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Infective endocarditis: Beyond the usual tests

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Release date: August 1, 2019
Expiration date: July 31, 2020
Estimated time of completion: 1 hour

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ABSTRACT

Infective endocarditis remains a diagnostic challenge. Although echocardiography is still the mainstay imaging test, it misses up to 30% of cases. Newer imaging tests—4-dimensional computed tomography (4D CT), fluorodeoxy­glucose positron emission tomography (FDG-PET), and leukocyte scintigraphy—are increasingly used as alternative or adjunct tests for select patients. They improve the sensitivity of clinical diagnosis of infective endocarditis when appropriately used, especially in the setting of a prosthetic valve.

KEY POINTS

  • Echocardiography can produce false-negative results in native-valve infective endocarditis and is even less sensitive in patients with a prosthetic valve or cardiac implanted electronic device.
  • 4D CT is a reasonable alternative to transesophageal echocardiography. It can also be used as a second test if echocardiography is inconclusive. Coupled with angiography, it also provides a noninvasive method to evaluate coronary arteries perioperatively.
  • Nuclear imaging tests—FDG-PET and leukocyte scintigraphy—increase the sensitivity of the Duke criteria for diagnosing infective endocarditis. They should be considered for evaluating suspected infective endocarditis in all patients who have a prosthetic valve or cardiac implanted electronic device, and whenever echocardiography is inconclusive and clinical suspicion remains high.


 

References

Prompt diagnois of infective endocarditis is critical. Potential consequences of missed or delayed diagnosis, including heart failure, stroke, intracardiac abscess, conduction delays, prosthesis dysfunction, and cerebral emboli, are often catastrophic. Echocardiography is the test used most frequently to evaluate for infective endocarditis, but it misses the diagnosis in almost one-third of cases, and even more often if the patient has a prosthetic valve.

Table 1. Imaging tests for assessment of infective endocarditis.

But now, several sophisticated imaging tests are available that complement echocardiography in diagnosing and assessing infective endocarditis; these include 4-dimensional computed tomography (4D CT), fluorodeoxyglucose positron emission tomography (FDG-PET), and leukocyte scintigraphy. These tests have greatly improved our ability not only to diagnose infective endocarditis, but also to determine the extent and spread of infection, and they aid in perioperative assessment. Abnormal findings on these tests have been incorporated into the European Society of Cardiology’s 2015 modified diagnostic criteria for infective endocarditis.1

This article details the indications, advantages, and limitations of the various imaging tests for diagnosing and evaluating infective endocarditis (Table 1).

INFECTIVE ENDOCARDITIS IS DIFFICULT TO DIAGNOSE AND TREAT

Infective endocarditis is difficult to diagnose and treat. Clinical and imaging clues can be subtle, and the diagnosis requires a high level of suspicion and visualization of cardiac structures.

Further, the incidence of infective endocarditis is on the rise in the United States, particularly in women and young adults, likely due to intravenous drug use.2,3

ECHOCARDIOGRAPHY HAS AN IMPORTANT ROLE, BUT IS LIMITED

Echocardiography remains the most commonly performed study for diagnosing infective endocarditis, as it is fast, widely accessible, and less expensive than other imaging tests.

Transthoracic echocardiography (TTE) is often the first choice for testing. However, its sensitivity is only about 70% for detecting vegetations on native valves and 50% for detecting vegetations on prosthetic valves.1 It is inherently constrained by the limited number of views by which a comprehensive external evaluation of the heart can be achieved. Using a 2-dimensional instrument to view a 3-dimensional object is difficult, and depending on several factors, it can be hard to see vegetations and abscesses that are associated with infective endocarditis. Further, TTE is impeded by obesity and by hyperinflated lungs from obstructive pulmonary disease or mechanical ventilation. It has poor sensitivity for detecting small vegetations and for detecting vegetations and paravalvular complications in patients who have a prosthetic valve or a cardiac implanted electronic device.

Transesophageal echocardiography (TEE) is the recommended first-line imaging test for patients with prosthetic valves and no contraindications to the test. Otherwise, it should be done after TTE if the results of TTE are negative but clinical suspicion for infective endocarditis remains high (eg, because the patient uses intravenous drugs). But although TEE has a higher sensitivity than TTE (up to 96% for vegetations on native valves and 92% for those on prosthetic valves, if performed by an experienced sonographer), it can still miss infective endocarditis. Also, TEE does not provide a significant advantage over TTE in patients who have a cardiac implanted electronic device.1,4,5

Regardless of whether TTE or TEE is used, they are estimated to miss up to 30% of cases of infective endocarditis and its sequelae.4 False-negative findings are likelier in patients who have preexisting severe valvular lesions, prosthetic valves, cardiac implanted electronic devices, small vegetations, or abscesses, or if a vegetation has already broken free and embolized. Furthermore, distinguishing between vegetations and thrombi, cardiac tumors, and myxomatous changes using echocardiography is difficult.

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