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Functional significance of post-myocardial infarction left ventricular hypertrophy: a beneficial response
L E Ginzton1, D Rodrigues, D Garner
1Department of Medicine, University of California at Los Angeles School of Medicine.
Insights
Post-myocardial infarction (heart attack) hypertrophy of the noninfarcted myocardium helps restore left ventricular function. This compensatory cardiac remodeling correlates with improved ejection fraction, suggesting a beneficial adaptation.
Area of Science:
- Cardiology
- Cardiac Physiology
- Myocardial Remodeling
Background:
- Hypertrophy of healthy heart muscle after a heart attack is a known response.
- The functional impact of this post-myocardial infarction (MI) hypertrophy on left ventricular (LV) function remains unclear.
- Previous studies have not linked changes in heart wall thickness to serial changes in LV function.
Purpose of the Study:
- To investigate the relationship between the development of post-MI hypertrophy and resting LV ejection fraction.
- To determine the functional significance of compensatory cardiac hypertrophy following myocardial infarction.
Main Methods:
- Myocardial infarction was induced in 11 dogs by occluding the left anterior descending coronary artery.
- Two-dimensional echocardiography was used to measure LV ejection fraction and wall thickness serially.
- LV mass was calculated and changes were correlated with functional parameters.
Main Results:
- LV ejection fraction acutely decreased post-MI but recovered to near baseline levels by 3.5 months.
- Noninfarcted LV end-diastolic wall thickness and LV mass significantly increased over 3.5 months.
- The improvement in ejection fraction correlated significantly with increases in LV mass and wall thickness.
Conclusions:
- Hypertrophy of the noninfarcted myocardium develops as a chronic adaptation to myocardial infarction.
- This cardiac remodeling is associated with the restoration of resting left ventricular function.
- Post-MI hypertrophy may play a beneficial role in preserving or improving LV function.
Abstract:
Hypertrophy of noninfarcted myocardium occurs as a chronic response to myocardial infarction, but no previous study has related the changes in wall thickness to serial changes in left ventricular function. Thus the functional significance of postinfarction hypertrophy is unknown. The purpose of this study was to determine the relationship between the development of postinfarction hypertrophy and the resting left ventricular ejection fraction measured by two-dimensional echocardiography. After occlusion of the proximal left anterior descending coronary artery in 11 dogs, the ejection fraction fell acutely (0.63 +/- 0.08 to 0.33 +/- 0.10, p less than 0.001) and rose at 3.5 months to 0.62 +/- 0.12. End-diastolic thickness of the noninfarcted left ventricle increased (11 +/- 1.0 mm to 13 +/- 1.4 mm, p less than 0.01) as did left ventricular mass (101 +/- 18 gm to 134 +/- 21 gm, p less than 0.0001). Restoration of the ejection fraction toward the baseline value correlated with the increases in left ventricular mass (r = 0.79, p = 0.007) and wall thickness (r = 0.71, p = 0.025). Hypertrophy of the noninfarcted myocardium correlated with the magnitude and approximately paralleled the time course of the improvement in the ejection fraction and therefore may have had a beneficial effect on resting left ventricular function as a chronic adaptation to myocardial infarction.