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Senior Citizen Health & Medicine
Mayo Clinic Studies Declare Atrial Fibrillation
Epidemic, Find Genetic Cause
Aging population may
be one reason for large increase
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About Atrial Fibrillation
Atrial fibrillation is the most common arrhythmia -- or
irregular heartbeat -- worldwide. In the United States alone,
more than 2 million Americans suffer from atrial fibrillation,
constituting a major public health epidemic. During a person's
lifetime, there is a 25 percent risk this rhythm disorder will
develop, and patients with atrial fibrillation have a fivefold
increased risk for stroke. Atrial fibrillation has been
increasingly recognized as an inherited disease.
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July 20, 2006 Earlier this month a researcher at
the Mayo Clinic called atrial fibrillation a "growing epidemic" and
today other researchers there announced the discovery of a genetic cause
of the life-threatening heart condition. Up to five percent of senior
citizens are thought to suffer from this arrhythmia.
Like so many conditions and diseases that are most
prominent among senior citizens, cases of atrial fibrillation (AF) are
rising at an alarming rate and may affect nearly 16 million Americans by
the year 2050, according to a study reported in Circulation: Journal of
the American Heart Association.
Atrial fibrillation is a major public health
problem that needs urgent attention, said Teresa S.M. Tsang, M.D.,
senior author of the study and associate professor at the Mayo Clinic
College of Medicine in Rochester, Minn. Atrial fibrillation and its
associated complications significantly decrease longevity and quality of
life. From a public health perspective, it exacts a major toll on our
healthcare resources.
Atrial fibrillation is a rhythm abnormality in
which the hearts upper chambers (atria) irregularly quiver rather than
beat regularly and effectively. This condition is associated with an
increased risk of stroke, heart failure, cognitive dysfunction and
premature death.
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Mayo Clinic researchers
discover a genetic cause for atrial fibrillation |
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July 20, 2006, Rochester, Minn. -- Mayo Clinic investigators
have discovered a gene mutation causing chaotic electrical
activation of the heart muscle and atrial fibrillation (AF), a
common heart-rhythm disturbance affecting millions of Americans.
Atrial fibrillation can lead to heart failure and stroke.
"The discovery underscores the significance of heredity in
susceptibility to atrial fibrillation," explains Timothy M.
Olson, M.D., director of the Cardiovascular Genetics Laboratory
at Mayo Clinic.
"Identification of a new molecular basis for atrial fibrillation
provides a critical step toward individualized diagnosis and
treatment of arrhythmia," adds Andre Terzic, M.D., Ph.D.,
director of Mayo Clinic's Marriott Heart Disease Research
Program.
Significance of the Mayo Clinic Research
The Mayo Clinic study provides new insight into a previously
unrecognized mechanism for electrical instability in the human
heart. The Mayo multidisciplinary team is the first to identify
a specific genetic mutation of the ion channel gene KCNA5 that
leads to a disease-causing condition called a channelopathy.
A channelopathy is an abnormality of specific miniature
transportation tubes in cell membranes. The job of these tubes
-- or channels -- is to selectively allow certain charged
particles in and out of the cell, and in this way, pass
electrical currents in and out of the cell to regulate each
heartbeat. The KCNA5 mutation causes loss of function of an
atrial-specific potassium ion channel, disrupting electrical
synchronization. This leads to susceptibility for atrial
fibrillation.
About the Study
The Mayo investigation used comprehensive genetic analysis to
identify a mutation in the DNA of a sibling pair with atrial
fibrillation in the absence of known risk factors for the
disease. This genetic anomaly was not present in the DNA of
individuals without atrial fibrillation.
The atrial fibrillation mutation occurred in the KCNA5 gene,
which produces a key heart protein known as Kv1.5. Loss of Kv1.5
function, in turn, made the atria -- the upper pumping chambers
of the heart -- more vulnerable to stress-induced chaotic
rhythms, and atrial fibrillation.
