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

Spontaneous monomorphic ventricular tachycardia (VT) recorded by cardiac implantable devices exhibits distinct initiation patterns, but their clinical significance remains unclear.

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.

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).

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.

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.