Ventricular arrhythmia risk estimation in Tetralogy of Fallot: impact of electro-anatomical mapping on long-term follow-up

Introduction: There has been considerable progress in risk estimation for ventricular arrhythmias (VAs) in patients with Tetralogy of Fallot (ToF). VAs remain a major cause for mortality. Recently, understanding of critical substrate in the right ventricle has added new parameters for risk stratification. However, long-term data on electro-anatomical mapping (EAM) and its additive impact on e.g. programmed ventricular stimulation alone is scarce.

Material and Methods: We report single-center results of ToF patients (pts) undergoing EAM for risk stratification. EAM was performed in pts at risk for VAs (related to history, 12-lead ECG, and Holter-parameters) and/or prior to pulmonary valve interventions. Baseline-characteristics were taken from the hospital files, long-term follow-up data was either taken from an outpatient visit or by telephone contact. EAM was performed using the CARTO^Ò 3D mapping system. Programmed stimulation was performed at two sites with up to 3 extra stimuli without and with isoprenaline administration. 

Results: Data from n=75 ToF pts undergoing EAM in our center were analyzed. EAM was performed 34.7±12.4 years after ToF repair. Mean age was 44.1±14.9 years. Age at total repair in the cohort was 6,2±5.9 years, n=26 pts (34.7%) had a palliative shunt prior to surgical repair. N=39 pts (52%) had a pulmonary valve (PV) replacement, n=13 (17.3%) two and n=3 (4%) three PV replacements. Mean Khairy score was 3.9±2.5, mean QRS width was 165.8±44.9 ms. 

N=11 pts (14.6%) were inducible though no VAs were clinically present prior to EAM.  In n=10 pts (71%) of the n=14 pts with a history of VAs, the clinical VT could be induced. EAM revealed at least one slow conducting isthmus in n=26 pat (34.7%) of which n=10 pts were not inducible by programmed stimulation. Therefore, in 13% of our cohort slow conducting areas were revealed solely by EAM. All pts with a slow conducting isthmus underwent catheter ablation to reduce the risk for VAs.

A higher Khairy Score was significantly associated with inducibility (p=0.05) and a slow conducting isthmus (p=0.008). Besides, QRS width was associated with inducibility (p=0.008) and a slow conducting isthmus (p=0.0045). In terms of EAM, a large transannular patch (15.8 vs. 8.2 cm²) predicted a slow conducting isthmus (p=0.015). In n=3 pts (5.3%) EAM was inconclusive (n=1 inducible, n=2 non-inducible but history of clinical VT). During a mean follow-up of 2,9 ±1.9 years after EAM no pt died. N=18 pat (24%) received an ICD because of the EAM results. N=3 (11.5%) pts received appropriate ICD interventions after catheter ablation.

Conclusion: Electro-anatomical mapping in addition to ventricular stimulation alone reveals a critical substrate in a relevant proportion of ToF patients (13%). Identification and ablation of a critical isthmus is challenging with 5.3% of maps being inconclusive and 11.5% long-term VT recurrence rate after ablation.