Diagnosis and Management of Infective Endocarditis

Diagnostic Criteria

• The European Society of Cardiology recommends obtaining at least 3 sets of blood cultures from separate venipuncture sites before initiating antibiotics, with the first and last samples drawn at least 1 hour apart 1, 2, 3
• Blood cultures should be incubated under both aerobic and anaerobic conditions 1, 4
• The American Heart Association suggests that blood cultures are positive in approximately 90% of IE cases when properly obtained, although this fact is based on a guideline from Praxis Medical Insights, a similar fact from the European Heart Journal states that prior antibiotic administration is the most common cause of blood culture-negative IE 1, 4, 5
• The European Heart Journal recommends performing transthoracic echocardiography (TTE) first in all suspected cases as the initial imaging modality, and proceeding immediately to transesophageal echocardiography (TEE) if TTE is negative but clinical suspicion remains high, or if a prosthetic valve is present, or if intracardiac device leads are present, or if optimal TTE windows cannot be obtained 2, 6
• The European Society of Cardiology states that TEE has a higher sensitivity than TTE for detecting vegetations, although the exact sensitivity values are not provided in this context 2
• The European Heart Journal recommends repeating echocardiography 7-10 days later if initially negative but clinical suspicion remains high, or earlier if S. aureus infection is suspected 5

Modified Duke Criteria

• The European Society of Cardiology defines the major criteria for the diagnosis of infective endocarditis, including typical organisms from 2 separate blood cultures, persistently positive blood cultures, and evidence of endocardial involvement on echocardiography 1, 4, 7
• The American Heart Association suggests that the minor criteria include predisposition, fever, vascular phenomena, immunologic phenomena, and microbiological evidence 1, 4, 7
• The European Heart Journal states that definite IE is diagnosed when 2 major criteria, or 1 major and 3 minor criteria, or 5 minor criteria are present 1, 7, 6

Blood Culture-Negative IE

• The European Society of Cardiology recommends specialized testing, including serological testing and molecular diagnostics, when blood cultures remain negative at 48 hours and clinical suspicion persists 1, 4, 5, 3
• The European Heart Journal suggests that serological testing for Coxiella burnetii, Bartonella spp., Brucella spp., Mycoplasma spp., and Legionella spp. may be useful in the diagnosis of blood culture-negative IE 1, 4, 5, 3

Histopathological Examination

• The European Society of Cardiology recommends pathological examination of resected valvular tissue or embolic fragments as the gold standard for diagnosis 1, 7, 5, 3
• The European Heart Journal suggests that all surgical specimens should be collected in sterile containers without fixative and sent immediately to microbiology 3

Critical Management Points

• The European Society of Cardiology recommends early consultation with an infectious disease specialist, especially for culture-negative cases or atypical organisms 1, 5
• The American Heart Association suggests referring complicated cases to reference centers with multidisciplinary "Endocarditis Teams" including cardiologist, infectious disease specialist, cardiac surgeon, and microbiologist 8, 6
• The European Heart Journal states that repeat blood cultures 48-72 hours after starting treatment to verify effectiveness 3
• The American College of Cardiology recommends that the Duke criteria are meant to guide diagnosis but must not replace clinical judgment - clinicians may appropriately decide to treat regardless of whether criteria are met 2

Diagnostic Criteria for Infective Endocarditis

Introduction to Diagnostic Classification

• The European Society of Cardiology recommends the modified Duke criteria for the diagnosis of infective endocarditis, which includes the use of cardiac CT, PET/CT imaging, and silent embolic events to improve diagnostic sensitivity, particularly for prosthetic valve and device-related infections 9, 10.

Major Criteria

• The diagnosis of infective endocarditis can be made with 2 major criteria, or 1 major criterion and 3 minor criteria, or 5 minor criteria, according to the modified Duke criteria 9, 10, 11.
• Typical organisms from 2 separate blood cultures, such as HACEK group organisms, can be used as a major criterion for the diagnosis of infective endocarditis 11.
• Echocardiography showing oscillating intracardiac mass on valve or supporting structures, or abscess, can be used as a major criterion for the diagnosis of infective endocarditis 9, 10, 11.
• The 2015 ESC additions to major criteria include paravalvular lesions detected by cardiac CT, and abnormal activity around prosthetic valve on 18F-FDG PET/CT, which can be used to improve diagnostic sensitivity 9, 10, 11.

Minor Criteria

• Predisposition, such as predisposing heart condition or injection drug use, can be used as a minor criterion for the diagnosis of infective endocarditis 9, 10, 11.
• Fever, defined as temperature ≥38°C, can be used as a minor criterion for the diagnosis of infective endocarditis 9, 10, 11.
• Vascular phenomena, such as major arterial emboli, septic pulmonary infarcts, or mycotic aneurysm, can be used as a minor criterion for the diagnosis of infective endocarditis 9, 10, 11.

Diagnostic Approach

• The modified Duke criteria have approximately 80% sensitivity when evaluated at the end of follow-up, but lower diagnostic accuracy for early diagnosis, particularly in prosthetic valve endocarditis and pacemaker/defibrillator lead IE 9, 10.
• The American Heart Association recommends that clinicians use their judgment when diagnosing infective endocarditis, and may appropriately decide to treat regardless of whether the modified Duke criteria are met 11, 12.