Targeting the Hidden Substrate Unmasked by Right Ventricular Extrastimulation Improves Ventricular Tachycardia Ablation Outcome After Myocardial Infarction

Objectives: This study sought to determine whether ablation of hidden substrate unmasked by right ventricular extrastimulation (RVE) improves ablation outcome of post-myocardial infarction (MI) ventricular tachycardia (VT).

Background: In patients with small or nontransmural scars after MI, part of the VT substrate may be functional and, in addition, masked by high-voltage far-field signals arising from adjacent normal myocardium.

Methods: In 60 consecutive patients, systematic analysis of electrograms recorded from the presumed infarct area was performed during sinus rhythm, RV pacing at 500 ms, and during a short-coupled RV extrastimulus. Sites showing low-voltage, near-field potentials with evoked conduction delay in response to RVE were targeted.

Results: In 37 (62%) patients, ablation target sites located in areas with normal voltage during sinus rhythm were unmasked by RVE (hidden substrate group). These patients had better left ventricular function (36 ± 11% vs. 26 ± 12%; p = 0.003), smaller electroanatomical scars (<1.5 mV), and smaller dense scars (<0.5 mV) (median 59 and 14 cm² vs. 82 and 44 cm²; p = 0.044 and p = 0.003) than did those in whom no hidden substrate was identified (overt substrate group). During a median follow-up of 16 months, 13 (22%) patients had VT recurrence. Patients with hidden substrate had a lower incidence of VT recurrence (12-month VT-free survival 89% vs. 50% in patients with overt substrate; p = 0.005). Compared with a historical cohort of 90 post-MI patients matched for left ventricular function and electroanatomical scar area, in whom no RVE was performed, patients in the hidden substrate group had a higher 1-year VT-free survival (89% vs. 73%; p = 0.039).

Conclusions: Hidden substrate ablation unmasked by RVE improves ablation outcome in post-MI patients with small or nontransmural scars.