Intraoperative cryoablation in late pulmonary valve replacement for tetralogy of Fallot

Ventricular tachyarrhythmia (VT) is a major cause of late morbidity and mortality in patients who underwent surgical repair of tetralogy of Fallot. The majority of VTs are monomorphic macro-reentrant VT (MVT) and depend on slow conducting areas of diseased myocardium bordered by unexcitable tissue (anatomical isthmuses). Myocardial fibrosis due to surgical incisions, patch material and valve annuli are typical boundaries of anatomical isthmuses (AI). The conducting myocardium between the pulmonary valve and ventricular septum defect patch is called isthmus 3, and the majority of MVTs originate from this area. During pulmonary valve replacement, there is excellent exposure of isthmus 3. Importantly, after pulmonary valve replacement, the homograft may cover important parts of isthmus 3, which makes percutaneous catheter ablation at a later stage impossible. In all patients who need pulmonary valve replacement late after tetralogy of Fallot repair, preoperative electrophysiology study and electroanatomical mapping can identify patients with inducible MVT or slow conduction carrying high risk of MVT. In these patients, intraoperative cryoablation of isthmus 3 should be performed and bidirectional conduction block across the cryoablation line should be demonstrated by intraoperative differential pacing.