Cardiovascular · PANCE / PANRE

Infective Endocarditis (IE)

Written & clinically reviewed by Ryan Busch, PA-C · Updated August 2026 · Report an error

Microbial infection of the endocardium or valve — diagnosed by modified Duke criteria; treated with prolonged IV antibiotics ± surgery.

Also known as: IE, endocarditis, bacterial endocarditis, SBE, ABE

Overview

Infection of the endocardial surface of the heart, most commonly involving heart valves, characterized by vegetations composed of platelets, fibrin, microorganisms, and inflammatory cells.

Epidemiology

Annual incidence 3-10 per 100,000. Rising in older adults with degenerative valve disease and prosthetic devices; injection drug use is a leading driver of right-sided IE in younger patients.

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Question 1CardiovascularMedium
A 38-year-old intravenous drug user (IVDU) has fever, tricuspid vegetation, and blood cultures positive for methicillin-sensitive Staphylococcus aureus (MSSA). Which of the following is the most appropriate first-line treatment?
  • ACeftriaxone
  • BNafcillin
  • CLinezolid
  • DVancomycin
Reveal answer & full explanation
Correct answer: B — Nafcillin
  • ACeftriaxone
  • BNafcillin✓
  • CLinezolid
  • DVancomycin

Why Nafcillin is correct

  • For methicillin-sensitive Staphylococcus aureus (MSSA) endocarditis, anti-staphylococcal penicillins (nafcillin or oxacillin) are superior to vancomycin, with lower mortality and faster bacteremia clearance.
  • This IVDU with a tricuspid vegetation and MSSA bacteremia has right-sided infective endocarditis, for which nafcillin is the agent of choice.

Why the others are wrong

  • Ceftriaxone — not first-line for MSSA endocarditis; lacks the anti-staphylococcal potency of nafcillin/oxacillin (right-concept-wrong-drug).
  • Linezolid — bacteriostatic oxazolidinone used as salvage for resistant gram-positive infection; it is not a recommended regimen for Staphylococcus aureus endocarditis, where bactericidal therapy is required (right-class-wrong-setting).
  • Vancomycin — reserved for MRSA or true penicillin anaphylaxis; inferior to nafcillin for MSSA (confused-with MRSA).

Additional high-yield points

  • Cefazolin is acceptable for non-anaphylactic penicillin allergy.
  • Duration: right-sided uncomplicated MSSA infective endocarditis (IE) in an IVDU typically 4-6 weeks; left-sided requires 6 weeks.
  • Daptomycin is an approved alternative for right-sided Staphylococcus aureus endocarditis and bacteremia; because it is inactivated by pulmonary surfactant, it must never be used to treat pneumonia.
Question 2CardiovascularEasy
A patient with infective endocarditis has tender, erythematous nodules on the finger pads and small retinal hemorrhages with pale centers. These findings are best classified as which Duke criterion category?
  • AImmunologic phenomena
  • BPredisposing condition
  • CVascular phenomena
  • DMajor endocardial involvement
Reveal answer & full explanation
Correct answer: A — Immunologic phenomena
  • AImmunologic phenomena✓
  • BPredisposing condition
  • CVascular phenomena
  • DMajor endocardial involvement

Why Immunologic phenomena is correct

  • Osler nodes (tender, painful, located on finger/toe pads) are immunologic phenomena from immune-complex deposition — minor Duke criteria
  • Roth spots (retinal hemorrhages with pale centers) are also immunologic phenomena from immune-complex deposition — minor Duke criteria

Why the others are wrong

  • C) Vascular phenomena — includes Janeway lesions (painless, on palms/soles) and splinter hemorrhages, which are embolic/vascular in origin; mnemonic: Osler = Ouch (painful, immunologic); Janeway = painless (embolic)
  • D) Major endocardial involvement — requires echo findings or new regurgitation, not peripheral immunologic findings
  • B) Predisposing condition — refers to underlying heart disease or IV drug use, not peripheral signs
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Risk factors

