Progressive ventricular remodeling in rat with myocardial infarction.

Ventricular dilatation may have important prognostic implications for the survival of patients with left ventricular (LV) dysfunction. To determine the manner and extent to which the left ventricle of the rat remodels and dilates after myocardial infarction, we obtained the passive pressure-volume relationships, chamber stiffness constants, and mass during both the early and late phases. In moderate and large infarcts as inflammation and edema developed, LV weight increased then progressively decreased as a thin scar formed, returning to normal values as a result of compensatory hypertrophy of the residual myocardium. LV dilatation occurred in all rats with infarcts but to different extents depending on infarct size and duration. In the early postinfarction phase, pressure-volume relationship was relatively unchanged in all infarct-size groups, except for significant rightward shift in low pressure range for rats with moderate and large infarcts and significant leftward shift in high pressure range for rats with small infarcts. During resolution of the inflammatory response, LV dilatation occurred in all infarct groups in relation to infarct size. As scar formation became complete, LV enlargement did not progress in rats with small infarcts but did so in rats with moderate and large infarcts. LV chamber stiffness remained within the range of normal values during the early phase in all rats with infarcts but decreased significantly during the late phase in rats with moderate and large infarcts in association with the extent of ventricular enlargement. Alterations in the volume-to-mass ratio (V/Vwt) were most marked in the late postinfarction phase, wherein both volume (increased) and mass (decreased, then increased) changed dramatically and V/Vwt progressively increased in rats with large infarcts.