Infective endocarditis is microbial infection of the endovascular structures of the heart.
It often presents in an occult fashion and early diagnosis depends on a high index of clinical suspicion especially in patients with congenital heart disease, prosthetic valves or previous infective endocarditis.
The established diagnosis of infective endocarditis is demonstrated by a positive blood culture and involvement of the endocardium detected during sepsis or systemic infection. It may also be established if there is involvement of the endocardium detected during sepsis or systemic infection but blood culture is negative.


Characteristics of IE

  • IE often presents in an occult fashion & early diagnosis depends on a high index of clinical suspicion esp in patients w/ congenital heart disease, prosthetic valves or previous IE
  • The established diagnosis of IE is demonstrated by a positive blood culture & involvement of the endocardium detected during sepsis or systemic infection
    • IE may also be established if there is involvement of the endocardium detected during sepsis or systemic infection but BC is negative



Definite IE

Pathologic Criteria

  • Microorganisms demonstrated by culture or histologic exam of a vegetation, a vegetation that has embolized, or an intracardiac abscess; or
  • Pathological lesions: Vegetation or intracardiac abscess is present & confirmed by histology showing active endocarditis

Clinical Criteria: Using specific definitions found below

  • 2 major criteria; or
  • 1 major criterion + 3 minor criteria; or
  • 5 minor criteria

Possible IE

  • 1 major criterion + 1 minor criterion; or
  • 3 minor criteria

Rejected IE

  • Firm alternate diagnosis for manifestations of endocarditis
  • Resolution of manifestations of endocarditis w/ antibiotic therapy for ≤4 days; or
  • No pathological evidence of IE at surgery or autopsy, after antibiotic therapy for ≤4 days; or
  • Does not meet the criteria for possible IE, as above


Major Criteria

1. Positive blood culture for IE

  • Typical microorganism consistent w/ IE from 2 separate BCs as noted below:
    • Viridans streptococci, Streptococcus bovis, HACEK group, or Staphylococcus aureus
    • Community-acquired enterococci in the absence of a primary focus; or
  • Microorganisms consistent w/ IE from persistently positive BCs defined as
    • ≥2 positive cultures of blood samples drawn >12 hr apart; or
    • All of 3 or a majority of ≥4 separate cultures of blood (w/ 1st & last sample drawn ≥1 hr apart)
  • Single positive BC for Coxiella burnetii or antiphase I IgG antibody titer >1:800

2. Evidence of endocardial involvement

  • Positive echocardiogram for IE [TEE recommended in patients w/ prosthetic valves & rated at least “possible IE” by clinical criteria, or complicated IE (paravalvular abscess); TTE as 1st test in other patients] defined as:
    • Oscillating intracardiac mass on valve or supporting structures, in the path of regurgitant jets, or on implanted material in the absence of an alternativeanatomic explanation; or
    • Abscess; or
    • New partial dehiscence of prosthetic valve, or
  • New valvular regurgitation (worsening or changing of preexisting murmur not sufficient)

Minor Criteria

  • Predisposition: Predisposing heart condition or IV drug use
  • Fever: Temp ≥38˚C
  • Vascular phenomena: Major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhages & Janeway lesions
  • Immunologic phenomena: Glomerulonephritis, Osler’s nodes, Roth spots & rheumatoid factor
  • Microbiological evidence: Positive BC but does not meet a major criterion as noted above or serological evidence of active infection w/ organismconsistent w/ IE

Adapted from references: Li JS, Sexton DJ, Mick N, et al. Proposed modifications to the Duke Criteria for the diagnosis of infective endocarditis. Clin Infect Dis. 2000;30:633-8; and Durack DT, Lukes AS, Bright DK. New criteria for diagnosis of infective endocarditis: Utilization of specific endocardiographic findings. Duke Endocarditis Service. Am J Med. 1994;96:200-9.


