A non-ST-segment elevation myocardial infarction (NSTEMI) is a type of heart attack that is caused by partial or near-total occlusion of the coronary artery by a thrombus or embolus. With an occluded coronary artery, the heart muscle, or myocardium, becomes ischemic, or deficient in blood and oxygen supply, leading to cell injury and possible cell death. A non-ST elevation myocardial infarction can only be distinguished from unstable angina (UA) and ST elevation myocardial infarction (STEMI) with laboratory results. Compared with STEMI, in which the full thickness of heart muscle supplied by a particular coronary artery is injured, a non-ST elevation myocardial infarction involves only the subendocardial region of the heart.
One of the manifestations of heart disease is acute coronary syndrome (ACS), referring to the affected blood vessel, which is the coronary artery. The spectrum of ACS includes angina pectoris, AU, and myocardial infarction. UA elevation and non-ST elevation myocardial infarction are difficult to distinguish from each other in the absence of laboratory results, and are sometimes grouped together and labeled UA/NSTEMI.
Stable angina is defined as chest or arm discomfort associated and reproducible with stress and physical exertion. It is relieved by resting for 5 to 10 minutes or by taking sublingual nitroglycerin. Unstable angina is angina that occurs at rest or for more than 10 minutes, is severe or acute, and lasts longer or more frequently than previously experienced episodes. A non-ST-segment elevation myocardial infarction is diagnosed when a patient has the symptoms of UA and develops evidence of myocyte death or necrosis, as detected through elevation of serum cardiac biomarkers, such as fractional troponin and creatinine kinase. -MB (CK-MB).
Four factors contribute to the pathophysiology of AU/NSTEMI. First is the rupture or erosion of an atherosclerotic plaque with superimposed nonocclusive thrombus formation. The second is dynamic obstruction, such as coronary artery spasm, and the third factor is progressive mechanical obstruction, usually due to thickening of the blood vessel walls, as occurs in atherosclerosis. The fourth factor is increased oxygen demand or decreased oxygen supply, such as what happens in anemia or increased heart rate. Any of these processes can occur in combination in the development of NSTEMI.
In the electrocardiogram (ECG), the electrical activity of the heart is recorded. Ischemia in NSTEMI is limited to the subendocardium, thus the vector or direction of the ST segment shifts toward it and is usually seen on ECG as ST segment depression. The ECG should be done when a person complains of chest pain and the doctor suspects an underlying cardiovascular problem. ST-segment changes require immediate treatment.
Treatment of UA/NSTEMI involves the use of anti-ischemic drugs that dilate blood vessels, such as nitrates and beta-blockers. Thrombus lysis involves the use of anticoagulant drugs, such as heparin, and antiplatelet drugs, such as aspirin. High-risk patients should undergo coronary angiography and coronary artery revascularization within 48 to 72 hours. This is to prevent further myocardial injury and restore the heart's blood supply.