Relative timing of isolated potentials during postinfarction ventricular tachycardia and sinus rhythm

In postinfarction patients, isolated potentials separated by an isoelectric segment from the ventricular electrogram indicate areas of block. Isolated potentials can be recorded during both sinus rhythm and ventricular tachycardia (VT). In an attempt to differentiate bystander pathways from critical sites within a reentry circuit, we compared the relative timing of isolated potentials during VT and sinus rhythm.

In 19 patients (mean age 68 +/- 6 years) with postinfarction VT who were referred for VT ablation, mapping was performed in the presence and absence of VT. Forty-three sites at which there was concealed entrainment during 35 VT's (mean cycle length 469 +/- 74 ms) displayed an isolated potential separated from the main portion of the ventricular electrogram by an isoelectric segment of >/=30 msec in the presence and absence of VT. The interval between the ventricular electrogram and the isolated potential was measured during VT and baseline rhythm, and the absolute difference (DeltaIPI) was calculated. The DeltaIPI was significantly greater at effective ablation sites (119 +/- 69 ms) than at ineffective ablation sites (30 +/- 28 ms, p < 0.001). The positive predictive value of a DeltaIPI > 85 ms for an effective ablation site was 100%.

At sites of concealed entrainment, an absolute difference >85 ms between the isolated potential intervals during sinus rhythm and VT is highly specific for a critical area of the VT reentry circuit in post-infarction patients.