Mechanism of ventricular tachycardia termination by pacing at left ventricular sites in patients with coronary artery disease

Objective: The mechanism by which pacing terminates ventricular tachycardia (VT) may depend on the location of the pacing site relative to the reentry circuit. The purpose of this study was to compare the mechanisms by which pacing terminates VT at left ventricular (LV) sites with and without concealed entrainment (CE) in patients with prior myocardial infarction. Methods and Results: LV mapping was performed in 29 patients (26 men, 3 women, mean age 67+/-11 years, ejection fraction 0.28+/-0.11) with 55 hemodynamically-tolerated VTs (mean cycle length 478+/-92 msec). A total of 408 pacing trains were delivered at 102 sites with CE. Radiofrequency catheter ablation was successful in 41 of 55 VT's. At sites with concealed entrainment, VT was terminated by pacing at 17/41 (41%) successful and at 4/61 (7%) unsuccessful ablation sites (p<0.01). Termination without global ventricular capture was the most frequent termination mode (10/21), followed by termination with orthodromic (4/21) and non-orthodromic capture (7/21). Conclusion: In patients with prior myocardial infarction, pacing at sites of CE during VT usually terminates VT either without global capture or by orthodromic capture. Termination of VT by pacing without global capture or with orthodromic capture at sites of CE suggests that the site is within a critical area of the reentry circuit.