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ST segment depression and T-wave changes may be seen in patients with unstable angina; Depressed but upsloping ST segment generally rules out ischemia as a cause. Also, it can be a normal variant or artifacts, such as: Pseudo-ST-depression, which is a wandering baseline due to poor skin contact of the electrode [3]
Illustration of ST segment elevation and depression The normal ST segment has a slight upward concavity. Flat, downsloping, or depressed ST segments may indicate coronary ischemia. ST elevation may indicate transmural myocardial infarction. An elevation of >1mm and longer than 80 milliseconds following the J-point.
12-lead electrocardiogram showing ST-segment elevation (orange) in I, aVL and V1–V5 with reciprocal changes (blue) in the inferior leads, indicative of an anterior wall myocardial infarction. When there is a blockage of the coronary artery , there will be lack of oxygen supply to all three layers of cardiac muscle (transmural ischemia).
Discrete or no ST segment elevation No loss of precordial R waves . Coronary angiogram , with video on the left showing tight, critical (95%) stenosis of the proximal LAD in a patient who had Wellens' warning; video on the right shows the same patient after reperfusion .
Plaques in the walls of the coronary arteries can rupture, resulting in occlusion of the artery and deprivation of blood flow and oxygen to the heart muscle, resulting in cardiac cell death. [9] This is known as myocardial infarction. [9] A heart attack can cause arrhythmias, as well as permanent damage to the heart muscle. [25]
Over time, however, as the heart undergoes ongoing remodeling, it becomes less elliptical and more spherical. Ventricular mass and volume increase, which together adversely affect cardiac function. Eventually, diastolic function, or the heart's ability to relax between contractions may become impaired, further causing decline. [7]
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Risk factors are similar to other types of ischemic heart disease. [1] The underlying mechanism is unclear; though may involve subendocardial ischemia or collateral circulation. [1] Diagnosis is based on an ECG showing ST-segment depression at the J-point of 1 to 3 mm in leads V1 to V6, with tall and symmetrical T waves. [1]