What does ST depression and T wave inversion indicate?

From the Guidelines

ST depression and T wave inversion are indicative of cardiac ischemia or injury, warranting immediate medical evaluation for potential myocardial ischemia, acute coronary syndrome, or myocardial infarction. These ECG changes occur because reduced blood flow alters the heart's electrical activity during repolarization, as noted in the 2014 AHA/ACC guideline for the management of patients with non-ST-elevation acute coronary syndromes 1. Specifically:

• ST depression: A downward sloping or horizontal depression of the ST segment below the baseline, with horizontal or downsloping ST depression ≥ 0.05 mV in two contiguous leads being highly suggestive of NSTE-ACS 1
• T wave inversion: The T wave is reversed, pointing downward instead of upward, with marked symmetrical precordial T-wave inversion (≥2 mm [0.2 mV]) suggesting acute ischemia, particularly due to a critical stenosis of the left anterior descending coronary artery 1 These findings may also indicate other cardiac conditions like pericarditis or cardiomyopathy. If seen on an ECG, the patient should receive:
• Immediate cardiac monitoring
• Blood tests to check cardiac enzymes (troponin)
• Aspirin 325 mg
• Consideration of urgent cardiac catheterization The third universal definition of myocardial infarction also provides guidance on ECG manifestations of acute myocardial ischemia, including new horizontal or down-sloping ST depression ≥ 0.05 mV in two contiguous leads and/or T inversion ≥ 0.1 mV in two contiguous leads with prominent R wave or R/S ratio > 1 1. However, the most recent and highest quality study, the 2014 AHA/ACC guideline, takes precedence in guiding clinical decision-making 1.

From the Research

ST Depression and T Wave Inversion Indications

• ST segment depression and T wave inversion are electrocardiographic (ECG) repolarization abnormalities that can predict future cardiovascular events 2
• These ECG abnormalities can be indicative of silent myocardial ischemia, even in asymptomatic patients 2
• The presence of ST segment depression and T wave inversion on an ECG can be associated with new onset heart failure in individuals transported by ambulance for suspected acute coronary syndrome 3
• ST depression is often suggestive of ischemia, but can also be indicative of posterior infarction or left main- or triple-vessel disease in certain leads 4
• T wave inversion can precede an inferior myocardial infarction, and can be a marker of localized subendocardial infarction within a one-vessel territory 4, 5

Clinical Implications

• ST depression and T wave inversion can have different clinical implications in non-Q wave myocardial infarction, with ST depression suggesting extensive ischemia in the subendocardium of multivessel territory, and T wave inversion indicating a recovery phase in transient transmural ischemia and localized subendocardial infarction 5
• The extent of ischemic area estimated by electrocardiography and two-dimensional echocardiography can be greater in patients with ST depression than in those with T wave inversion 5
• Cardiac status on admission can be lower in patients with ST depression than in those with T wave inversion, with a higher mortality rate after 1 month 5

ECG Interpretation

• ECG abnormalities, including ST depression and T wave inversion, should be carefully inspected and not misinterpreted, as misinterpretation can occur in 20-40% of misdiagnosed myocardial infarctions 4
• The pattern and timing of changes in Q waves, ST segment, and T waves can be markers of the patency status of the infarct-related artery 6
• ECG scoring systems can be used to provide information regarding the potential myocardial reserves in patients with STEAMI 6