Previous studies have defined various clinical and laboratory findings, which have prognostic significance in patients treated for infective endocarditis [5, 8–12, 18]. These studies have shown that the outcome of endocarditis may be associated with a number of clinical variables, e.g. age or underlying diseases of the patient, development of complications, echocardiographic findings, laboratory parameters of inflammation, and the virulence of the causative microorganisms. However, some inconsistencies between the results from different hospitals are evident. At least to some extent, this may be due to differences between the institutions or patient populations studied, or even between environmental or genetic factors. We sought to define the prognostic significance of some of the conventional risk predictors in patients treated for infective endocarditis in a Finnish teaching hospital.
Of the laboratory parameters of inflammation, the level of CRP on admission was most prominently associated with the outcome of endocarditis throughout the study period, the prognosis being significantly worse in the patients with high CRP values. Illustratively, in the patients who had CRP values ≥100 mg/l on admission, the hazard ratio for in-hospital death was 2.9-fold and the hazard ratio for 1-year death was 3.9-fold as compared to the patients with lower CRP values (table 4). We are not aware of any previous study focusing on the level of the first CRP value as a prognostic sign in infective endocarditis, although Wallace et al.  have shown that in-hospital and 6-month mortalities were not affected by an abnormal or normal CRP value within 48 hours of admission. Instead, these authors found that mortality was strongly associated with abnormal WBC counts or serum creatinine concentrations. In our patients, elevated WBC counts on admission did not predict a poor outcome, but there was a tendency for a higher mortality in the patients with elevated serum creatinine concentrations. This probably reflected the worse general condition in these patients.
In many previous studies, S. aureus as the causative agent has been associated with an adverse outcome [9, 11, 19–23]. For example, in a recent study of Cabell et al. , S. aureus endocarditis had a 1.5-fold increase in the risk of death over 1 year as compared to the patients with endocarditis due to other pathogens. Also in the present study, there was a tendency for a higher mortality in S. aureus endocarditis as compared to the rest of the cases excluding S. pneumoniae endocarditis, but the association was significant only at 3 months. In another recent study , S. aureus did not confer a worse prognosis than other microorganisms. The authors assumed that this unconventional finding might have been due to the fact that among their patients with S. aureus endocarditis there was a high incidence of tricuspid valve involvement in which no deaths occurred. Consistently in our series, 20 of the 75 cases of S. aureus endocarditis were in patients with IVDU. Of these patients, 15 had tricuspid valve endocarditis with no mortality. We believe that this may have contributed to the fact that in the present study, the outcome of S. aureus endocarditis was not significantly worse than the outcome of endocarditis caused by other microorganisms. The high mortality rate of 45.5% in our patients with pneumococcal endocarditis is in line with previous findings , demonstrating the aggressive and destructive course of this disease.
Due to conflicting results of even the recent studies, the relation between survival and echocardiographic findings in infective endocarditis remains controversial. In their comprehensive study on risk classification for mortality, Hasbun et al.  found that the presence of a vegetation was not associated with increased 6-month mortality of endocarditis. Correspondingly, in a recent series of Chu et al.  echocardiographic findings were not predictive of in-hospital mortality. It is notable that in these two studies, the vegetation size and mobility were not analysed. Quite the opposite, there are many other studies showing that certain echocardiographic findings are significantly associated with mortality. In a prospective multicentre study, Thuny et al.  found that vegetation length was a strong predictor of 1-year mortality. When studying patients with aortic or mitral valve endocarditis, Cabell et al.  showed that vegetation size was a predictor of mortality at 30 days and 1 year. Further, in right-sided endocarditis in drug users, size of vegetation >2 cm proved a major prognostic factor of in-hospital mortality . In another recent series , a visible vegetation on echocardiography significantly influenced 6-month mortality, but not in-hospital mortality. Our results are in good correlation with many of these findings, since at 3 and 6 months, and 1 year, mortality of the patients with a vegetation on echocardiography was significantly higher than mortality of the patients without a vegetation. A visible vegetation increased the hazard for death within 1 year to 2.6-fold (table 4). Regrettably, the size and mobility of vegetations were not recorded in the present study.
The role of echocardiography in predicting embolic events has also been disputable, although recent studies suggest that vegetations, and especially certain characteristics of vegetations, are associated with a greater stroke rate . In this respect, our results are different, since a visible vegetation on echocardiography significantly predicted only peripheral emboli, not cerebral emboli or other neurological complications.
In our patients, heart failure was the complication, which was most significantly associated with an adverse outcome during the index hospitalisation and up to 1 year from admission. This corroborates other studies, which have found heart failure to be a major risk factor for mortality in endocarditis [11, 27]. Also neurological complications and peripheral emboli significantly predicted both in-hospital and 1-year mortality. These findings compare with many previous reports [5, 12]. Among the underlying diseases, diabetes has been shown to be associated with a higher mortality rate . The results of the present study do not corroborate this finding, as mortality in our patients was not dependent of diabetes, or of any other underlying conditions assessed.
Assessment of the role of cardiac surgery as a prognostic factor is very complicated. Patients may not be operated on because they are critically ill while some patients undergo cardiac surgery only because they have large vegetations. In the present study, mortality was somewhat higher for the surgically treated patients than for the patients treated conservatively. This finding is evidently due to a more severe disease with valve destructions in the patients who underwent surgery. The severity of the disease in these surgically treated patients is illustrated e.g. by their having a higher frequency of complications of endocarditis. The association between the requirement for surgery and heart failure was highly significant and, in addition, peripheral emboli were more common in patients who needed surgical treatment, although the association was significant only at the time point of 3 months. Also, these patients had a somewhat higher frequency of neurological complications than those treated conservatively. It is of note that all of these complications were shown to significantly predict mortality in our patients.
Although infective endocarditis is an uncommon disease, the long study period of 25 years made it possible for us to include a considerable number of patients with endocarditis. It is of concern, however, that during such a long period of time, there may have been changes in several aspects of diagnostic and therapeutic management of endocarditis. This is evidently one limitation of the present study.