Revisiting the link between substrate and ventricular tachycardia rate: The critical role of conduction-isthmus...

Ventricular tachycardia (VT) rate determines hemodynamic tolerance and informs risk stratification and ablation strategy. Although global-substrate metrics have been associated with VT dynamics, the relative contribution of local conduction-isthmus properties remains incompletely defined.

We compared the predictive value of global with isthmus-specific substrate features on VT rate.

In a prospective cohort, 62 patients undergoing ablation for scar-related VT underwent high-density electroanatomic mapping and late gadolinium enhancement cardiac magnetic resonance. Functional metrics included total activation time, deceleration zone (DZ) duration/area, and late potential (LP) area; structural metrics included scar/border-zone mass and conduction channel (CC) length, protected volume, and 2-dimensional architecture. The primary outcome was fast VT defined as >180 beats/min.

We analyzed 107 VT episodes, and 39% (n = 42) were classified as fast. Only isthmus-specific features independently predicted fast VT: a DZ duration of <110 ms (adjusted odds ratio 21.16; P < .001) and a CC length of <3 cm (adjusted odds ratio 10.18; P = .02). These thresholds showed strong discrimination (area under the curve of 0.88 for a DZ duration of <110 ms and 0.89 for a CC length of <30 mm); an LP area of <20 cm² yielded an area under the curve of 0.79-each with ≥80% global accuracy. Structural-functional coupling was observed: CC length correlated with DZ duration (ρ = 0.54), DZ area (ρ = 0.35), and LP area (ρ = 0.55) (all P ≤ .01). Compared with ischemic cardiomyopathy, nonischemic cardiomyopathy had faster VT and a more compact isthmus; however, etiology was not an independent predictor and did not modify isthmus-VT rate associations.

Conduction-isthmus properties predominate as determinants of VT rate. Quantitative characterization of VT-related conducting segments may support procedural planning in structural heart disease.