by Conn Hastings (RCSI)
What is Myocardial Infarction (MI)?
A healthy heart with free-flowing cardiac vessels, which supply the heart muscle with blood, is shown on the left. On the right a blockage has formed in a coronary artery (inset) which has deprived a large area of the heart muscle of blood. This has caused the formation of a scar, which is depicted as an area of discolouration in the heart muscle.
Myocardial Infarction (MI), more commonly known as a heart attack, occurs when a blood vessel feeding part of the heart muscle becomes blocked, depriving the muscle of blood, a condition known as ischemia. This can happen due to a build-up of fatty deposits, known as atherosclerotic plaque and/or the formation of a blood clot. The ischemic muscle is deprived of oxygen and nutrients and consequently cells in the blood-deprived area (called the infarct) begin to die. As cells die, the ability of the affected muscle to beat and pump blood around the body is compromised. This can result in death if the affected area is large enough, or if medical assistance is not available or delayed. In many cases, the affected artery can be unblocked by a medical intervention, resulting in blood being allowed to flow back into the infarct region, and helping to improve the chances of survival. However, cardiac muscle cells begin to die very quickly during a myocardial infarction, often before medical staff can restore blood flow, resulting in lasting damage and impairment in heart function. Frequently, surviving patients are left with a large scar in the heart muscle which has no ability to contribute to the pumping action of the heart.