The coronary arteries supply oxygen-rich blood to the heart muscles itself. Coronary artery disease (CAD) or coronary heart disease (CHD) is therefore the medical condition where the walls of the coronary arteries are damaged impairing their ability to properly supply the heart with blood/oxygen. This is typically due to prolonged buildup of waxy atherosclerotic plaque over many years which significantly narrows the lumen of the coronary arteries thereby starving the heart of the much-needed oxygen. If sustained oxygen deprivation persists, then the patient presents with angina pectoris (excruciating chest pains). In cases of severe deprivation, chest pain can sometimes be present even at rest. Over time, this can lead to tissue destruction and eventual death of the heart muscle due to lack of oxygen – a heart attack. A myocardial infarction (MI) is the medical term for a heart attack.
In an acute coronary syndrome, there is a sudden reduction of coronary blood flow e.g. caused by plaque rupture and/or thrombus formation in a narrowing in the coronary artery. If this situation is not quickly treated, it will also lead to a heart attack (MI).
NSTEMI or non-STEMI stands for non ST elevation myocardial infarction – a type of heart attack where the ST segment is not elevated on an electrocardiogram (ECG) printout. The ST segment is the portion of the ECG heart tracing that is used in diagnosing a heart attack.
Not all MIs are implicated by the ECG as having an ST segment elevation. Apart from the subjective report of chest pain, a heart attack is usually diagnosed through 2 ways. The first is through a blood test that shows elevated levels of certain markers for heart damage such as cardiac troponin. Secondly is by looking at the ECG heart tracing. If there is a pattern known as ST-elevation on the ECG, then this is a called a STEMI or ST elevation myocardial infarction. If there is elevation of the blood markers suggesting heart damage, but no ST elevation seen on the ECG tracing, then this is known as a NSTEMI. NSTEMI may be associated with other ECG changes such as ST segment depression (see Fig. 1). Often looking at the ECG helps to locate the area of the heart that is affected.
Fig. 1. ST segment on normal, STEMI and NSTEMI EKG tracings
Both STEMIs and NSTEMIs are heart attacks and are equally serious. STEMI is considered more of an immediate emergency because there is a known total occlusion of a heart vessel that needs to be reopened urgently. However, in terms of long-term outcomes, they both have equal health implications. Patients with NSTEMI often have other illnesses such as ongoing critical illness, diabetes, kidney disease etc. Both STEMI and NSTEMI require aggressive treatment over the short and long term.