Hypertrophy is the enlargement of a tissue or organ due to an increase in the size of its individual cells, driven by increased workload or other stimuli. Unlike hyperplasia (which involves an increase in the number of cells), hypertrophy involves existing cells becoming larger and producing more structural proteins.
In the heart, myocardial hypertrophy is both an adaptive and a pathological process. The heart muscle responds to chronically increased workload by enlarging individual cardiomyocytes. Concentric hypertrophy (the ventricular wall thickens without the chamber enlarging) occurs in pressure overload such as hypertension or aortic stenosis. Eccentric hypertrophy (the heart dilates and the wall becomes relatively thinner) occurs in volume overload such as mitral regurgitation or dilated cardiomyopathy. Pathological hypertrophy due to genetic mutations in sarcomeric proteins is the hallmark of hypertrophic cardiomyopathy.
Initially, cardiac hypertrophy is an adaptive response that maintains normal cardiac output against the increased load. Over time, pathological hypertrophy is associated with fibrosis, impaired diastolic filling, arrhythmias, and ultimately heart failure. The degree of left ventricular hypertrophy (LVH) on ECG or echocardiography is an independent cardiovascular risk factor and is associated with an increased risk of sudden cardiac arrest.
The right ventricle undergoes hypertrophy in response to pulmonary hypertension or conditions obstructing pulmonary blood flow (such as severe pulmonary valve stenosis or advanced COPD), which can eventually cause right heart failure (cor pulmonale).
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