patients with acute ST elevation myocardial infarction (STEMI) specifically. Coronary flow is regulated by myocardial oxygen consumption and can be increased by four-fold in healthy individuals. The ability to increase coronary flow is referred to as coronary flow reserve. Increased coronary flow is required for increased oxygen supply to the myocardium, as each molecule of hemoglobin that enters the coronary circulation delivers all the carried oxygen during its pass through the myocardium. Thus, only increased flow can provide more oxygen to the heart muscle. Blood flow in the coronary circulation is determined by intramyocardial resistance arteries. Vasodilation of these arteries increases coronary flow, which leads to some degree of vasodilation of the epicardial coronary arteries. In STEMI, all these physiological mechanisms are disrupted. For more details regarding physiology of the coronary system see references^1-5.