Velocity Vector Analysis for Slowly Conducting Anatomical Isthmuses in Patients with Tetralogy of Fallot.

BACKGROUND: Slowly conducting anatomical isthmuses (SCAI) represent the main substrate for ventricular arrhythmias (VAs) in tetralogy of Fallot (TOF). However, the optimal conduction velocity (CV) threshold and the best approach for measurements remain to be determined. OBJECTIVE: This study aimed at evaluating a new method for CV analysis. METHODS: This single-center retrospective study included consecutive patients with TOF undergoing right ventricular electroanatomic activation mapping. CV across anatomical isthmus 3 was assessed using both automated Local Activation Time Velocity Vector (LVV) analysis and conventional manual measurements. The primary outcome was inducibility of sustained monomorphic ventricular tachycardia (SMVT). RESULTS: A total of 44 patients were included (mean age 44.6±13.8 years, 56.8% males). Overall, a SMVT was inducible in 23 (52.3%) patients, including 12/14 (85.7%) patients referred for catheter ablation of VT (history of clinical VT) and 11/30 (36.7%) patients referred for EPS without spontaenous VT. LVV-CV demonstrated a strong correlation with manual measurements (r = 0.81). The optimal cutoff value of LVV-CV based on the Youden index was 0.5 m/s. AUC, sensitivity, and specificity were 0.81, 0.96, and 0.71 using LVV-CV vs. 0.75, 0.57, and 0.81 using manual CV measurements, respectively. LVV analysis reduced the number of classification errors from 14 (31.8%) cases with manual CV measurement to 7 (15.9%) cases when LVV-CV was used. CONCLUSION: This novel, reproductible, and easy-to-use LVV-based approach to CV measurement for substrate evaluation in patients with TOF suggest that LVV-CV provides superior discriminative performance compared with manual CV measurements for identifying SCAIs associated with SMVT inducibility. Further studies are warranted to evaluate this approach in larger populations.