Proactive slow-conducting anatomical isthmus ablation vs conventional approach in preventing ventricular arrhythmias in repaired tetralogy of Fallot before pulmonary valve replacement

Introduction

Slowly conducting anatomical isthmuses (SCAI) represent the substrate of spontaneous re-entrant monomorphic ventricular tachycardia (VT) in tetralogy of Fallot (ToF). Proactive evaluation of SCAI with electrophysiological study (EPS) in patients without history of VT undergoing pulmonary valve replacement late in adulthood may reduce arrhythmic burden. Comparison between traditional and proactive (with EPS) approaches are lacking.

Methods

A retrospective evaluation of consecutive ToF patients undergoing PVR without history of VT as conducted, and data regarding adverse arrhythmic outcomes were collected. A prospective evaluation of consecutive ToF patients undergoing PVR with proactive EPS and SCAI evaluation was conducted. Electroanatomical mapping was performed with systematic evaluation of anatomical isthmuses (AI; pace-, activation in sinus/paced rhythm, bipolar voltage mapping) was performed (AI1: anterior scar/patch to tricuspid annulus; AI2: anterior scar to pulmonary annulus; AI3: pulmonary annulus to ventricular septal defect – VSD- patch; AI4: VSD to tricuspid annulus). Conduction velocity (CV) across all documented AI was calculated (distance among the nearest point with biV >1.5 mV ovef difference in activation timing). Ventricular programmed stimulation was performed at 2 sites with three extrastimuli (basal+isoproterenol). Radiofrequency catheter ablation was performed in all patients with inducible VT and/or SCAI, aiming at conduction block across the SCAI validated with differential pacing. All patients receiving RFCA underwent loop-recording implantation.

Results

The retrospective cohort consisted of 139 prevalently male (70.5%) patients (median age at surgical correction 32, iqr 14-60 months) enrolled until 2022. The contemporary cohort, enrolled in 2022-2025, consisted of 18 patients, median age at correction 35 months (iqr 23-47), 73% males, age 46±10 years; 54% with a previous shunt, 46% with a previous transannular patch, 27% pulmonary valvotomy/infundibular resection. AI1 was present in all patients, AI2 in 11, AI3 in 14, AI 4 in 4. There were no SCAI1; there were 3 SCAI 2 (mean CV 0.43 m/s), 9 SCAI 3 (mean CV 0.3 m/s), 2 SCAI 4 (CV 0.4 m/s). RFCA was performed on all SCAI; acute success was 100% achieving bidirectional conduction block across treated SCAI and non-inducibility of VT.

On follow-up, there were no adverse events in proactive group (median follow-up 17 months, iqr 8-21 months) while there were 11 VT in the retrospective cohort on a median follow-up duration of 66 months (iqr 1.2-145 months).

Conclusions

When compared to conventional approach, a proactive EPS strategy in tetralogy of Fallot patiemts undergoing PVR shows a lower incidence in late ventricular events EPS; SCAI evaluation and ablation is safe and effective over a relatively long systematic follow-up. A longer follow-up is however needed to further enforce systematic EPS in rToF candidate to PVR.