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.