cardiovascular disorders
Hypertrophic Cardiomyopathy
Pathophysiology of Hypertrophic Cardiomyopathy
The myocardium is abnormal with cellular and myofibrillar disarray, although this finding is not specific for hypertrophic cardiomyopathy. In the most common phenotype, the anterior septum and contiguous anterior free wall below the aortic valve are markedly hypertrophied and thickened, with little or no hypertrophy of the left ventricular (LV) posterior wall. Sometimes isolated apical hypertrophy occurs; however, virtually any asymmetric pattern of left ventricular hypertrophy can be observed, and in a small minority of patients even symmetric hypertrophy has been noted. About two thirds of patients exhibit obstructive physiology at rest or during exercise. Obstruction is the result of mechanical impedance to LV outflow during systole due to systolic anterior motion (SAM) of the mitral valve. During SAM, the mitral valve and valve apparatus are sucked into the LV outflow tract by a Venturi effect of high-velocity blood flow, resulting in obstruction of flow and decrease in cardiac output. Mitral Regurgitation can also occur as the result of distortion of leaflet motion by SAM of the mitral valve. This obstruction and valvular regurgitation contribute to the development of symptoms related to Contractility is grossly normal, resulting in a normal ejection fraction (EF). Later, EF is elevated because the ventricle has a small volume and empties nearly completely to maintain cardiac output. Hypertrophy results in a stiff, noncompliant chamber (usually the left ventricle) that resists diastolic filling, elevating end-diastolic pressure and thus increasing pulmonary venous pressure. As resistance to filling increases, cardiac output decreases, an effect worsened by any outflow tract gradient present. Because tachycardia allows less time for filling, symptoms tend to appear mainly during exercise or tachyarrhythmias. (See also Heart failure with preserved ejection fraction (HFpEF) .) Coronary blood flow may be impaired, causing Angina Pectoris , In some cases, myocytes gradually die, probably because capillary/myocyte imbalance causes chronic diffuse ischemia. As myocytes die, they are replaced by diffuse fibrosis. Then, the hypertrophied ventricle with diastolic dysfunction gradually dilates and systolic dysfunction develops. 