The patient underwent urgent reoperation. At surgery, partial aortic valve dehiscence as a result of a large subprosthetic abscess was discovered. Both aortic and mitral valve were replaced. Admission and operative cultures were negative on antibiotic therapy.
Comment: This is a classic presentation of early-onset prosthetic valve endocarditis. Usual organisms are S. epidermidis and S. aureus Streptococci, vancomycin-resistant enterococci (VRE), diphtheroids, gram-negative bacilli, and fungi (yeast and molds) are all seen in this setting, albeit less frequently.
S. epidermidis is of special interest because it produces hemolysins, grows very slowly on cell surfaces, and binds to host and foreign proteins. This biofilm creates a barrier to host defenses and appears to neutralize certain antibiotics. In addition there is clonal variability, with some isolates fully susceptible to oxacillin, while other clones are resistant.
Standard therapy for staphylococcal prosthetic valve endocarditis is oxacillin with gentamicin and rifampin. For oxacillin-resistant species, vancomycin is substituted. Prosthetic valve enterococcal endocarditis resistant to both penicillin and vancomycin is a growing concern. Some medical centers report VRE colonization rates as high as 30%. Therapy is daunting. For strains with a minimum inhibitory concentrations (MIC) less than 128 gr/mL to ampicillin, ampicillin/sulbactam plus an aminoglycoside has been recommended. For strains totally resistant to ampicillin, quinupristin/dalfopristin, linezolid, or daptomycin may be tried, but the overall success rate is probably no better than 50%.
Case 4 A 31-year-old automobile mechanic underwent aortic valve and graft replacement for severe aortic regurgitation with a large aneurysm of the ascending aorta. His post-operative course was complicated by massive bleeding at the distal graft anastomosis, and respiratory failure. After prolonged hospitalization, the patient was discharged improved, but 2 days later he complained of blurred vision and fevers. His wife noted a green hue from his right pupil. The patient was readmitted and started on intravenous acyclovir for presumed acute retinal necrosis. However, several days later, vitrectomy fluid grew Pseudoallescheria boydii.
Therapy was switched to intravenous miconazole but, shortly afterward, the patient suffered a cardiac arrest. Although his pulse and blood pressure were restored, he remained comatose and support was withdrawn. At autopsy, invasive prosthetic aortic valve and graft endocarditis was noted. Blood and tissue cultures also grew P. boydii.
Comment: Fungal prosthetic valve endocarditis is a devastating disease. Predisposing factors are prolonged use of central vascular catheters, often for antibiotic therapy or parenteral nutrition, and immunosuppression. Most success has been reported combining surgery with intravenous antifungal therapy. Patients should be continued on oral suppressive therapy afterward to prevent relapse later in life.
“Pacemaker endocarditis,” seen with increasing frequency, applies to pacemakers, defibrillators, or combinations thereof. Usual causes are skin flora microbes (staphylococci and Propionibacterium species) that gain access through a generator pocket wound. An echocardiogram may not show vegetations unless they extend to the tricuspid valve. Removal of all hardware, combined with intravenous antibiotic therapy, is necessary for cure. Some impacted leads require open heart surgery for removal.
Hospital-associated bacteremia from another source may spread to a heart valve or pacemaker lead, causing endocarditis. S. aureus bacteremia from intravenous catheters, hemodialysis fistula, and surgical wounds is most likely to do this. Patients on hemodialysis may be colonized with methicillin-resistant S. aureus (MRSA), a risk factor for infection. While intra-nasal mupirocin ointment may reduce MRSA colonization transiently, it is probably not effective for long-term prophylaxis.
Case 5 A 54-year-old accountant was admitted with chills and palpitations for several days. A bovine aortic valve prosthesis had been implanted 2 years earlier. The patient had complained of intermittent fevers for 6 months. A single blood culture had grown Propionibacterium acnes. Although a TEE was interpreted as normal, he was treated with intravenous vancomycin. Follow-up blood cultures were negative and a TTE was read as normal.