Speeding up heartbeat may improve sleep apnea

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Speeding up heartbeat may improve sleep apnea

By Merritt McKinney

NEW YORK, Feb 06 (Reuters Health) - Speeding the heartbeat with a

pacemaker relieves some cases of sleep apnea, results of a French study

suggest.

How a pacemaker might reduce the severity of the sleep disorder is

uncertain, but the study's authors suspect that the implanted device

counteracts the " decelerating " part of the nervous system.

People with sleep apnea stop breathing dozens of times each night,

causing them to gasp for breath. The condition is conservatively

estimated to affect from 2% to 4% of middle-aged Americans, and is

particularly common among obese people. Sleep apnea has been linked to

daytime sleepiness, as well as an increased risk of high blood pressure

and cardiovascular disease.

There are several treatments available for sleep apnea, including

surgery and a therapy called CPAP, or continuous positive airway

pressure, in which a facemask is used to introduce a gentle stream of

air to keep the airways open during the night.

Dr. Stephane Garrigue of the University of Bordeaux, France, and

colleagues noticed that breathing disorders improved in several patients

who had received a pacemaker to correct an abnormal heartbeat. The

researchers decided to see whether setting a pacemaker to speed the

heartbeat might improve sleep apnea.

The study included 15 patients who had a pacemaker implanted to correct

a slow heartbeat called symptomatic sinus bradycardia.

Garrigue's team found that episodes of sleep apnea decreased

significantly when the pacemaker was set to 15 beats per minute faster

than the patient's average nighttime heart rate. In 13 of the 15

patients, the apnea-hypopnea index--a measure of the frequency of slow

or stopped breathing at night--declined by more than 50%.

" We thought that stimulating the heart at a relatively high resting rate

might have beneficial effects on sleep apnea occurrence, " Garrigue told

Reuters Health.

" Our observations are compatible with this hypothesis, " he added, " so

that patients with low heart rate during sleep and sleep apnea syndrome

could potentially benefit from a pacemaker for sleep apnea episodes. "

But Garrigue noted that the study is preliminary. Despite the promising

findings, the French researcher emphasized that the study included

people who already had a pacemaker for other reasons, so it is uncertain

whether the device would be effective in sleep apnea patients who have

normal heart rates.

Garrigue's team found that a pacemaker relieved both types of sleep

apnea--central and obstructive apnea. Obstructive apnea occurs when the

airway becomes blocked by tissue, such as the tonsils or the base of the

tongue. Central apnea, in contrast, occurs when the respiratory system

stops working in the absence of a blockage.

The researchers speculate that speeding the heartbeat with a pacemaker

might improve central apnea by counteracting increases in so-called

vagal tone--the part of the nervous system that tends to slow down the

body's activities.

But Garrigue's team does not know why a pacemaker was effective at

relieving obstructive sleep apnea.

" Obstructive sleep apnea and central sleep apnea are by and large

different conditions, " Dr. J. Gottlieb, of Boston University

School of Medicine in Massachusetts, told Reuters Health. What is

interesting about the results, according to Gottlieb, is that the

pacemaker seems to improve both types of apnea. Gottlieb is the author

of an accompanying editorial.

" The results are very surprising, " Gottlieb said. " There is no clear

prior hypothesis to explain why pacing should work. "

" While pacemaker insertion is not likely to be a generally useful

therapy, " he added in an interview with Reuters Health, " it is possible

that understanding the mechanism by which cardiac pacing improves sleep

apnea will provide clues to the development of drug therapy for

obstructive sleep apnea. "

" It was a surprise to some extent " that these pacemakers improved sleep

apnea, Dr. M. Drazen, the editor-in-chief of The New England

Journal of Medicine, told Reuters Health in an interview.

But according to Drazen, central and obstructive sleep apnea " are in

fact closely related. " Central apnea occurs when the brain does not send

out the initial signals to start breathing, he explained. In obstructive

apnea, some of the signals that direct the muscles involved in breathing

do not get sent out, Drazen noted. The two conditions are probably

connected on some level, he said.

Still, he emphasized that the study does not prove that pacing relieves

sleep apnea by counteracting increased vagal tone in patients with the

condition. But if enhanced vagal tone does turn out to be blame for some

cases of sleep apnea, then preventing it " could offer a new treatment

for this common condition, " he notes in his editorial.

SOURCE: The New England Journal of Medicine 2002;346:390, 404-412,

444-445.