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When does S aureus bacteremia require transesophageal echocardiography?

Aibek E. Mirrakhimov, MD, Michael E. Jesinger, MD, Taha Ayach, MD and Adam Gray, MD
Cleveland Clinic Journal of Medicine July 2018, 85 (7) 517-520; DOI: https://doi.org/10.3949/ccjm.85a.16095

Staphylococcus aureus is the most common infective agent in native and prosthetic valve endocarditis, and 13% to 22% of patients with S aureus bacteremia have infective endocarditis.1

See related editorial, page 521

Transthoracic echocardiography (TTE) is a good starting point in the workup of suspected infective endocarditis, but transesophageal echocardiography (TEE) plays a key role in diagnosis and is indicated in patients with a high pretest probability of infective endocarditis, as in the following scenarios:

  • Clinical picture consistent with infective endocarditis

  • Presence of previously placed port or other indwelling vascular device

  • Presence of a prosthetic valve or other prosthetic material

  • Presence of a pacemaker

  • History of valve disease

  • Injection drug use

  • Positive blood cultures after 72 hours despite appropriate antibiotic treatment

  • Abnormal TTE result requiring better visualization of valvular anatomy and function and confirmation of local complications

  • Absence of another reasonable explanation for S aureus bacteremia.

Forgoing TEE is reasonable in patients with normal results on TTE, no predisposing risk factors, a reasonable alternative explanation for S aureus bacteremia, and a low pretest probability of infective endocarditis.1 TEE may also be unnecessary if there is another disease focus requiring extended treatment (eg, vertebral infection) and there are no findings suggesting complicated infective endocarditis, eg, persistent bacteremia, symptoms of heart failure, and conduction abnormality.1

TEE also may be unnecessary in patients at low risk who have identifiable foci of bacteremia due to soft-tissue infection or a newly placed vascular catheter and whose bacteremia clears within 72 hours of the start of antibiotic therapy. These patients may be followed clinically for the development of new findings such as metastatic foci of infection (eg, septic pulmonary emboli, renal infarction, splenic abscess or infarction), the new onset of heart failure or cardiac conduction abnormality, or recurrence of previously cleared S aureus bacteremia. If these should develop, then a more invasive study such as TEE may be warranted.

INFECTIVE ENDOCARDITIS: EPIDEMIOLOGY AND MICROBIOLOGY

The US incidence rate of infective endocarditis has steadily increased, with an estimated 457,052 hospitalizations from 2000 to 2011. During that period, from 2000 to 2007, there was a marked increase in valve replacement surgeries.2 This trend is likely explained by an increase in the at-risk population—eg, elderly patients, patients with opiate dependence or diabetes, and patients on hemodialysis.

Although S aureus is the predominant pathogen in infective endocarditis,2–5 S aureus bacteremia is often observed in patients with skin or soft-tissue infection, prosthetic device infection, vascular graft or catheter infection, and bone and joint infections. S aureus bacteremia necessitates a search for the source of infection.

S aureus is a major pathogen in bloodstream infections, and up to 14% of patients with S aureus bacteremia have infective endocarditis as the primary source of infection.3 The pathogenesis of S aureus infective endocarditis is thought to be mediated by cell-wall factors that promote adhesion to the extracellular matrix of intravascular structures.3

A new localizing symptom such as back pain, joint pain, or swelling in a patient with S aureus bacteremia should trigger an investigation for metastatic infection.

Infectious disease consultation in patients with S aureus bacteremia is associated with improved outcomes and, thus, should be pursued.3

A cardiac surgery consult is recommended early on in cases of infective endocarditis caused by vancomycin-resistant enterococci, Pseudomonas aeruginosa, and fungi, as well as in patients with complications such as valvular insufficiency, perivalvular abscess, conduction abnormalities, persistent bacteremia, and metastatic foci of infection.6

