Researchers from the Massachusetts General Hospital report that mitral valve prolapse, an abnormality of a heart valve, does not appear to be associated with an increased risk of stroke among young people. Earlier studies, many using outdated imaging techniques, had led to the belief that mitral valve prolapse was a significant risk factor for stroke.
The MGH report appears in the July 1 New England Journal of Medicine. It accompanies a report from the Framingham Heart Study that found mitral valve prolapse to be much less common in the general population 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. Some may have to pay higher insurance premiums because of the diagnosis," 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.
Ferdinando Buonanno, MD, of the MGH Stroke Service, a co-author of the paper, adds, "The studies indicating that mitral valve prolapse was a risk factor for stroke were based on criteria that overdiagnosed the condition in both healthy patients and those who had experienced strokes. It now appears that even those with true mitral valve prolapse have no increased risk of stroke."
The mitral valve - one of four valves controlling the flow of blood through the heart - lies between the left atrium, which receives oxygenated blood from the lungs, and the left ventricle, which pumps blood out into the body. It is made of two flaps or leaflets that open to let blood pass through and close to prevent blood from moving backwards. In mitral valve prolapse, one or both of the leaflets do not close properly, bulging back and allowing blood to leak into the atrium, a process called regurgitation. Patients with serious mitral valve prolapse may develop endocarditis, an infection of the heart; stress on the heart muscle can lead to heart failure or irregular heart rhythm. In severe cases, patients may need to have their valves repaired or replaced.
The belief that mitral valve prolapse was common came from studies using some of the earliest forms of cardiac ultrasound or echocardiography. Based on the assumption that the mitral valve had a simple saucer-like shape with a central depression where the leaflets came together, researchers in the late 1970s believed that any image showing part of the valve bulging up in the middle reflected the backward motion of a prolapse.
That assumption was incorporated into a set of diagnostic criteria for mitral valve prolapse, which also included the presence of clicks and murmurs audible through a stethoscope. When researchers used those criteria to analyze the prevalence of mitral valve prolapse among the general population and among patients with cardiovascular conditions such as stroke, they diagnosed the condition in from 10 to 15 percent of apparently health individuals - with even higher rates among young women - leading to the belief that there was a hidden epidemic of a serious heart defect. In addition, a 1980 study of young people who had experienced strokes or related events diagnosed mitral valve prolapse in 40 percent of those studied, implying that the condition was a serious risk factor for stroke.
However, in the early 1980s a group of MGH researchers led by Levine began applying more advanced techniques of echocardiography to study the mitral valve and mitral valve prolapse. Observing that very few of those diagnosed with mitral valve prolapse actually had symptoms of illness or other signs of diseased valves, they theorized that poor understanding of the shape of the valve may have led to significant overdiagnosis of prolapse.
Using 3-dimensional ultrasound techniques pioneered at the MGH, they first published in 1987 evidence that, instead of being shaped like a saucer, the mitral valve actually is shaped like a saddle - or a Pringles potato chip - with a surface that curves in two opposing directions. Front-to-back ultrasound images show the central depression considered the normal valve's shape; however, images taken side-to-side would show an upward bulging in a normal valve, the appearance that the earlier criteria would have diagnosed as prolapse.
This observation, confirmed by subsequent studies at the MGH and elsewhere, has led to the development of more stringent diagnostic criteria for mitral valve prolapse. Armed with the new criteria, researchers are revisiting earlier studies of the condition, questioning beliefs about its prevalence and relation to a variety of diseases. Using new criteria, the Framingham Study analysis - conducted by Lisa Freed, MD, then a cardiology fellow at the MGH - found mitral valve prolapse in only 2.4 percent of a general population, with more serious prolapse observed in 1.3 percent of those studied. Rates of heart failure, atrial fibrillation (a serious heart-rhythm disturbance), stroke, fainting and chest pain were no more common among those with prolapse than those without the condition.
The current MGH study, conducted by Dan Gilon, MD, and colleagues, recreated the original 1980 study of stroke in young people. Analyzing cardiac ultrasound results for all patients under 45 treated for strokes or mini-strokes (transient ischemic attacks) at the MGH over a period of 10 years (1985 to 1995), the research team found the prevalence of mitral valve prolapse to be nearly identical to that seen in a control group without cardiovascular disease; prolapse was found in 1.9 percent of young stroke patients compared with 2.7 percent of controls, a statistically insignificant difference.
"There is no doubt that people with true mitral valve prolapse have some health risks, but stroke does not seem to be among them," adds Levine. "And if someone who had been diagnosed with prolapse several years ago asked me what to do, I would recommend they have it rechecked by an echocardiographer using the most up-to-date criteria, particularly if the diagnosis caused them to take antibiotics or otherwise affected their health care."
In addition to Gilon, who now is head of echocardiography at Hadassah University in Israel, Buonnano, and Levine, co-authors of the MGH study are Marcia Leavitt, Jane Marshall, RDCS, and Philip Kistler, MD, of the MGH and Marshall Joffe, MD, MPH, PhD, then at the Harvard School of Public Health. The study was supported by grants from the National Institutes of Health and the American Physicians Fellowship for Medicine in Israel.
Journal
New England Journal of Medicine