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Quantitative histology of the hypertrophied human heart
Insights
Cardiac hypertrophy due to pressure overload maintains function initially. However, decreased capillary density and increased collagen in hypertrophied hearts may contribute to later cardiac failure.
Area of Science:
- Cardiology
- Pathology
- Physiology
Background:
- Myocardial hypertrophy commonly results from pressure overload conditions like systemic hypertension and aortic stenosis.
- Cardiac failure in humans typically develops after prolonged pressure overload, despite maintained cardiac function during the initial stages.
- The structural changes underlying cardiac failure in hypertrophied hearts have been extensively investigated.
Purpose of the Study:
- To investigate the structural correlates of cardiac failure in pressure-overloaded hypertrophied hearts.
- To evaluate the roles of muscle fiber alignment, capillary density, and collagen content in cardiac function during hypertrophy.
Main Methods:
- Application of morphometric techniques to quantitatively assess structural components of the heart.
- Analysis of muscle fiber alignment, capillary density, and collagen content in normal and hypertrophied hearts.
Main Results:
- Muscle fiber alignment remains normal in pressure-overloaded hypertrophied hearts, even with clinical failure.
- Capillary density is reduced, while collagen content is increased in hypertrophied hearts.
- Chemical studies on collagen concentration have yielded inconsistent results.
Conclusions:
- Structural changes like reduced capillary density and increased collagen content are characteristic of hypertrophied hearts.
- The precise contribution of microcirculation and collagen to myocardial oxygen availability, mechanical function, and failure requires further study.
Abstract:
Myocardial hypertrophy accompanies systemic hypertension and aortic stenosis, i.e., pressure overload. In man cardiac failure only appears after years of pressure overload, during which time cardiac function had been maintained. The structural correlates of cardiac failure have been a subject of much interest for many years. Several hypotheses relating alterations in muscle fiber alignment, capillary density, or collagen content have been offered. The application of morphometric techniques has provided essential quantitative information on the structural components of the normal and diseased heart. These data indicate that muscle fiber alignment remains normal in the pressure overloaded heart despite the presence of hypertrophy or the appearance of clinical failure. On the other hand, capillary density is decreased and collagen content is increased in hypertrophied hearts. Chemical studies on collagen concentration however have yielded inconsistent results. The relative contribution of the microcirculation and collagenous structure of the myocardium on its respective O2 availability, mechanical behavior, and deterioration in pump function will require further investigation.