Which of the following types of cardiomyopathy does not affect cardiac output?
A. Dilated
B. Hypertrophic
C. Restrictive
D. Obliterative
Correct Answer: B. Hypertrophic
Cardiac output isn’t affected by hypertrophic cardiomyopathy because the size of the ventricle remains relatively unchanged. Three explanations for the systolic anterior motion of the mitral valve have been offered, as follows: (1) the mitral valve is pulled against the septum by contraction of the papillary muscles, which occurs because of the valve’s abnormal location and septal hypertrophy altering the orientation of the papillary muscles; (2) the mitral valve is pushed against the septum because of its abnormal position in the outflow tract; (3) the mitral valve is drawn toward the septum because of the lower pressure that occurs as blood is ejected at high velocity through a narrowed outflow tract (Venturi effect).
Option A: Dilated cardiomyopathy causes a decrease in cardiac output. Progressive dilation can lead to significant mitral and tricuspid regurgitation, which may further diminish the cardiac output and increase end-systolic volumes and ventricular wall stress. In turn, this leads to further dilation and myocardial dysfunction.
Option C: Restrictive cardiomyopathy causes decreased cardiac output. Reduced LV filling leads to reduced stroke volume resulting in low cardiac output symptoms such as fatigue and lethargy. Increased filling pressures cause pulmonary and systemic congestion and symptomatic dyspnea.
Option D: Obliterative cardiomyopathy may affect cardiac output because a thrombus hampers ventricular filling, which may decrease the cardiac output.