Cardiac conduction abnormalities complicating native valve active infective endocarditis.

Two hundred eleven episodes of native valve active infective endocarditis treated at the Massachusetts General Hospital between 1975 and 1983 were reviewed. The aortic (36%) and mitral (33%) valves were most frequently involved, but in 21% of the cases the site of infection could not be localized. Streptococcal (50%) and staphylococcal (35%) species were the most frequently isolated pathogens. New or changing ("unstable") conduction abnormalities developed in 9% of the patients, while an additional 7% had conduction abnormalities of "indeterminate" age. Unstable conduction block was more likely to develop in patients with aortic valve infective endocarditis than in those with mitral infection. Surgery was performed in 23% of the patients. Unstable conduction abnormalities were significantly associated with valve replacement, but in a multivariate analysis, this effect could be explained by the site of valvular infection. The mortality rate was 20%. Patients with unstable conduction abnormalities had a significantly higher mortality rate, even after other significant predictors of death (age, type of causative organism) were taken into account. Patients whose conduction changes persisted had a worse prognosis than those with transient conduction abnormalities. Although more hemodynamically compromised, patients with unstable conduction block who underwent valve replacement did at least as well as those given medical therapy alone. Patients with native valve active infective endocarditis in whom persistent, unstable conduction abnormalities develop without other identifiable cause, especially in the presence of aortic valve infection, should be considered for valve replacement.