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Atrioventricular (AV) node reentrant tachycardia (AVNRT) is a type of supraventricular tachycardia characterized by a reentrant circuit involving the atrioventricular (AV) node. It is a common cause of supraventricular tachycardia in adults, accounting for approximately 15% of cases. AVNRT typically presents with a regular narrow complex tachycardia, with a cycle length of 200-300 milliseconds. The ECG may show a characteristic "delta wave" or "lambda wave," which is a slurred upstroke of the QRS complex.

The pathophysiology of AVNRT involves a reentrant circuit that includes the AV node, the His bundle, and the atria. The most common mechanism is a slow-fast pathway, where a slow pathway (usually the AV node) is activated by a fast pathway (usually the accessory pathway). This results in a reentrant circuit that can sustain tachycardia.

The diagnosis of AVNRT is typically made based on the ECG findings and the patient's clinical presentation. Other diagnostic tests, such as Holter monitoring or electrophysiology study, may be used to confirm the diagnosis and to identify the specific mechanism of the tachycardia.

The treatment of AVNRT depends on the patient's symptoms and the underlying cause of the tachycardia. In many cases, the tachycardia can be terminated with vagal maneuvers, such as the Valsalva maneuver or carotid sinus massage. If the tachycardia is not terminated with vagal maneuvers, or if the patient is symptomatic, electrical cardioversion may be used. In some cases, catheter ablation may be performed to eliminate the reentrant circuit and prevent recurrence of the tachycardia.