Atrioventricular nodal reentry tachycardia is best treated with catheter ablation aimed at disruption of conduction of the slow pathway. There are currently two possible options for this ablation: radiofrequency ablation and cryoablation. The first seems to result in superior success rate, however carries a small risk of collateral damage of the heart conduction system, specifically the atrioventricular (AV) node. Cryoablation seems less effective, but safer as AV nodal damage can be avoided. The aim of this study is to prospectively test possible improved efficcacy of cryoablation of the slow pathway with the use intraprocedural intracardiac echocardiography.

We will prospectively enroll all patients that will be referred to our center for ablation of supraventricular tachycardia and will have an electrophysiologically proven atrioventricular nodal reentry tachycardia. In order to prove the mechanism specific maneuvers will be performed during induced sustained tachycardia. Navigation in the heart will be performed in a fluoroless fashion, with the use of a three-dimensional electro-anatomic mapping (3DEAM) system. Detailed anatomical definition and navigation in the area of the Koch triangle will be done with intracardiac echocardiography (ICE). Also, in sinus rhythm, when present, the Jackman potential will be tagged on the 3DEAM map. Cryomapping will be performed at the presumed location of the slow pathway (position of the Jackman potential or only anatomical location as defined with ICE) during ongoing tachycardia with the aim to terminate it and continue with cryoablation at the successful site.

Noninducibility will be tested with programmed and fast atrial stimulation. Patients will be followed clinically for up to 12 months.

Inclusion Criteria:

• ECG or holter ECG evidence of regular narrow QRS complex tachycardia, intraprocedural pacing maneuvers in sinus rhythm and during ongoing tachycardia indicating presence of AVNRT

Exclusion Criteria:

• terminal or severe medical condition with expected survival of less then 12 months, deep venous thrombosis preventing access to the femoral vein, intracardiac thrombi, anatomical irregularities of pelvic veins and/or inferior vena cava, inability to induce AVNRT after the initial induction and diagnosis - enables exclusion of procedures where accidental mechanical termination of slow pathway conduction with the cryoablation catheter occurs

All adult and pediatric patients with the body weight above 15 kg with documented regular narrow QRS complex tachycardia referred for catheter ablation in accordance with current guidelines (EHRA, AEPC and/or HRS).