Atherosclerosis is the process that causes gradual buildup in the inner lining of the artery and therefore narrowing of the coronary artery. Although its exact mechanism is unknown, certain factors in a person increase the likelihood of this process. These include smoking, diabetes mellitus, high blood pressure, cholesterol and strong family history.
When the narrowing inside the lumen of the artery is severe, the amount of blood supply is unable to meet the demand of the heart muscle, especially when the person is exerting or exercising. The condition whereby the heart muscle is starved of essential nutrients is called myocardial ischaemia. When myocardial ischaemic occurs only upon exertion, it is called angina (i.e. chest pain). Stable angina is not life threatening and is usually promptly relieved by rest to reduce heart muscle demand or medications to dilate the coronary artery to increase the blood supply.
Conversely, heart attack is due to sudden, complete blockage of the coronary artery causing permanent damage to part of the heart muscle (myocardial infarction). This is usually due to sudden breakage of the lining of a narrowing (plaque rupture) inside the artery. This causes clot formation at the site of rupture (a process known as Atherothrombosis) and subsequent complete blockage of the artery. Myocardial ischaemia occurs at rest and if the artery is not opened promptly, heart muscle cells will die within minutes. If ischaemia persists for more than 6 hours, majority of the muscles supplied by that artery will be permanently damaged.
When a heart attack occurs, the patient will usually feel severe chest discomfort.
In spite of treatment given, there is still a 10% mortality rate in patients with heart attack. This is usually caused by abnormal heart rhythm (ventricular fibrillation) due to electrical instability of the heart or
heart failure due to massive heart attack. Occasionally, heart muscle can rupture after a heart attack and this is usually fatal.