What are the different types of endocarditis?

Types of Endocarditis

Endocarditis should be classified according to three distinct frameworks: anatomic location/presence of foreign material, mode of acquisition, and microbiological findings, as these classifications directly impact treatment decisions and prognosis. 1

Classification by Anatomic Location and Presence of Foreign Material

The European Society of Cardiology provides four primary categories that must be distinguished to avoid overlap in management 1:

• Left-sided native valve IE - infection of native left-sided heart valves without prosthetic material 1

• Left-sided prosthetic valve IE (PVE) - further subdivided into:

  • Early PVE: occurring <1 year after valve surgery 1
  • Late PVE: occurring ≥1 year after valve surgery 1

• Right-sided IE - typically affects the tricuspid valve, commonly seen in intravenous drug users 1

• Device-related IE - involving permanent pacemakers or implantable cardioverter-defibrillators 1

Classification by Mode of Acquisition

This classification has critical implications for empirical antibiotic selection 1:

Health Care-Associated IE

• Nosocomial: Signs and symptoms of IE in a patient hospitalized >48 hours prior to onset 1

• Non-nosocomial: Signs and symptoms starting <48 hours after admission in patients with healthcare contact defined as:

  • Home-based nursing, IV therapy, hemodialysis, or IV chemotherapy within 30 days before IE onset 1
  • Hospitalization in acute care facility, nursing home, or long-term care facility within 90 days before IE onset 1
  • Resident in a nursing home or long-term care facility 1

Community-Acquired IE

• Signs and symptoms of IE starting <48 hours after admission in patients not fulfilling criteria for healthcare-associated infection 1

Intravenous Drug Abuse-Associated IE

• IE in an active injection drug user without alternative source of infection 1

Classification by Microbiological Findings

IE with Positive Blood Cultures (85% of cases)

The most common causative organisms are staphylococci, streptococci, and enterococci 1:

• Streptococcal and enterococcal IE: Oral (formerly viridans) streptococci include S. sanguis, S. mitis, S. salivarius, S. mutans, and Gemella morbillorum, which are almost always penicillin-susceptible 1

  • The S. milleri/anginosus group (S. anginosus, S. intermedius, S. constellatus) must be distinguished due to their abscess-forming tendency 1, 2

• Staphylococcal IE: S. aureus has become the leading cause in industrialized countries, associated with healthcare exposure, hemodialysis, diabetes mellitus, and intravascular devices 1

Culture-Negative IE

Represents approximately 15% of cases and requires specialized diagnostic approaches 1:

• Fastidious organisms including Bartonella, Coxiella, and HACEK group organisms may be identified through serological testing or PCR in up to 62.7% of culture-negative cases 1

• Noninfectious causes that mimic IE must be excluded 1:

  • Neoplasia-associated: Atrial myxoma, marantic endocarditis, neoplastic disease, carcinoid 1
  • Autoimmune-associated: Rheumatic carditis, systemic lupus erythematosus, polyarteritis nodosa, Behçet disease, antiphospholipid antibody syndrome 1
  • Post-valvular surgery: Thrombus, stitch, other postsurgery changes 1
  • Miscellaneous: Eosinophilic heart disease, ruptured mitral chordae, myxomatous degeneration 1

Classification by Clinical Course (Historical)

While less emphasized in modern guidelines, the acute versus subacute distinction remains clinically relevant 3, 4:

• Acute IE: Fulminant course with high fever, leukocytosis, and death in <6 weeks if untreated, most often caused by S. aureus, S. pneumoniae, or S. pyogenes 3

• Subacute/Chronic IE: Slow, indolent course with low-grade fever, night sweats, and weight loss, typically occurring in patients with prior valvular disease, usually caused by viridans streptococci 3

Additional Clinical Categories

Active IE

Defined by persistent fever and positive blood cultures, active inflammatory morphology at surgery, ongoing antibiotic therapy, or histopathological evidence of active IE 1

Recurrent IE

• Relapse: Repeat episodes caused by the same microorganism <6 months after the initial episode 1
• Reinfection: Repeat episode caused by a different microorganism or the same microorganism >6 months after the initial episode 1

Critical Clinical Pitfall

The classification system you use must match your clinical question: Use anatomic classification for surgical planning, mode of acquisition for empirical antibiotic selection, and microbiological classification for definitive therapy 1. Failure to consider all three frameworks simultaneously can lead to inappropriate management, particularly in culture-negative cases where empirical therapy must account for both the anatomic location and acquisition mode 1.