Biphasic temporal pattern in exercise capacity after myocardial infarction in the rat: relationship to left ventricular remodeling.

After myocardial infarction (MI), there is progressive left ventricular (LV) remodeling and impaired exercise capacity. We tested the hypothesis that LV remodeling results in structural and functional changes that determine exercise impairment post-MI. Rats underwent coronary artery ligation (n = 12) or sham (n = 11) surgery followed by serial exercise tests and echocardiography for 16 wk post-MI. LV pressure-volume relationships were determined using a blood-perfused Langendorff preparation. Exercise capacity was 60% of shams immediately post-MI (P < 0.05) followed by a recovery to near normal during weeks 5-8. Thereafter, there was a progressive decline in exercise capacity to +/-40% of shams (P < 0.01). At both 8 and 16 wk post-MI, fractional shortening (FS) was reduced and end-diastolic diameter (EDD) was increased (P < 0.01). However, neither FS nor EDD correlated with exercise at 8 or 16 wk (r(2) < 0.12, P > 0.30). LV septal wall thickness was increased at both 8 (P = 0.17 vs. shams) and 16 wk (P = 0.035 vs. shams) post-MI and correlated with exercise at both times (r(2) >/= 0.50 and P </= 0.02 at 8 and 16 wk). Neither end-diastolic volume nor maximum LV developed pressure at 16 wk correlated with exercise capacity. Exercise capacity follows a biphasic time course post-MI. An immediate decrease is followed by an early recovery phase that is associated with compensatory LV hypertrophy. Subsequently, there is a progressive decrease in exercise capacity that is independent of further changes in LV volume or contractile function.