Prosthetic valve endocarditis: clinicopathological correlates in 122 surgical specimens from 116 patients (1985-2004).
BACKGROUND
Few studies have documented the clinicopathological features of prosthetic valve endocarditis independently of native valve endocarditis.


STUDY DESIGN
Retrospective analysis of patients undergoing cardiac surgery for prosthetic valve endocarditis at our institution (1985-2004).


METHODS
Medical records and microscopic slides were reviewed from 116 patients for demographics, infecting organisms, comorbidities, and pathologic features.


RESULTS
Patients were 12-86 years old (mean, 59 years). Among 122 valves, 64% were from men and 67% were purely regurgitant. Aortic prosthetic valve endocarditis frequently affected men (76%); mitral prosthetic valve endocarditis often affected women (62%). Embolization occurred in 35% and heart failure in 32%. Prevalent predisposing conditions were the prosthetic valve alone (43%) and diabetes mellitus (20%). Prosthetic valve endocarditis was aortic or mitral in 98% and was active in 70%. Annular abscess or paravalvular leak affected mechanical valves more frequently than bioprosthetic (89% vs. 65%; P=.001). Causative organisms (n=116) included Staphylococcus aureus (30%), coagulase-negative staphylococcus (22%), viridans streptococci (18%), enterococci (10%), other streptococci (8%), and other organisms (12%). S. aureus was the most prevalent cause of early-onset (38%) and late-onset (30%) prosthetic valve endocarditis. Coagulase-negative staphylococcus caused early-onset (31%) and most intermediate-onset (40%) disease and had a shorter median implantation-to-infection time than other organisms (6.5 vs. 61.3 months; P<.001). Viridans streptococci and enterococci primarily caused late-onset endocarditis. For active infections by cocci, most cases exhibited strong Gram staining, but four showed only strong Grocott methenamine silver staining.


CONCLUSIONS
Cocci accounted for 83% of infections. Early-onset prosthetic valve endocarditis was primarily staphylococcal, and late-onset prosthetic valve endocarditis resembled native valve endocarditis. Both Gram and Grocott methenamine silver stains were necessary to reliably identify organisms microscopically.