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Cardiomyopathies refer to a heterogeneous group of myocardial pathology that impairs normal cardiac function in the absence of acute coronary ischemia or chronic valvular dysfunction. The group can be classified into primary cardiomyopathies, which predominantly affect the myocardium and secondary cardiomyopathies, capable of impairing normal myocyte function, while producing widespread systemic dysregulation and multiorgan dysfunction. Primary cardiomyopathies can be further subdivided according to the etiology producing the cardiac pathology: (1) genetic; (2) mixed; and (3) acquired.
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HYPERTROPHIC CARDIOMYOPATHY
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Hypertrophic cardiomyopathy (HCM) is the most common primary cardiomyopathy with a genetic origin. It refers to a heterogeneous group of autosomal dominant disease with variable genetic penetrance and expressivity that produces diastolic dysfunction as well as asymmetric hypertrophy of the upper interventricular septum with subsequent dynamic obstruction of the left ventricular outflow tract (LVOT). The flow acceleration produced in the LVOT during cardiac systole generates a Venturi effect on the anterior mitral leaflet, which distorts the mechanical geometry of the mitral valve and the mitral subvalvular apparatus. The coaptation point of the anterior and posterior mitral leaflets moves anteriorly into the LVOT, producing systolic anterior motion (SAM), incomplete closure of the mitral valve leaflets, and mitral regurgitation, which significantly diminishes the effective antegrade cardiac output, leading to systemic hypotension (Figure 70-1).
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Clinical parameters that exacerbate SAM of the anterior mitral valve leaflet include positive inotropic support (i.e., increased myocardial contractility), decreased preload (i.e., hypovolemia, venodilation), and decreased afterload (i.e., decreased systemic vascular resistance [SVR] and arterial vasodilators). Factors that help to alleviate SAM of the anterior mitral valve leaflet include negative inotropy (i.e., decreased myocardial contractility), increased preload (i.e., intravenous administration of crystalloid, colloid, or blood products), and increased afterload (i.e., increased SVR and arterial hypertension).
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All patients presenting with HCM should be considered at high risk of developing dysrhythmias as well as myocardial ischemia, primarily as a result of (1) the mismatch between the increased oxygen demand of the thickened myocardium and the decreased supply provided by the coronary arteries; (2) the diastolic dysfunction contributing to a decreased left ventricular filling time; and (3) the decreased coronary perfusion gradient caused by the increase in left ventricular end-diastolic pressure (LVEDP).
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On physical examination, patients with HCM often have an audible murmur as a result of the turbulent, accelerated blood flow in the LVOT. An ECG can help support the diagnosis of HCM as it typically displays evidence of left ventricular hypertrophy (i.e., increased QRS voltage). The ECG may also occasionally reveal the presence of Q ...