Introduction
Infective Endocarditis (IE) is a life-threatening infection of the endocardial surface of the heart, most commonly affecting the cardiac valves. Despite advances in antimicrobial therapy and surgical techniques, IE carries significant morbidity and mortality. Prompt recognition through structured diagnostic criteria and microbiological evaluation is critical.
Etiology and Pathogenesis
The pathology of IE begins with endothelial damage, leading to platelet-fibrin deposition (Non-Bacterial Thrombotic Endocarditis). Subsequent bacteremia leads to colonization of these vegetation sites.
Native Valve Endocarditis (NVE):
Streptococcus viridans (Most common in community-acquired, subacute cases).
Staphylococcus aureus (Common in acute cases and intravenous drug users).
Enterococcus faecalis (Associated with genitourinary/gastrointestinal procedures).
Prosthetic Valve Endocarditis (PVE):
Early ($<1$ year post-surgery): Staphylococcus epidermidis (coagulase-negative staphylococci).
Late ($>1$ year post-surgery): Similar to NVE spectrum (Streptococci, S. aureus).
Culture-Negative Endocarditis:
HACEK group (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella), Coxiella burnetii, Bartonella species.
Endothelial Lesion -> Platelet-Fibrin Deposition -> Transient Bacteremia -> Vegetation Formation -> Embolization / Valve Destruction
Modified Duke Criteria for Diagnosis
Definite diagnosis requires 2 Major Criteria, 1 Major + 3 Minor Criteria, or 5 Minor Criteria.
Major Criteria
Positive Blood Cultures for IE:
Typical microorganisms consistent with IE from 2 separate blood cultures (S. viridans, S. bovis, HACEK group, S. aureus, or enterococci).
Persistently positive blood cultures drawn $>12$ hours apart.
Single positive blood culture or IgG antibody titer $>1:800$ for Coxiella burnetii.
Evidence of Endocardial Involvement:
Echocardiogram positive for IE: Oscillating intracardiac mass on valve/supporting structures, abscess, or new partial dehiscence of prosthetic valve.
New valvular regurgitation.
Minor Criteria
Predisposition: Heart condition or IV drug use.
Fever: Temperature $> 38.0^\circ\text{C}$ ($100.4^\circ\text{F}$).
Vascular Phenomena: Major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, Janeway lesions.
Immunological Phenomena: Glomerulonephritis, Osler nodes, Roth spots, Rheumatoid Factor.
Microbiological Evidence: Positive blood culture not meeting major criteria or serological evidence of active infection.
Principles of Management
Empiric Antibiotic Therapy: Native valve (Ampicillin/Sulbactam or Ceftriaxone + Vancomycin); Prosthetic valve (Vancomycin + Gentamicin + Rifampin).
Surgical Indications: Refractory heart failure, uncontrolled infection/abscess formation, persistent bacteremia, or large vegetations ($>10\text{ mm}$) with high embolic risk.