Methicillin-Resistant Staphylococcus aureus Prosthetic Valve Endocarditis: Pathophysiology, Epidemiology, Clinical Presentation, Diagnosis, and Management

Abstract

Staphylococcus aureus prosthetic valve endocarditis (PVE) remains among the most morbid bacterial infections, with mortality estimates ranging from 40% to 80%. The proportion of PVE cases due to methicillin-resistant Staphylococcus aureus (MRSA) has grown in recent decades, to account for more than 15% of cases of S. aureus PVE and 6% of all cases of PVE. Because no large studies or clinical trials for PVE have been published, most guidelines on the diagnosis and management of MRSA PVE rely upon expert opinion and data from animal models or related conditions (e.g., coagulase-negative Staphylococcus infection). We performed a review of the literature on MRSA PVE to summarize data on pathogenic mechanisms and updates in epidemiology and therapeutic management and to inform diagnostic strategies and priority areas where additional clinical and laboratory data will be particularly useful to guide therapy. Major updates discussed in this review include novel diagnostics, indications for surgical management, the utility of aminoglycosides in medical therapy, and a review of newer antistaphylococcal agents used for the management of MRSA PVE.

Keywords: methicillin-resistant Staphylococcus aureus; prosthetic valve endocarditis.

FIG 1

Prosthetic valves explanted from patients with MRSA prosthetic valve endocarditis, and received at the microbiology laboratory to perform valve culture and 16S PCR (courtesy of Mercedes Marín, Hospital General Universitario Gregorio Marañón, Madrid, Spain). Shown are a mechanical valve, a mitral ring, an aortic bioprosthesis, and a mitral bioprosthesis.

FIG 2

Pathogenesis of MRSA (methicillin-resistant Staphylococcus aureus) PVE. MSCRAMMs, microbial surface components recognizing adhesive matrix molecules.

FIG 3

An original electron scanning microscope image of a methicillin-resistant Staphylococcus aureus biofilm on a patient’s mechanical heart prosthesis. The image was prepared at both the Clinical Microbiology and Infectious Diseases Department and the Pathology Department of the Hospital General Universitario Gregorio Marañón and was taken at the National Center of Electron Microscopy (JSM 6400, CNME, Madrid, Spain).

FIG 4

Surgery image (courtesy of Gregorio Cuerpo, Cardiac Surgery, Hospital General Universitario Gregorio Marañón, Madrid). Shown is mitral prosthetic valve endocarditis caused by S. aureus.

FIG 5

Global epidemiology of MRSA involved in prosthetic valve endocarditis (PVE). The causative agents of PVE differ geographically (4, 6). Data from Wang et al. (6) were collected between June 2000 and August 2005 from 556 patients with infective prosthetic valve endocarditis in 53 sites worldwide (P = 0.003 for Staphylococcus aureus; P = 0.001 for MRSA [methicillin-resistant Staphylococcus aureus]). MSSA, methicillin-sensitive Staphylococcus aureus.

FIG 6

Electrocardiogram at 25 mm/s of a patient with aortic MRSA PVE with nonspecific findings, including tachycardia (heart rate of approximately 125 beats per minute), a first-degree block with a PR interval exceeding a duration of 0.2 s (indicated by the arrow), and ST segment changes (indicated by the circle).

FIG 7

Imaging modalities for MRSA prosthetic valve endocarditis diagnosis. (A) Transesophageal echocardiography demonstrating a 1.4- by 1.2-cm highly mobile echodensity at the ventricular side of the bioprosthetic aortic valve (indicated by the arrow), without significant valvular dysfunction. (B) Transthoracic echocardiogram image showing a parasternal view with the prosthetic aortic valve, right ventricular outflow tract, and aorta on the top; the left atrium and mitral valve at the bottom; and the left ventricle on the left. The prosthetic aortic valve is not well visualized, but there is a vegetation on the ventricular side (indicated by the circle) and anterior aortic root thickening (indicated by the arrow), suggestive of an aortic root abscess. There is also mild prosthetic aortic valve regurgitation, but it cannot be appreciated in the still image. (C) Electrocardiogram-gated multidetector CT angiography demonstrating a 4- by 8-mm vegetation on the bioprosthetic aortic valve. (D) PET/CT image at the posterior prosthetic aortic valve, after 16.29 mCi [¹⁸F]fluorodeoxyglucose uptake. The arrow notes an area of hyperintensity, suggesting a focus of inflammation or infection consistent with prosthetic valve endocarditis.