Prophylactic Versus Reactive Ventricular Tachycardia Ablation in Repaired Tetralogy of Fallot: A Narrative Review

Figures

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  Figure 1. Schematic representation of the four anatomical isthmuses (AI) underlying ventricular tachycardia in repaired tetralogy of Fallot, shown in relation to two common surgical repair strategies. (Left) Transannular patch repair, in which the ventriculotomy and pulmonary annulus are bridged by a non-conducting patch, eliminating the corridor between the RVOT incision and the pulmonary valve and leaving isthmus 1 (between the RVOT patch and the tricuspid annulus) as an AI. (Middle) Limited ventriculotomy repair with preservation of the pulmonary annulus, in which both isthmus 1 (RVOT incision–tricuspid annulus) and isthmus 2 (RVOT incision–pulmonary annulus) can be present. (Right) Endocardial view of the opened right ventricle illustrating Isthmus 3 (VSD patch–pulmonary annulus) and isthmus 4 (VSD patch–tricuspid annulus). The color gradient encodes the reported frequency with which each AI harbors the critical isthmus of clinical or inducible VT, with deep red indicating the highest frequency (~90%) and pale yellow indicating uncommon involvement (~10%); Isthmus 3 is the most consistently arrhythmogenic substrate, identified in approximately 94% of postmortem rTOF specimens and…

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  Figure 2. Conceptual schematic of arrhythmogenic substrate evolution and the corresponding windows for ablative intervention across the lifespan in repaired tetralogy of Fallot. The lower band depicts progressive maturation of the substrate from inert surgical scar in infancy and childhood, through formation of anatomical isthmuses and emergence of slowly conducting anatomical isthmuses (SCAI) during adolescence and adulthood, to inducible and ultimately clinically manifest VT or sudden cardiac death in middle and older age. SCAI become identifiable on electroanatomical mapping from adolescence onward, and the prevalence of inducible VT increases with age in parallel with ongoing fibrosis and right ventricular remodeling. The two intervention strategies are aligned to this trajectory. Proactive ablation (green) targets the SCAI before any clinical arrhythmia, typically electively in young adulthood or when the substrate is first demonstrated. Specifically Pre-PVR proactive substrate ablation (blue) is performed peri-procedurally at the time of pulmonary valve replacement, before transcatheter or surgical valve deployment may render Isthmus 3 anatomically inaccessible. Reactive ablation…

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  Figure 3. Example of a reactive VT ablation. The patient is a 65-year-old man with rTOF (repaired at age 9) presenting with sustained VT, who underwent secondary-prevention ICD implantation at another institution prior to arrival to our service. Cardiac magnetic resonance showed a dilated right ventricle with transmural late gadolinium enhancement of the RVOT and septum; LVEF was 68%. Three monomorphic VT morphologies were inducible during the EP study: VT1 that had similar morphology with the clinical VT; VT2 and VT3 were also induced on programmed ventricular stimulation. (A–C) Twelve-lead ECG of VT1 (clinical), VT2, and VT3, each with a distinct QRS morphology. (D) Right ventricular bipolar voltage map (0.1–1.5 mV) demonstrating extensive low-voltage scar involving the anterior RV wall and anatomical Isthmus 3, with preserved voltage inferiorly and basally. (E) Pace-mapping at the anterior RVOT, within anatomical isthmus 1, yielded a 97% match to VT. (F) Pace-mapping superior to this site, within the same anatomical isthmus 1, yielded a 96% match to VT2. (G) Pace-mapping at the lateral aspect of anatomical Isthmus 3 yielded a 94% match to VT3. (H) Limited activation map of VT3 with…

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  Figure 4. Example of a proactive VT ablation. Proactive EPS and substrate-based VT ablation in a 47-year-old woman with rTOF and no prior clinical VT performed prior to pulmonary valve replacement. Two distinct monomorphic VT morphologies were inducible during programmed ventricular stimulation. (A) Twelve-lead ECG of VT1 (cycle length 243 ms), with left bundle branch block morphology and superior axis. (B) Twelve-lead ECG of VT2, non-sustained, with a distinct morphology of left bundle branch block and inferior axis consistent with a separate exit site. (C) Right ventricular bipolar voltage map (0.1–1.5 mV scale) demonstrating a heterogeneous low-voltage area at the region of AI3 as well as a large area of dense scar along the anterior RV most likely corresponding to an RVOT patch. (D) Right ventricular isochronal late activation map (ILAM) demonstrates marked isochronal crowding within the region of AI3, indicating slow conduction. (E) Local conduction velocity measurements across the AI3, calculated as the distance between paired sampling points divided by the difference in local activation time. All three measurements yielded conduction velocities below 0.5 m/s, establishing the…

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  Figure 5. Proposed clinical framework for VT management in adults with repaired tetralogy of Fallot, organized around two entry decisions: a prior history of sustained VT or resuscitated SCD (reactive pathway, red) and the presence of a planned native-RVOT PVR (proactive pathway, green). The reactive pathway is supported by published outcome data; the proactive pathway is supported by published evidence in the pre-PVR setting (solid border) and falls within a data-sparse zone (dashed border) for asymptomatic patients without a planned PVR, in whom decisions are individualized through shared decision-making (handshake icon). Decision points are shown as blue diamonds. The framework is consistent with the 2022 AHA Scientific Statement on arrhythmias in repaired tetralogy of Fallot, the 2018 AHA/ACC guideline for adults with congenital heart disease, the 2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias, and the 2022 ESC guidelines on ventricular arrhythmias and prevention of sudden cardiac death, and is intended as a general guide rather than a prescriptive algorithm, applied within shared decision-making and adapted to local expertise, and…