Endocarditis: the complementary roles of CT and echocardiography

In-hospital mortality from infective endocarditis remains high, ranging from 9.6 to 26%, and relates to many factors including associated co-morbidities (including previous valve replacement), the complications of endocarditis present, the micro-organism involved, and a number of echocardiographic features.¹ Currently, echocardiography remains the mainstay of imaging for diagnosis and evaluation of complications, monitoring of response to therapy, intra-operative evaluation (where relevant), and follow-up.^1,2 Indeed, three echocardiographic features are considered major criteria in the diagnosis: vegetation, abscess and new dehiscence of a prosthetic valve. Although the limitations of echocardiography are well recognised, the use of other imaging modalities for evaluation of endocarditis remains limited. Indeed, 2009 European Society of Cardiology (ESC) guidelines state that “Other advances in imaging technology have had minimal impact in routine clinical practice … alternative modes of imaging (computed tomography [CT], magnetic resonance imaging [MRI], positron emission tomography [PET], and radionuclide scanning) have yet to be evaluated in infective endocarditis”.¹ 

The case study in this issue (see pages 46–7) demonstrates a potential use of CT scanning in the diagnosis of a patient with endocarditis. Electrocardiogram (ECG)-gated multi-detector cardiac computed tomography (MDCT) scanning has been proposed by many to have potential in the evaluation of endocarditis by demonstration of vegetations, complications (coronary artery occlusion, fistulae) and peripheral embolism.³ The major limitations of the technique include availability, spatial resolution, failure to demonstrate leaflet perforations and lack of haemodynamic information (table 1). Further, CT findings have not been correlated with clinical outcomes, and radiation dosage may preclude its use for the repeated studies required for monitoring response to therapy and for follow-up. The main strengths of the technique may, however, lie in specific clinical circumstances, outlined below.

Evaluation of prosthetic valve endocarditis (PVE)

The sensitivity of transthoracic echocardiography (TTE) in PVE is relatively poor, and although transoesophageal echocardiography (TOE) is mandated in patients with suspected PVE, its diagnostic value is less than in native valve endocarditis.^1,2 MDCT is potentially superior in demonstration of prosthetic valve malfunction due to pannus and/or thrombus (in particular where multiple valve replacements are present), and may be superior in demonstration of paraprosthetic complications and vegetations.^3,4

Patients scheduled for surgery

The risks of undertaking conventional coronary angiography in patients with aortic valve endocarditis include potentially fatal embolisation during catheter manipulation. Assessment using multi-slice CT allows non-invasive coronary artery imaging, has been shown to reliably exclude significant coronary artery stenosis, demonstrate localisation and course of coronary arteries with respect to aneurysms/masses, and may be useful in patients judged to be at high risk of embolisation due to the size and/or position of their vegetations.^4,5 Further, superior visualisation by CT of the perivalvular extension (including myocardial, pericardial and coronary sinus involvement) and three-dimensional reconstruction of peri-annular tissue destruction/perivalvular pseudoaneurysm have been proposed as an aid for pre-surgical planning in complex cases of endocarditis.⁴

Negative echocardiography but high index of suspicion: enhanced imaging

Combined PET and CT with 18-F-flourodeoxyglucose has been shown to have a high sensitivity for endocarditis in one small study.⁶ Further, an additional report suggested this technique could confirm suspected endocarditis where echocardiography had been negative, simultaneously excluding a potential extra-cardiac source of infection.⁷ In another case study, a patient with previous aortic valve replacement with a permanent pacing system underwent echocardiography and standard CT with no identification of infective focus. Here, gallium single-photon emission CT (⁶⁷Ga-SPECT) imaging helped to correctly identify the prosthetic aortic value as the source of sepsis, and demonstrate resolution of changes on subsequent imaging.⁸

Evaluation of embolic complications

Case reports and small series have suggested that the main advantage of CT over echocardiography may be in the demonstration of systemic and pulmonary embolisation.^9,10 Reported central nervous system complications of endocarditis range from 20–40%, and CT scanning may be used to localise mycotic aneurysms, demonstrate haematoma, haemorrhage and cerebral abscesses. Due to limits of the technique, CT is not adequate for the diagnosis of cerebritis, microabscesses, or microinfarcts. Where suspected, MRI may be indicated.¹¹

Thus, although this case report highlights the potential use of CT scanning in the diagnosis of endocarditis, its routine use is not currently recommended. Under certain circumstances, expertly performed and interpreted CT scanning may potentially be of value in answering specific questions, and as a complementary imaging technique to echocardiography, however, widespread application should be considered
with caution.

Conflict of interest

SP has an educational contract with Medtronic

Editors’ note

See also the Case Report by Howe and Purvis on pages 46–7 of this issue.

References

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