In which of the following types of cardiomyopathy does cardiac output remain normal?
A. Dilated
B. Hypertrophic
C. Obliterative
D. Restrictive
Correct Answer: B. Hypertrophic
Cardiac output isn’t affected by hypertrophic cardiomyopathy because the size of the ventricle remains relatively unchanged. All other choices cause decrease cardiac output. During this cardiac cycle, the mitral valve is pulled towards the septum by several proposed mechanisms: contraction of the papillary muscles, abnormal location in the outflow tract, and low pressure that occurs as blood is ejected at high velocity through a narrowed outflow tract (Venturi effect).
Option A: The progressive dilatation of the ventricles leads to significant tricuspid and mitral valve insufficiency, which further lowers the ejection fraction and increases the ventricular wall stress and end-systolic volumes. Early compensatory mechanisms include an increase in heart rate and tone of the peripheral vascular system.
Option C: Irrespective of the etiology, terminology, or nature of the myocardial process, the ventricles are small (generally <110 mL/m2), and stiff, restricting ventricular filling. Despite normal (or near-normal) systolic function at rest, ventricular diastolic, jugular, and pulmonary venous pressures are increased.
Option D: Patients with RCM primarily present with advanced disease and obvious signs of cardiopulmonary compromise, but in some circumstances, the diagnosis is incidental. It is important to suspect RCM in any patient with a normal or close to normal systolic function and evidence of diastolic dysfunction with a restrictive filling pattern on echocardiogram.
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