Echocardiography in MRSA Bacteremia with Septic Emboli
In a patient with MRSA bacteremia and septic emboli, obtain a transthoracic echocardiogram (TTE) immediately, followed by transesophageal echocardiogram (TEE) regardless of TTE findings, as the presence of embolic phenomena mandates comprehensive evaluation for infective endocarditis and its complications. 1
Immediate Echocardiography Protocol
Start with TTE
- Perform TTE as soon as infective endocarditis is suspected in any patient with MRSA bacteremia, given the high virulence of S. aureus and its devastating effects once intracardiac infection is established. 1
- TTE is the recommended first-line imaging modality (Class I, Level B recommendation). 1
- In S. aureus bacteremia specifically, echocardiography should be considered in all adult patients (Class IIa, Level B recommendation). 1
Proceed to TEE
- TEE is mandatory in your patient because septic emboli are present. The 2015 ESC Guidelines explicitly state that repeat TTE and/or TEE are recommended as soon as a new complication of IE is suspected, including embolism (Class I, Level B recommendation). 1
- TEE should be performed even when TTE is positive to rule out local complications such as perivalvular abscess, valve perforation, or additional vegetations. 1
- TEE has 76-100% sensitivity for detecting vegetations compared to only 50-60% for TTE, making it essential when endocarditis is likely. 2
Why Both Studies Are Needed in Your Patient
High-Risk Features Present
- Embolic phenomena (septic emboli) place your patient in the "complicated bacteremia" category, requiring 4-6 weeks of therapy rather than 2 weeks for uncomplicated cases. 1
- Up to 25% of patients with infective endocarditis present with embolic complications at diagnosis, and emboli occur in 30% of IE patients overall. 1
- A prospective study of 103 patients with S. aureus bacteremia found that TEE detected IE in 25% of cases, with TTE missing 68% of these diagnoses. 3
Detection of Complications
- TEE is superior for identifying perivalvular abscesses, valve perforations, and prosthetic valve dysfunction—complications that dramatically alter surgical decision-making. 4
- In patients with persistent bacteremia (≥48 hours), which carries a 90-day mortality risk of 39%, TEE is essential for risk stratification. 5
Timing Considerations
Immediate Imaging
- Perform TTE within 24 hours of identifying MRSA bacteremia with emboli. 1
- Proceed to TEE within 24-48 hours, or sooner if TTE is non-diagnostic or shows vegetations requiring complication assessment. 1
Repeat Imaging
- If initial echocardiography is negative but clinical suspicion remains high (persistent fever, ongoing positive blood cultures, new embolic events), repeat TTE and/or TEE within 5-7 days. 1
- A negative TEE does not completely exclude IE in high-risk patients; one study found 5 of 65 patients with initially negative TEE ultimately had proven endocarditis. 6
Critical Pitfalls to Avoid
Don't Skip TEE Based on Negative TTE
- TTE alone is insufficient in MRSA bacteremia with emboli. TTE has only 32% sensitivity for detecting IE in S. aureus bacteremia, while adding TEE increases sensitivity to 100%. 3
- TEE detected evidence of IE in 21% of patients with indeterminate TTE findings. 3
Don't Delay for Clinical Improvement
- Even if fever resolves with antibiotics, proceed with planned echocardiography, as vegetations and complications may still be present. 1
- Death due to sepsis is significantly more likely in patients with IE (15%) compared to those without (3%), making early diagnosis critical. 3
Additional Diagnostic Steps
- Obtain at least 2 sets of blood cultures before starting antibiotics, and repeat cultures 2-4 days after initial positive cultures to document clearance of bacteremia. 1
- Perform additional imaging (CT or MRI) based on symptoms to identify other metastatic infection sites such as vertebral osteomyelitis, epidural abscess, or splenic abscess. 5