Native Valve Endocarditis Detection of Vegetation

Vegetation is the hallmark of the disease and most frequently is attached to the upstream side of the cardiac valves. Unusual locations such as

Table 7.1. Indications for Echocardiography in Infective Endocarditis

Diagnosis in patients with medium to high likelihood of endocarditis Strong suspicion for culture negative endocarditis Persistent bacteremia with virulent organism and no known cause High-risk patients including patients with prior endocarditis, congenital heart disease or prosthetic heart valve Prognosis and management issues

Identify underlying valvular and non-valvular lesions and associated abnormalities

Assess hemodynamic severity and ventricular function Reassessment in complicated cases including clinical change and symptomatic deterioration the myocardium or aorta have been recognized. Left atrial mural vegetations have been found at the site of impingement of a jet of mitral regurgitation due to infectious endocarditis. The finding of a mural vegetation on the left atrial wall should prompt a careful search for evidence of mitral valve endocarditis and mitral regurgitation. The ability of ultrasound to produce images of the heart offers clinicians the opportunity to identify valvular vegetations, which previously required direct inspection at surgery or autopsy.

Transthoracic Echo

The first series describing vegetations detected by echocardiography with pathological correlation was in 1973 using M-mode transthoracic echocardiography (TTE). The M-mode criteria for diagnosis of a valvular vegetation are a nonuniform, shaggy echogenic mass attached to a valve leaflet but not interfering with its motion [1-4]. When compared to autopsy or surgical findings, this definition of vegetation is specific but insensitive [3]. False-positive findings include old vegetations from remote episodes of endocarditis, thickened leaflets of myxomatous mitral valves, sclerotic aortic valves and mitral valve fluttering related to aortic insufficiency [3]. Important prognostic information can be derived from findings such as ruptured mitral valve chordae, torn and flail aortic cusps, and premature closure of the mitral valve due to severe aortic insufficiency, all of which may require surgical intervention [5].

Two-dimensional echocardiography provides spatial orientation superior to M-mode and has rapidly replaced M-mode in the detec tion of vegetation, which is defined as an irregularly shaped echogenic mass adherent to valves, endothelial surfaces, or intracardiac prosthetic devices often with high-frequency motion independent of the underlying cardiac structure. Usually it can be imaged throughout the cardiac cycle in multiple views [6-8]. Vegetations can be characterized by morphologic features including size, location, number, shape, mobility, and consistency (Figure 7.1) [8]. The size of a vegetation that can be detected by TTE depends on the image quality. With fundamental imaging, 90% of vegetations diagnosed on TTE are greater than 5 mm in maximum dimension [8]. Harmonic imaging may be more able to detect smaller vegetations particularly in patients with suboptimal images [9]. However, TTE (with and without harmonics) underestimates vegetation size by up to 50% compared to TEE [9], and TTE is not sensitive enough to detect small vegetations particularly in patients with preexisting valvular abnormalities (Table 7.2) [10,11]. The causes of false-negative and false-positive findings for vegetations are listed in Table 7.3.

The overall sensitivity and specificity of TTE for detecting valvular vegetations are 48% and 94%, respectively (Table 7.4). These are average values from a number of series published over the past two decades using a variety of ultrasound machines in patients with varying pre-test likelihoods of endocarditis [10-15]. For many series, the pre-test likelihood of endocarditis was high, which may contribute to an overestimation of the specificity of transthoracic echo findings for vegetations.

Transesophageal Echo

Transesophageal echo (TEE) involves the insertion of an ultrasound transducer mounted on a gastroscope into the esophagus and stomach to image the heart. The close proximity of the heart to the esophagus and the lack of intervening structures such as chest wall and lungs ensure higher image quality using TEE compared to TTE. Transesophageal echo has higher sensitivity and specificity in the detection of vegetations in patients with suspected endocarditis (Table 7.5) [10,12-15]. The superior image quality of TEE permits the visualization of small vegetations

Figure 7.1. A long filamentous vegetation attaching to the aortic valve and protruding into the left ventricular outflow tract during diastole. This is detected by both transthoracic (A) and transesophageal (B) echocardiography.

Figure 7.1. A long filamentous vegetation attaching to the aortic valve and protruding into the left ventricular outflow tract during diastole. This is detected by both transthoracic (A) and transesophageal (B) echocardiography.

Endocarditis Small Vegitation

Table 7.2. Relationship Between Vegetation Size and Sensitivity of

Transthoracic Echocardiography*

Vegetation size (mm) Sensitivity (%)

5-10 50-69

*Based on studies by Erbel et al., 1988, and Reynolds et al., 2003,with transesophageal echocardiographic findings used as the reference standard.