RISK FACTORS

Risk factors for infective endocarditis include injection drug abuse, valvular heart disease, congenital heart disease (unrepaired, repaired with residual defects, or fully repaired within the past 6 months), previous infective endocarditis, prosthetic heart valve, and cardiac transplant.2–4,6 Other risk factors are poor dentition, hemodialysis, ventriculoatrial shunts, intra-vascular devices including vascular grafts, and pacemakers.2,3 Many risk factors for infective endocarditis and S aureus bacteremia overlap.3

DIAGNOSTIC PRINCIPLES

The clinical presentation of infective endocarditis can vary from a nonspecific infectious syndrome, to overt organ failure (heart failure, kidney failure), to an acute vascular catastrophe (arterial ischemia, cerebrovascular accidents, myocardial infarction). Patients may present with indolent symptoms such as fever, fatigue, and weight loss,6 or they may present at an advanced stage, with fulminant acute heart failure due to valvular insufficiency or with arrhythmias due to a perivalvular abscess infiltrating the conduction system. Extracardiac clinical manifestations may be related to direct infective metastatic foci such as septic emboli or to immunologic phenomena such as glomerulonephritis or Osler nodes.

Thus, a thorough review of systems is important to screen for signs of complications (eg, edema, changes in urine output and appearance) and metastatic infection (eg, splenic infarction, splenic abscess, psoas muscle abscess, vertebral infection).

The diagnosis of infective endocarditis does not rely solely on echocardiographic findings or other imaging studies; it is a clinical diagnosis based on the modified Duke criteria, which incorporate clinical, laboratory and microbiologic findings (Tables 1 and 2).7 Most patients with infective endocarditis have both clinical and imaging evidence of it.

View this table:
TABLE 1

Modified Duke criteria for infective endocarditis

View this table:
TABLE 2

Applying the Duke criteria for infective endocarditis

ECHOCARDIOGRAPHY’S ROLE IN DIAGNOSIS

TTE plays an important role in diagnosis and risk stratification of infective endocarditis.6 TTE is usually done first because of its low cost, wide availability, and safety; it has a sensitivity of 70% and a specificity over 95%.8 While a normal result on TTE does not completely rule out infective endocarditis, completely normal valvular morphology and function on TTE make the diagnosis less likely.8,9

If suspicion remains high despite a normal study, repeating TTE at a later time may result in a higher diagnostic yield because of growth of the suspected vegetation. Otherwise, TEE should be considered.

TEE provides a higher spatial resolution and diagnostic yield than TTE, especially for detecting complex pathology such as pseudoaneurysm, valve perforation, or valvular abscess. TEE has a sensitivity and specificity of approximately 95% for infective endocar-ditis.8 It should be performed early in patients with preexisting valve disease, prosthetic cardiac material (eg, valves), or a pacemaker or implantable cardioverter-defibrillator.6,7

Detecting valve vegetation provides answers about the cause of S aureus bacteremia with its complications (eg, septic emboli, mycotic aneurysm) and informs decisions about the duration of antibiotic therapy and the need for surgery.3,6

As with any diagnostic test, it is important to compare the results of any recent study with those of previous studies whenever possible to differentiate new from old findings.

WHEN TO FORGO TEE IN S AUREUS BACTEREMIA

Because TEE is invasive and requires the patient to swallow an endoscopic probe,10 it is important to screen patients for esophageal disease, cervical spine conditions, and baseline respiratory insufficiency. Complications are rare but include esophageal perforation, esophageal bleeding, pharyngeal hematoma, and reactions to anesthesia.10

As with any diagnostic test, the clinician first needs to consider the patient’s pretest probability of the disease, the diagnostic accuracy, the associated risks and costs, and the implications of the results.

While TEE provides better diagnostic images than TTE, a normal TEE study does not exclude the diagnosis of infective endocarditis: small lesions and complications such as paravalvular abscess of a prosthetic aortic valve may still be missed. In such patients, a repeat TEE examination or additional imaging study (eg, gated computed tomographic angiography) should be considered.6

Noninfective sterile echodensities, valvular tumors such as papillary fibroelastomas, Lambl excrescences, and suture lines of prosthetic valves are among the conditions and factors that can cause a false-positive result on TEE.

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