  • Prosthetic heart valve or prior infective endocarditis
  • Congenital heart disease (especially cyanotic)
  • Injection drug use (right-sided IE — tricuspid valve)
  • Hemodialysis, indwelling intravascular catheters, pacemaker/ICD leads
  • Poor dentition and recent dental procedures (oral streptococci)
  • Acquired valve disease (rheumatic, degenerative, MVP with MR)
  • Immunosuppression, diabetes

Pathophysiology

Endothelial injury exposes subendothelial matrix; sterile platelet-fibrin thrombus forms (nonbacterial thrombotic endocarditis). Transient bacteremia seeds this nidus, producing a vegetation that grows and embolizes, destroys leaflets (perforation, regurgitation), invades adjacent tissue (abscess, conduction block), or seeds distal organs.

Clinical presentation

Symptoms

  • Fever (most common — present in >90%), chills, night sweats, malaise, weight loss
  • Constitutional symptoms over weeks (subacute) or fulminant sepsis (acute)
  • New or worsening dyspnea from valve destruction and heart failure
  • Focal neurologic deficits (septic embolic stroke), back pain (vertebral osteomyelitis), flank pain (renal infarct)
  • Right-sided IE in IDU: pleuritic chest pain, cough, hemoptysis from septic pulmonary emboli

Signs / physical exam

  • New regurgitant murmur (especially MR or AR)
  • Janeway lesions (painless erythematous palms/soles — embolic)
  • Osler nodes (painful nodules on finger pads — immune complex)
  • Splinter hemorrhages, Roth spots (retinal hemorrhages with pale centers)
  • Splenomegaly, petechiae
  • Signs of complications: stroke, heart failure, AV block (perivalvular abscess)

Classic findings

FROM JANE — Fever, Roth spots, Osler nodes, Murmur, Janeway lesions, Anemia, Nail-bed splinters, Embolic phenomena.

Differential diagnosis

  • Nonbacterial thrombotic endocarditis (marantic) — Sterile vegetations in advanced malignancy or chronic illness; embolic events with negative cultures
  • Libman-Sacks endocarditis (SLE) — Verrucous sterile lesions on either side of valve leaflets; positive ANA / anti-dsDNA
  • Atrial myxoma — Embolic events and constitutional symptoms; mobile LA mass on echo without bacteremia
  • Rheumatic carditis — Following strep pharyngitis; multiple Jones criteria; rising ASO
  • Catheter-related bacteremia without IE — Persistent positive cultures but no vegetation; resolves with line removal
  • Septic pulmonary emboli of other source — May mimic right-sided IE; identify primary site and rule out tricuspid vegetation

Diagnostic workup

Diagnostic criteria

Modified Duke criteria — Definite IE: 2 major OR 1 major + 3 minor OR 5 minor. Major: typical organism in 2 separate blood cultures (S. viridans, S. gallolyticus/bovis, HACEK, S. aureus, community Enterococcus without primary source) OR persistent bacteremia OR echocardiographic evidence (vegetation, abscess, new dehiscence) OR new regurgitation. Minor: predisposition, fever ≥38°C, vascular phenomena, immunologic phenomena, microbiologic evidence not meeting major.

Labs

  • ≥3 blood cultures from separate venipuncture sites at least 1 hour apart BEFORE antibiotics
  • CBC (anemia, leukocytosis), ESR/CRP elevated
  • UA (microscopic hematuria, proteinuria — embolic glomerulonephritis)
  • BMP, LFTs, rheumatoid factor (Duke minor criterion)
  • HIV testing in IDU and high-risk populations

Imaging

  • Transthoracic echo — initial; sensitivity ~70% for native valve, lower for prosthetic
  • Transesophageal echo — sensitivity >90%; perform if TTE negative but high suspicion, prosthetic valve, or to assess for abscess
  • ECG: new AV block suggests perivalvular abscess at aortic root
  • CT chest/abdomen/pelvis or PET-CT for embolic foci, splenic/renal infarcts, mycotic aneurysms
  • Brain MRI if neurologic symptoms

