Risk of infective endocarditis in mitral valve prolapse with and without precordial systolic murmurs.

The risk of infective endocarditis (IE) associated with a systolic murmur in patients with mitral valve prolapse (MVP) was investigated in a case-control study. The case group comprised all patients with MVP (n = 19) from a series of 136 consecutive adult admissions for IE. Three matched control subjects were chosen for each case from a series of 144 MVP patients without IE. Seventeen of the 19 cases (89%) had documented evidence of systolic murmurs existing before the IE episode; systolic murmurs were documented in 25 of the 57 control subjects (47%). The data indicate a significant increase in the risk of IE in MVP patients with a systolic murmur (p less than 0.01). The absolute probability of IE developing in a patient with MVP and a murmur was estimated to be approximately 1 in 1,400 per year; this was 35 times greater than the probability in a patient with MVP without a murmur. The results suggest that by restricting prophylaxis to MVP patients with a systolic murmur, cover would be provided for almost 90% of those with MVP in whom IE would be likely to develop.