About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- IE = infection of heart valve endocardium, forming vegetations of fibrin, platelets, and bacteria
- Most common organisms: S. aureus (acute IE, IVDU), Streptococcus viridans (subacute IE), Enterococcus, coagulase-negative staphylococci (prosthetic valve)
- Modified Duke criteria: requires 2 major, 1 major + 3 minor, or 5 minor criteria. Major: positive blood cultures (typical organism) + echo evidence of vegetation/abscess
- Treatment: prolonged IV antibiotics (4–6 weeks). Empirical: amoxicillin + gentamicin (native valve) or vancomycin + gentamicin + rifampicin (prosthetic valve)
- NICE CG64: antibiotic prophylaxis is NOT routinely recommended before dental or other procedures in the UK
Overview
Infective endocarditis (IE) is a microbial infection of the endocardial surface of the heart, almost invariably involving the heart valves. Vegetations composed of fibrin, platelets, inflammatory cells, and micro-organisms form on valve leaflets. IE is classified as acute (rapid onset, fulminant course — usually S. aureus) or subacute (insidious, weeks to months — usually viridans streptococci). Native valve IE most commonly affects the mitral and aortic valves. Prosthetic valve endocarditis is divided into early (<1 year post-surgery, usually coagulase-negative staphylococci) and late (>1 year, similar organisms to native valve IE). Right-sided IE (tricuspid valve) is strongly associated with intravenous drug use.
Epidemiology
IE has an incidence of approximately 3–10 per 100,000 per year in the UK, and the incidence is increasing. Risk factors include pre-existing valvular disease (rheumatic, degenerative, bicuspid aortic valve), prosthetic heart valves, previous IE, intravenous drug use, poor dental hygiene, congenital heart disease, and intracardiac devices (pacemakers, ICDs). S. aureus has overtaken viridans streptococci as the commonest cause in developed countries. In-hospital mortality remains 15–20%, rising to 40% at one year.
Clinical Features
Symptoms
Fever (present in >90%) — may be low-grade and intermittent in subacute IE
Night sweats, malaise, weight loss, anorexia
New or changing heart murmur
Symptoms of embolic phenomena: stroke, limb ischaemia, abdominal pain
Arthralgia and myalgia
Symptoms of heart failure (valve destruction)
Back pain (vertebral osteomyelitis, discitis, or septic emboli)
Signs
Fever (may be absent in elderly, immunosuppressed, or partially treated)
New or changing murmur (especially new regurgitant murmur)
Splinter haemorrhages (linear, under nail beds)
Osler nodes (painful, red, raised nodules on fingers/toes — immune-complex mediated)
Janeway lesions (painless, erythematous lesions on palms/soles — septic emboli)
Roth spots (retinal haemorrhages with pale centre on fundoscopy)
Splenomegaly (especially subacute IE)
Petechiae (conjunctival, oral, skin)
Signs of heart failure
Focal neurological deficit (embolic stroke, mycotic aneurysm)
Investigations
First-line
Blood cultures (3 sets from different sites)Take BEFORE antibiotics. Must be from separate venepuncture sites at ≥30-min intervals (ideally). Positive in ~90% of cases. Typical organisms fulfil a major Duke criterion
BloodsFBC (normocytic anaemia, leucocytosis), raised CRP/ESR, U&Es (renal impairment from immune complexes or emboli), LFTs
UrinalysisMicroscopic haematuria (immune-complex glomerulonephritis)
Second-line
TTE (transthoracic echo)First-line imaging. Sensitivity ~75% for native valve vegetations
TOE (transoesophageal echo)If TTE negative but clinical suspicion remains high; superior for prosthetic valve IE, abscess detection. Sensitivity >90%
Specialist
CT (whole body)Assess for embolic complications: splenic infarcts, mycotic aneurysms, vertebral abscess
MRI brainIf neurological symptoms — stroke, mycotic aneurysm, abscess
PET-CTIncreasing role for prosthetic valve IE and cardiac device-related IE where echo is inconclusive
1
Empirical IV antibiotics (before culture results)
- Native valve: amoxicillin 2 g IV 4-hourly + low-dose gentamicin (check local guidelines)
- Prosthetic valve: vancomycin IV + gentamicin + rifampicin PO
- If penicillin allergy: vancomycin + gentamicin
- IVDU (right-sided): flucloxacillin 2 g IV 6-hourly (covers S. aureus) ± gentamicin
2
Targeted therapy (guided by sensitivities)
- Streptococcus viridans (penicillin-sensitive): benzylpenicillin 4–6 weeks ± gentamicin first 2 weeks
- Staphylococcus aureus (MSSA): flucloxacillin 2 g IV 6-hourly for 4–6 weeks
- MRSA: vancomycin IV + rifampicin ± gentamicin
- Prosthetic valve IE: minimum 6 weeks of antibiotics
3
Surgical indications (urgent/early surgery)
- Heart failure from severe valvular regurgitation or obstruction
- Uncontrolled infection despite appropriate antibiotics (persistent bacteraemia >7 days, abscess, fistula)
- Large mobile vegetation (>10 mm) with embolic events
- Prosthetic valve dehiscence
- Fungal endocarditis (almost always requires surgery)
4
Antibiotic prophylaxis (NICE CG64)
- Antibiotic prophylaxis is NOT routinely recommended before dental or other procedures in the UK (unique NICE position)
- However, SDCEP implementation advice supports considering prophylaxis for high-risk patients undergoing high-risk dental procedures
- Educate patients about maintaining good oral hygiene and seeking early treatment of infections
Complications
- Heart failure: Valve destruction (most common cause of death) — acute severe MR or AR
- Embolic phenomena: Stroke (20–40%), splenic infarct, renal infarct, pulmonary emboli (right-sided IE), mesenteric ischaemia
- Mycotic aneurysm: Infected arterial wall weakening, particularly cerebral — risk of rupture
- Periannular abscess: Especially aortic root — may cause conduction abnormalities (new heart block on ECG)
- Immune complex phenomena: Glomerulonephritis, Roth spots, Osler nodes
- Sepsis: Metastatic infection — osteomyelitis, discitis, septic arthritis
UKMLA Exam Tips
- 1Fever + new murmur + splinter haemorrhages = think IE until proven otherwise — take blood cultures BEFORE antibiotics
- 2Modified Duke criteria: need 2 major, or 1 major + 3 minor, or 5 minor for definite diagnosis
- 3NICE does NOT recommend routine antibiotic prophylaxis for dental procedures — a classic exam question
- 4S. aureus = acute aggressive IE (native or IVDU); Strep viridans = subacute, more indolent
- 5New conduction abnormality (PR prolongation, new LBBB) in IE = suspect aortic root abscess
- 6Culture-negative endocarditis causes (HACEK organisms, Coxiella, Bartonella, Brucella) — remember if standard cultures are negative
- 7Right-sided IE (tricuspid) = IVDU, septic pulmonary emboli (multiple lung abscesses on CXR)
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