Appropriate Use of Echo and Suggested Approach to a Patient Suspected of Having Endocarditis

The meaning and significance of the term "clinically suspected IE" will vary between observers. The range may include patients with unexplained isolated fever as well as those with the classic findings of fever, new regurgitant murmur, embolic phenomenon, and persistent bacteremia. Jassal et al., at our institution, found significant variation between the assessment of probability of IE between the attending team and the research team [32]. The latter employed a standardized scoring system to determine pre-test likelihood of IE. The determination of probability or likelihood of disease may have a bearing on the selection and timing of echocardioaphic evaluation [33]. Various studies have demonstrated no to very minimal utility of echocar-diography in patients with low pretest likelihood of the disease [32-34].

In practice, we propose that the selection and timing of echocardiographic evaluation (TTE, TEE, both) be based on an assessment of the clinical likelihood of IE as well as the clinical risk of an adverse event (see Figure 6.5) [20,35]. Although systematic prospective evaluation of the utility of echocardiography in different patient subsets has not been well defined, we operationally define high clinical risk as any one of a number of high-risk features which include any of the following:

Table 6.4. Modified Duke Criteria for Diagnosis of Infective Endocarditis

Major Criteria

Positive blood cultures for infective endocarditis

In the absence of a primary focus, positive cultures from two separate blood cultures of one of the following typical organism:

Streptococci viridans Streptococcus bovis

HACEK group (Haemophilus species, Actinobacillus actinomycetes comitants, Cardiobacterium hominis, Eikenlla species, Kingella kingae) Community-acquired Staphylococcus aureus or entercocci

Persistently positive blood cultures of a microorganism consistent with IE

Single blood culture for Coxiella burnetii or antiphase I IgG antibody titre > 1:800. Evidence of endocardial involvement New valvular regurgitation

Positive echocardiogram (oscillating intracardiac mass in the absence of an alternative anatomic explanation OR abscess OR new partial dehiscence of prosthetic valve)

Minor criteria

Predisposing heart condition OR intravenous drug use Fever(at least 38.0 °C)

Vascular phenomena (major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhage,Janeway lesions) Immunologic phenomena (glomerulonephritis, Osler's nodes, Roth spots, rheumatoid factor)

Microbiologic evidence of positive blood culture not meeting major criterion but excluding single positive culture for coagulase negative Staphylococci and organisms that do not cause endocarditis OR serologic evidence of active infection with organism consistent with IE.


Two major criteria

One major and three minor criteria

Five minor criteria

Microorganism demonstrated by culture or histology of a vegetation, embolized vegetation or in an intracardiac abscess

Histologic evidence of active endocarditis (vegetation or intracardiac abscess)


One major and one minor critieria

Three minor criteria Rejected

Firm alternative diagnosis

Resolution of manifestations of endocarditis with 4 or less days of antibiotics

No pathologic evidence of infective endocarditis at surgery or autopsy after 4 or less days of antibiotics

Does not meet criteria for possible infective endocarditis (above) Source:Adapted from [26].

1) hemodynamic compromise from suspected significant valvular abnormality (e.g., shock, CHF, clinical evidence of prosthetic valve dysfunction)

2) overwhelming infection (persistent fever despite treatment, new heart block or suppu-rative pericarditis suggesting periannular abscess, persistent S. aureus bacteremia)

3) underlying valvular abnormality known to be poorly responsive to medical treatment (e.g., prosthetic valve, AV shunt)

4) multiple embolic phenomenon.

The patients with evidence of high clinical risk features deserve prompt echocardiographic evaluation that may lead to important and

Suspected IE

Preliminary clinical assessment of risk (see text)

Echo only if deterioration

Complete clinical assessment

Likelihood category (see text)

Intermediate High

TTE IE clinically confirmed

TEE as needed ^ +A TEE to assess complications and prognosis


TEE as needed

Echo only if deterioration

Figure 6.5. Suggested diagnostic algorithm for a patient with suspected infective endocarditis.

timely medical or surgical intervention. Although we still recommend baseline TTE in all patients, there should be a very low threshold to proceed to TEE in this high-risk group, especially in the setting of persistent S. aureus bacteremia or suspected prosthetic valve endocarditis. These special circumstances will be discussed later in this chapter.

In patients with more stable status (low clinical risk), we recommend waiting for the results of initial blood culture and full evaluation of the clinical criteria before embarking on the use of echocardiography. Often, the results of blood cultures and other tests are available within the first few days. This will allow stratification of patients into high-likelihood (confirmed diagnosis), intermediate-likelihood, and low-likelihood groups prior to echocardiography [32]. It must be remembered that any low-risk patient may deteriorate to high-risk over time; serial careful clinical assessment is therefore required. In addition, although the diagnostic yield of echocardiography is generally felt to be very low in patients with objectively derived low clinical likelihood, diagnostic tests may still be requested on occasion by physicians for the pur pose of reassurance to themselves or their patients [32]. A diagnostic algorithm is presented (see flow chart, Figure 6.5).

Low-likelihood patients (no major Duke criteria, 0-2 minor criteria) should be observed only [32]. In those patients who are found to have an alternative source of infection, treatment should be directed to that source and echocardiography (TTE and TEE) safely deferred unless there is a clinical change [33,34].

A high-likelihood patient—based upon the constellation of clinical and bacteriologic criteria (two major Duke criteria or 1 major and 3 minor)—should be treated as a confirmed case of IE with a prolonged course of antibiotics [32]. Echocardiography (TTE) should be performed promptly to help determine prognostic information that may help with timing of surgery. Routine TEE in this population remains uneval-uated, and should be at the discretion of the clinical team in consultation with the echocardi-ologist.

The intermediate likelihood subgroup where the diagnosis of IE is suspected but not confirmed on clinical and bacteriologic grounds is a sample in whom the addition of a positive

Table 6.5. High-Risk Features for Presence of Endocarditis in Patients with S. aureus Bacteremia

Community-acquired infection Absence of apparent source of infection Presence of metastatic infectious foci Presence of hematuria

Underlying native valvular disease or known prosthetic valves Previous endocarditis Intravenous drug use Persistent fever at 72 hours.

Persistent bacteremia, usually 3 days after initiation of therapy echo finding would greatly assist in establishing a firm diagnosis of IE. We define intermediate likelihood as one major criterion or three minor criteria prior to echocardiography [32]. There is some controversy in determining the best initial echocardiographic strategy in this population. The American College of Cardiology/ American Heart Association guidelines recommend that such patients be evaluated initially with TTE [36]. In those who have indeterminate studies, TEE should be pursued. This is supported by our experience [22]. Heidenreich et al. suggest initial use of TEE for the population with pretest likelihood between 4% and 60% [37]. In practice, the choice of modality depends on the anticipated image quality in the individual patient and the practical setup of the individual laboratory. TEE requires additional personnel and training and has small but finite risk of procedural complication as well as failed esophageal intubation [38]. Further larger prospective comparative evaluations using modern-day TTE equipment are required [21,22]. In the intermediate likelihood subgroup, a negative TTE or TEE does not necessarily exclude the diagnosis of IE [21,35]. A subset of these patients with negative echo findings (TTE, TEE) may still manifest positive findings with time [19]. Occasionally, a firm alternative diagnosis is subsequently discovered by other means [35].

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