To validate the finding, the researchers reproduced the disease
features at the molecular, cellular and organism levels and
corrected the mutation, restoring the defective ionic current.
More about study:
The Mayo Clinic discovery is published in the July 15 issue of
the journal
Human Molecular Genetics.
Drs. Olson and Terzic, the principal investigators of the study,
said this work was made possible through the efforts of a
multidisciplinary team integrating human genetics, recombinant
DNA technology, patch-clamp electrophysiology and
pharmacotherapy.
The Mayo Clinic
collaborative team also included Alexey Alekseev, Ph.D.; Xiaoke
Liu, M.D., Ph.D.; Sungjo Park, Ph.D.; Leonid Zingman, M.D.;
Martin Bienengraeber, Ph.D.; Srinivasan Sattiraju, M.D.; Jeffrey
Ballew; and Arshad Jahangir, M.D. Their work was supported by
grants from the National Institutes of Health, Marriott Heart
Disease Research Program, Marriott Foundation and Mayo Clinic. |
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The condition has previously been thought to affect
2.2 million Americans. This new research study, spanning 21 years, has
re-estimated this figure to 5.1 million. The investigators also made a
projection of a three-fold increase over the next five decades, if the
rate of rise continues.
The researchers in this community-based study
investigated the trends in age-adjusted incidence of AF in Olmsted
County, Minn., from 1980 to 2000. A total of 4,618 adults (51 percent
men, average age 73) who developed first-documented AF during this time
were identified.
The unified medical record for each patient
containing details of all in-patient and out-patient encounters was
reviewed comprehensively. Final inclusion in the study required
electrocardiographic (ECG) confirmation of AF, and verification of the
AF episode being the first recognized AF event for each person.
We found a significant increase in the number of
people who newly developed this rhythm problem over the past two decades
in Olmsted County, and this increase was not just because people were
living longer, Tsang said.
The investigators believe that the underlying cause
for such an increase is multifactorial, but the trends in obesity over
the same period could account for a large part of the observed increase.
Based on trends seen during the 21-year study
period and U.S. census projections, the researchers projected that 12.1
million to 15.9 million people in the United States will have AF by the
year 2050.
Clinically, as cardiologists, we deal with this
problem every day. Although atrial fibrillation is treatable, and some
of the potential complications are preventable, the overriding goal from
the clinical and societal perspective should be one of primary
prevention, Tsang said. That is, we need to prevent the first episode
of AF and the risk factors contributing to its development, if we are to
turn the tide of this growing epidemic.
Co authors are: Yoko Miyasaka, M.D., Ph.D.; Marion
E. Barnes, M.Sc.; Bernard J. Gersh, M.B., Ch.B., D.PhiL; Stephen S. Cha,
M.S.; Kent R. Bailey, Ph.D.; Walter Abhayaratna, M.B., B.S.; and James
B. Seward, M.D.
The study was supported by the American Heart
Association National Scientist Development Grant.
More Information About Atrial
Fibrillation and Arrhythmias
Atrial Fibrillation
By American Heart Association
What is atrial fibrillation (AF)?
Atrial fibrillation is a disorder found in about
2.2 million Americans. During atrial fibrillation, the heart's two small
upper chambers (the atria) quiver instead of beating effectively. Blood
isn't pumped completely out of them, so it may pool and clot. If a piece
of a blood clot in the atria leaves the heart and becomes lodged in an
artery in the brain, a stroke results. About 15 percent of strokes occur
in people with atrial fibrillation.
The likelihood of developing atrial fibrillation
increases with age. Three to five percent of people over 65 have atrial
fibrillation.
Click for more information.
Editors Note: Get information on atrial
fibrillation treatment options, possible side effects and questions to
ask your healthcare provider by registering for the American Heart
Associations free Heart Profilers program at
americanheart.org/heartprofilers. For information on heart disease
visit
americanheart.org or 1 (800) AHA-USA1.
What Are Arrhythmias?
