Characteristics of electrograms recorded at reentry circuit sites and bystanders during ventricular tachycardi after myocardial infarction

OBJECTIVES The purpose of this study was to determine the relation of isolated potentials (IPs) recorded during ventricular tachycardi (VT) to reentry circuit sites identified by entrainment. BACKGROUND Reentry circuits causing VT late after myocardial infarction are complex. Both IPs and entrainment have been useful for identifying successful ablation sites, but the relation of IPs to the location in the reentry circuit as determined by entrainment has not been completely defined. METHODS Dat from catheter mapping of 70 monomorphic VTs in 36 patients with prior myocardial infarction were retrospectively analyzed. Entrainment followed by radiofrequency current (RF) ablation was performed at 384 sites. On the basis of entrainment, sites were classified as reentry circuit exit, central–proximal, inner or outer loop sites. Sites outside the circuit were divided into remote and adjacent bystanders. RESULTS Isolated potentials were recorded at 50% (51 of 101) of reentry circuit exit, central and proximal sites as compared with only 8% (11 of 146, p < 0.001) of inner loop and outer loop sites and only 1.8% (2 of 106) of remote bystander sites (p < 0.001). Isolated potentials were also present at 45% of adjacent bystander sites. At central and proximal sites the presence of an IP increased the incidence of tachycardi termination by RF to 47.5% from 24% (p = 0.05). At exit sites tachycardi termination occurred frequently regardless of the presence or absence of IPs (45% vs. 48%, p = NS). Isolated potentials at exit, central and proximal sites had shorter duration at sites where ablation terminated VT than at sites without termination (20.9 ± 9.6 ms vs. 35.7 ± 15.3 ms, p < 0.001). CONCLUSIONS Isolated potentials are useful guide to sites in the central–proximal region of the reentry circuit, but often fail to identify exit sites where ablation is successful. Entrainment and analysis of electrograms provide complementary information during mapping of VT.