USMLE题库Cardiology(二)21-31.pptxVIP

Cardiology 2 题库 Q 21 Autopsy of a 56-year-old Caucasian male who died in a motor vehicle accident shows increased thickness of the left ventricular (LV) wall and decreased LV cavity size. The structural changes observed in this patients heart are most likely associated with: Recent myocardial infarction Mitral insufficiency Atrial septal defect Hemochromatosis Longstanding hypertension Wolff-Parkinson-White syndrome Normal aging A 21 Correct answer: F The changes in this patients LV are consistent with concentric hypertrophy due to hypertensive heart disease. Concentric hypertrophy uniformly thickens the ventricular wall while the outer dimensions of the ventricle remain almost unchanged, thus resulting in a narrowed ventricular cavity size. Concentric hypertrophy results from chronic elevation of the ventricular pressure during systole (pressure overload), as is typically seen in hypertension due to the increased LV afterload. (Choice A) The ventricular remodeling that occurs after an acute myocardial infarction involves expansion, thinning, and fibrous healing of the infarcted zone of myocardium. At the same time, regional dysfunction of the infarct causes volume overload for the remaining viable myocardium. To compensate for the loss of contractile function of the infarcted region, there is hypertrophy of the remaining myocardium. The net result is usually dilated ventricular hypertrophy, with enlargement of the LV cavity. (Choice B) Mitral insufficiency tends to increase the LV end-diastolic volume, causing LV dilatation. Additionally, because the LV needs to pump out both forward flow through the aortic valve and regurgitant flow through the mitral valve during systole, there is LV hypertrophy as well. Thus, the net structural consequence of mitral insufficiency is dilated/eft ventricular hypertrophy. Although the LV mass is increased, LV wall thickness may be increased, unchanged, or even decreased depending upon the degree of LV dilatation. (Choice C) An