The utility of cardiac MRI in diagnosis of infective endocarditis: preliminary results

PURPOSE

We aimed to evaluate the utility of cardiac magnetic resonance imaging (MRI) for the diagnosis of infective endocarditis (IE).

METHODS

Sixteen patients with a preliminary diagnosis of IE (10 women and six men; age range, 4–66 years) were referred for cardiac MRI. MRI sequences were as follows: echo-planar cine true fast imaging with steady-state precession (true-FISP), dark-blood fast spin echo T1-weighted imaging, T2-weighted imaging, dark-blood half-Fourier single shot turbo spin echo (HASTE), and early contrast-enhanced first-pass fast low-angle shot (FLASH). Delayed contrast-enhanced images were obtained using three-dimensional inversion recovery FLASH after 15±5 min. The MRI features were evaluated, including valvular pathologies on cine MRI and contrast enhancement on the walls of the cardiac chambers, major thoracic vasculature, and paravalvular tissue, attributable to endothelial extension of inflammation on contrast-enhanced images.

RESULTS

Fourteen valvular vegetations were detected in eleven patients on cardiac MRI. It was not possible to depict valvular vegetations in five patients. Vegetations were detected on the aortic valve (n=7), mitral valve (n=3), tricuspid and pulmonary valves (n=1). Delayed contrast enhancement attributable to extension of inflammation was observed on the aortic wall and aortic root (n=11), paravalvular tissue (n=4), mitral valve (n=2), walls of the cardiac chambers (n=6), interventricular septum (n=3), and wall of the pulmonary artery and superior mesenteric artery (n=1).

CONCLUSION

Valvular vegetation features of IE can be detected by MRI. Moreover, in the absence of vegetations, detection of delayed enhancement representing endothelial inflammation of the cardiovascular structures can contribute to the diagnosis and treatment planning of IE.The definition of infective endocarditis (IE) has now been expanded from infection of leaflets and chordae found in cardiac cavities, to infection of any structure in the heart, including the endothelial surface, valves, and myocardium, as well as prosthetic valves and implanted devices (1). Cardiac endothelium and valves are generally resistant to bacterial and fungal infection. However, some highly virulent microbial pathogens are capable of infecting normal cardiac valves (2). Animal studies suggest that the first stage of infection is endothelial damage, followed by deposition of platelet-fibrin, which sets the stage for bacterial colonization (3). Infection may also expand to the tissues surrounding the leaflets, including the sinotubular junction, annulus, myocardium, and the conduction system (1).There have been developments in treatment of IE, as well as prevention and detection of possible complications. Nevertheless, hospital mortality remains at the high rate of 20% (4). Despite advances in diagnostic methods, diagnosis is complicated as IE does not exhibit specific clinical signs in the early stage and has variable features (5). The diagnostic criteria for IE, known as the Duke criteria, were defined by Durack et al., in 1994 (6). These criteria have recently been expanded to include the use of transesophageal echocardiography and microbial antibody titers, and the proposed changes have been published and confirmed by other authors (1).While computed tomography (CT) and magnetic resonance imaging (MRI) are common modalities in diagnosis of stroke and embolic events, their functionality in cardiac pathology imaging is not entirely clear. Several studies report using MRI for diagnosis of IE (7–10), but no large series studies have been conducted to date.Diagnosis of IE by cross-sectional imaging has been restricted to depiction of valvular vegetations and other valvular pathologies. However, diagnosis of IE based on contrast enhancement pattern of the endothelial lining on MRI has not been previously studied. In the present study, in addition to the depiction of valvular pathologies on cine MRI, contrast enhancement pattern of the endothelial lining was evaluated by early and delayed contrast-enhanced images to contribute to the diagnosis of IE.