AKT · Cardiovascular/Valves & endocardium

Infective endocarditis

Microbial infection of the endocardium/valves — Staph. aureus, viridans streptococci, enterococci

Overview

Infection of the endocardial surface, usually a heart valve, producing vegetations. Risk factors are prosthetic valves, prior endocarditis, structural/congenital heart disease and IV drug use. Diagnosis uses the modified Duke criteria (positive blood cultures + echo evidence). It is a great mimic — fever with a new murmur and embolic/immunological phenomena — and needs prolonged IV antibiotics ± surgery.

Recognise

Fever, new or changing heart murmur, malaise, weight loss, night sweats
Embolic phenomena (stroke, splenic/renal infarcts, septic pulmonary emboli) and immunological signs (Roth spots, Osler's nodes, Janeway lesions, splinter haemorrhages, glomerulonephritis)
Organisms: Staph. aureus (acute, IVDU, prosthetic), viridans streptococci (subacute, dental), enterococci, HACEK; Strep. bovis → look for colorectal cancer

Red flags

Heart failure from valve destruction, uncontrolled infection or large/embolising vegetations → early surgery
Prosthetic valve endocarditis or perivalvular abscess (new conduction block) → urgent surgical assessment

Differentials & how to tell them apart

Other causes of fever + murmurflow murmur with sepsis from another source; negative echo/cultures

Atrial myxomaconstitutional symptoms + embolism but sterile, mass on echo

Rheumatic fever / vasculitis / SLEsterile cultures; different immunological pattern

Janeway lesions — non-tender erythematous macules (infective endocarditis)
Warfieldian / CC BY-SA 4.0 — Wikimedia Commons

Investigations

Three sets of blood cultures from different sites BEFORE antibiotics; transthoracic then transoesophageal echo (vegetations, abscess, regurgitation); inflammatory markers; modified Duke criteria; ECG (PR prolongation = aortic root abscess); urinalysis.

Management

Blood cultures then prolonged IV antibiotics; surgery for HF/abscess/large vegetations

1Take three sets of blood cultures before antibiotics and arrange echo (TTE → TOE). Apply the modified Duke criteria. Start empirical IV antibiotics, then target to the organism.Gate: Heart failure from valve destruction, uncontrolled/abscess-forming infection, or large mobile vegetations → early surgery, not antibiotics alone.
2Complete a prolonged (often 4–6-week) IV course guided by microbiology and an endocarditis team; investigate the source (dental, colonic for Strep. bovis).

Empirical IV antibiotics after cultures (e.g. amoxicillin ± gentamicin; vancomycin if prosthetic/MRSA risk) — then targeted to the organism; prolonged course (often 4–6 weeks)

Targeted therapy by organism/valve — per microbiology/endocarditis team; native vs prosthetic differs

Surgery — for heart failure, uncontrolled infection, abscess, large/embolising vegetations or prosthetic involvement

Key points

Fever + new murmur + embolic/immunological signs = infective endocarditis → 3 sets of blood cultures BEFORE antibiotics, then echo and the Duke criteria. Strep. bovis bacteraemia → colonoscopy (colorectal cancer). Surgery for heart failure/abscess/big vegetations.

Monitor & prognosis

Repeat cultures/inflammatory markers, serial echo, ECG (PR interval for root abscess), drug levels.

Serious; mortality is high with complications, better with prompt targeted therapy ± surgery.

Source: NICE; ESC endocarditis; antibiotic prophylaxis only for high-risk per NICE CG64