By Amy Norton, Medical Tribune News Service
A type of heart-valve defect that has been linked to serious
complications is less common and less severe than the medical world
has thought, according to two reports.
Only a small portion of the general population suffers from
mitral-valve prolapse, and the condition is more benign than
previous research has suggested, researchers reported in Thursday's
issue of The New England Journal of Medicine.
Looking at more than 1,600 men and women involved in a
government heart-health study, researchers found that just 2.4
percent had mitral-valve prolapse -- far fewer than estimates from
past studies that suggested 5 percent to 35 percent of Americans
have the condition. The study was led by Dr. Emelia J. Benjamin, an
associate professor of medicine at Boston University School of
Medicine.
In a second study, Boston researchers found that mitral-valve
prolapse was no more common among 213 young stroke victims than
among 263 subjects with healthy hearts -- contradicting previous
studies that have linked the two conditions in patients age 45 and
younger. Dr. Robert A. Levine, an associate professor of medicine
at Harvard Medical School, led the study.
Mitral-valve prolapse occurs when the valve that regulates blood
flow from the heart's left atrium to the left ventricle sinks from
its normal position. Normally, the mitral valve shuts when the
heart contracts; a prolapsed valve may fail to close properly,
allowing some blood to flow back through the valve, sometimes
causing a murmer. A condition called mitral regurgitation may
develop, and this sometimes requires repair or replacement of the
valve.
But in the Boston University study, few patients with
mitral-valve prolapse experienced severe mitral regurgitation, the
most common complication of prolapse. Just 7 percent of patients
with ``classic'' prolapse suffered regurgitation, and none with the
``non-classic'' form did. In contrast to some past studies, the
rates of heart failure and other heart disease were no higher among
prolapse patients than controls.
Previous reports of a much higher prevalence of prolapse largely
came from hospital-based studies -- an imperfect way to measure its
frequency in the general public. In the 1970s and 1980s, Benjamin
noted, mitral-valve prolapse appeared to be epidemic, often being
diagnosed in otherwise healthy young people -- particularly women --
who had unexplained chest pain or heart palpitations.
But after mitral-valve prolapse was first recognized in the late
1960s, the ensuing prolapse ``fad,'' Benjamin explained, was
largely due to physicians' ``enthusiasm for making the diagnosis.''
She noted that in her team's study the condition was no more common
among women than men.
In the 1980s, the condition was linked to stroke in younger
patients when some studies showed a high prevalence of prolapse
among stroke victims 45 and younger. One study of young stroke
patients revealed that 40 percent had mitral-valve prolapse.
In both current reports, however, the researchers noted that
improved, two-dimensional imaging of the heart allowed them to more
accurately discern mitral-valve prolapse, compared with these past
studies.
Doctors have in recent years gained a better understanding of
the mitral valve itself, Benjamin noted.
``We now know that the valve is saddle-shaped,'' she said,
adding that this knowledge has perfected the way in which
echocardiographers interpret heart images.
``The brain attached to the machine knows more,'' said Levine,
who led the stroke study.
Using diagnostic criteria updated from the early studies of
stroke and mitral-valve prolapse, Levine's team found ``no evidence
of an association.''
In fact, prolapse was slightly more common among subjects who
did not suffer a stroke -- 2.7 percent had the condition, compared
with 1.9 percent among stroke patients. Instead, Levine said, most
of the stroke patients had other risk factors -- such as high blood
pressure, artery disease or diabetes -- that explained the early-age
strokes.
``Even in patients with unexplained stroke,'' Levine added,
``prolapse wasn't more frequent [compared with controls].''
People who have been diagnosed with mitral-valve prolapse, said
Benjamin, should consider when the diagnosis was made. Those
diagnosed before the late 1980s might not really have the
condition, she noted.
``Complications are very real,'' Benjamin said, ``but the
majority of patients don't have complications.''
