Infective endocarditis

Overview

Infective endocarditis (IE) is a microbial infection of the endocardial surface, most commonly affecting cardiac valves. Left-sided valves (mitral > aortic) are most affected; right-sided (tricuspid) IE is classic in IV drug users.

Risk factors

Key risk factors
Prosthetic heart valves
Previous IE
Congenital heart disease
Rheumatic/degenerative valve disease
Bicuspid aortic valve / MVP
IV drug use (IVDU) - tricuspid IE
Intravascular devices / central lines
Poor dental hygiene / dental procedures

Presentation

•Fever - >90% of patients; may be low-grade/swinging in subacute IE

•New or changing regurgitant murmur - critical examination finding

•Constitutional - night sweats, malaise, weight loss, anorexia (especially subacute)

•Heart failure - raised JVP, pulmonary oedema (valve incompetence)

•Palpitations / heart block - conduction defect from perivalvular abscess

Peripheral stigmata of IE
SignCharacterMechanism
Osler's nodesTender, raised nodules - finger/toe padsImmune complex vasculitis
Janeway lesionsNon-tender, flat macules - palms/solesSeptic microemboli
Splinter haemorrhagesSubungual linear streaksMicroemboli occluding nail-bed capillaries
Roth's spotsOval pale-centred retinal haemorrhagesImmune complex vasculitis

Sign	Character	Mechanism
Osler's nodes	Tender, raised nodules - finger/toe pads	Immune complex vasculitis
Janeway lesions	Non-tender, flat macules - palms/soles	Septic microemboli
Splinter haemorrhages	Subungual linear streaks	Microemboli occluding nail-bed capillaries
Roth's spots	Oval pale-centred retinal haemorrhages	Immune complex vasculitis

•Embolic events - stroke/TIA (left-sided), pulmonary emboli (right-sided/IVDU), splenic/renal infarction

•Back pain - ~15%; immune complex deposition in disc spaces or vertebral septic emboli

🧠
Osler = Ouch (tender, immune-mediated, finger/toe pads); Janeway = Just there (painless, embolic, palms/soles).

Investigations

•Blood cultures - minimum 3 sets from separate sites before any antibiotics; ideally spaced ≥1 hour apart; positive in ~90% of IE

•First-line echo - TTE: non-invasive, sensitivity ~60-75%; adequate for large vegetations on native valves

•Gold standard - TOE: sensitivity ~90%; preferred if TTE non-diagnostic, prosthetic valve IE suspected, or abscess suspected

•ECG - serial monitoring; PR prolongation or heart block suggests perivalvular abscess

•FBC - leucocytosis (acute); normocytic anaemia (subacute)

•CRP/ESR - elevated; useful for monitoring treatment response

•Urinalysis - microscopic haematuria and proteinuria (immune complex glomerulonephritis)

•Culture-negative IE - Coxiella, Bartonella, Brucella serology; 16S rRNA PCR on blood or excised valve tissue

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Blood cultures must always be taken before starting antibiotics. A new prolonged PR interval in aortic valve IE is a red flag for perivalvular abscess - urgent cardiothoracic surgical review required.

Management

•Multidisciplinary 'endocarditis team': cardiology, cardiac surgery, infectious diseases, microbiology

•Empirical therapy (native valve, community-acquired, non-penicillin allergic): amoxicillin (or ampicillin) + flucloxacillin + low-dose gentamicin - follow local microbiology guidance

•Streptococcal native valve IE: benzylpenicillin for 4 weeks (or 2 weeks + gentamicin if uncomplicated)

•Staph. aureus native valve IE: flucloxacillin for 4-6 weeks; vancomycin if MRSA or penicillin allergy

•Prosthetic valve IE: 6 weeks total antibiotic duration

•Q fever (Coxiella) endocarditis: doxycycline + hydroxychloroquine for ≥18 months

•Serial echocardiography and daily ECGs to monitor for complications

Prevention

•NICE CG64: does NOT recommend routine antibiotic prophylaxis before dental, GI, GU, or respiratory procedures - even in high-risk patients (prosthetic valves, previous IE, congenital heart disease)

•High-risk patients should maintain excellent oral hygiene, be educated on IE symptoms, and seek prompt review for unexplained fever

Complications

•Acute valve regurgitation - most common cause of death; rapidly decompensating heart failure

•Perivalvular abscess - most common with aortic valve IE; tracks to AV node causing heart block

•Stroke/TIA - cerebral emboli in up to 20-40% of left-sided IE; haemorrhagic transformation complicates anticoagulation

•Mycotic aneurysm - arterial wall infection from embolic seeding; risk of rupture

•Immune complex glomerulonephritis - haematuria, proteinuria, AKI

•Septic pulmonary emboli (right-sided IE) - cavitating lung lesions, empyema

Prognosis

•In-hospital mortality ~15-30%; rises to 40-50% in prosthetic valve IE or with Staph. aureus/embolic stroke

•~60-70% of survivors require valve surgery within 5 years; previous IE is a major risk factor for recurrence

Causative organisms

•Staph. aureus - most common overall; acute, aggressive; IVDU; prosthetic valves

•Streptococcus viridans - subacute; associated with dental procedures; native valves

•Strep. bovis (S. gallolyticus) - strongly associated with colorectal carcinoma; colonoscopy mandatory

•Enterococcus - GI/GU tract source

•HACEK organisms - culture-negative IE; require specialist cultures

•Coxiella burnetii (Q fever) - culture-negative; serology required

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Strep. bovis (S. gallolyticus) bacteraemia = colonoscopy required to exclude colorectal carcinoma, even without GI symptoms.

Modified Duke Criteria

•Major criteria: (1) positive blood cultures - typical organisms in ≥2 separate cultures, or persistently positive cultures; (2) positive echocardiogram - vegetation, abscess, new partial dehiscence of prosthetic valve, or new valvular regurgitation

•Minor criteria: predisposing cardiac condition/IVDU; fever ≥38°C; vascular phenomena (emboli, Janeway lesions, septic pulmonary infarcts); immunological phenomena (Osler's nodes, Roth's spots, RF); microbiological evidence not meeting major criteria

Duke criteria classification
ClassificationCriteria required
Definite IE2 major; OR 1 major + 3 minor; OR 5 minor
Possible IE1 major + 1 minor; OR 3 minor
RejectedFirm alternative diagnosis; resolution ≤4 days antibiotics; no pathological evidence at surgery/autopsy

Classification	Criteria required
Definite IE	2 major; OR 1 major + 3 minor; OR 5 minor
Possible IE	1 major + 1 minor; OR 3 minor
Rejected	Firm alternative diagnosis; resolution ≤4 days antibiotics; no pathological evidence at surgery/autopsy

Surgical Indications

•Heart failure from acute severe valve regurgitation or obstruction - most common surgical indication

•Uncontrolled infection - persistent bacteraemia/fever despite appropriate antibiotics >7-10 days; abscess, fistula, false aneurysm

•Prevention of embolism - large (>10 mm) or highly mobile vegetation, especially after embolic event

•Prosthetic valve IE caused by Staphylococci, fungi, or resistant organisms

•New heart block - conduction defect suggesting abscess extension into conducting system