Cardiology: Infective Endocardits

Infective endocarditis (IE) is microbial infection of the endocardial surface, usually affecting heart valves, prosthetic material or cardiac devices. Circulating organisms adhere to susceptible tissue and form infected platelet–fibrin vegetations; the consequences are local valve destruction, sustained bacteraemia and systemic embolisation.

• Acute IE: May progress rapidly, with severe sepsis, acute valve regurgitation and heart failure.
• Subacute IE: May cause weeks of fever, malaise, night sweats and weight loss before a diagnosis is made.
• Right-sided IE: More likely to produce septic pulmonary emboli; left-sided disease may produce stroke or peripheral emboli.

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9.02 Organisms and Predisposing Conditions

Typical organisms

• Staphylococcus aureus: Frequently acute or healthcare-associated; may infect previously normal valves and needs prompt assessment.
• Oral streptococci: Often associated with native-valve, more indolent infection.
• Enterococci: Particularly important in older or healthcare-associated patients.
• Coagulase-negative staphylococci: Important with prosthetic valves and devices.
• Culture-negative IE: Prior antibiotics or fastidious organisms (e.g. Coxiella, Bartonella); requires specialist microbiological investigation.

Predisposing conditions

• Previous endocarditis; prosthetic valves (including TAVI) or intracardiac devices.
• Selected congenital cardiac lesions, structural valve disease, haemodialysis and injection drug use.
• IE also occurs without a known pre-existing valve lesion; the absence of an obvious risk factor must not exclude it.

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9.03 Clinical Presentation and Examination

Suspect IE in a patient with unexplained persistent fever, bacteraemia (especially S. aureus), a new murmur or embolic phenomena. A murmur may be absent, particularly early in disease.

• Constitutional: Fever, rigors, malaise, sweats, anorexia and weight loss.
• Cardiac: New or changing regurgitant murmur, acute heart failure, pulmonary oedema; new AV block can signal a peri-annular abscess.
• Vascular/embolic: Stroke or TIA, limb or splenic/renal infarction, painless Janeway lesions, splinter haemorrhages, septic pulmonary emboli in right-sided IE.
• Immune manifestations: Tender Osler nodes, Roth spots and glomerulonephritis with haematuria.
• Other clues: Back pain from vertebral infection or persistent bacteraemia despite seemingly appropriate treatment.

Do not miss: Fever with a prosthetic valve or cardiac device deserves urgent assessment; do not prescribe empiric oral antibiotics without considering blood cultures.

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9.04 Blood Cultures, Echocardiography and Investigations

First investigations

• Blood cultures: Obtain at least three sets from separate venepunctures before antimicrobials if clinically safe. In sepsis or shock, collect cultures promptly but do not delay emergency antibiotic treatment.
• Bloods: FBC, CRP, U&E, renal/liver function and urinalysis; ECG for conduction change.
• Transthoracic echo (TTE): Initial imaging for vegetations, valve destruction, regurgitation and ventricular function.
• Transoesophageal echo (TOE): Particularly valuable for prosthetic valves/devices, abscess, unexplained high clinical suspicion or uncertain TTE; repeat imaging may be required if early studies are negative.
• Specialist imaging: Cardiac CT or PET/CT can help assess complications or prosthetic/device infection in selected patients.

Key interpretive point: A normal initial echo does not rule out IE when clinical suspicion remains high; combine microbiology, imaging and clinical assessment.

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9.05 Duke/ISCVID Diagnostic Criteria

The Duke/ISCVID approach combines microbiology, imaging and clinical evidence; it supports but does not replace clinical judgement.

• Major evidence: Characteristic positive blood cultures or qualifying imaging evidence of IE (including vegetation, abscess or new destructive valve lesions).
• Minor evidence: Predisposing condition, fever, vascular phenomena, immunological phenomena or supportive microbiology not meeting a major criterion.
• Classic "definite IE" patterns: Two major criteria, or one major plus three minor, or five minor (pathological evidence may also establish the diagnosis).

MLA pearl: A patient with S. aureus bacteraemia and a new murmur needs prompt IE assessment even when the first echocardiogram is nondiagnostic.

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9.06 Treatment and Indications for Surgery

Management requires coordinated input from cardiology, microbiology/infectious diseases and cardiac surgery, ideally through an endocarditis team.

• Antibiotics: Begin promptly after appropriate cultures when possible; select organism-directed bactericidal therapy using susceptibility and local specialist protocols. Treatment is prolonged and depends on pathogen, native versus prosthetic valve, complications and response.
• Monitor: Repeat cultures to document clearance; monitor inflammatory response, renal function and drug toxicity; reassess with echo for complications.
• Early surgical consideration — three principal indications:
  • Heart failure from acute severe valve regurgitation or obstruction.
  • Uncontrolled infection: Perivalvular abscess, persistent infection or difficult-to-eradicate organisms.
  • Embolic risk: Large or recurrently embolising vegetations in selected patients.
• Device-related infection: Specialist evaluation of complete device and lead extraction where indicated.

Safety: Endocarditis itself is not an indication to start anticoagulation; decisions about pre-existing anticoagulation require individual specialist assessment, especially after cerebral embolism.

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9.07 Complications, Follow-up and Prevention

Major complications

• Cardiac: Acute valve regurgitation, heart failure, root or annular abscess, conduction block and prosthetic dysfunction.
• Systemic: Ischaemic or haemorrhagic stroke, peripheral or visceral emboli, vertebral osteomyelitis, splenic abscess and glomerulonephritis.
• Long-term: Residual valve disease, recurrent IE and complications related to prosthetic material.

UK prevention advice

• Maintain good dental and skin hygiene; promptly assess persistent unexplained fever or suspected infection in at-risk patients.
• NICE CG64: Antibiotic prophylaxis is not recommended routinely before dental and specified other procedures. Exceptional high-risk decisions should be individualised with specialist input; this differs from the 2023 ESC recommendation for selected high-risk patients undergoing invasive dental procedures.
• Explain warning symptoms and ensure appropriate follow-up for valve function and relapse after treatment.

MLA pearl: "Not routinely recommended" is not equivalent to "never". Discuss high-risk exceptions rather than giving a blanket answer.