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.