USMLE Step 3 - Question 1

A 62 year old male with a history of hypertension, diabetes, rheumatoid arthritis and prior mechanical aortic valve replacement, presents to the emergency department with fevers for 3 days. He denies any chest pains or shortness of breath. 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 at the left lower sternal border, and a very soft S1 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 the most approtriate test to obtain at this time?


A) Coronary angiography

B) Transthoracic echocardiogram

C) Transesophageal echocardiogram

D) Cardiac magnetic resonence imaging

The patient in question #1 is high risk for endocarditis given his aortic valve replacement (remember prosthetic valves are quite susceptable to infection), fevers, murmur of aortic insufficiency (which should not be present with a mechanical prostetic valve), and elevated ESR. The ECG shown in question #1 shows normal sinus rhythm with a first degree heart block (prolonged PR interval). This is usually the first sign of aortic valve abscess, thus a transesophageal echocardiogram is appropriate to confirm the diagnosis. With prostetic heart valves, transthoracic echocardiography is not sufficienct to exclude endocarditis. A transthoracic echocardiogram is approriate if there is no prosthetic valve and the clinical suspicion for endocarditis is low to intermediate.

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. Remember that 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.

Related Topics: Endocarditis