Arrhythmogenic anatomical isthmuses identified by electroanatomical mapping are the substrate for ventricular tachycardia in repaired Tetralogy of Fallot

Aims The majority of ventricular tachycardias (VTs) in repaired tetralogy of Fallot (rTOF) are related to anatomically defined isthmuses. We aimed to identify specific electroanatomical characteristics of anatomical isthmuses (AI) related to VT which may allow for individualized risk stratification and tailored ablation. Methods and results Seventy-four consecutive rTOF patients (40 +/- 16 years, 63% male) underwent VT induction and right ventricular electroanatomical voltage and activation mapping during sinus rhythm (SR) to identify the presence and characteristics of AI (isthmus width, length and conduction velocity index [CVi]). Twenty-eight patients were inducible for 41 VTs. All 74 patients had at least one AI. However, AI in patients with VT were longer (22 +/- 7 vs. 16 +/- 7 mm, P = 0.001), narrower (20 +/- 8 vs. 28 +/- 11 mm, P < 0.001) and had lower CVi (0.36 +/- 0.34 vs. 0.78 +/- 0.24 m/s, P < 0.001). Thirty-seven VTs in 24 patients were mapped (pace-, entrainment mapping, and/or VT termination by ablation) to 28 AI. All 28 AI related to VT had a CVi < 0.5 m/s (slow conducting AI (SCAI)). In contrast, 87 of 89 AI of the 46 patients without VT had CVi = 0.5 m/s. Sixty-two patients were discharged without the presence of an SCAI (44 had no SCAI at baseline, 18 underwent ablation of the SCAI) and 10 still had an SCAI (no/failed ablation). During follow-up (50 +/- 22 months), no patient without SCAI had any VT, which occurred in 5/10 patients with SCAI (P < 0.001). Conclusion In rTOF, slow conducting anatomical isthmuses identified by electroanatomical mapping during SR are the dominant substrate for VT allowing individualized risk stratification and preventive ablation.