Atrioventricular reciprocating tachycardia

Atrioventricular reciprocating/reentry tachycardia (AVRT) is a paroxysmal tachycardia characterised by the formation of a re-entry circuit consisting of the AV node and the accessory pathway, usually precipitated by a premature atrial beat. AVRT may be orthodromic, which is the case in 95% of cases, or antidromic, in the remaining cases. AVRT is most commonly seen in Wolff-Parkinson-White syndrome.

Orthodromic AVRT

In orthodromic AVRT, the antegrade conduction (from atria to ventricles) occurs through the AV node and the signal travels back from the ventricles to the atria (retrograde conduction) through the accessory pathway. This creates a re-entry circuit which sustains itself, maintaining the tachycardia. Orthodromic AVRT is a narrow-complex tachycardia. There may be retrograde P waves (after the QRS complex), and no delta-wave is visible.

Orthodromic AVRT is treated acutely by the same algorithm as other narrow-complex tachycardias. Haemodynamically unstable paroxysmal tachycardias should be treated with synchronised electrical cardioversion. In stable patients, vagal manoeuvres or IV adenosine can terminate the tachycardia, by blocking the conduction through the AV node, breaking the re-entry circuit.

Antidromic AVRT

In antidromic AVRT, the conduction circuit goes the opposite direction. The antegrade conduction is through the accessory pathway, while the retrograde conduction is through the AV node. Antidromic AVRT is a wide-complex tachycardia, and it’s often difficult to distinguish from ventricular tachycardia on an ECG. The delta wave may be visible.

Because antidromic AVRTs can be impossible to distinguish from VT, it should be treated similarly as other wide-complex tachycardias. Haemodynamically unstable paroxysmal tachycardias should be treated with synchronised electrical cardioversion. Stable patients should receive antiarrhythmics. AV-nodal blocking agents like adenosine are contraindicated as they may precipitate pre-excited atrial fibrillation.