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Equadon predominates hence distension impairs

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Unformatted text preview: Concentric, in response to chronic pressure overload, aorDc valve stenosis –  Hypertrophy and fibrosis in chronic post ­MI 5 4/9/13 Net Effect of Compensatory Mechanisms HF Mechanical Effects •  A\erload = wall stress, S •  Laplace equaDon: P = 2Sw/r P=pressure; r=radius; w=wall thickness •  By Frank Starling mechanism, ventricular distension causes increased contracDlity •  However, by Laplace equaDon, ventricular distension (increased r) reduces the amount of pressure that can be generated by a given contracDle force •  In normal hearts, mild distension has minimal effect and Frank Starling mechanism predominates; however, in grossly dilated hearts, Laplace equaDon predominates hence distension impairs contracDlity RaDonale of TherapeuDc Strategies •  Vasodilators – decrease preload and/or a\erload –  Angiotensin converDng enzyme (ACE) inhibitors, Angiotensin receptor blockers (ARBs) –  Venous selecDve vasodilators, e.g. organic nitrates, reduce preload –  Arterial selecDve vasodilators, e.g. Hydralazine, reduce a\erload •  DiureDcs, decrease a\erload •  PosiDve inotropic agents increase contracDlity, e.g. beta1 receptor agonists, cardiac glycosides (digitalis) •  Calcium channel blockers for diastolic dysfuncDon 6 4/9/13 Acute MI •  Le\ anterior...
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