Acute coronary syndromes (ACS) refers to a spectrum of acute clinical manifestations of coronary artery disease. The hallmark of ACS is the presence of myocardial ischaemia caused by an abrupt reduction of coronary blood flow. Myocardial ischemia is the term we use when the heart muscle is starved of essential nutrient and this commonly leads to symptoms of chest pain (called angina).

Coronary Artery Disease (CAD) and its manifestations

CAD is due to a process called coronary atherosclerosis, which is an accumulation of fatty deposits in the coronary artery wall. As coronary atherosclerosis progresses, this leads to gradual narrowing of the coronary arteries that are responsible for supplying nutrient to the muscle of the heart. Although the exact mechanism is unknown, certain risk factors in a person increase the likelihood of atherosclerosis. These include smoking, diabetes mellitus, high blood pressure, high cholesterol and strong family history of premature CAD.

Once the narrowing in the arteries becomes critical, the amount of blood may not be able to meet the demand of the heart muscle. When angina occurs only on exertion, it is due to a stable narrowing (plaque) which only gives rise to symptoms when the demand exceeded what the narrowed artery can supply. This is called stable angina. It is promptly relieved by rest which reduce the demand of the heart muscle or by medications to dilate the narrowed artery, so as to increase the blood supply to the heart muscle.

In contrast, ACS is due to sudden disruption of the lining of the narrowing within the artery wall (called plaque rupture) and subsequent clot (thrombus) formation on the site, leading to sudden complete or near complete blockade of the coronary artery. This can lead to worsening of angina or death of portion of heart muscle (i.e. heart attack/myocardial infarction). Without treatment, a high proportion of patients with ACS may subsequently develop further heart attacks or even death.