Risk of Endocarditis among Patients with Prosthetic Valves and Staphylococcus Aureus Bacteremia
El-Ahdab F, Benjamin DK, Wang A, , et al. Risk of endocarditis among patients with prosthetic valves and Staphylococcus aureus bacteremia. Am J Med. 2005;118:225-9.
The risk of developing endocarditis in patients with Staphylococcus aureus bacteremia and prosthetic valves increases as more than 600,000 prosthetic valves are implanted annually in the United States. A prospective study at Duke University identified 51 patients with prosthetic valves or mitral ring who developed S. aureus bacteremia. The modified Duke criteria were used for the diagnosis of endocarditis. The onset and sources of bacteremia, locations of acquiring bacteremia, as well as clinical outcome were analyzed. The overall incidence of definite prosthetic valve endocarditis was as high as 51%, with the remaining 49% patients meeting Duke criteria for possible endocarditis. The results showed that endocarditis occurred more frequently in mitral (62%) and aortic positions (48%), and with mitral ring the rate of endocarditis was slightly lower (33%). Among prostheses, mechanical and bioprosthetic valves had endocarditis rates of 62% and 44%, respectively. About 63% of patients had early onset of bacteremia (<1 year after valve placement), and 37% had late onset of bacteremia (>1 year after valve placement). Overall, the most common source of bacteremia was from infected surgical wound sites (33%). Early bacteremia was more likely to result from infected surgical wound sites (59%), while late bacteremia was more likely to have an unidentified source (48%). The majority of episodes of bacteremia (47%) were hospital-acquired (i.e., a positive blood culture occurred >72 hours after admission). The frequency of healthcare-associated bacteremia and community-acquired bacteremia was about 26%–27%.
In terms of mortality, there was no difference for a patient with early and late S. aureus bacteremia, bioprosthetic and mechanical valves, and infection due to methicillin-resistant or methicillin-susceptible S. aureus. However, mortality was higher among patients with definite endocarditis (62%) vs. possible endocarditis (28%). Patients with endocarditis who underwent valve surgery had lower mortality than those who did not undergo valve surgery due to inoperable comorbid conditions, such as stroke, multiorgan system failure, and mediastinitis. Persistent fever (≥ 38°C after 72 hours of adequate parenteral antibiotics) and persistent bacteremia (positive blood culture within 2–4 days of the initial positive blood culture) were independently associated with definite endocarditis with odds ratio of 4.4 and 11.7, respectively. Overall, 96% of patients underwent echocardiography (55% with both transesophageal and transthoracic echo, 14% with only transesophageal echo, 27% with only transthoracic echo). However, 10% patients with definite endocarditis had no diagnostic finding on either transthoracic or transesophageal echocardiography.
S. aureus bacteremia is a common phenomenon in inpatient settings. This study demonstrated an approximately 50% rate of definite prosthetic valve endocarditis in patients with S. aureus bacteremia. The risks of endocarditis were independent of valve type, location, and duration of implantation. This study highlights the need for aggressive treatment and evaluation of S. aureus bacteremia in patients with prosthetic valves. Clinically, persistent fever and bacteremia were independently associated with definite endocarditis in this study population. Clinicians cannot over-rely on transesophageal echocardiogram to identify occult endocarditis in high-risk patients.
Optimizing the Prediction of Perioperative Mortality in Vascular Surgery by Using a Customized Probability Model
Kertai MD, Boersma E, Klein J, van Urk H, Poldermans D. Optimizing the prediction of perioperative mortality in vascular surgery by using a customized probability model. Arch Intern Med. 2005;165:898-904.
Traditional perioperative risk-assessment models and indexes have focused primarily on cardiac outcomes and involved mainly clinical risk factors. The model proposed in this paper focused instead on overall mortality and incorporated not only clinical risk factors but also more precise surgery-specific risks and the use of beta-blocker and statin agents.