Atrial standstill
The atria have stopped producing electrical activity altogether. Nothing is driving them, so a backup pacemaker lower down keeps the ventricles going.
Key ECG features
- ✓No P waves anywhere on the strip
- •Slow escape rhythm driving the ventricles
- •Ventricular response regular, unlike atrial fibrillation
- ±Tall peaked T waves and a widening QRS when hyperkalemic
✓ required · • typical · ± may be present
ECG characteristics
No P waves anywhere on the strip, with a junctional or ventricular escape rhythm at a slow, regular rate. That regularity is what separates it from atrial fibrillation, where P waves are also absent but the ventricular response is irregularly irregular.
This illustration is schematic. Dashed line is a normal rhythm. The grid is not drawn to scale.
Common causes
Two very different situations. Persistent atrial standstill is associated with an atrial cardiomyopathy or muscular dystrophy, classically in English Springer Spaniels. Transient atrial standstill is a sign of severe hyperkalemia, in which P waves disappear as serum potassium climbs.
Why it matters
Checking potassium urgently is critical: hyperkalemic atrial standstill is rapidly reversible but fatal if missed. Persistent atrial standstill carries a poorer prognosis and often needs pacing.
Differentiate from
- Atrial fibrillationNeither shows P waves. Atrial standstill gives a slow, regular escape rhythm; atrial fibrillation gives an irregularly irregular ventricular response.
- Junctional escape rhythmThe rhythm driving the ventricles in atrial standstill is itself a junctional or ventricular escape rhythm. The diagnosis rests on the silence above it.
- Peaked T waveBoth belong to the hyperkalemic progression. Peaked T waves appear earlier, so finding them is the chance to intervene before the atria fall silent.