Mitral valve prolapse as a risk factor for infective endocarditis.

The frequency of mitral valve prolapse was assessed in 48 patients with mitral valve endocarditis and in 96 controls matched for age and sex, attending a routine family screening clinic or having surgery of the limbs. The frequency of mitral valve prolapse in cases with endocarditis (9 of 48 patients) was more than three times that in controls (6 of 96) (odds ratio 3.5; 95% confidence interval [CI] 1.1-10.5). When patients with rheumatic heart disease, an established risk factor for infective endocarditis, were excluded from the study group, patients were nearly six times more likely to have infective endocarditis than were controls (odds radio 5.7; 95% CI 1.8-18.4). However, a higher risk of infective endocarditis was seen only in the subjects with mitral valve prolapse and a previously known systolic murmur (odds ratio 14.5; 95% CI 1.7-125). The results indicate that mitral valve prolapse constitutes a true risk factor for infective endocarditis only when associated with the presence of a precordial systolic murmur.