Figure 5: Increased interstitial fibrosis and inflammation in atria of swimming exercised mice.

(a) Representative images of picrosirius red-stained hearts showing increased myocardial collagen in atria but not ventricles of exercised mice (red). (b) Summary of % tissue collagen derived from picrosirius red stained sections. (c) Representative Mac-3-stained atrial sections showing increased macrophage counts with exercise (shown by red arrows). (d) Normalized macrophage counts. (e) Isochronal activation maps of paced left atrial appendages showing time to activation of the left atrial appendage from site of stimulation. (f) Averaged conduction velocities (CV) calculated from activation maps of the left atrial appendage. (g) Representative surface ECG recordings showing prolonged P-wave durations in exercised mice (dashed line). In all, 55% of exercised compared with 10% of sedentary mice showed +/− p-wave morphology. (h) Average P-wave durations. The n values indicated on bars represent number of mice used. Data presented as mean±s.e.m. *P<0.05 when exercised is compared with sedentary using Student’s t-test. **P<0.05 when exercised is compared with sedentary using Welch’s t-test. Scale bars indicate 100 μm. NS, not significant.