July 9, 1999

MGH study shows mitral valve prolapse not a stroke risk factor

MGH researchers reported in the July 1 New England Journal of Medicine that mitral valve prolapse, a heart valve abnormality, is not associated with an increased risk of stroke among young people. Earlier studies had led to the belief that mitral valve prolapse was a significant risk factor for stroke. The MGH report accompanies one from the Framingham Heart Study that found mitral valve prolapse to be much less common than previously believed and less strongly associated with health problems. MGH researchers also were co-authors of the Framingham study, which used techniques developed at the MGH to diagnose mitral valve prolapse accurately.

"As many as 10 to 15 percent of the population have been told they have mitral valve prolapse, that they need to take antibiotics when having dental or other procedures, and that they are at increased risk for stroke, heart failure, heart rhythm abnormalities or other serious problems," says Robert Levine, MD, of the MGH Cardiac Ultrasound Laboratory. "We now know that this condition actually occurs in only about 2 percent of the population." Levine is the senior author of the MGH article and a co-author of the Framingham Study report.

The mitral valve lies between the left atrium, which receives oxygenated blood from the lungs, and the left ventricle, which pumps blood out into the body. In mitral valve prolapse the valve does not close properly, allowing blood to leak into the atrium. Studies using early forms of echocardiography – ultrasound studies of the heart – led researchers to believe that mitral valve prolapse was present in a significant portion of the population. Levine and his colleagues used three-dimensional ultrasound techniques pioneered at the MGH to show that the shape of the valve was poorly understood.

Instead of being shaped like a saucer with a depressed area in the middle, as believed, the valve actually is shaped like a saddle. Depending on the angle from which an ultrasound study is taken, a normal valve can show either as a central depression or looking like it is bulging up in a way that would be diagnosed as prolapse. The MGH studies led to the development of new criteria for diagnosing mitral valve prolapse, which now are being used to revisit earlier studies of the condition and its relation to such problems as stroke, heart failure or abnormal heart rhythms.

Lisa Freed, MD, formerly an MGH cardiology fellow, was first author of the Framingham report. Co-authors of the MGH study were Dan Gilon, MD, first author and a former MGH fellow; Ferdinando Buonanno, MD; Marcia Leavitt; Jane Marshall, RDCS, and Philip Kistler, MD, of the MGH; and Marshall Joffe, MD, MPH, PhD, formerly of the Harvard School of Public Health.