MRCP2-0314

A 75-year-old woman, previously healthy, arrived at the Emergency department complaining of fevers, chills, and fatigue for the past four weeks. Upon examination, she had a soft pansystolic murmur and a temperature of 39°C. She also had bilateral palmar erythema and splinter hemorrhages on both hands. Blood cultures were taken, and all three sets grew Streptococcus viridans. A transthoracic echocardiogram revealed a mobile mass on the posterior mitral valve leaflet with moderate mitral regurgitation. The patient was immediately started on appropriate IV antibiotics. What factor has the greatest impact on prognosis?