Identification of reentry circuit sites during catheter mapping and radiofrequency ablation of ventricular tachycardia late after myocardial infarction

Ventricular tachycardia reentry circuits in chronic infarct scars can contain slow conduction zones, which are difficult to distinguish from bystander areas adjacent to the circuit during catheter mapping. This study developed criteria for identifying reentry circuit sites using computer simulations. These criteria then were tested during catheter mapping in humans to predict sites at which radiofrequency current application terminated ventricular tachycardia. In computer simulations, effects of single stimuli and stimulus trains at sites in and adjacent to reentry circuits were analyzed. Entrainment with concealed fusion, defined as ventricular tachycardia entrainment with no change in QRS morphology, could occur during stimulation in reentry circuit common pathways and adjacent bystander sites. Pacing at reentry circuit common pathway sites, the stimulus to QRS (S-QRS) interval equals the electrogram to QRS interval (EG-QRS) during tachycardia. The postpacing interval from the last stimulus to the following electrogram equals the tachycardia cycle length. Pacing at bystander sites the S-QRS exceeds the EG-QRS interval when the conduction time from the bystander site to the circuit is short but may be less than or equal to the EG-QRS interval when the conduction time to the circuit is long. The postpacing interval, however, always exceeds the tachycardia cycle length. When conduction in the circuit slows during pacing, the S-QRS and postpacing intervals increase and the slowest stimulus train most closely reflects conduction times during tachycardia. Endocardial catheter mapping and radiofrequency ablation were performed during 31 monomorphic ventricular tachycardias in 15 patients with drug refractory ventricular tachycardia late after myocardial infarction. During ventricular tachycardia, trains of electrical stimuli or scanning single stimuli were evaluated before application of radiofrequency current at the same site. Radiofrequency current terminated ventricular tachycardia at 24 of 241 sites (10%) in 12 of 15 patients (80%). Ventricular tachycardia termination occurred more frequently at sites with entrainment with concealed fusion (odds ratio, 3.4; 95% confidence interval [CI], 1.4 to 8.3), a postpacing interval approximating the ventricular tachycardia cycle length (odds ratio, 4.6; 95% CI, 1.6 to 12.9) and an S-QRS interval during entrainment of more than 60 milliseconds and less than 70% of the ventricular tachycardia cycle length (odds ratio, 4