Diagnostic algorithm

Modified Duke CriterionTypeDefinition
Typical organism × 2 culturesMajorS. viridans, S. gallolyticus, HACEK, S. aureus, community Enterococcus
Persistent bacteremiaMajor≥2 positive cultures >12 h apart, or majority of 3+ cultures positive
Echo evidenceMajorVegetation, abscess, or new prosthetic valve dehiscence
New regurgitation murmurMajorDocumented new valvular regurgitation
PredispositionMinorPredisposing heart condition or IV drug use
Fever ≥38°CMinor
Vascular phenomenaMinorArterial emboli, septic pulmonary infarcts, mycotic aneurysm, ICH, conjunctival hemorrhage, Janeway lesions
Immunologic phenomenaMinorGN, Osler nodes, Roth spots, RF positivity
Microbiologic evidenceMinorPositive cultures not meeting major criterion
Modified Duke criteria for infective endocarditis (Definite: 2 major OR 1 major + 3 minor OR 5 minor).

Treatment

First-line

  • Empiric therapy AFTER cultures drawn — native valve acute: vancomycin (target trough 15-20 mcg/mL) + ceftriaxone 2 g IV q24h
  • Prosthetic valve (within 12 months): vancomycin + gentamicin + rifampin
  • Streptococcal IE (penicillin-susceptible): penicillin G 12-18 million units/day IV or ceftriaxone 2 g IV daily × 4 weeks
  • S. aureus native valve: nafcillin or oxacillin 2 g IV q4h × 6 weeks (MSSA); vancomycin or daptomycin (MRSA)
  • Enterococcus: ampicillin + ceftriaxone OR ampicillin + gentamicin × 4-6 weeks
  • HACEK organisms: ceftriaxone × 4 weeks
  • Duration typically 4-6 weeks IV from first negative culture

Second-line / adjunct

  • Surgical valve repair/replacement — Class I for heart failure from valve dysfunction, perivalvular abscess, heart block, persistent bacteremia >5-7 days on appropriate antibiotics, large mobile vegetation >10 mm with embolic event, fungal IE, or prosthetic valve dehiscence
  • Lifelong removal of injection drug paraphernalia, addiction counseling
  • Endocarditis prophylaxis for future high-risk procedures (dental work) — amoxicillin 2 g PO 30-60 min pre-procedure; if penicillin-allergic use cephalexin 2 g, azithromycin/clarithromycin 500 mg, or doxycycline 100 mg (clindamycin is NO LONGER recommended per 2021 AHA update)

Complications

  • Heart failure from valve destruction (leading cause of mortality)
  • Septic embolization: stroke, splenic/renal infarct, septic pulmonary emboli
  • Perivalvular abscess and conduction block (especially aortic)
  • Mycotic aneurysm (intracranial, peripheral)
  • Acute kidney injury (immune-complex glomerulonephritis, antibiotic toxicity)
  • Death — overall mortality 15-30%

PANCE pearls

  • Always draw at least 3 separate blood cultures BEFORE antibiotics unless septic shock dictates otherwise.
  • New AV block in a febrile patient with IE strongly suggests aortic root abscess — get TEE.
  • S. gallolyticus (formerly S. bovis) endocarditis is associated with colorectal cancer — colonoscopy is required.
  • Right-sided endocarditis in an IDU classically presents with septic pulmonary emboli; tricuspid is the most common valve.
  • Endocarditis prophylaxis is only indicated for HIGH-RISK cardiac conditions undergoing high-risk procedures, not routine MVP or bicuspid valve.

References

  • AHA 2015 — Infective Endocarditis in Adults: Diagnosis, Antimicrobial Therapy, and Management of Complications (Baddour et al., Circulation 2015)
  • ESC 2023 — 2023 ESC Guidelines for the Management of Endocarditis (Delgado et al., Eur Heart J 2023)
  • Duke Criteria — Modified Duke Criteria for Infective Endocarditis (Li et al., Clin Infect Dis 2000)
  • AHA 2007 — Prevention of Infective Endocarditis (Wilson et al., Circulation 2007)

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