Cardiovascular System MCAT Practice Question
A 68-year-old man with a history of hypertension and type 2 diabetes mellitus presents for evaluation of dyspnea on exertion. Physical examination reveals an S4 gallop. Transthoracic echocardiography shows normal left ventricular ejection fraction (LVEF 55%), normal wall thickness, and a prolonged isovolumetric relaxation time (IVRT) of 120 milliseconds (normal <90 ms). Doppler imaging demonstrates impaired early diastolic filling with preserved atrial contribution. Which of the following best explains the mechanism underlying the prolonged IVRT in this patient?
Answer choices
- AImpaired myocardial calcium reuptake by the sarcoplasmic reticulum secondary to reduced SERCA2a expressionCorrect answer
- BIncreased left ventricular cavity size reducing the pressure gradient needed to open the mitral valve
- CEnhanced sympathetic tone accelerating active myocardial relaxation
- DMitral annular calcification increasing mitral valve opening resistance
- EDecreased aortic diastolic pressure from reduced arterial compliance shortening the aortic pressure decay
- FIncreased left atrial pressure compensating for ventricular stiffness and promoting earlier mitral valve opening
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