4.5 Infective Endocarditis & Cardiovascular Infection

Infective endocarditis and healthcare-associated infections like Clostridioides difficile colitis and central venous catheter bloodstream infections represent high-stakes clinical scenarios requiring strict adherence to evidence-based diagnostic criteria and surgical timing.

1. Infective Endocarditis (IE)

Infective endocarditis is an infection of the endocardial surface of the heart, most commonly affecting native or prosthetic cardiac valves or implanted intracardiac devices.

Pathophysiology & Microbiology

• Endothelial Injury: Turbulent blood flow (valvular stenosis/regurgitation, congenital defects) damages endothelium, exposing subendothelial collagen and tissue factor, triggering platelet and fibrin deposition to create a sterile non-bacterial thrombotic endocarditis (NBTE) nidus.
• Bacteremic Seeding: Transient bacteremia leads to microbial adhesion to the sterile vegetation, followed by bacterial proliferation and biofilm formation.

The Modified Duke Criteria for Diagnosis

Definitive diagnosis requires: 2 Major Criteria, OR 1 Major + 3 Minor Criteria, OR 5 Minor Criteria.

A. Major Criteria

1. Positive Blood Cultures for Infective Endocarditis:
   • Typical microorganisms consistent with IE from 2 separate blood cultures: Viridans streptococci, Streptococcus gallolyticus, HACEK group, Staphylococcus aureus, or community-acquired Enterococci in the absence of a primary focus; OR
   • Microorganisms consistent with IE from persistently positive blood cultures: blood cultures drawn >12 hours apart, or all of 3, or majority of >=4 separate cultures (with first and last drawn >=1 hour apart); OR
   • Single positive blood culture for Coxiella burnetii or antiphase I IgG antibody titer >1:800.
2. Evidence of Endocardial Involvement:
   • Positive Echocardiogram: Oscillating intracardiac mass/vegetation on valve or supporting structures, perivalvular abscess, or new partial dehiscence of a prosthetic valve; OR
   • New Valvular Regurgitation (worsening or changing of pre-existing murmur not sufficient).

B. Minor Criteria

1. Predisposition: Predisposing heart condition (prosthetic valve, prior IE, rheumatic valve disease, congenital heart defect) or injection drug use.
2. Fever: Temperature >= 38.0°C (100.4°F).
3. Vascular Phenomena: Major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhages, or Janeway lesions (painless, flat, erythematous/hemorrhagic macules on palms and soles caused by septic microemboli).
4. Immunologic Phenomena: Glomerulonephritis, Osler nodes (painful, violaceous, tender subcutaneous nodules on the pulp of fingers and toes caused by immune complex deposition), Roth spots (retinal hemorrhages with pale/white fibrin centers), or positive Rheumatoid Factor (RF).
5. Microbiological Evidence: Positive blood culture not meeting a major criterion or serological evidence of active infection with an organism consistent with IE.

Antimicrobial Therapy for Endocarditis

• Empiric Regimen for Native Valve IE: Vancomycin (15–20 mg/kg IV q8–12h targeting trough 15–20 mcg/mL) PLUS Ceftriaxone (2 g IV daily) OR Ampicillin-sulbactam (3 g IV q6h).
• Empiric Regimen for Prosthetic Valve IE (PVE): Vancomycin (15–20 mg/kg IV q8–12h) PLUS Cefepime (2 g IV q8h) or Gentamicin (1 mg/kg IV q8h) PLUS Rifampin (300 mg PO/IV q8h).
  • Rifampin Clinical Pearl: Rifampin penetrates staphylococcal biofilms on prosthetic materials; it should ideally be added 2–3 days after initiating vancomycin once bacteremia has cleared to prevent emergence of rifampin resistance.
• Treatment Duration: Minimum 4 to 6 weeks of targeted IV bactericidal therapy calculated from the date of the first negative blood culture.

Indications for Urgent Cardiac Surgery (Class I)

1. Acute Valvular Dysfunction Causing Heart Failure: Severe acute aortic or mitral regurgitation or valve obstruction resulting in cardiogenic shock or refractory pulmonary edema.
2. Uncontrolled Infection / Persistent Bacteremia: Persistent positive blood cultures or unrelenting fever >5 to 7 days after initiation of appropriate targeted antimicrobial therapy.
3. Locally Invasive Infection / Extension: Development of perivalvular abscess (aortic root abscess), pseudoaneurysm, fistula, or new cardiac conduction abnormalities (e.g., new 1st-degree AV block or bundle branch block, which indicates extension of an aortic root abscess into the AV node and bundle of His).
4. Fungal Endocarditis: Endocarditis caused by Candida spp. or Aspergillus spp. (medical therapy alone is uniformly fatal).
5. Prevention of Embolism: Recurrent embolic events or large mobile vegetations (>10 mm in diameter) despite appropriate antimicrobial therapy, especially on anterior mitral valve leaflets.

Infective Endocarditis Prophylaxis Guidelines

Antimicrobial prophylaxis is recommended ONLY for high-risk cardiac conditions undergoing high-risk dental procedures involving manipulation of gingival tissue, periapical region of teeth, or perforation of oral mucosa.

• High-Risk Cardiac Conditions:
  1. Prosthetic cardiac valves or prosthetic material used for cardiac valve repair.
  2. Previous history of infective endocarditis.
  3. Unrepaired cyanotic congenital heart disease (CHD), or repaired CHD with residual shunts or prosthetic material.
  4. Cardiac transplant recipients who develop cardiac valvulopathy.
• Recommended Prophylaxis Regimen: Oral Amoxicillin 2 g administered as a single dose 30 to 60 minutes prior to the procedure (if penicillin-allergic without history of anaphylaxis: Cephalexin 2 g, or Azithromycin/Clarithromycin 500 mg, or Doxycycline 100 mg).