Supraventricular tachycardia (SVT) is defined as a rhythm arising above the ventricles with heart rate exceeding 100 bpm. Which rhythm is most commonly responsible for SVT?

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SVT most often comes from a reentrant circuit within the AV node, known as AV nodal reentrant tachycardia. This mechanism creates a rapid, narrow-complex rhythm that arises above the ventricles and is classically responsive to vagal maneuvers or adenosine because these interventions interrupt conduction in the AV node and terminate the reentrant loop. On an ECG, you typically see a very fast, regular, narrow QRS complex tachycardia, with P waves often hidden in or right after the QRS complex due to retrograde atrial activation.

Atrial flutter can cause a fast ventricular rate, but it’s generated by a macro-reentrant circuit in the atria and usually presents with a characteristic sawtooth atrial activity and a consistent but different pattern of AV conduction; it’s not the most common mechanism of SVT. Atrial fibrillation involves chaotic atrial activity with an irregularly irregular rhythm and variable ventricular response, which is a different type of supraventricular rhythm. Ventricular tachycardia originates in the ventricles and typically presents with wide QRS complexes, not a narrow-complex SVT.

So the rhythm most commonly responsible for SVT is AV nodal reentrant tachycardia, the classic narrow-complex, above-ventricular tachycardia mechanism.