Endocarditis


Table of Contents

  1. Table of Contents
  2. Overview
  3. Epidemiology
  4. Pathophysiology
  5. Etiology and Risk Factors
  6. Clinical Presentation
  7. Diagnosis
  8. Treatment
  9. Complications
  10. Prognosis
  11. Prevention
  12. Recent Research and Advances
  13. Research Papers
  14. Connections
  15. Featured Videos

Table of Contents

  1. Overview
  2. Epidemiology
  3. Pathophysiology
  4. Etiology and Risk Factors
  5. Clinical Presentation
  6. Diagnosis
  7. Treatment
  8. Complications
  9. Prognosis
  10. Prevention
  11. Recent Research and Advances
  12. References
  13. Featured Videos

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1. Overview

Infective endocarditis (IE) is a life-threatening infection of the endocardial surface of the heart, most commonly affecting the cardiac valves (native or prosthetic), though it may also involve intracardiac devices, septal defects, or the mural endocardium. The hallmark pathologic lesion is the vegetation — an irregular, friable mass composed of platelets, fibrin, microorganisms, and inflammatory cells adherent to damaged endothelium.

IE is classified by the affected valve and setting:

IE remains associated with high in-hospital mortality (15–30%) and high rates of cardiac and embolic complications, necessitating prompt diagnosis, multidisciplinary management, and often surgical intervention.


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2. Epidemiology

The annual incidence of IE is approximately 3–10 cases per 100,000 population in high-income countries, with consistent increases observed over the past two decades. In the United States, incidence increased from 8.5 to 12.7 per 100,000 between 1998 and 2009, largely driven by the opioid epidemic and increased use of intravascular devices.

IE demonstrates clear demographic patterns:


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3. Pathophysiology

IE development requires the confluence of three key elements: endothelial damage or abnormality, bacteremia, and bacterial adherence and proliferation.

Step 1: Endothelial Damage and Non-Bacterial Thrombotic Endocarditis (NBTE)

Normal intact endothelium is resistant to bacterial colonization. Mechanical trauma (turbulent blood flow across abnormal valves, jet lesions from regurgitant streams, prosthetic material), immune complex deposition, or catheter-induced injury disrupts the endothelial surface, exposing subendothelial collagen and extracellular matrix. This triggers a thrombotic response — platelet and fibrin deposition — creating the sterile NBTE (or marantic endocarditis) lesion that serves as the nidus for bacterial seeding.

Step 2: Bacteremia

Transient bacteremia occurs during numerous daily activities (toothbrushing, dental procedures, gastrointestinal procedures, intravascular catheter insertion, surgery). In most individuals, circulating bacteria are rapidly cleared by immune defenses. In predisposed individuals, bacteria reach the NBTE lesion and adhere to the thrombotic matrix.

Step 3: Bacterial Adherence and Vegetation Formation

Bacterial adhesins mediate attachment to host matrix proteins on the NBTE lesion. Staphylococcus aureus expresses fibronectin-binding proteins (FnBPA, FnBPB), clumping factors (ClfA, ClfB), and collagen-binding protein (Cna), enabling adherence to damaged endothelium. Viridans streptococci produce extracellular polysaccharides (dextrans) that facilitate adhesion.

Once adherent, bacteria proliferate within the vegetation, protected from host immune defenses by the fibrin matrix. Colony-forming biofilms develop, with bacteria transitioning to a slow-growing "persister" state with markedly reduced antibiotic susceptibility. Platelets aggregate and fibrin is continuously deposited, enlarging the vegetation. Bacterial density within mature vegetations can reach 10⁹–10¹¹ colony-forming units per gram, explaining why prolonged bactericidal antibiotic therapy is required.

Inflammatory and Embolic Consequences

Cytokines (IL-1β, IL-6, TNF-α) drive systemic inflammatory response, fever, and leukocytosis. Vegetation fragments embolize to systemic (left-sided IE) or pulmonary (right-sided IE) circulations. Perivalvular tissue destruction — driven by bacterial proteases, matrix metalloproteinases, and local inflammatory response — leads to valve leaflet destruction, perforation, rupture of chordae tendineae, annular abscess formation, and fistulae, with resulting acute hemodynamic compromise.


