Infective Endocarditis
Cardiology
Illness script · Cardiology
Infective Endocarditis
Microbial infection of native or prosthetic heart valves producing vegetations, bacteremia, and systemic embolic phenomena.
This illness script for Infective Endocarditis covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- IV drug use (tricuspid valve predominance, S. aureus)
- Prosthetic heart valves — highest absolute risk
- Structural heart disease: bicuspid aortic valve, MVP with regurgitation
- Poor dentition / recent dental procedures (Strep viridans)
- Intracardiac devices (pacemaker leads, ICDs)
- Hemodialysis access; immunosuppression
02
Presentation
- Fever + new regurgitant murmur = classic pairing — never ignore together
- Osler nodes: tender nodules on finger/toe pads (immune complex)
- Janeway lesions: non-tender hemorrhagic macules on palms/soles (septic emboli)
- Roth spots: retinal hemorrhages with pale center on fundoscopy
- Splinter hemorrhages under nails; splenomegaly
- Subacute (Strep viridans): weeks of low-grade fever, fatigue; Acute (S. aureus): days, toxic-appearing
03
Pathophysiology
- Endothelial damage → platelet-fibrin thrombus formation on valve
- Bacteremia seeds thrombus → vegetation of organisms + fibrin
- Vegetation fragments embolize to brain, kidneys, spleen, lungs (right-sided)
- Ongoing infection → valve destruction, abscess, regurgitation, HF
04
Diagnostics
- Blood cultures × 3 sets (separate sites, before antibiotics) — cornerstone
- Echocardiography: TTE first-line; TEE gold standard (superior sensitivity ~95%)
- Modified Duke Criteria: 2 major, 1 major + 3 minor, or 5 minor = definite IE
- Major criteria: positive blood cultures + echo evidence (vegetation, abscess, new valve dehiscence)
- Pitfall: HACEK organisms require prolonged culture incubation; culture-negative IE in ~10%
05
Management
- Blood cultures × 3 before starting antibiotics — never delay cultures
- Empiric: vancomycin IV (covers MRSA); narrow based on sensitivities
- Native valve Strep viridans: penicillin G or ceftriaxone × 4 weeks
- Native valve S. aureus: nafcillin (MSSA) or vancomycin (MRSA) × 6 weeks
- Surgery indications: refractory HF, periannular abscess, fungal IE, persistent bacteremia, large vegetation with emboli
- Dental prophylaxis (amoxicillin) for future high-risk procedures in high-risk patients
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Acute Rheumatic Fever
ARF causes pancarditis/mitral stenosis late; no vegetations on echo; elevated ASO titer; follows GAS pharyngitis, not bacteremia
Marantic (Non-bacterial Thrombotic) Endocarditis
Sterile vegetations in malignancy/SLE; blood cultures negative; no fever or leukocytosis
Atrial Myxoma
Cardiac tumor mimics emboli + constitutional symptoms but echo shows pedunculated mass, not vegetation; cultures negative
Septic Pulmonary Emboli (Right-sided IE mimic)
Multiple cavitary lung lesions + tricuspid murmur + IVDU = right-sided IE; PA chest X-ray cavities are the clue
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Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.