USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

Which cardiac anomaly is characterized by an opening snap and a diastolic rumble on auscultation?

1. Coarctation of the aorta

2. Patent ductus arteriosus

3. Aortic stenosis

4. Mitral stenosis

The correct answer is: Mitral stenosis

Mitral stenosis is characterized by an opening snap and a diastolic rumble on auscultation due to the obstruction of blood flow from the left atrium to the left ventricle during diastole. This obstruction is primarily a result of thickening and fusion of the mitral valve leaflets, often due to rheumatic heart disease. As the mitral valve opens during diastole, the increased pressure in the left atrium causes a distinct "snap" sound, which is the opening snap, indicative of the decreased compliance of the valve. Following this, the turbulent flow of blood across the narrowed valve creates a diastolic rumble, particularly best heard at the apex of the heart while the patient is in the left lateral decubitus position. In contrast, other cardiac anomalies such as coarctation of the aorta, patent ductus arteriosus, and aortic stenosis have different auscultation findings, primarily associated with systolic ejections, continuous murmurs, or features relevant to their specific hemodynamic changes rather than diastolic abnormalities like the opening snap and rumble associated with mitral stenosis. This distinction helps solidify the understanding of various cardiac conditions and their presentation.