EKG Changes Indicating Myocardial Ischemia

Diagnostic Criteria

Horizontal or downsloping ST-segment depression ≥0.5 mm at the J-point in 2 or more contiguous leads is diagnostic for myocardial ischemia, according to the American College of Cardiology 1
ST depression of this magnitude is classified as UA/NSTEMI (Unstable Angina/Non-ST Elevation Myocardial Infarction) when accompanied by symptoms, as stated by the American Heart Association 2
New T-wave inversion greater than 1 mm in at least two contiguous leads is indicative of myocardial ischemia, as recommended by the American College of Cardiology 1, 3

These ECG changes establish a gradient of risk: ST depression carries the highest risk, followed by T-wave inversion, with normal ECGs having the lowest risk, according to the American Heart Association 4, 6
The prognostic information from these ECG patterns remains independently predictive of mortality even after adjustment for clinical findings and cardiac biomarker measurements, as stated by the American Heart Association 7
More profound ST-segment shifts or T-wave inversions involving multiple leads/territories correlate with greater myocardial ischemia and worse prognosis, as reported by the American Heart Association 5

Always compare with previous ECGs when available to identify new changes, as recommended by the American College of Cardiology 1, 6
Consider alternative causes of ST-segment and T-wave changes, including pericarditis 5, left ventricular hypertrophy 5, bundle branch blocks 3, electrolyte abnormalities 5, central nervous system events 7, certain medications (tricyclic antidepressants, phenothiazines) 4, and pulmonary embolism 5, 7

Any of these ECG changes accompanied by symptoms warrant immediate evaluation for acute coronary syndrome, as stated by the American College of Cardiology 1, 2
Obtain serial cardiac biomarkers (preferably high-sensitivity troponin), as recommended by the American College of Cardiology 1, 2
Perform continuous ECG monitoring to detect dynamic changes, as suggested by the American Heart Association 4
Initiate appropriate anti-ischemic and antiplatelet therapy while further evaluation is underway, as recommended by the American College of Cardiology 1