New Risk Factor for Heart Disease Death Found in
Healthy Senior Citizens
Older people not
expected to die of cardiac causes found in danger by abnormal heart rate
turbulence - appear healthy but they're not
Study author, Phyllis K. Stein, Ph.D
Feb. 16, 2011 -
Abnormal heart rate turbulence is associated with an increased risk of
heart disease death in otherwise low-risk senior citizens, finds a new
study. The research indicates that an abnormal response to an early beat
in the left ventricle, the heart’s main pumping chamber, can identify
high-risk patients even when they have no other evidence of
cardiovascular disease.
“These are
people we do not expect to die of cardiac causes,” says study author
Phyllis K. Stein, Ph.D., a research associate professor of medicine and
director of the Heart Rate Variability Laboratory at Washington
University School of Medicine in St. Louis.
“They appear
healthy, but they’re not. We have shown a way they’re not healthy that
isn’t showing up using standard tests.”
This study,
funded by the National Heart, Lung, and Blood Institute (NHLBI), part of
the National Institutes of Health, appears in the Feb. 15 edition of the
Journal of Cardiovascular Electrophysiology.
"These findings
suggest that apparently healthy people might be at increased risk of
death from cardiovascular disease, and heart rate turbulence may help us
identify them," said Susan B. Shurin, M.D., acting director of the NHLBI.
"It will be important to see if we can replicate this finding in other
populations."
A ventricular
premature beat (VPB) occurs when the ventricle gets an inappropriate
signal causing it to beat before it should. VPBs are common, even in
healthy people. The question is not whether VPBs occur, but how the body
responds to them. The heart’s response to a VPB is called heart rate
turbulence. It can be measured with a Holter monitor, a device worn for
24 hours that records a person’s electrocardiogram, the electrical
signals produced by the heart.
When the
ventricle beats early, the heart has not finished filling and it pumps
less blood to the body than it should. To compensate, the heart rate
speeds up to increase blood flow.
But an early
beat also empties the heart early, leaving extra filling time afterward.
So on the second beat after the VPB, the heart is extra full and pumps
more blood to the body than it should. To compensate properly, the heart
rate slows down.
A healthy heart
will alternately speed up and slow down to compensate for the over- and
under-filling that follows a VPB until the amount of blood filling the
heart returns to normal.
Abnormal heart
rate turbulence occurs when the heart can’t compensate in this way.
“It’s a clear
test of whether the autonomic nervous system, which regulates your heart
rate, can adapt to a challenge,” Stein says.
Among the nearly
1,300 senior citizen study participants, heart rate turbulence, which
reflects how well the heart reacts to occasional premature contractions,
was an even stronger heart disease risk factor than elevated levels of
C-reactive protein. CRP is a potential heart disease biomarker that has
emerged in recent years.
Study
participants considered at low risk of heart disease based on
traditional risk factors were on average 8 to 9 times more likely to die
of heart disease during the roughly 14-year follow-up period if they had
abnormal heart rate turbulence values.
Traditional risk
factors include age, gender, high blood cholesterol, high blood
pressure, obesity, diabetes, and smoking. Low-risk individuals with
elevated CRP in their blood were about 2.5 times more likely to die than
those with normal or low CRP.
This study
followed 1,272 adults aged 65 and older as part of the NHLBI's
Cardiovascular Health Study. Participants were categorized as healthy
(no sign of heart disease risk except possibly diabetes), subclinical
(some signs of heart disease) or clinical (had a cardiovascular event,
such as a heart attack).
Use of Holter
monitor
At the onset,
participants underwent 24-hour monitoring of their hearts’ electrical
activity through a small electrocardiographic, or ECG, device called a
Holter monitor attached to their skin.
Abnormal heart
rate turbulence and CRP levels both appeared to independently correlate
with an increased likelihood of dying of heart disease in the group that
was categorized as healthy, even after controlling for other risk
factors. Abnormal heart rate turbulence - present in about 7 percent of
the study participants - also predicted an increased likelihood of heart
disease death in the subclinical and clinical groups, though these
results were not as pronounced.
Heart rate
turbulence refers to how smoothly the heart rate returns to normal after
a premature ventricular contraction, a fairly common event in which the
second portion of a heart beat is triggered too soon. Due to the
improper timing between the atrial and ventricular contractions, the
ventricles haven’t fully filled with blood and therefore do not push out
enough blood to the body.
The brain
detects this sub-optimal release of blood and instantly increases the
heart rate to pump more blood. However, this overcompensation raises
blood pressure, causing the brain to react again and lower the heart
rate until blood pressure returns to normal.
By analyzing the
heart's electrical signals, physicians can measure the magnitude of the
initial heart rate jump (turbulence onset) and the speed at which heart
rate returns to normal (turbulence slope), and then determine if the
heart rate turbulence response is normal or abnormal.
"A heart rate
turbulence measurement is insightful because it offers a sign of how
well the autonomic, or subconscious, nervous system is functioning,"
said Stein.
"If someone's
heart doesn't react well to these uncoordinated beats that might mean
it's not good at reacting to other issues like sudden stress or severe
arrhythmias."
Researchers
don't yet know if abnormal heart rate turbulence can be treated or
prevented. In the meantime, said Stein, interest might grow within the
medical community in measuring heart rate turbulence in clinical
practice. Currently, this type of measurement is not widely available.
"This study
shows a great potential value for heart rate turbulence in diagnostic
settings," said Robin Boineau, M.D., a medical officer in the NHLBI's
Division of Cardiovascular Sciences.
"It appears that
signs of heart rate turbulence are also generally present a year or more
before clinical manifestations of heart disease, indicating that this
may be an opportunity for disease prevention in addition to disease
prediction."
Though the
Holter monitor is a common, noninvasive device, Stein says the software
needed to measure heart rate turbulence is only available for clinical
use on one commercial Holter monitor. She speculates that this work and
other studies showing the value of measuring heart rate turbulence may
make the software more widely available.
In addition to
the NHLBI, the National Institute of Neurological Disorders and Stroke
also contributed funding to this study.
Information
Sources: Parts of this news story came from a report by Julia Evangelou
Strait
Senior Medical Sciences Writer, Washington University School of
Medicine, and information provided by the National Heart, Lung, and
Blood Institute (NHLBI).
