Diagnostic Strategy for Infective Endocarditis in Patients With Adult Congenital Heart Disease

Infective endocarditis (IE) is a life-threatening but relatively rare disease in the general population,^1–3 but the risk is dramatically high in patients with underlying heart disease such as congenital heart diseases.

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IE has various presentations, and the diagnostic workup is performed for patients with a clinical suspicion of typically unexplained fever or constitutive symptoms with cardiac risk.⁴ The modified Duke criteria (2 major criteria: blood culture and endomyocardial damage mainly diagnosed using echocardiography; and 5 minor criteria) are the cornerstone of IE diagnosis.⁵ Diagnosing endomyocardial damage using echocardiography is challenging in patients with prosthetic materials. Cardiac computed tomography (CT) and ¹⁸F-fluorodeoxyglucose positron emission tomography/CT (¹⁸F-FDG PET/CT) are emerging technologies being used to diagnose endomyocardial damage in patients suspected of having IE (Table).^1–3 Cardiac CT provides detailed anatomical images of perivalvular abscesses and/or aneurysms, for example. ¹⁸F-FDG PET/CT, a molecular functional imaging technique, detects inflammation in the heart and systemic inflammatory lesions caused by septic embolisms.⁶ Although ¹⁸F-FDG PET/CT is useful for diagnosing prosthetic valve endocarditis and perivalvular abscesses in left-sided IE,^7,8 its diagnostic capability is limited in patients with native valve endocarditis.^8,9 Thus, current guidelines recommend using ¹⁸F-FDG PET/CT as a supplement to the modified Duke criteria only in cases of prosthetic valve endocarditis.^1,2

Table. Comparison of Imaging Modalities Used to Diagnose Infective Endocarditis

	TTE	TEE	Cardiac CT	18F-FDG PET/CT
Mobile vegetation	++	+++	+	±
Valvular dysfunction/hemodynamics	++	++	+	−
Right-sided infection	++	+	+	++
Abscess/aneurysm	+	++	+++	+++
Prosthetic valve infection	+	+	+	++
Prosthetic conduit infection	±	±	+	++
Device infection	+	+	±	++
Contraindication	None	Esophageal pathology	Renal insufficiency, contrast allergy, pregnancy	Uncontrolled diabetes, pregnancy
Susceptibility to metallic artifacts	+++	+++	++	+
Availability	++	+	+	+/−

CT, computed tomography; ¹⁸F-FDG PET/CT, ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography; TEE, transesophageal echocardiography; TTE, transthoracic echocardiography.

Adult congenital heart disease (ACHD) cases are increasing in number due to the evolution in treatment of congenital heart disease, and consequently IE in this population is also increasing.¹⁰ Most patients with ACHD undergo cardiac surgery for implantation of prosthetic materials (prosthetic valves and/or prosthetic vascular conduits).¹¹ These patients have the highest IE risk; not only do they have a high incidence of IE, but also morbidity and mortality increases after the occurrence of IE in this population.^1,2

The use of ¹⁸F-FDG PET/CT as a diagnostic modality for IE in patients with ACHD is reasonable. Pizzi et al reported that ¹⁸F-FDG PET/CT had diagnostic accuracy in these patients.¹² However, using several diagnostic tools to diagnose this complex disease can be confusing. In this issue of the Journal, Ishikita et al¹³ further clarify the role of ¹⁸F-FDG PET/CT in the diagnostic strategy of IE in this population. Importantly, ¹⁸F-FDG PET/CT detects inflammation around prosthetic materials, which is rarely detected by echocardiography (transthoracic or transesophageal echocardiography).¹³ Additionally, ¹⁸F-FDG PET/CT is sensitive in detecting inflammatory lesions in right-sided IE.¹³ Furthermore, the clinical profile that is inappropriate for the use of ¹⁸F-FDG PET/CT is clarified.¹³ The low sensitivity of ¹⁸F-FDG PET/CT to detect vegetation on native valves is probably due to its low sensitivity for detecting highly mobile small vegetations. False-positive ¹⁸F-FDG PET/CT results may be obtained in the early postoperative period and obtained constantly in patients with prosthetic vascular grafts; intensity values may be used to discriminate true- and false-positive results.¹⁴

The sensitivity of echocardiography to detect inflammatory lesions in patients with prosthetic materials is also low; hence, in patients who have ACHD and prosthetic materials and who are clinically suspected of having IE, ¹⁸F-FDG PET/CT may be incorporated in the initial workup to increase the initial diagnostic sensitivity for IE (Figure). ¹⁸F-FDG PET/CT is not exclusive to echocardiographic, cardiac CT, and microbiological examinations; rather, it complements the other imaging modalities to diagnose IE in this population. ¹⁸F-FDG PET/CT has potential benefits as functional imaging to detect inflammation without anatomical abnormalities, whereas cardiac CT is better for depicting detailed anatomical abnormalities (Table). ¹⁸F-FDG PET/CT may be useful to assess the treatment effect in this population, especially those treated medically.¹² In patients with ACHD without prosthetic materials, ¹⁸F-FDG PET/CT may be disregarded considering its low sensitivity.

Figure.

Proposed strategy to diagnose infective endocarditis (IE) in patients with adult congenital heart disease (ACHD). The initial workup to diagnose IE in patients ACHD and prosthetic materials may incorporate ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT). Transthoracic/esophageal echocardiography and ¹⁸F-FDG PET/CT should be used in conjunction with embolic imaging, cardiac computed tomography (CT), and repeat microbiological examinations. Repeat echocardiography should be performed to observe native and left-sided valves, and ¹⁸F-FDG PET/CT should be performed to evaluate prosthetic materials, right-sided valves, and systemic embolic events. In patients with ACHD without prosthetic materials who are suspected to have IE, ¹⁸F-FDG PET/CT has low sensitivity. ¹⁸F-FDG PET/CT may be used to evaluate treatment effects in patients with prosthetic materials, especially those treated medically. TEE, transesophageal echocardiography; TTE, transthoracic echocardiography.

Most advanced medical institutions are equipped with ¹⁸F-FDG PET/CT systems; however, growing numbers of patients with ACHD may be followed up by local hospitals and those suspected of having IE may first visit hospitals that are not equipped with ¹⁸F-FDG PET/CT systems. Therefore, it is necessary to use diagnostic resources in the medical area; local hospitals initially in charge of these patients should communicate with advanced medical institutions equipped with ¹⁸F-FDG PET/CT systems for diagnosis and management of the disease.

Acknowledgment

Thanks are given to Editage (www.editage.com) for English language editing.

References

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