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4. Etiology and Risk Factors

Causative Organisms

Host Risk Factors


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5. Clinical Presentation

Acute vs. Subacute Presentations

Acute IE (typically S. aureus): Rapid onset (<2 weeks), high-grade fever, rigors, and rapid valve destruction with hemodynamic deterioration; high early mortality without prompt treatment.

Subacute IE (viridans streptococci, HACEK): Indolent course (>2 weeks), low-grade fever, weight loss, malaise, anemia; symptoms may be attributed to viral illness or non-specific malaise, delaying diagnosis.

Cardinal Features

Embolic and Immunologic Phenomena (Peripheral Stigmata)

Right-Sided IE (IVDU)

Tricuspid valve IE presents with septic pulmonary emboli: pleuritic chest pain, dyspnea, hemoptysis, and multiple bilateral nodular pulmonary infiltrates on imaging. Fever is prominent. Left-sided murmur is absent or a tricuspid regurgitation murmur may be heard.


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6. Diagnosis

Blood Cultures

Blood cultures are the most critical diagnostic test. Recommended protocol: at least 3 sets of blood cultures drawn from separate venipuncture sites over 24 hours (not from indwelling catheters), each set including one aerobic and one anaerobic bottle. Blood cultures are positive in 85–95% of IE cases if obtained before antibiotic administration. Volume of blood cultured is critical: 10 mL per bottle, 20 mL per set.

For culture-negative IE: additional cultures in specialized media; serology for Coxiella burnetii (anti-phase I IgG ≥1:800), Bartonella spp. (anti-B. henselae/quintana IgG), Brucella spp.; PCR of blood or valve tissue; broad-spectrum 16S ribosomal RNA PCR; metagenomic next-generation sequencing.

Echocardiography

Echocardiography is essential for diagnosis, risk stratification, and surgical planning:

Modified Duke Criteria

The Modified Duke Criteria (Li et al., 2000) remain the diagnostic standard, classifying IE as definite, possible, or rejected:

Major criteria:

Minor criteria:

Definite IE: 2 major, 1 major + 3 minor, or 5 minor criteria (or pathologic criteria: organisms/lesions from surgery or autopsy).

Additional Imaging

Laboratory Findings


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7. Treatment

Antibiotic Therapy

Prolonged parenteral bactericidal antibiotic therapy is essential. Treatment duration is typically 4–6 weeks for most NVE and 6 weeks or longer for PVE. Antibiotic selection is pathogen-specific:

Outpatient Parenteral Antibiotic Therapy (OPAT)

The POET trial (2019) demonstrated non-inferiority of oral step-down antibiotic therapy (following ≥10 days IV therapy) vs. continued IV therapy in stabilized patients with left-sided IE caused by streptococci, enterococci, S. aureus, or CoNS; published in NEJM. Requires: hemodynamic stability, no perivalvular complications, vegetation <20 mm, competent patient with follow-up availability.

Surgical Indications

Approximately 50% of IE patients require cardiac surgery. Indications include:

The optimal timing of surgery in the setting of neurologic complications remains challenging: ischemic stroke is not a contraindication to urgent surgery if deficits are mild; hemorrhagic stroke requires deferral of 4 weeks if possible to avoid hemorrhagic transformation with cardiopulmonary bypass anticoagulation.

Supportive Measures


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8. Complications


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9. Prognosis

IE carries high mortality: in-hospital mortality 15–30%; 1-year mortality 20–40%. Prognosis varies significantly by patient, organism, and management factors.


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10. Prevention

Antibiotic Prophylaxis

Current guidelines (AHA 2007, ESC 2015/2023) significantly restrict IE prophylaxis recommendations based on evidence that most IE cases are not preceded by procedure-related bacteremia and that routine prophylaxis would need to be given to an enormous number of patients to prevent one case.

IE prophylaxis is recommended ONLY for patients at highest risk:

Dental procedures warranting prophylaxis (in above high-risk patients): Procedures involving manipulation of gingival tissue, periapical region, or oral mucosa perforation.

Prophylaxis regimens (dental procedures):

General Preventive Strategies


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11. Recent Research and Advances

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Research Papers

The following PubMed topic searches return current peer-reviewed literature relevant to this condition. Each link opens a live PubMed query.

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Connections

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