Clinical Presentation

Signs & Symptoms

  • Moderate & remitting fever is the most common symptom
  • Anorexia, wt loss, malaise & night sweats
  • Fatigue, diaphoresis, chills, N/V, arthralgia, myalgia

Physical Examination

Physical Exam

  • Heart murmur consistent w/ valvular regurgitation
  • Petechiae on the skin, conjunctivae or oral mucosa
  • Osler’s nodes: Red, painful, indurated lesions, 2-15 mm in diameter seen on the palms or soles & usually in the digital phalanges
  • Janeway lesions: Non-tender, erythematous macules that appear on the palms or soles
  • “Blue toe syndrome”: Embolization of small vegetation fragments
  • Roth’s spots: Red, retinal hemorrhages w/ a pale center
  • Splenomegaly
  • Signs of CHF

Laboratory Tests

Lab Tests

Blood Culture (BC)

  • Most important lab test
  • At least 3 BCs should be taken as soon as possible at 30-min intervals
    • Delaying blood sampling to coincide w/ peaks of fever is unnecessary
  • It is recommended to postpone antimicrobial therapy until BCs become positive (unless the patient is septic)
  • If antimicrobial therapy has been started, wait for at least 3 days after discontinuing short-term antibiotic treatment before taking BC
    • If patient has been on long-term antibiotic treatment, positive BCs may not appear until after 6-7 days w/o antibiotic
  • Identification of causative organism should be up to species level

Other Lab Tests

  • CBC w/ differential
    • Many patients have leukocytosis: 15,000-25,000/microlitre w/ a left shift
    • Anemia is common: Normocytic & normochromic w/ low serum Fe level & TIBC
  • Serum electrolytes
    • Some patients may have elevated serum creatinine
  • Urinalysis: May reveal microscopic hematuria, pyuria, RBC casts, bacteriuria, proteinuria
  • ESR: Elevated in most cases
  • C-reactive protein level: Elevated
  • Rheumatoid factor: Elevated in approx half of the presenting patients



  • Diagnostic test of choice in detecting vegetations in cardiac valves

Three Echocardiographic Findings Considered to be Major Criteria in the Diagnosis of IE

  • Mobile, echodense mass attached to the valvular or the mural endocardium esp if present on the preferred locations, or attached to implanted prosthetic material w/ no alternative anatomical explanation
  • Demonstration of abscesses or fistulas
  • A new dehiscence of a valvular prosthesis esp when occurring late after implantation

Transthoracic Echocardiography (TTE): 2-Dimensional Transthoracic Echocardiography (2-D Echo)

  • Vegetation appears as a discrete mobile echogenic mass attached to the valvular surface downstream from a high- to low-pressure chamber
  • Vegetations ≥2 mm may be visualized; the larger the size, the more likely a vegetation will be detected
  • TTE detection rate is 40-63% in patients w/ clinically suspected IE
  • If the clinical suspicion of IE is low, the TTE is of good quality & the result is negative, endocarditis is unlikely

Transesophageal Echocardiography (TEE)

  • Has superior resolution, thus carries a greater sensitivity (90-100%) in detecting vegetations as compared w/ TTE
  • If suspicion of IE is high (eg staphylococcal bacteremia), then TEE should be performed in all negative TTE cases
  • TEE should be performed in all suspected PVE cases, in cases of aortic location, prior to cardiac surgery during active IE, & when intracardiac device leads are present
  • If TEE is negative but suspicion of IE remains, repeat TEE after 7-10 days, or earlier if Staphylococcus aureus infection is suspected

Other Diagnostic Studies


  • May be taken upon admission in patients w/ suspected acute IE
    • Evidence of low septal abscesses w/ involvement of the intraventricular conduction system is detected on ECG
    • Can be used to rule out conduction abnormalities & to establish baseline

Chest Radiograph

  • May delineate the presence of CHF
  • May show septic pulmonary emboli & infiltrates w/ cavitation that are associated w/ right-sided IE

CT Scan

  • Obtain in any patient w/ neurologic signs & symptoms
  • Multislice CT is useful in evaluating IE-associated valvular abnormalities eg perivalvular extent of abscess, pseudoaneurysm

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