Infective endocarditis — Duke criteria, organisms and the surgical decision viva

Interpretation

The examiner presents a clinical vignette — a patient with fever, a new murmur and peripheral stigmata, plus positive blood cultures and an echocardiographic vegetation — and asks: "How do you make the diagnosis, which organism is likely and what empiric therapy would you start, and when would you operate?"

• Diagnosis: integrate clinical features, blood cultures and echo through the modified Duke criteria; definite = 2 major, or 1 major + 3 minor, or 5 minor.^[5]
• Organism by scenario: viridans streptococci (native valve, poor dental hygiene); S. aureus (acute, IV drug use, healthcare); enterococci (elderly, genitourinary); coagulase-negative staphylococci (prosthetic, early).^[3]
• Pivotal investigation: at least three sets of blood cultures from separate sites before antibiotics, plus echocardiography (TTE first, TOE if negative or prosthetic).^[3]

Key points

The examiner will probe each of these; be ready to defend them at viva depth:

1. Duke criteria verbatim — MAJOR: (a) typical positive blood culture (two separate cultures for viridans strep, S. aureus, HACEK or enterococci, no primary focus); (b) endocardial involvement on echo (vegetation, abscess, new partial dehiscence of a prosthetic valve, or new regurgitation). MINOR: predisposition (predisposing heart condition or IV drug use), fever, vascular phenomena, immunologic phenomena, microbiology not meeting a major criterion. Definite = 2 major OR 1 major + 3 minor OR 5 minor; possible = 1 major + 1 minor or 3 minor.^[5]
2. Pathophysiology — turbulent jet damages the low-pressure downstream endothelium; a sterile platelet-fibrin nidus forms; transient bacteraemia seeds it. The avascular vegetation shelters organisms, justifying bactericidal, high-dose, IV, 4-6 week therapy.^[3]
3. Osler vs Janeway — Osler = tender, immune-complex, on pulps; Janeway = painless, septic emboli, on palms/soles. Both are minor criteria.^[5]
4. Empiric therapy — native valve: benzylpenicillin/ampicillin + gentamicin ± anti-staph agent; prosthetic: vancomycin + gentamicin + cefepime + rifampin (biofilm); MRSA/allergy: vancomycin or daptomycin.^[3]
5. Targeted therapy — viridans strep: benzylpenicillin 1.2 g IV 4-hourly or ceftriaxone 2 g IV daily for 4 weeks; MSSA: flucloxacillin 2 g IV 6-hourly; MRSA: vancomycin; enterococcus: ampicillin + gentamicin.^[3]
6. Surgery — three ESC indications — (1) heart failure (commonest, from acute severe regurgitation); (2) uncontrolled infection (persistent bacteraemia/fever > 5-7 days, perivalvular abscess/fistula/new heart block); (3) prevention of embolism (> 10 mm mobile vegetation, especially after a prior embolic event).^[1]
7. Kang 2012 cited correctly — early surgery reduced the composite of in-hospital death and embolic events, driven by fewer emboli; mortality alone was NOT significantly different. New PR prolongation = aortic-root abscess = surgical emergency.^[7][1]

References

1. Baddour LM, et al. AHA Scientific Statement: Infective Endocarditis in Adults. Circulation 2015.^[3]
2. Li JS, et al. Proposed modifications to the Duke criteria. Clin Infect Dis 2000.^[5]
3. Delgado V, et al. 2023 ESC Guidelines for the management of endocarditis. Eur Heart J 2023.^[1]
4. Kang DH, et al. Early surgery versus conventional treatment for IE. N Engl J Med 2012.^[7]

References4ShowHide

1. [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
2. [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
3. [1]Delgado V, Ajmone Marsan N, et al. 2023 ESC Guidelines for the management of endocarditis. European Heart Journal, 2023.PMID 37622656
4. [7]Kang DH, Kim YJ, et al. Early surgery versus conventional treatment for infective endocarditis. New England Journal of Medicine, 2012.PMID 22738096