MBBS SAQ · Cardiology / General Medicine
Infective endocarditis — diagnosis, antibiotic strategy and surgical indications
A final-prof / NEET-PG SAQ on native-valve viridans-streptococcal infective endocarditis — applying the Duke criteria for a definite diagnosis, choosing a 4-week bactericidal regimen of benzylpenicillin or ceftriaxone, and stating the three ESC surgical indications (heart failure, uncontrolled infection, prevention of embolism) with thresholds.
On this page
Study tools
Exam tags
Write your answer
Saved on this device. No marking — you are the marker.
Question
A 52-year-old man with a bicuspid aortic valve presents with three weeks of low-grade fever, weight loss and new dyspnoea. Examination shows a temperature of 38.4 degrees C, a new early diastolic murmur, splinter haemorrhages and tender nodules on his finger pulps. Three sets of blood cultures grow penicillin-susceptible viridans streptococci. Transthoracic echocardiography shows a 9 mm mobile aortic-valve vegetation with mild aortic regurgitation. Outline the diagnosis using the Duke criteria, your definitive antibiotic strategy (drug, dose, route, duration), and the indications for early surgery.
Model answer
Show the model answerShowHide
Diagnosis — definite infective endocarditis (modified Duke). This case meets two MAJOR criteria: (1) a typical positive blood culture (two or more separate cultures positive for viridans streptococci), and (2) echocardiographic evidence of endocardial involvement (a mobile aortic-valve vegetation, plus new aortic regurgitation). Two major criteria = definite IE (the alternative paths are one major + three minor, or five minor). The Osler nodes (tender pulp nodules) and fever are minor/immunologic criteria that further support the diagnosis.[5]
Definitive antibiotic strategy. For penicillin-susceptible viridans streptococci on a native valve: benzylpenicillin 1.2 g intravenously every 4 hours (or ceftriaxone 2 g IV once daily) for 4 weeks. Therapy must be bactericidal, high-dose, intravenous and prolonged, because the avascular vegetation shelters organisms from phagocytes and bacteriostatic agents. In selected uncomplicated cases a 2-week course adding gentamicin 1 mg/kg IV every 8 hours for synergy is acceptable. Monitor inflammatory markers (CRP), renal function and repeat echocardiography.[3]
Indications for early surgery (the three ESC indications).[1]
- Heart failure — the commonest indication; acute severe regurgitation from valve destruction not controllable medically. (His regurgitation is only mild, so this is not yet triggered — but watch for it.)
- Uncontrolled infection — persistent bacteraemia or fever beyond 5-7 days on correct antibiotics, or perivalvular extension (abscess, fistula, new atrioventricular block); fungal or resistant organisms not responding medically.
- Prevention of embolism — a large (> 10 mm), mobile vegetation, especially after a prior embolic event, or a vegetation > 10 mm with severe valve dysfunction; embolic risk is highest in the first days of therapy.
His 9 mm vegetation does not yet meet the > 10 mm surgical threshold, so the immediate plan is medical therapy with close monitoring for heart failure, emboli, perivalvular extension (new conduction block on ECG) and a rising vegetation — any of which would trigger urgent surgical referral.[1]
Common errors
- Not applying the Duke criteria explicitly — stating "endocarditis" without naming the two major criteria that make it definite.
- Recommending oral or short-course antibiotics — endocarditis therapy must be intravenous, bactericidal, high-dose and 4-6 weeks.
- Quoting the wrong surgical indication as commonest — heart failure (not emboli) is the commonest reason for surgery.
- Operating on a small vegetation — a 9 mm mobile vegetation without embolism or dysfunction does not yet meet the > 10 mm threshold.
- Forgetting to monitor for perivalvular extension — a new PR prolongation on ECG signals an aortic-root abscess and is a surgical emergency.
Examiner notes
- The answer must move cleanly: Duke definite (two major criteria) → 4-week bactericidal IV regimen (benzylpenicillin/ceftriaxone) → the three surgical indications with heart failure as commonest and the > 10 mm embolic threshold.[1][3]
- A strong candidate states why therapy is bactericidal/IV/prolonged (the avascular vegetation) and applies the > 10 mm threshold to this patient's 9 mm vegetation to justify continued medical management with surveillance.[5]
- Discriminating details: the Osler nodes are immunologic (minor criterion), the new murmur and vegetation are major criteria, and the ECG must be watched for PR prolongation.
References3ShowHide
- [3]Baddour LM, Wilson WR, et al. Infective Endocarditis in Adults: Diagnosis, Antimicrobial Therapy, and Management of Complications (AHA Scientific Statement). Circulation, 2015.PMID 26373316
- [5]Li JS, Sexton DJ, et al. Proposed modifications to the Duke criteria for the diagnosis of infective endocarditis. Clinical Infectious Diseases, 2000.PMID 10770721
- [1]Delgado V, Ajmone Marsan N, et al. 2023 ESC Guidelines for the management of endocarditis. European Heart Journal, 2023.PMID 37622656