Infections of prosthetic heart valves and cardiac pacemakers.

Prosthetic valve endocarditis may be considered present when two fo the following criteria are met: (1) two or more blood cultures are positive with the same organism in the absence of extracardiac infections, (2) evidence of bacterial endocarditis by histology or cultures is obtained from surgical or autopsy specimens, and/or (3) a clinical picture compatible with endocarditis (fever, new or changing regurgitant murmur, splenomegaly, hematuria, or evidence of peripheral emboli) is present. The overall incidence of PVE ranges from 0.98 to 4.4 per cent. Early and late PVE (that is endocarditis developing less than 60 and 60 or more days following valve implantation, respectively) accounts for 18 to 36 per cent and 64 to 82 per cent of infections, respectively. The overall mortality is 53 per cent and is higher in patients with early versus late PVE. Coagulase-negative staphylococci are responsible for a higher percentage of early (43 per cent) than late (28 per cent) infections. Streptococci are more common in late (27 per cent) than in early (3 per cent) PVE, while diphtheroids are most common in early PVE. The diagnosis of PVE may be difficult to establish, especially in patients with postoperative bacteremias who have other potential sources of extracardiac infections. Antimicrobial therapy is generally based on the susceptibility of the offending pathogen. With respect to the use of synergistic combinations, results are controversial, and most available data are derived from patients with native-valve endocarditis. Surgery remains an important aspect of treatment, and the mortality among patients who undergo early surgical intervention, particularly if their illness is complicated, is less than in those who are treated only with antibiotics. Indications for surgery include: (1) moderate-severe refractory congestive heart failure, (2) persistent bacteremia or fungemia, (3) multiple emboli, (4) myocardial abscesses, (5) relapsing PVE, and possibly (6) patients with clinical evidence of PVE and negative blood cultures and persistent fever despite 1 week or more of appropriate antibiotics. Pacemaker infections occur in less than 6 per cent of patients who undergo pacemaker insertion. These infections generally result from wound contamination at the time of surgery, and 75 per cent of infections are due to staphylococci. Staphylococcus aureus causes most infections occurring within 2 weeks after surgery, while S. epidermidis causes most later infections. The need to remove infected pacemakers is controversial.