USMLE Step 2 - Question 11

A 82 year old male with a history of recent aortic valve replacement, hypertension, and diabetes presents to the emergency department with fevers for 5 days. No chest pains or shortness of breath are present. His medications include lisinopril, hydrochlorothiazide, aspirin, and coumadin. His temperature is 38.4 C, blood pressure is 160/60, heart rate 100, respirations 20, and oxygen saturation 99% on room air. Physical examination reveals normal lung sounds, a II/IV early diastolic decrescendo murmur, and a very soft 1st heart sound.  Laboratory studies reveal a white blood cell count of 15 thousand and an ESR of 110. A portion of his ECG is below. Which of the following is causing his abnormal finding on his ECG?

Step2-Q11-PIC1

A. Aortic valve endocarditis

B. Aortic valve regurgitation

C. Aortic valve annular abscess

D. Aortic valve stenosis

This patient is high risk for endocarditis given his recent aortic valve replacement (remember prosthetic valves are quite susceptable to infection). Five days of fevers, a markedly elevated ESR, and a murmur of aortic regurgitation in a prosthetic valve (which indicates valve malfunction) should raise the suspicion of endocarditis. The most common bacteria causing endocarditis soon after valve surgery is Staph aureus whereas Strep species are more likely months to years after surgery. Aortic valve endocarditis or regurgitation itself does not cause any ECG abnormality, however if an abscess develops around the aortic valve annulus, it can compress and inflame the nearby AV node causing AV nodal conduction disease. The ECG shown in this question shows normal sinus rhythm with a first degree AV block (prolonged PR interval). This is usually the first sign of aortic valve abscess. A prolonged PR interval causes the first heart sound to be soft since there is extra time the the mitral valve to close after atrial contraction, thus is closes more slowly and with less force.