Functional Substrate Mapping and Its Correlation With Ventricular Tachycardia Critical Sites: A Blinded Study.

BACKGROUND: Functional substrate mapping identifies areas of decremental conduction, which are critical targets for ventricular tachycardia (VT) ablation. The evidence for this observation is derived from unblinded studies. OBJECTIVES: In a blinded study, we evaluated the correlation between areas of decremental conduction unveiled with functional substrate mapping and VT critical sites identified using traditional substrate mapping. METHODS: We studied consecutive patients with structural heart disease undergoing VT ablation whereby the operator simultaneously acquired 2 maps: a baseline substrate map (unblinded) simultaneous with a functional substrate map (blinded) using an extra-stimulus pacing protocol. Ablation was performed using conventional mapping techniques without access to functional mapping data. Postprocedure, blinded analyses evaluated the spatial concordance between decremental conduction areas and VT critical sites. RESULTS: Among 33 patients who underwent the extra-stimulus protocol, 20 patients completed mapping and had inducible VT (mean age: 62 [IQR: 54-73] years; 55% ischemic cardiomyopathy [ICM]). Among 51 VTs with putative isthmi or breakthrough sites identified, these sites colocalized with decremental conduction regions in 78% and 73% using 10-milliseconds and 20-milliseconds cutoffs, respectively (P = 0.25). Although colocalization rate did not differ between thresholds, the 20-milliseconds decremental area was smaller (P < 0.01). Colocalization rate was higher in ICM compared with nonischemic cardiomyopathy (NICM) patients (93% vs 59%, P < 0.01 for 10-ms; 86% vs 55%, P = 0.03 for 20-ms). CONCLUSIONS: In a blinded evaluation, areas of decremental conduction identified by functional substrate mapping showed a high degree of colocalization with VT critical sites, particularly in ICM patients. This relationship was less consistent in NICM patients.