705-2 Catheter Ablation of the Mitral Isthmus for Ventricular Tachycardia Associated with Inferior Infarction

Abstract

Catheter ablation (CA) of ischemic sustained monomorphic ventricular tachycardia (SMVT) remains problematic due to the presence of multiple potential functional circuits. We identified 3 pts with SMVT and a posterior akinetic/dyskinetic segment in whom anatomic constraints on the reentrant circuit facilitated CA. Each pt had 2-40 episodes of spontaneous SMVT in the previous month despite amiodarone. SMVT had either a LBBB (rS in V1, R in V6) right superior axis morphology (M), or a RBBB (R in V1, QS in V6) left superior axis M. Both M were reproducibly induced in each pt (cycle length [CL] 600-320 ms). In each pt, both M appeared to share a similar slow conduction zone in the inferobasal left ventricle adjacent to the mitral valve annulus. During SMVT of either M, these sites were characterized by diastolic potentials with electrogram-ORS intervals of 115-251 ms (24-58% of SMVT CL) and concealed entrainment during pacing associated with stimulus-ORS intervals of 105-411 ms (23-92% of SMVT CL). Application of radiofrequency energy (50 W for 90-120 s) at one of these sites in each pt (figure) resulted intermination of SMVT within 2-12 complexes. Following CA, neither M couldbe induced in any pt. In 1 pt, SMVT with a third nonclinical ORS M (CL 250 ms) remained inducible. All pts had implantable defibrillators with RR interval and/or electrogram storage. During 1-5 mo follow-up, no pt has had spontaneous SMVT or shocks. An isthmus of surviving myocardium adjacent to the mitral valve annulus may constitute a critical region of slow conduction in some pts with inferior MI and recurrent SMVT, providing a vulnerable and anatomically localized target for CA. Characteristic SMVT morphologies may identify candidates for this approach.