Infective endocarditis (modified Duke criteria) is a severe microbial infection involving the endocardial surface of the heart, most commonly affecting native or prosthetic heart valves, mural endocardium, or intracardiac foreign bodies 1,2. The global incidence is rising due to an aging population, increased prevalence of implantable cardiac electronic devices, and frequent intravascular healthcare contact 3,5. Despite modern antimicrobial therapy and advanced surgical techniques, the disease maintains a high 1-year mortality rate exceeding 30%, making prompt recognition and multidisciplinary management imperative 2,6.

1. Etiology & Risk Factors

  • Gram-Positive Cocci: Staphylococcus aureus is the most frequent pathogen globally, particularly in healthcare-associated and intravenous drug use (IVDU) settings, commonly targeting tricuspid and native aortic/mitral valves 1,6. Viridans group streptococci (e.g., Streptococcus sanguinis, S. mitis) remain the leading cause of community-acquired native valve endocarditis via oral flora translocation 1,2. Enterococcus faecalis and E. faecium are increasingly isolated in elderly patients following genitourinary or gastrointestinal procedures 3,6.
  • HACEK Group: Fastidious gram-negative bacilli (Haemophilus species, Aggregatibacter species, Cardiobacterium hominis, Eikenella corrodens, and Kingella species) account for culture-negative endocarditis and indolent presentations 1,5.
  • Fungi & Other Organisms: Candida species and Aspergillus species are prominent in immunosuppressed hosts, prosthetic valve recipients, and long-term central venous catheter users 1,2.
  • Anatomical & Patient Risk Factors: Pre-existing structural heart disease (rheumatic heart disease, mitral valve prolapse with regurgitation, congenital bicuspid aortic valves), prior history of infective endocarditis, prosthetic heart valves, pacemakers, implantable cardioverter-defibrillators (ICDs), and chronic hemodialysis 1,3,5.

2. Pathophysiology

The pathogenesis of infective endocarditis begins with hemodynamic alterations or direct mechanical trauma (such as from a catheter or turbulent jet stream) that disrupts the single-layer endocardial endothelial lining of the heart valve 5,7. This endothelial denudation exposes subendothelial extracellular matrix proteins like collagen and tissue factor, triggering the local deposition of platelets and fibrin to form sterile sterile vegetations known as non-bacterial thrombotic endocarditis (NBTE) 5,7. During periods of transient asymptomatic or symptomatic bacteraemia (originating from dental manipulation, mucosal barriers, or cutaneous foci), circulating microorganisms adhere to the adhesive matrix proteins on the NBTE surface via microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) 5,7. Once adherent, the pathogens are engulfed by platelets and fibrin, creating a protective, avascular vegetation matrix that shields the microbes from host immune clearance and circulating leukocytes 5,7. Proliferation within the vegetation causes local tissue destruction, valve leaflet perforation, ring abscess formation, and ongoing septic embolisation to the central nervous system, spleen, kidneys, and extremities 5,7.

Infective endocarditis (modified Duke criteria) — Pathophysiological Cascade & Clinical Flowchart 1 Trigger / Primary Insult Endothelial disruption of heart valves via turbulent blood flow or catheter trauma 2 Cellular / Pathophysiological Cascade Deposition of fibrin and platelets forming non-bacterial thrombotic endocarditis (NBTE) 3 Target Organ / Structural Change Transient bacteraemia seeding the NBTE matrix with microbial organisms and vegetation growth 4 Hallmark Clinical & Diagnostic Manifestation Persistent fever, new regurgitant murmurs, and septic embolization to systemic organs 5 Complications if Untreated & Therapeutic Target Valvular destruction, heart failure, and stroke requiring IV antibiotics and valve surgery