(2-5 mm) on native heart valves that are commonly missed by TTE (Figure 7.2) [10,11]. Despite the superior image quality, TEE faces similar limitations in terms of false-positive and false-negative studies (Table 7.3). Libman-Sacks endocarditis refers to the case of vegetations that occur on the valves of patients with systemic lupus erythematosus (SLE) in the absence of infection [16]. Pathologically these vegetations

Table 7.3. Pitfalls in the Detection of Vegetations by Echocardiography

Mimics of vegetation (false positives) Preexisting valvular abnormalities Sequelae of prior valve surgery Components of prosthetic valves Normal structures Thrombi Tumor

Extrinsic mediastinal masses Artifacts

Vegetation not detected (false negatives) Preexisting valvular abnormalities Prior endocarditis Prosthetic material Suboptimal images Early disease with small vegetation are made up of inflammatory cells associated with fibrous tissue and fibrin. They appear as small protrusions usually 2 to 4 mm in diameter adherent to endocardium, more frequently at valve commisures [16]. Echo studies of patients with SLE have documented these non-infectious vegetations in up to 18% of patients [17]. They are indistinguishable from vegetations due to IE; therefore the clinical context is essential to avoid misdiagnosis of infectious endocarditis. Anti-phospholipid antibody syndrome can be seen as an isolated clinical entity or in association with SLE and also causes Limans-Sachs vegetations [18]. Nonbacterial thrombotic endocarditis refers to the occurrence of noninfective valvular vegetations in the setting of metastatic cancer, and their echocardiographic appearance is indistinguishable from infectious vegetations [19]. In the setting of preexisting valvular disease such as severe myxomatous changes, detection of vegetation can be difficult. False-negative TEE studies can occur in the early stage of endocarditis which has not resulted in a vegetation large enough to permit visualization by TEE. In such situations, a repeat TEE in 7-14 days can increase the sensitivity for detecting valvular vegetations [9,20]. The overall sensitivity of TEE for valvular vegetations is 92% and specificity is 94% (Table 7.5). Again, this is derived from series where the pre-test likelihood of endocarditis was high, which may result in an overestimate of the accuracy of TEE for diagnosis of vegetations.

Summary

1. A vegetation is an irregularly shaped echogenic mass adherent to valves, endothelial surfaces, or intracardiac prosthetic

Table 7.4. Transthoracic Echocardiography in the Diagnosis of Valvular Vegetation

Proportrion

Proportion with

Reference

Sensitivity %

Specificity %

PPV %

NPV %

with IE (%)

Prostheses (%)

Erbel etal.,1988 [10]

63

98

92

91

96/176(55)

ND

Shivley etal.,1991 [12]

44

98

88

84

16/24 (24)

3/66 (5)

Birmingham etal.,1992 [13]

30

100

100

57

33/63 (52)

2/64 (3)

Shapiro etal.,1994 [14]

60

91

86

72

30/64 (47)

0/64 (0)

Lowry etal.,1994 [15]

36

83

ND

ND

28/85 (33)

29/85 (34)

Reynolds etal.,2003 [11]

55

ND

ND

ND

51/101 (50)

ND

Average

48

94

91.5

76

254/513 (50)

34/269(13)

IE = infective endocarditis, ND =

not determined, NPV =

negative predictive value, PPV =

positive predictive value.

Table 7.5. Transesophageal Echocardiography in the Diagnosis of Valvular Vegetation

Proportrion

Proportion with

Reference

Sensitivity (%)

Specificity (%)

PPV (%)

NPV (%)

with SBE (%)

Prostheses (%)

Erbel etal.,1988 [10]

100

98

95

100

96/176(55)

ND

Shivley etal.,1991 [12]

94

100

100

98

16/24 (24)

3/66 (5)

Birmingham etal.,1992 [13]

88

97

97

88

33/63 (52)

2/64 (3)

Shapiro etal.,1994 [14]

87

91

90

88

30/64 (47)

0/64 (0)

Lowry etal.,1994 [15]

93

91

ND

ND

28/85 (33)

29/85 (34)

Average

92

95

96

94

254/513(50)

34/269 (13)

IE = infective endocarditis, ND =

not determined, NPV =

negative predictive value, PPV =

positive predictive value.

Figure 7.2. A small vegetation on the posterior mitral leaflet on transesophageal echocardiography. This is not detected by transthoracic echocardiography.

Figure 7.2. A small vegetation on the posterior mitral leaflet on transesophageal echocardiography. This is not detected by transthoracic echocardiography.

devices with high-frequency motion independent of the associated valve or prosthesis which is apparent throughout the cardiac cycle in multiple views.

2. Important causes of false-negative TTE images for endocarditis are small vegetations (< 5 mm), prosthetic valves, and poor image quality.

3. TEE is more sensitive and specific than TTE for detecting vegetations.

4. Echo findings specific for endocarditis should be used in conjunction with clinical findings to avoid misdiagnosis of endocarditis.

5. Mural vegetation can be seen on the left atrial wall in the path of mitral regurgitation jet.

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Responses

  • marco
    What size vegetation can TTE and TEE detect?
    5 years ago

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