What is the recommended workup for a patient with suspected infective endocarditis?

Workup for Suspected Infective Endocarditis

At the first clinical suspicion of infective endocarditis, immediately obtain at least three separate sets of blood cultures from different venipuncture sites before any antimicrobial therapy, with the first and last draws spaced ≥1 hour apart, and perform transthoracic echocardiography (TTE) without delay. 1, 2

Initial Diagnostic Steps

Blood Culture Protocol

• Obtain ≥3 blood culture sets from separate venipuncture sites before initiating any antibiotics, ensuring temporal spacing of ≥1 hour between first and last draws to maximize pathogen recovery 2, 3
• Blood cultures may be negative if antibiotics were administered prior to collection, which is why pre-treatment cultures are critical 1
• In patients with Staphylococcus aureus bacteremia, echocardiography is justified given the high frequency of IE and devastating consequences once intracardiac infection is established 1

Echocardiographic Evaluation

Initial TTE:

• Perform TTE immediately as the first-line imaging modality in all patients with suspected IE 1, 3
• TTE has 70% sensitivity for detecting vegetations on native valves and 50% for prosthetic valves 1

Proceed to TEE when:

• TTE is negative or non-diagnostic but clinical suspicion remains high 1, 2
• A prosthetic heart valve or intracardiac device is present 1
• Initial TTE is positive, to rule out local complications (except in isolated right-sided native valve IE with good quality TTE and unequivocal findings) 1
• TEE provides >95% sensitivity for detecting vegetations versus 60-75% for TTE 4

Repeat echocardiography within 5-7 days if initial examination is negative but clinical suspicion remains high 1

Key Echocardiographic Findings to Identify

Target the following major diagnostic criteria 2:

• Mobile vegetations on valve leaflets
• Perivalvular abscesses or pseudoaneurysms
• New prosthetic valve dehiscence
• Severe valvular regurgitation with eccentric jets
• Flail leaflet indicating chordal rupture (triangular mobile structure prolapsing into atrium)
• Left ventricular dysfunction from acute volume overload
• Elevated LV filling pressures with pulmonary congestion

Advanced Imaging Modalities

When to employ additional imaging:

• Use when echocardiography and blood cultures are inconclusive (resulting in "possible" diagnosis or "rejected" diagnosis with persistent high suspicion) 1

18F-FDG PET/CT and Cardiac CT:

• For prosthetic valve endocarditis: 18F-FDG PET/CT evaluates abnormal metabolic activity around the prosthetic valve implantation site 1, 5
• Cardiac CT angiography: Superior to echocardiography for detecting and visualizing the full extent of paravalvular abscesses, pseudoaneurysms, or fistulae, particularly in prosthetic valves 1
• CT has 100% sensitivity, specificity, PPV, and NPV for vegetations >1 cm but only 55.5% NPV for native valve vegetations <1 cm 1
• Timing consideration: Employ these modalities early when diagnostic uncertainty exists, as delayed imaging after weeks of antibiotic therapy reduces 18F-FDG uptake intensity 1

CT Chest:

• Primary role is evaluating pulmonary complications, particularly helpful in right-sided endocarditis for demonstrating septic pulmonary infarcts and abscesses 1

Cerebral MRI:

• Employ to detect embolic events when clinically indicated 1

Multidisciplinary Team Involvement

Immediate consultation with the "Endocarditis Team" is mandatory for: 1

• Complicated IE (heart failure, abscess, embolic events, neurological complications)
• Prosthetic valve involvement
• Congenital heart disease

The team should include: 1

• Infectious disease specialist
• Cardiologist
• Cardiac surgeon
• Microbiologist
• Imaging specialists
• When needed: specialists in valve diseases, pacemaker extraction, neurologists

Critical Pitfalls to Avoid

• Never initiate empiric antibiotics before obtaining blood cultures—pre-treatment antibiotics markedly reduce culture yield and may obscure diagnosis 2, 4
• Do not rely solely on physical examination to grade valve dysfunction; quantitative echocardiographic assessment is essential for accurate severity grading and complication detection 2
• Do not delay TEE in prosthetic valve cases—TTE alone is insufficient for prosthetic valve evaluation 1
• In elderly or immunocompromised patients, maintain high index of suspicion even when fever is absent, as atypical presentations are common 1

When to Refer to Reference Center

Immediate referral for complicated IE: 1

• Heart failure
• Paravalvular abscess
• Embolic or neurological complications
• Congenital heart disease

For uncomplicated IE managed at non-reference centers: maintain regular communication with reference center and arrange consultations/visits as needed 1