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Heart Failure - Pathophysiology (view source)
Revision as of 09:26, 30 June 2016
, 09:26, 30 June 2016→Myocardial hypertrophy
Chronic increase in cardiac work results in a geometric alteration of the chambers involved. Remodelling of the ventricular myocardium occurs in two forms: '''concentric''' and '''eccentric''' hypertrophy. Factors implicated in the development of hypertrophy include adrenergic stimulation, angiotensin II and increased intracellular calcium.
Chronic increase in cardiac work results in a geometric alteration of the chambers involved. Remodelling of the ventricular myocardium occurs in two forms: '''concentric''' and '''eccentric''' hypertrophy. Factors implicated in the development of hypertrophy include adrenergic stimulation, angiotensin II and increased intracellular calcium.
Concentric hypertrophy develops in response to pressure overload (increased afterload). Increased afterload causes replication of sarcomeres in parallel, resulting in an increase in wall thickness and a decrease in internal diameter with no overall change in the external diameter of the chamber. This is better understood by considering the '''Laplace''' law, which states that ventricular wall stress is elevated by increased pressure and increased chamber diameter; whereas wall stress decreases as the ventricular wall thickens. Therefore concentric hypertrophy occurs as a compensatory mechanism to normalise ventricular wall stress in the face of pressure overload.
'''Concentric hypertrophy''' develops in response to pressure overload (increased afterload). Increased afterload causes replication of sarcomeres in parallel, resulting in an increase in wall thickness and a decrease in internal diameter with no overall change in the external diameter of the chamber. This is better understood by considering the '''Laplace''' law, which states that ventricular wall stress is elevated by increased pressure and increased chamber diameter; whereas wall stress decreases as the ventricular wall thickens. Therefore concentric hypertrophy occurs as a compensatory mechanism to normalise ventricular wall stress in the face of pressure overload.
'''Eccentric hypertrophy''' develops in response to volume overload (increased preload). The sarcomeres replicate in series, leading to elongation of the myocytes, an increase in internal diameter and an approximately normal wall thickness with an overall increase in external diameter of the chamber.
Although initially compensatory, increased myocardial mass associated with hypertrophy eventually leads to an increase in myocardial oxygen demand. The increase in oxygen demand outstrips the ability of the coronary circulation to provide sufficient oxygen, which results in myocardial ischaemia. This can result in damage to the myocardium (myocardial necrosis) with replacement by scar tissue (fibrosis), further compromising cardiac function.
== Classification ==
== Classification ==