[Mechanical function is normal in remanent myocardium during the healing period of myocardial infarction--despite congestive heart failure]

Abstract

Objective: The temporal relation between ventricular dysfunction (VD) after myocardial infarction (MI) and remanent myocardium mechanics is not yet clear. The present work investigated--through Doppler echocardiography (ECHO)--ventricular function in rats with extensive MI, as well as the mechanical function of papillary muscles (PM) at the end of the healing period.

Methods: ECHO and PM of 9 Wistar rats (MI) were studied against 9 controls (C) three weeks after LV myocardial infarction. The following were determined: developed tension (DT) and its first negative and positive derivative, time-to-peak tension (TPT), resting tension (RT), and relaxation time at 50% of DT at 0.5, 1.0, 1.5, 2.0 and 2.5 calcium concentrations (mM). Tetanic contractions were carried out after ryanodine administration at 1.5, 2.5 and 5.0 calcium concentrations.

Results: VD was characterized by ECHO, with marked abnormality of diastolic volume and LV and ejection fraction in addition to clear restrictive pattern of blood flow through the mitral valve. No significant difference was found in myocardial mechanics data either for MI or for C rats.

Conclusion: The heart failure (HF) reported by MI rats with > 40% MI at the end of the healing period is not myocardial function dependent. Chamber structural changes and lower population of myocites should base VD and HF.