Many ischemic ECGs do not show dramatic ST elevation. Subtle ischemia is common, clinically important, and frequently overlooked (see The Masterclass in Advanced Electrocardiography). Mechanism‑based interpretation helps clinicians identify these early warning signs.
Hyperacute T Waves
These represent early transmural ischemia and are often the first detectable change. Features:
- broad bases
- increased amplitude
- loss of normal asymmetry
Minimal ST Depression
Even 0.5 mm of ST depression can indicate significant subendocardial ischemia, especially when:
- horizontal or downsloping
- present in multiple contiguous leads
Terminal QRS Distortion
Loss of the S wave or J‑point elevation without a distinct S wave suggests severe ischemia.
Early Reciprocal Changes
Reciprocal ST depression may appear before ST elevation becomes obvious (see “Jones’s Rule” in Getting Acquainted With Ischemia and Infarction).
Related: Key Mechanism‑Based Concepts in Ischemia and Infarction