Figure 5. Altered neuroeffector distribution underlies perturbed myocardial sympathetic control after chronic infarction.

(A) Eighty percent of action potential duration (APD₈₀) maps of representative sham heart at baseline and after infusion of 5 μM tyramine. (B) Change in APD₈₀ (ΔAPD₈₀) map of sham heart. (C) APD₈₀ maps of representative MI heart at baseline and after infusion of 5 μM tyramine. Gray region denotes dense scar. (D) APD₈₀ map of MI heart. (E–G) Representative action potentials at baseline (black) and after tyramine (magenta) in anatomically segmented regions of MI heart. (H) Comparison of regional, tyramine-mediated changes in APD₈₀ between sham and MI hearts, with MI hearts showing significant regional variation in tyramine effect (Kruskal-Wallis, *P = 0.0132, n = 4 mice per group) while sham hearts showed no significant regional variation (Kruskal Wallis, P = 0.7463, n = 4 mice per group). (I) Plot of regional small-fiber prevalence in MI hearts versus tyramine-mediated APD change, with positive correlation in left ventricular (LV) base and right ventricular (RV) regions (Spearman’s r = 0.7381, P = 0.0458, n = 8 regions from 4 mice) but no correlation when border zone (BZ) is included (Spearman’s r = 0.021, P = 0.956, n = 12 regions from 4 mice). Scale bars: 1 mm (A–D).