Endocarditis Quiz: Ace Your Exams

A 67-year-old man presents to the cardiologist with a several week history of fatigue, shortness of breath, fever, and chills. The patient underwent catheter-directed ablation for medication resistant atrial fibrillation six days ago. He additionally reports he recently underwent a root canal procedure several weeks ago. Past medical history is significant for rheumatic heart disease, mitral valve prolapse, mitral valve repair, and atrial fibrillation. Temperature is 38.1°C (100.6 °F), pulse is 105/min, respirations are 22/min, blood pressure is 122/63 mmHg, and oxygen saturation is 95% on room air. Physical examination demonstrates a holosystolic murmur heard at the cardiac apex. A surgical incision site over the patient’s left neck shows no erythema, discharge, or swelling. Laboratory findings are demonstrated below:  

Laboratory value	Result
Serum
Hemoglobin	13.5 g/dL (reference range: 13.5-17.5 g/dL)
Hematocrit	40.5% (reference range: 41-53%)
Leukocyte count	14,100/mm3 (reference range: 4,500-11,000/mm3)
Platelet count	400,000/mm3 (reference range: 150,000-400,000/mm3)
ESR	34 mm/hr  (reference range: 0-15 mm/hr)
C-reactive protein	6 mg/dL (reference range: 0.08–3.1 mg/dL)
Microbiology
Blood cultures	Gram-positive, coagulase-negative bacteria in 3 consecutive plates

     
Which of the following is the most commonly affected structure in this disease process?