Infective endocarditis (acute and subacute)

1. Concept

Infective endocarditis (IE) is microbial invasion of the heart valves/endocardium (via bacteremia) producing vegetations — friable masses of fibrin, platelets, inflammatory cells, necrotic debris, and organisms. Classified into acute and subacute forms.

2. Acute vs subacute

	Acute IE	Subacute IE
Organism	Highly virulent (S. aureus)	Low virulence (S. viridans)
Valve	Previously normal valves	Previously abnormal valves
Course	Rapid; ~50% mortality	Insidious; recovers with antibiotics

• Other organisms: HACEK group (oropharyngeal flora); ~10% culture-negative.
• IV drug users → often right-sided (tricuspid) disease.

3. Pathogenesis & predisposition

Microorganisms enter circulation (dental/surgical procedures, IV drug use, catheters, GI portal) → attach to endocardium. Predisposing conditions: rheumatic heart disease, congenital heart disease (jet lesions), mitral valve prolapse, bicuspid aortic valve, prosthetic valves, host factors (neutropenia, immunodeficiency, malignancy, diabetes, alcoholism, drug abuse).

4. Morphology

• Friable, bulky, destructive vegetations deform the valves; can erode into myocardium → ring abscesses.
• Fragmentation → septic emboli → metastatic (septic) infarcts.
• Healing → fibrosis, calcification, valve deformity.

5. Clinical features & complications

• Non-specific: fever, fatigue, weight loss, weakness; murmurs (~90%), splenomegaly (subacute). Diagnosis: blood culture.
• Complications: immune-complex glomerulonephritis (hematuria), microemboli (petechiae, splinter hemorrhages, Janeway/Osler-type lesions), systemic emboli (brain, kidney, lung), arrhythmia.

💡 High-yield: Acute IE = S. aureus on normal valves (virulent, ~50% mortality); subacute = S. viridans on abnormal valves (after dental work). Vegetations → ring abscess, septic emboli. IV drug users → tricuspid. Dx = blood culture; murmurs in 90%. Complications: glomerulonephritis, emboli.