Effect of scar and pacing location on repolarization in a porcine myocardial infarction model

BACKGROUND The effect of chronic ischemic scar on repolarization is unclear, with conflicting results from human and animal studies. An improved understanding of electrical remodeling within scar and border zone tissue may enhance substrate-guided ablation techniques for treatment of ventricular tachycardia. Computational modeling studies have suggested increased dispersion of repolarization during epicardial, but not endocardial, left ventricular pacing, in close proximity to scar. However, the effect of endocardial pacing near scar in vivo is unknown. OBJECTIVE The purpose of this study was to investigate the effect of scar and pacing location on local repolarization in a porcine myocardial infarction model. METHODS Six model pigs underwent late gadolinium enhancement cardiac magnetic resonance (LGE-CMR) imaging followed by electroanatomic mapping of the left ventricular endocardium. LGE-CMR images were registered to the anatomic shell and scar defined by LGE. Activation recovery intervals (ARIs), a surrogate for action potential duration, and local ARI gradients were calculated from unipolar electrograms within areas of late gadolinium enhancement (aLGE) and healthy myocardium. RESULTS There was no significant difference between aLGE and healthy myocardium in mean ARI (304.20 +/- 19.44 ms vs 300.59 +/- 19.22 ms; P 5.43), ARI heterogeneity (23.32 +/- 11.43 ms vs 24.85 +/- 12.99 ms; P =.54), or ARI gradients (6.18 +/- 2.09 vs 5.66 +/- 2.32 ms/mm; P = .39). Endocardial pacing distance from scar did not affect ARI gradients. CONCLUSION Our findings suggest that changes in ARI are not an intrinsic property of surviving myocytes within scar, and endocardial pacing close to scar does not affect local repolarization.