By American Heart Association
The heart is a muscle that works like a pump. It's
divided into four chambers two atria at the top of the heart and two
ventricles at the bottom. The heart beats (contracts) when an electrical
impulse from the heart's "natural pacemaker" the sinoatrial or SA
node moves through it. The normal sequence, called the sinus
rhythm, begins in the right atrium, spreads throughout the atria and to
the atrioventricular (AV) node. From the AV node, the impulses (signals)
travel down a group of specialized fibers (the His-Purkinje system) to
all parts of the ventricles. This exact route must be followed for the
heart to pump properly. As long as the electrical impulse is transmitted
normally, the heart pumps and beats at a regular pace. A normal heart
beats 60 to 100 times a minute.
The term arrhythmia refers to any change from the
normal sequence of electrical impulses, causing abnormal heart rhythms.
This can cause the heart to pump less effectively. Some arrhythmias are
so brief (for example, a temporary pause or premature beat) that the
overall heart rate or rhythm isn't greatly affected. But if arrhythmias
last for some time, they may cause the heart rate to be too slow or too
fast or the heart rhythm to be erratic.
>> More from American Heart Association
click here.
Mayo Clinic Risk Factors of Heart
Arrhythmias
Certain factors may increase your risk of
developing an arrhythmia. These include:
● Age. With age, your heart muscle naturally
weakens and loses some of its suppleness. This may affect how electrical
impulses are conducted.
● Genetics. Being born with a heart abnormality,
such as the extra electrical pathway that occurs with
Wolff-Parkinson-White syndrome, may affect your heart's electrical
function.
● Coronary artery disease. Narrowed heart
arteries, heart attack or other heart damage are risk factors for almost
any kind of arrhythmia.
● Thyroid problems. Your metabolism speeds up
when your thyroid gland releases excess hormones. This may cause fast or
irregular heartbeats and is most commonly associated with atrial
fibrillation. Your metabolism slows when your thyroid gland releases too
few hormones, which may cause a bradycardia.
● Drugs and supplements. Over-the-counter cough
and cold medicines containing pseudoephedrine and certain prescription
drugs may contribute to arrhythmia development. The herbal supplement
ephedra also increased the risk of arrhythmia, but in early 2004, the
Food and Drug Administration banned ephedra from the marketplace because
of such health concerns.
● High blood pressure. This increases your risk
of developing coronary artery disease. It may also cause the walls of
your left ventricle to thicken, possibly altering how your heart's
electrical impulses are conducted.
● Obesity. Along with being a risk factor for
coronary artery disease, obesity may increase your risk of developing an
arrhythmia.
● Diabetes. Your risk of developing coronary
artery disease and hypertension greatly increase with uncontrolled
diabetes. In addition, episodes of low blood sugar (hypoglycemia) can
trigger an arrhythmia.
● Obstructive sleep apnea. This disorder can
cause bradycardia and bursts of atrial fibrillation.
● Electrolyte imbalance. Electrolytes, such as
potassium, sodium, calcium and magnesium, help trigger and conduct the
electrical impulses in your heart. Electrolyte levels that are too high
or too low can affect your heart's electrical impulses and contribute to
arrhythmia development.
● Alcohol consumption. Drinking too much alcohol
can affect factors that alter the conduction of electrical impulses in
your heart or increase the chance of developing atrial fibrillation. In
fact, development of atrial fibrillation after an episode of heavy
alcohol intake is sometimes called "holiday heart syndrome." Chronic
alcohol abuse may depress the function of your heart and can lead to
cardiomyopathy. Both are factors in arrhythmia development.
● Stimulant use. Stimulants, such as caffeine and
nicotine, can cause premature heartbeats and may contribute to the
development of more serious arrhythmias. Illicit drugs such as
amphetamines and cocaine may profoundly affect the heart and lead to
many types of arrhythmias or to sudden death due to ventricular
fibrillation.
>> For more information from Mayo Clinic
click here.
>> Cleveland Clinic has good information on
arrhythmia
click here
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