Prosthetic Valve Endocarditis Detection of Vegetation

Endocarditis can affect bioprosthetic or mechanical heart valves as well as indwelling central lines and pacemaker wires. Vegetations have a predilection to affect the sewing ring of both the bioprosthetic and mechanical valves, although the leaflets of the bioprosthetic valve can also be involved. The presence of new perivalvular regurgitation is generally indicative of IE. Echocardiographic evaluation of endocarditis in the setting of prosthetic valves can be more challenging due to the reverberations created by prosthetic material.

Transthoracic Echo

The sensitivity of TTE for diagnosing endocarditis is lower for prosthetic valves than for native valves (Table 7.13) [50-52]. Trans-thoracic echo detects evidence of prosthetic valve endocarditis in only about a third of the cases. Therefore TEE should be performed if prosthetic valve endocarditis is suspected even though TTE shows no evidence to support the diagnosis. False-positive echocardiographic findings for IE in the setting of prosthetic valves include echogenic masses of non-infectious origin such as sutures, pannus, and thrombus. Correlation with clinical and microbiological data is required to avoid misdiagnosis. For bio-prostheses, the main cause of false positives is non-infectious degeneration of bioprosthetic valve leaflets [52]. Typically degenerated bio-prosthetic valve cusp has bright and echodense nodules which can therefore be distinguished from the soft, shaggy, mobile echodensity more typical of a vegetation.

Transesophageal Echo

Transesophageal echo is more sensitive and specific for evidence of prosthetic valve endocarditis compared to TTE (Figure 7.14). While TTE detects prosthetic valve endocarditis in about a third of the cases, the sensitivity of TEE for detecting prosthetic valve IE is 77% to 100% (Table 7.13). The most common situation where

Table 7.12. Indications for Transesophageal Echocardiography in Injection Drug Users with Suspected Right-Sided Endocarditis.

Poor transthoracic images

History of prior endocarditis

Preexisting valve abnormalities

Suspected left-sided endocarditis

Suspected pulmonic valve endocarditis

Patients considered to have possible endocarditis and negative TTE

TTE = transthoracic echocardiogram.

Reproduced from Chan, KL, Echocardiography in right sided endocarditis (Editorial) Clin Invest Med. 2002 Aug; 25(4): 134—6,with permission from the Canadian Society for Clinical Investigation.

Table 7.13. Comparison of Transthoracic with Transesophageal Echocardiography in the Diagnosis of Prosthetic Valve Endocarditis

Sample Sensitivity Sensitivity References size of TTE (%) of TEE (%)

Mugge etal.,1989 [50] 22 27 77

Taams etal.,1990 [51] 12 25 100

TEE = transesophageal echocardiography, TTE = transthoracic echocardiography.

Figure 7.14. A vegetation involving a leaflet of a bioprosthetic aortic valve on transesophageal echocardiography. Also present is an aortic root pseudoaneurysm.

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TEE misses evidence of IE is in patients with aortic prosthetic valves [52]. This problem is magnified in the setting of aortic prosthetic valve infection when there is also a mitral prosthesis, as reverberations from the mitral prosthesis can mask the aortic prosthesis. For bioprostheses, the enhanced image quality of TEE often allows visualization of degenerative leaflets in greater detail than TTE. The bright echogenic appearance of degenerating biopros-thetic valve cusps can usually be distinguished from valvular vegetation (Figure 7.15). The high image quality of TEE images often reveals bright filaments on the sewing rings, which are generally non-infectious in origin and are readily distinguished from vegetation. Prosthetic valve strands are thin (< 1 mm) mobile echodensities of variable length, and pathological examination suggests that these strands are composed of collagen rather than vegetation [53]. Prosthetic valve thrombosis appears indistinguishable from vegetation on TEE. It is important to combine TEE imaging data with clinical and laboratory evidence of infection to distinguish thrombus from vegetation due to endocarditis.

Figure 7.15. Degenerative changes of an aortic homograft mimicking vegetations on transesophageal echocardiography.

Figure 7.15. Degenerative changes of an aortic homograft mimicking vegetations on transesophageal echocardiography.

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The presence of a periprosthetic regurgitation, if it is a new finding, raises the possibility of IE, underscoring the importance of baseline echo study in patients with prosthetic valves (Figure 7.16). Trace to mild perivalvular regurgitation is not uncommon in patients with prosthetic valves and no IE. The finding of an isolated, tiny perivalvular leak with no other echo findings of endocarditis in the setting of a prosthesis should be interpreted with caution [54]. In bileaflet mechanical valves, normal prosthetic regurgitation is eccentric and should not be confused with perivalvular leak.

Summary

1. TTE is specific but insensitive for the diagnosis of prosthetic valve endocarditis.

2. TEE is more sensitive and specific for prosthetic valve endocarditis than TTE. Most patients with prosthetic valves and suspected IE should have TEE.

3. Important false positive TEE findings include echodensities of non-infectious origin such as prosthetic valve strands, thrombi, and degenerating changes on bioprosthetic leaflets.

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Figure 7.16. Localized dehiscence of a mechanical mitral valve on transesophageal echocardiography (A). Color flow imaging shows the perivalvular mitral regurgitation traversing the defect (B).

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