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Contractile function in chronic gradually developing subcoronary aortic stenosis
Insights
Gradually developing cardiac hypertrophy in dogs did not impair heart muscle function. This study suggests that chronic hypertrophy, unlike acute overload, maintains normal myocardial contractile performance.
Area of Science:
- Cardiovascular Physiology
- Cardiac Hypertrophy Research
Background:
- Controversy exists regarding the functional status of hypertrophied cardiac muscle.
- Previous animal studies often used acute pressure overload, potentially causing myocardial injury.
- The impact of chronic, slow-developing hypertrophy on cardiac function remains less understood.
Purpose of the Study:
- To investigate if chronic, gradually developing cardiac hypertrophy is associated with normal myocardial function.
- To develop and utilize an experimental model for slow-onset left ventricular hypertrophy in dogs.
Main Methods:
- Aortic banding was performed on puppies to gradually increase afterload as they grew.
- Two groups were studied: early banding (group A) and late banding (control group B).
- Cardiac function was assessed by measuring ejection fraction, dP/dt, Vcf, and stroke work per gram of myocardium.
Main Results:
- Group A animals exhibited moderate cardiac hypertrophy, indicated by an increased left ventricular weight to body weight ratio (5.3 +/- 0.24) compared to controls (3.9 +/- 0.14).
- Key indicators of myocardial contractile performance, including ejection fraction, dP/dt, Vcf, and stroke work per gram of myocardium, were virtually identical between the hypertrophied and control groups.
- The experimental model successfully induced moderate cardiac hypertrophy without acute myocardial injury.
Conclusions:
- Moderate cardiac hypertrophy that develops gradually, as induced by this model, is associated with normal myocardial contractile performance.
- This finding challenges the notion that cardiac hypertrophy invariably leads to functional impairment.
- The method of inducing hypertrophy is critical when assessing its functional consequences.
Abstract:
Whether hypertrophied cardiac muscle functions normally or abnormally is a point of controversy in the literature. Most animal studies showing depressed performance of hypertrophied cardiac muscle have used experimental methods in which hypertrophy was produced by acutely imposing a pressure overload on the left or right ventricle, which may cause myocardial injury. To assess the possibility that chronic, slowly developing hypertrophy is associated with normal myocardial function, we developed an experimental model in which increased afterload is imposed gradually on the left ventricle in the dog. A snug band was placed around the aorta beneath the left coronary artery in puppies without producing a stenosis. As the puppies grew, relative aortic stenosis developed as increased cardiac output flowed across that fixed outflow area. One group (group A) of six puppies was banded early, whereas a second group (group B, five puppies) was banded late and served as controls. Left ventricular weight (g) to body weight (kg) ratio remained normal in group B animals (3.9 +/- 0.14), whereas this ratio was increased to 5.3 +/- 0.24 (P < 0.001) in group A animals indicating development of moderate cardiac hypertrophy. Ejection fraction, dP/dt, Vcf, and stroke work per gram of myocardium were virtually identical in both groups. We conclude that moderate, gradually developing cardiac hypertrophy as produced by this model is associated with normal myocardial contractile performance.