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Cardiac hypertrophy due to pressure and volume overload: distinctly different biological phenomena?
1Department of Pathology, Faculty of Medicine of Ribeirão Preto, University of São Paulo, Brazil.
Insights
Myocardial hypertrophy, an adaptive heart response, includes concentric and eccentric types. In rats, anemia-induced volume overload causes eccentric hypertrophy, a magnified normal heart growth dependent on catecholamines.
Area of Science:
- Cardiology
- Physiology
- Pathology
Background:
- Myocardial hypertrophy is an adaptive response to chronic heart workload.
- Two types exist: concentric (pressure overload, increased wall thickness) and eccentric (volume overload, enlarged chamber).
- The terms 'concentric' and 'eccentric' can be confusing; hypertrophy is fundamentally concentric, differing in chamber volume changes.
Purpose of the Study:
- To investigate the characteristics of adaptive myocardial hypertrophy in response to volume overload.
- To explore the role of catecholamines in mediating cardiac growth during volume overload.
- To compare the adaptive process in anemic rats to normal cardiac growth.
Main Methods:
- Induction of anemia in rats via iron deficiency to create a volume overload model.
- Morphological and functional assessment of the heart under chronic volume overload conditions.
- Investigation of the involvement of catecholamines in the observed cardiac adaptation.
Main Results:
- Anemia-induced volume overload resulted in adaptive cardiac hypertrophy with a dilated ventricle, termed eccentric hypertrophy.
- This process was dependent on catecholamines, suggesting their role as signaling molecules for myocardial growth.
- The cardiac muscle maintained preserved ultrastructure and contractile performance.
- The heart underwent harmonious growth, resembling a magnified normal heart.
Conclusions:
- Eccentric hypertrophy, as observed in anemic rats, is a form of adaptive cardiac growth mediated by catecholamines.
- This adaptive response preserves cardiac function and structure.
- The process mirrors normal cardiac growth driven by increased metabolic demands and blood volume.
Abstract:
Myocardial hypertrophy is a morphological adaptive response to chronic work overload imposed on the heart. It has been categorized into two distinct basic types: concentric hypertrophy, occurring in response to a sustained pressure overload in which wall thickness increases without chamber enlargement, and eccentric hypertrophy, in response to a chronic volume overload in which chamber volume enlarges without a relative increase in its wall thickness. It should be emphasized, in this context, that these adjectives are somewhat confusing, since the hypertrophy observed is not eccentric in the fashion often seen in the left ventricle of patients with hypertrophic cardiomyopathy. In fact, the hypertrophy is concentric in both instances, but is associated with an increase in chamber volume when described as eccentric, yet occurring with a maintained volume when said to be concentric. In rats made anemic by iron deficiency, the volume overloaded heart achieves an adaptive increase in mass characterized as hypertrophy occurring in the setting of dilated ventricle. This so-called eccentric hypertrophy depends on catecholamines as possible signals for myocardial growth, and progresses with preserved ultrastructure and contractile performance of the cardiac muscle. A gradually imposed volume overload results in a harmonious growth of the heart (it retains a relative normal shape, becoming a magnified normal heart), probably mediated by release of catecholamines into the myocardium. This process resembles the normal cardiac growth in response to the obligatory volume load imposed by an increasing cardiac output (greater metabolic demands) and blood volume.(ABSTRACT TRUNCATED AT 250 WORDS)