3. Clinical Presentation & Classic Clinical Signs

  • History & Cardinal Symptoms: Persistent, relapsing, or low-grade fevers and chills are present in over 85% of cases 1,4. Constitutional symptoms include profound fatigue, anorexia, weight loss, night sweats, generalized malaise, and dyspnoea secondary to acute valvular regurgitation or heart failure 1,3.
  • Physical Examination & Named Clinical Signs: A newly detected or changing regurgitant heart murmur (present in up to 85% of patients) 1. Peripheral manifestations of immunothrombosis and microvascular embolisation include:
    • Janeway lesions: Non-tender, haemorrhagic macules or papules located on the palms and soles (immune/embolic origin) 1.
    • Osler nodes: Painful, erythematous subcutaneous nodules situated on the pulp of the digits (immune-complex deposition) 1.
    • Splinter haemorrhages: Linear, non-blanching dark brown or reddish streaks under the nail beds parallel to the long axis of the finger 1.
    • Roth spots: Retinal haemorrhages with pale white centres visualised on fundoscopic examination 1.
    • Clubbing: Chronic digital clubbing in prolonged subacute cases 1.

4. Diagnostic Workup & Interpretation (Laboratory, Imaging & ECG/Pathology)

Diagnostic Modality / Test Expected Clinical & Radiological / Laboratory Finding
Gold-Standard InvestigationThree separate sets of peripheral blood cultures (drawn at least 30–60 minutes apart from separate venepuncture sites) prior to initiating antimicrobial therapy, coupled with Transoesophageal Echocardiography (TOE/TEE) to evaluate vegetation size, valve morphology, and perivalvular extension 1,2.
Laboratory PanelNormocytic normochromic anaemia of chronic disease, elevated inflammatory markers (erythrocyte sedimentation rate [ESR] and C-reactive protein [CRP]), leukocytosis with a left shift (in acute staphylococcal cases), microscopic haematuria, proteinuria, and sterile pyuria indicative of focal glomerulonephritis or immune complex deposition 1,3.
Imaging / Radiology (X-ray, US, CT, MRI)Transthoracic Echocardiography (TTE) as initial screening (sensitivity 50–70% for native valves); TOE for high clinical suspicion, negative TTE with high suspicion, or prosthetic valves (sensitivity >90%) 1,2. Cardiac CT or 18F-FDG PET/CT imaging to identify paravalvular abscesses, pseudoaneurysms, or device-related infection when echocardiography is inconclusive 3,5. Brain MRI to detect silent or active septic emboli and mycotic aneurysms 7.
ECG / Histopathology / ProceduralElectrocardiogram (ECG) to monitor for new conduction delays or heart block indicative of aortic root extension/abscess formation. Histopathological examination and broad-range PCR of surgically excised valve tissue or vegetation 1,3.

5. Staging, Classification & Clinical Scoring Systems

Criterion / Stage / Score Component Clinical Threshold, Points & Management Implication
Modified Duke Criteria: Pathological CriteriaMicroorganisms demonstrated by culture or histopathology in a vegetation, in a vegetant or intracardiac abscess, or in a pathological specimen; or active endocarditis histologically confirmed on valve tissue 1,3. Definitive diagnosis achieved with 1 pathological criterion.
Modified Duke Criteria: Major Clinical Criteria1. Blood cultures positive for typical IE microorganisms from two separate cultures, or persistently positive blood cultures, or single positive culture for Coxiella burnetii. 2. Evidence of endocardial involvement demonstrated by positive echocardiogram (vegetation, abscess, new partial dehiscence of prosthetic valve) or new valvular regurgitation murmur 1,3.
Modified Duke Criteria: Minor Clinical Criteria1. Predisposition (underlying cardiac condition or IVDU). 2. Fever (>38.0°C). 3. Vascular phenomena (major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial haemorrhage, conjunctival haemorrhages, Janeway lesions). 4. Immunological phenomena (glomerulonephritis, Osler nodes, Roth spots, rheumatoid factor). 5. Microbiological evidence not meeting major criteria 1,3.
Definitive vs. Possible IEDefinitive IE: 2 major criteria, OR 1 major and 3 minor criteria, OR 5 minor criteria. Possible IE: 1 major and 1 minor criterion, OR 3 minor criteria. Rejected: Firm alternate diagnosis, resolution of symptoms with antibiotic therapy for ≤4 days, or lack of pathological/clinical evidence upon surgery/autopsy 1,3.

