Quantification of Large Transmural Biopsies Reveals Heterogeneity in Innervation Patterns in Chronic Myocardial Infarction

Abstract

Background: Abnormal cardiac innervation plays an important role in arrhythmogenicity after myocardial infarction (MI). Data regarding reperfusion models and innervation abnormalities in the medium to long term after MI are sparse. Histologic quantification of the small-sized cardiac nerves is challenging, and transmural analysis has not been performed.

Objectives: This study sought to assess cardiac innervation patterns in transmural biopsy sections in a porcine reperfusion model of MI (MI-R) using a novel method for nerve quantification.

Methods: Transmural biopsy sections from 4 swine (n = 83) at 3 months after MI-R and 3 controls (n = 38) were stained with picrosirius red (fibrosis) and beta-III-tubulin (autonomic nerves). Biopsy sections were classified as infarct core, border zone, or remote zone. Each biopsy section was analyzed with a custom software pipeline, allowing calculation of nerve density and classification into innervation types at the 1 × 1-mm resolution level. Relocation of the classified squares to the original biopsy position enabled transmural quantification and innervation heterogeneity assessment.

Results: Coexisting hyperinnervation, hypoinnervation, and denervation were present in all transmural MI-R biopsy sections. The innervation heterogeneity was greatest in the infarct core (median: 0.14; IQR: 0.12-0.15), followed by the border zone (median: 0.05; IQR: 0.04-0.07; P = 0.02) and remote zone (median: 0.02; IQR: 0.02-0.03; P < 0.0001). Only in the border zone was a positive linear relation between fibrosis and innervation heterogeneity observed (R = 0.79; P < 0.0001).

Conclusions: This novel method allows quantification of nerve density and heterogeneity in large transmural biopsy sections. In the chronic phase after MI-R, alternating innervation patterns were identified within the same biopsy section. Persistent innervation heterogeneity, in particular in the border zone biopsy sections, may contribute to late arrhythmogenicity.

Keywords: arrhythmia; autonomic nervous system; cardiac innervation; denervation; hyperinnervation; myocardial infarction; nerve sprouting; neural remodeling; reperfusion therapy.