A 26-year-old man is hospitalized for fevers and chills. Blood cultures grow gram-positive cocci in clusters. Chest examination is unremarkable. Echocardiogram shows a mobile density on the posterior mitral leaflet but is otherwise unremarkable. On the third day of hospitalization, the patient exhibits shortness of breath and an inability to lie flat. On examination, bibasilar crackles are present. A 2/6 holosystolic murmur is heard at the apex. Which of the following is likely to be present on repeat echocardiogram?

Question

Quizplus · Accepted Answer

Explanation: 11ec25c8_d872_5086_bc81_930cbf6c59ec_MD0003_00 This patient meets modified Duke criteria for infective endocarditis (ie, positive blood culture likely representing Staphylococcus aureus, echocardiographic valvular vegetation). He now has acute-onset dyspnea and pulmonary edema and a holosystolic murmur concerning for acute mitral regurgitation (MR), which can develop as a complication of endocarditis (eg, chordae tendineae rupture). modified Duke criteria In acute MR, there is sudden-onset large-volume backflow of blood from the left ventricle to the left atrium. Because of the large volume (and rapid equilibration of left ventricular [LV] and left atrial pressures), the associated murmur is often low-grade (eg, 2/6) or absent, unlike in chronic MR. The clinical features primarily reflect the heart chambers' lack of time to adapt to the hemodynamic changes. The left atrium has inadequate time to stretch to accommodate the increased blood volume and remains normal in size. The consequent increase in left atrial pressure is transmitted backward to the pulmonary circulation, resulting in pulmonary edema (eg, bibasilar crackles). The left ventricle receives increased blood volume from the left atrium with each diastole (representing the additional regurgitant volume from the previous systole); this results in increased LV end-diastolic pressure. The ejected blood can flow either forward through the aortic valve or backward through the relatively low-resistance pathway to the left atrium (ie, total resistance [LV afterload] is reduced). Although absolute volume of forward blood flow (cardiac output) is decreased, total stroke volume (forward and backward) is increased, resulting in a normal or hyperdynamic LV ejection fraction (>70%). In contrast to acute MR, the slower development of chronic MR allows time for compensatory atrial stretch to accommodate the regurgitant blood volume at a lower filling pressure, preventing pulmonary edema. In addition, the volume-overloaded left ventricle undergoes eccentric hypertrophy to compensate and temporarily maintain cardiac output (Choice A). However, overwhelming wall stress eventually leads to LV contractile dysfunction and decompensated heart failure (Choice C). eccentric hypertrophy Educational objective: Acute mitral regurgitation results in sudden-onset large-volume backflow of blood from the left ventricle to the left atrium. Neither chamber has time for compensatory dilation, leading to a rapid increase in left ventricular end-diastolic pressure and left atrial pressure, resulting in pulmonary edema. Although forward blood flow is reduced, left ventricular ejection fraction is normal or hyperdynamic due to a large amount of stroke volume flowing backward into the left atrium through the low-resistance regurgitant pathway. References: 2017 ACC Expert Consensus Decision Pathway on the management of mitral regurgitation: a report on the American College of Cardiology Task Force on Expert Consensus Decision Pathways. (http://www.ncbi.nlm.nih.gov/pubmed/29055505)

A 26-Year-Old Man Is Hospitalized for Fevers and Chills