6. Differential Diagnosis

Differential Condition Distinguishing Clinical, Biochemical & Imaging Features
Non-Bacterial Thrombotic Endocarditis (Marantic Endocarditis)Associated with advanced malignancy or hypercoagulable states (e.g., systemic lupus erythematosus via Libman-Sacks endocarditis). Blood cultures are consistently negative, and systemic thromboembolism occurs without persistent fever or systemic sepsis 1,5.
Acute Rheumatic FeverPresents with migratory polyarthritis, carditis, erythema marginatum, and Sydenham chorea. Accompanied by elevated anti-streptolysin O (ASO) titres and recent streptococcal pharyngitis, but lacks echocardiographic valvular vegetations and persistent bacteraemia 1,2.
Systemic Lupus Erythematosus (SLE)Multisystem autoimmune disorder featuring malar rash, serositis, cytopenias, positive antinuclear antibodies (ANA), and anti-dsDNA antibodies. Valvular lesions (Libman-Sacks) are sterile verrucous vegetations involving both sides of the valve leaflets 1,3.
Atrial Myxoma or Cardiac TumoursBenign or malignant intracardiac masses that can mimic vegetations on echocardiography, causing embolic events or constitutional symptoms. Blood cultures are negative, and mass attachment is typically to the interatrial septum rather than valve closure lines 1,2.

7. Management & Treatment Protocol

  • Initial Stabilization & Resuscitation: Hemodynamic stabilization, continuous cardiac telemetry, and immediate referral to a multidisciplinary Endocarditis Team (comprising cardiologists, cardiothoracic surgeons, infectious disease specialists, and microbiologists) 2,5.
  • First-Line Medical / Pharmacological Therapy (with exact adult dosing):
    • Empiric Therapy (Pending Blood Cultures): Intravenous Ampicillin (2 g IV every 4 hours) plus Flucloxacillin (2 g IV every 4 hours) plus Gentamicin (1 mg/kg IV every 8 hours, target peak 3–5 mcg/mL, trough <1 mcg/mL) for native valves. For penicillin-allergic patients or healthcare-associated/prosthetic valve endocarditis suspecting MRSA: Vancomycin (15–20 mg/kg IV every 12 hours, target trough 15–20 mcg/mL) plus Gentamicin 1,3.
    • Targeted Therapy: Adjusted based on susceptibilities for 4–6 weeks total duration. For methicillin-susceptible S. aureus (MSSA): Flucloxacillin 2 g IV every 4 hours for 4–6 weeks. For MRSA: Vancomycin 15–20 mg/kg IV every 12 hours for 6 weeks 1,3.
  • Surgical / Interventional Indications: Urgent or early surgical valve repair/replacement is indicated in the presence of heart failure refractory to medical therapy, destructive paravalvular complications (abscess, fistula, heart block), persistent infection (positive blood cultures >7–10 days despite appropriate antimicrobial therapy), large mobile vegetations (>10 mm) with recurrent systemic embolisation, and fungal or multiresistant bacterial aetiologies 2,3,6.

8. Complications & Prognosis

  • Acute Cardiovascular Complications: Acute congestive heart failure secondary to severe valvular regurgitation, intracardiac fistulae, paravalvular abscess formation, and conduction disturbances or complete heart block due to extension into the cardiac conduction system 1,3.
  • Neurological & Systemic Embolic Complications: Embolic stroke, transient ischaemic attacks, cerebral abscesses, mycotic aneurysms, meningitis, and septic infarction of the spleen, kidneys, mesentery, and lower extremities (occurring in 20–40% of patients) 6,7.
  • Prognosis & Mortality: In-hospital and 1-year mortality remain high (approx. 20–30%) even with optimal guideline-directed antimicrobial and surgical intervention, driven largely by patient comorbidities, delayed diagnosis, S. aureus aetiology, and intractable heart failure 2,6.