Diagnosis of Infective Endocarditis

Diagnosis of infective endocarditis is usually made using Duke criteria which combines clinical, pathological, microbiological and echocardiographic characteristics.

Major blood culture criteria:

• Discovery of microorganisms - typical for patients with infective endocarditis in two blood cultures. This includes Staphylococcus aureus, Streptococcus viridans and bovis, HACEK group of organism and enterococci.
• Blood cultures are persistently positive for one of the microorganisms mentioned above.
• Three or more positive blood cultures taken at least 1 hour apart.

Major echocardiographic criteria:

• Echocardiogram positive for infective endocarditis. Discovery of an oscillating intracardiac mass on a valve or on implanted material.
• Development of partial dehiscence of the valves.
• Myocardial abscess.
• New-onset valvular regurgitation.

Minor diagnostic criteria:

• Intravenous drug use or predisposing heart condition.
• Fever of 38 degrees Celsius and above.
• Vascular phenomenon, such as septic pulmonary infarcts, major arterial emboli, intracranial hemorrhage, mycotic aneurysm, Janeway lesions or conjunctival hemorrhage.
• Immunological phenomenon including glomerulonephritis, Roth spots, rheumatoid factor and Osler nodes.
• Positive blood culture that doesn’t meet major blood culture criteria.
• Echocardiogram results that may point toward infective endocarditis but do not meet major echocardiographic criteria.

Definitive pathological diagnosis can also be made by demonstrating microorganisms, by histology or culture, in drainage of an intracardiac abscess, embolectomy or in vegetation removed during surgery. Alternatively, a definite diagnosis is made if: 2 major criteria are present, 1 major criterion is combined with 3 minor criteria, or if 5 minor criteria are present.

Diagnosis of infective endocarditis is discarded if:

• A firm alternative diagnosis was found.
• Resolution of endocarditis just after 4 or fewer days after the start of antimicrobial therapy.
• No evidence of infective endocarditis during surgery after 4 days (or fewer) after the start of antimicrobial therapy.

Other diagnostic tools include:

• Electrocardiogram (ECG) - is made if the doctor suspects that endocarditis has resulted in arrhythmia.
• Chest X-ray- Endocarditis can sometimes lead to the enlargement of the heart which can be clearly seen on an X-ray. Chest X-ray can also discover pulmonary microinfarctions caused by the infective endocarditis.
• Computerized tomography or magnetic resonance imaging is used when the doctor suspects that emboli have spread throughout the systemic blood circuit which can seriously damage the brain, liver, kidneys and other parts of the body.

Next Chapter: Treatment of Endocarditis