ST segment deviation
Displacement of the ST segment above or below the isoelectric baseline, so the stretch between the end of the QRS and the start of the T wave no longer sits level with the rest of the trace.
Key ECG features
- ✓Segment sits above or below the TP baseline
- ✓Judged from the J point onward
- •Persists across consecutive complexes
- ±Shape differs: smooth coving, flat shelf, or sagging downslope
✓ required · • typical · ± may be present
ECG characteristics
The segment running from the J point to the onset of the T wave sits above or below the baseline taken from the TP or PR segment. Its shape carries information: a smooth coving, a flat shelf and a sagging downslope do not all mean the same thing. Judge it on a steady baseline across several consecutive complexes, because panting, movement and a wandering baseline mimic it convincingly.
This illustration is schematic. Dashed line is a normal complex. The grid is not drawn to scale.
Common causes
Myocardial hypoxia from any cause, including anemia, hypoxemia, shock and gastric dilatation-volvulus. Also pericardial disease, myocardial inflammation or infiltration, blunt chest trauma involving the myocardium, potassium disturbance, and an expected effect of cardiac glycoside therapy. Baseline artifact remains the most common reason the segment merely looks displaced.
Why it matters
A reproducible shift on a clean tracing is a real signal that the myocardium is under stress, but it is not specific and it does not name a cause. It is worth acting on when it persists and fits the clinical picture, and worth repeating when it does not.
Differentiate from
- Peaked T waveA tall T wave rising straight out of a displaced segment blurs where one ends and the other begins. Potassium disturbance can produce both at once.
- Prolonged QT intervalA displaced ST segment shifts the baseline the T wave returns to, so where the T wave ends, and with it the QT, becomes harder to place.