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.

Infective%20endocarditis Diagnosis


Characteristics of Infective Endocarditis (IE)

  • IE 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 IE
  • The established diagnosis of IE is demonstrated by a positive blood culture (BC) and 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 and 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; or
  • Resolution of manifestations of endocarditis with 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 with IE from 2 separate BCs as noted below:
    • Viridans streptococci, Streptococcus gallolyticus (formerly known as S bovis), HACEK group, or Staphylococcus aureus
    • Community-acquired enterococci in the absence of a primary focus; or
  • Microorganisms consistent with IE from persistently positive BCs defined as
    • ≥2 positive cultures of blood samples drawn >12 hours apart; or
    • All of 3 or a majority of ≥4 separate cultures of blood (with first and last sample drawn ≥1 hour apart)
  • Single positive BC for Coxiella burnetii or antiphase I IgG antibody titer ≥1:800

2. Evidence of endocardial involvement

  • Positive echocardiogram for IE [transesophageal echocardiogram (TEE) recommended in patients with prosthetic valves and rated at least “possible IE” by clinical criteria, or complicated IE (paravalvular abscess); TTE as first 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 alternative anatomic 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: Temperature ≥38˚C
  • Vascular phenomena: Major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhages and Janeway lesions
  • Immunologic phenomena: Glomerulonephritis, Osler’s nodes, Roth spots and rheumatoid factor
  • Microbiological evidence: Positive BC but does not meet a major criterion as noted above or serological evidence of active infection with organism consistent with 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 and Symptoms

  • Moderate and remitting fever is the most common symptom
  • Anorexia, weight loss, malaise and night sweats
  • Fatigue, diaphoresis, chills, nausea and vomiting, arthralgia, myalgia

Physical Examination

Physical Exam

  • Heart murmur consistent with 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 and 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 with a pale center
  • Splenomegaly
  • Signs of congestive heart failure (CHF)

Laboratory Tests

Laboratory Tests

Blood Culture (BC)

  • Most important laboratory test
  • At least 3 BCs should be taken as soon as possible at 30-minute intervals
    • Delaying blood sampling to coincide with 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 without antibiotic
  • Identification of causative organism should be up to species level

Other Lab Tests

  • Complete blood count (CBC) with differential
    • Many patients have leukocytosis: 15,000-25,000/microliter with a left shift
    • Anemia is common: Normocytic and normochromic with low serum iron level and total iron binding capacity (TIBC)
  • Serum electrolytes
    • Some patients may have elevated serum creatinine
  • Urinalysis: May reveal microscopic hematuria, pyuria, red blood cell (RBC) casts, bacteriuria, proteinuria
  • Erythrocyte sedimentation rate (ESR): Elevated in most cases
  • C-reactive protein level: Elevated
  • Rheumatoid factor: Elevated in approximately 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 especially if present on the preferred locations, or attached to implanted prosthetic material with no alternative anatomical explanation
  • Demonstration of abscesses or fistulas
  • A new dehiscence of a valvular prosthesis especially when occurring late after implantation

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

  • Recommended initial diagnostic test for native valve endocarditis (NVE) and prosthetic valve endocarditis (PVE) 
  • 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 sensitivity in detecting vegetations in native and prosthetic valves is 50-90% and 40-70%, respectively, with a specificity of 90%
  • If the clinical suspicion of IE is low, the TTE is of good quality and the result is negative, endocarditis is unlikely

Transesophageal Echocardiography (TEE)

  • Has superior resolution, thus carries a greater sensitivity of 90-100% and 86% in detecting vegetations in native and prosthetic valves, respectively, as compared with 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, and when intracardiac device leads are present
  • If TEE is negative but suspicion of IE remains, repeat TEE in 5-7 days, or earlier if Staphylococcus aureus infection is suspected

Other Diagnostic Studies

Electrocardiogram (ECG)

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

Chest Radiograph

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

Computed Tomography (CT) Scan

  • Obtain in any patient with neurologic signs and symptoms
  • Cardiac CT may be used as an adjunctive diagnostic test when the anatomy is not clear on echocardiography
  • Multislice CT (MSCT) is useful in evaluating IE-associated valvular abnormalities eg perivalvular extent of abscess, pseudoaneurysm
Magnetic Resonance Imaging (MRI)
  • More sensitive than CT and increases the rate of detecting cerebral emboli lesions
Nuclear Imaging
  • Single-photon emission computed tomography (SPECT) and positron emission tomography (PET) are new modalities which may be used as supplementary tests in patients with IE and diagnostic difficulties


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