Tissue characteristics underlying endocardial local impedance subtypes in chronic myocardial infarction.

Background: Local impedance (LI) mapping is feasible and provides additional tissue characterization of the ventricular tachycardia substrate. Data on tissue composition underlying the LI spectrum are lacking.

Objective: To describe the tissue composition underlying different LI subtypes in a chronic myocardial infarction (MI) swine model.

Methods: One month after non-reperfused anterior MI, 18 Landrace Large White pigs underwent delayed-enhancement cardiac magnetic resonance (DE-CMR) and endocardial left ventricular (LV) LI mapping. DE-CMR images were post-processed off-line to obtain LV wall thickness, scar subtypes, and border zone (BZ) corridors, and were co-registered with LI maps. Tissue samples were obtained from abnormal LI sites.

Results: Low LI zones exhibited more pronounced wall thinning compared to intermediate LI tissue (2.8 ± 0.7 vs 3.8 ± 0.9 mm; P < .001) and correlated with DE-CMR dense endocardial scarring (91.4%) and with epicardial scarring (75% dense and 24% BZ tissue). Intermediate LI tissue exhibited predominantly subendocardial scarring, with more heterogeneous distribution (45% dense, 47% BZ, and 8% healthy tissue) and less epicardial involvement (73% healthy tissue). Most DE-CMR BZ corridors (75.6%) colocalized with intermediate LI tissue. Histologically, tissue from intermediate LI zones displayed less collagen I (P = .008), collagen III (P = .053), and collagen volume fraction (P = .021), and greater vascular density (P = .075), compared to low LI zones.

Conclusions: Areas of low LI had a higher proportion of dense, transmural scar and wall thinning compared to intermediate LI areas. DE-CMR BZ corridors colocalized with intermediate LI in most cases. LI subtypes showed distinctive histological composition.