What is the appropriate workup for suspected infective endocarditis?

Workup for Infective Endocarditis

When you suspect infective endocarditis, immediately obtain at least 3 sets of blood cultures from separate venipuncture sites (with the first and last drawn at least 1 hour apart) and perform transthoracic echocardiography (TTE) expeditiously 1.

Blood Cultures: The Microbiological Foundation

Obtain at least 3 blood culture sets from separate venipuncture sites, with the first and last samples drawn at least 1 hour apart 1. The 2023 Duke-ISCVID criteria have removed strict timing requirements between cultures, but spacing them remains clinically prudent 2. These cultures are critical for identifying the causative organism and guiding antimicrobial therapy.

For culture-negative cases, consider expanded microbiological testing including:

• Enzyme immunoassay for Bartonella species
• Polymerase chain reaction (PCR)
• Amplicon/metagenomic sequencing
• In situ hybridization 2

Echocardiography: The Imaging Cornerstone

Initial TTE Approach

Start with TTE in all suspected cases 1. TTE should be performed expeditiously as it provides the first echocardiographic assessment for vegetations, valvular regurgitation, abscess formation, and prosthetic valve dehiscence—all major Duke criteria 1.

When to Proceed to TEE

Proceed immediately to transesophageal echocardiography (TEE) if:

• TTE is negative but clinical suspicion remains high
• Patient has prosthetic valves
• Patient has intracardiac devices
• New atrioventricular block is present
• TTE windows are suboptimal (chronic obstructive lung disease, prior thoracic surgery, morbid obesity)
• Complications are suspected 1

Critical pitfall: A negative TTE in high-risk patients (prosthetic valves, previous endocarditis, new murmur, heart failure) does not exclude IE—TEE must follow 1.

Advanced Multimodality Imaging

For cases with prosthetic material or when echocardiography is inconclusive, add cardiac imaging with:

• 18F-fluorodeoxyglucose PET/CT (particularly valuable for prosthetic valve endocarditis)
• Cardiac CT (excellent for assessing perivalvular extension and complications)
• Cardiac MRI 3, 2, 4

The 2023 Duke-ISCVID criteria now include PET/CT and cardiac CT as major imaging criteria, reflecting their proven diagnostic value 2. These modalities have become part of major society guidelines for diagnostic workup 3, 5.

Clinical Assessment: High-Risk Features to Identify

Actively search for these high-risk factors that should trigger IE workup:

• Injection drug use (past or current)—the most critical red flag 6
• Prior endocarditis (the most common risk factor) 6, 7
• Prosthetic heart valves or transcatheter valve implants 2
• Intracardiac devices 2
• Structural heart disease 6
• Recent cardiac surgery or catheter-related bloodstream infections with S. aureus 1
• Poor dentition or recent dental procedures 6

Look for these clinical manifestations:

• Fever (present in majority but may be absent initially) 6
• New or changing murmur 1
• Embolic phenomena: neurological deficits, shortness of breath, multiple sites of infection 6, 8
• Immunologic phenomena (though Roth spots, Janeway lesions, Osler nodes are uncommon) 6

Diagnostic Framework: Modified Duke Criteria

Use the 2023 Duke-ISCVID criteria as your diagnostic schema, which includes:

Major criteria:

• Positive blood cultures (≥2 sets with typical organisms)
• Imaging evidence (vegetation, abscess, dehiscence on echo/CT/PET)
• Intraoperative visualization (newly added) 2

Minor criteria include: predisposing conditions, fever, vascular/immunologic phenomena, and microbiological evidence not meeting major criteria 1.

Important caveat: The Duke criteria serve as a guide but must not replace clinical judgment 1. You may appropriately decide to treat a patient regardless of whether they meet formal criteria, particularly in high-risk scenarios.

Timing and Urgency

The diagnosis must be made as soon as possible to initiate empirical antibiotic therapy and identify high-risk patients who may need early surgery 1. In high-suspicion cases (injection drug use, S. aureus bacteremia, prior IE), presume IE and begin workup before culture results return 1.

For patients meeting sepsis criteria, initiate intravenous antimicrobials within one hour while completing diagnostic workup 8.

When Echocardiography is Negative

If TTE is negative and clinical suspicion is low, search thoroughly for alternative sources of fever and sepsis 1. However, if risk factors are present or suspicion remains, do not stop—proceed to TEE and consider advanced imaging 1.