16 may 2009--Abnormal heartbeat called atrial fibrillation is associated with later development of Alzheimer's disease, a large-scale study finds.
There are three possible explanations for the relationship, each of which could lead to early treatment aimed at preventing the dementia, said study author Dr. T. Jared Bunch, an electrophysiologist at Intermountain Healthcare in Salt Lake City. His group was to present the finding Friday in Boston at the Heart Rhythm Society's annual meeting.
The study used data on 37,000 people treated at the 20 hospitals run by Intermountain Healthcare in Utah, Idaho and Wyoming. It found that people with atrial fibrillation, in which the upper chambers of the heart can quiver uselessly rather than pumping blood, were 44 percent more likely to develop dementia over a five-year period than those without the heart disorder.
The association was especially strong for people under the age of 70. Those with atrial fibrillation were 130 percent more likely to develop Alzheimer's disease.
And the combination could be lethal. The study found that people with atrial fibrillation and dementia were 61 percent more likely to die during the five-year study period.
Earlier studies have shown that people with atrial fibrillation are at higher risk of some forms of dementia, Bunch said. But this was the first large-scale population study to show an association of atrial fibrillation and increased risk of developing Alzheimer's disease, he said.
"We can't say yet that it is causal," Bunch said of the relationship. "We can say it is related to heightened risk. The next step is to look at the mechanistic association, to understand how one predisposes to the other."
One possibility, he said, is that both problems are related to high blood pressure, which could cause heart function to deteriorate so that blood flow to the brain is reduced, starving brain cells of oxygen. Early and intensive treatment of high blood pressure thus might prevent dementia, Bunch said.
It is also possible that inflammation is the underlying problem in both conditions, he said, since indicators of increased inflammation, such as the molecule C-reactive protein, have been found in both cases. Treatment with statins, which have anti-inflammatory properties, or medications aimed directly at inflammation, could thus be used.
"Finally, multiple studies show the presence of sub-clinical strokes in atrial fibrillation and dementia," Bunch said. "Many small strokes over time can cause the damage."
If that theory proves out, the treatment would be aimed at preventing the blood clots that caused such small strokes, he said. The clot-preventing drug Coumadin now is often prescribed for people with atrial fibrillation, because the condition heightens the risk of clot formation. Other clot-preventing measures could also be used, Bunch said.
All of those preventive treatments would have to be started early, he said. "We're going to begin looking at 50-year-olds," Bunch said.
One question is whether truly aggressive therapy for atrial fibrillation is warranted, said Dr. John Day, director of heart rhythm services at Intermountain, and a member of the research team.
"Unfortunately, for this condition, it takes a number of years to see if it makes a difference," Day said.
One aggressive therapy is catheter ablation, in which a catheter is threaded into the heart to cauterize the area where atrial fibrillation originates, he said.
"We should have a pretty good idea over the next few years whether this works out," Day said. "We have done it with 2,000 patients, and we are following these patients."