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Heterogeneity of ventricular remodeling after acute myocardial infarction in rats
1Department of Medicine, New York Medical College, Valhalla 10595.
Insights
Acute myocardial infarction significantly alters rat heart shape and increases wall stress, particularly diastolic stress, on surviving heart muscle. This remodeling may contribute to poor long-term outcomes after infarction.
Area of Science:
- Cardiovascular Physiology
- Cardiac Remodeling
- Myocardial Infarction Research
Background:
- Acute myocardial infarction (AMI) causes significant myocyte loss and left ventricular (LV) dysfunction.
- Understanding the impact of AMI on myocardial stress distribution is crucial for predicting long-term outcomes.
Purpose of the Study:
- To investigate the effects of AMI on systolic and diastolic wall stress in surviving myocardium.
- To characterize the changes in cardiac geometry and function following experimental myocardial infarction.
Main Methods:
- Rats underwent coronary artery occlusion to induce myocardial infarction, followed by hemodynamic measurements.
- Hearts were fixed in vitro to mimic end-diastole and peak systole for anatomical analysis.
- Systolic and diastolic wall stress were quantified on the surviving myocardium.
Main Results:
- Infarction led to LV failure, increased LV volumes, and reduced cardiac output.
- Ventricular remodeling resulted in a shift from an ellipsoidal to a cylindrical heart shape.
- Diastolic wall stress increased 6.8-fold, while systolic stress increased 1.1-fold, with overall stress increasing 1.9-fold.
Conclusions:
- Large myocardial infarcts induce significant adverse cardiac remodeling and alter wall stress distribution.
- Elevated diastolic wall stress in the surviving myocardium may predispose to unfavorable long-term prognosis after infarction.
Abstract:
To determine the effects of acute myocardial infarction on the extent and distribution of systolic and diastolic wall stress on the surviving myocardium, coronary artery occlusion was produced in rats, and the animals were killed 1 wk later. After hemodynamic measurements in vivo, the characteristics of cardiac anatomy at end diastole and peak systole were mimicked in vitro by fixing hearts under diastolic conditions or barium-induced contracture. In the presence of infarcts inducing a 48% loss of myocytes, left ventricular failure was documented by increases in left ventricular minimal and end-diastolic pressures and decreases in peak systolic pressure and positive and negative rates of pressure change with time. End-diastolic and end-systolic volumes increased, whereas stroke volume and cardiac output diminished. Ventricular remodeling in diastole consisted of an increase in the longitudinal axis while both longitudinal and transverse mid-chamber diameters were augmented after systolic contraction. Left ventricular chamber volume enlarged by 44% through a 20% augmentation in the longitudinal diameter and increases in the transverse luminal diameter of 13, 21, 32, and 37% in four consecutive sites from the equatorial region to the apex. As a consequence of infarction, systolic thickening of the spared myocardium of the free wall was reduced progressively from the base to the apex. In the interventricular septum of the infarcted heart, systole thickening occurred mostly in the equatorial region and was reduced at the basal and apical portions. The interaction of hemodynamic impairment with the architectural rearrangements of the wall and chamber provoked a 1.9-fold increase in overall stress on the spared myocardium. However, diastolic stress was augmented by 6.8-fold, markedly exceeding the 1.1-fold increase in systolic stress. Thus large infarcts of the rat left ventricle due to left main coronary occlusion lead to a change in shape of the heart from ellipsoidal to cylindrical. The elevation in overall stress may condition the unfavorable long-term outcome of the infarcted heart.