Significance of Different Electrogram Morphologies at the Onset of Ventricular Tachycardia Episodes.

BACKGROUND: Spontaneous monomorphic ventricular tachycardia (VT) recorded by cardiac implantable devices exhibits distinct initiation patterns, but their clinical significance remains unclear. OBJECTIVE: To determine whether spontaneous VT initiation morphology on cardiac implantable device electrograms is associated with the number of inducible VTs, substrate characteristics, and outcomes in patients with structural heart disease. METHODS: We retrospectively studied 113 patients with structural heart disease who underwent catheter ablation for monomorphic VT and had analyzable spontaneous VT episodes recorded by an implantable cardioverter-defibrillator. Spontaneous VT was classified as having a matching-morphology initiation if the initiating beat matched the sustained VT (Type A); and a different-morphology initiation if the initial beat differed from the subsequent VT beats (Type B). RESULTS: Among 257 spontaneous VT episodes 147 were Type A and 110 were Type B. Of 113 patients, 58 had Type A only, 47 had Type B only, and 8 had both types. Type B initiation was associated with longer pre-VT RR intervals and more frequent ventricular-paced baseline rhythm. During ablation, the Type B only group had more inducible VT morphologies (P = 0.012), which remained significant after multivariable adjustment (incidence rate ratio 1.47, 95% confidence interval 1.15-1.87; P = 0.002), despite similar scar extent (P = 0.184). Acute procedural outcomes, complications, VT recurrence, and composite outcomes were not significantly different between groups. CONCLUSION: VT with an initiation morphology distinct from the subsequent VT is associated with a greater number of inducible VT morphologies despite comparable gross scar extent.