Supraventricular tachycardia (SVT)
A fast rhythm that starts somewhere above the ventricles, either in the atria or around the AV node, and then travels down the normal conduction system, so the QRS stays narrow. A fast sinus rate is supraventricular too, but the term is usually kept for the abnormal fast rhythms rather than for sinus tachycardia.
Key ECG features
- ✓Fast rate, usually regular
- •Narrow QRS
- •P waves absent, abnormally shaped, or buried in the T
- ±Abrupt onset and offset
✓ required · • typical · ± may be present
ECG characteristics
A rapid, usually regular rhythm with narrow QRS complexes. P waves are absent, abnormally shaped, or buried in the preceding T wave, and the rate is typically too fast and too abruptly established to be sinus.
This illustration is schematic. Dashed line is a normal rhythm. The grid is not drawn to scale.
Common causes
Either a spot in the atria or the junction firing on its own, or an impulse caught going round a loop that involves the AV node or an extra conduction pathway. Underlying atrial enlargement or structural disease is common.
Why it matters
Sustained rates reduce ventricular filling and, over time, can cause a tachycardia-induced cardiomyopathy. A narrow QRS is the main thing pointing away from ventricular tachycardia, which is the more urgent diagnosis.
Differentiate from
- Sinus tachycardiaSinus tachycardia has a normal P wave before every QRS and an explainable driver; SVT is typically faster, more abrupt in onset, and its P waves are absent, abnormal, or buried in the preceding T wave.
- Ventricular tachycardiaQRS width is the first thing to weigh: narrow suggests the impulse used the normal conduction system, wide suggests it did not.