Peaked T wave
A T wave that is tall, narrow and sharply pointed, taking up more of the complex than usual, instead of the broader and more rounded shape normally seen.
Key ECG features
- ✓Tall, narrow, sharply peaked T wave
- •Narrow base
- ±QT shortening as it develops
- ±More convincing as a change from that patient's own tracing
- ±In hyperkalemia: P waves flatten and the QRS widens as it worsens
✓ required · • typical · ± may be present
ECG characteristics
A narrow, symmetrically pointed T wave on a narrow base, often with the QT shortening as it develops. T wave size and polarity vary naturally between dogs and cats and between leads, so a change from that patient's own earlier tracing is far more convincing than one tall T in isolation. In hyperkalemia the picture usually advances in order: the T peaks, the P waves flatten and vanish, the QRS widens, and the trace finally degenerates towards a sine wave.
This illustration is schematic. Dashed line is a normal complex. The grid is not drawn to scale.
Common causes
Hyperkalemia is the one that matters, and the classic presentations split by species. Urethral obstruction in the male cat and reperfusion after feline aortic thromboembolism are the feline ones; hypoadrenocorticism is largely a canine diagnosis. A ruptured bladder, acute kidney injury and reperfusion after gastric dilatation-volvulus occur in both. Myocardial hypoxia and some intraventricular conduction disturbances can also produce a tall, narrow T.
Why it matters
Treat this as a reason to measure potassium immediately rather than as an ECG curiosity. Hyperkalemia advances to atrial standstill and then to arrest, and it is rapidly reversible when it is caught.
Differentiate from
- Atrial standstillTwo points on the same hyperkalemic progression. Peaked T waves come first; by the time the P waves have gone the situation is further along and more urgent.
- ST segment deviationWhere a tall T rises out of a displaced segment the two run together. Look at the shape of the whole stretch from the J point onward rather than at the peak alone.
- Prolonged QT intervalThe two move in opposite directions, which makes the pair worth knowing: a peaking T wave usually comes with a shortening QT, so a long QT points away from hyperkalemia rather than towards it.