The Stroke Connection
By Michael Lasalandra
Beth Israel Deaconess Medical Center Correspondent
Atrial fibrillation and
stroke are closely linked.
In fact, people suffering from atrial fibrillation --
irregular heartbeat episodes stemming from faulty electrical signals in the heart -- have a five to 17-fold increased incidence of stroke, compared to those who do not suffer from AF.
"In people with AF and no heart disease the risk of stroke is about 5 percent a year," said
Dr. Charles Haffajee, a cardiac electrophysiologist and director of device trials and the electrophysiology network at the
CardioVascular Institute at Beth Israel Deaconess Medical Center.
One of the goals of treating AF is to reduce the risk of stroke. This is typically done by putting patients on a blood thinner such as Coumadin®. With such treatment, the risk can be reduced to about 1 percent a year, Dr. Haffajee said.
AF causes stroke because the atrium does not contract properly, and blood moves slowly, pooling and clotting in the left atrium, particularly in an area known as the left atrial appendage. The change in heart rhythm causes the clots to leave the atrium, moving to the brain and elsewhere in the body, resulting in stroke.
"That's the biggest risk of AF," said Dr. Haffajee.
Blood clots are known to form whenever blood remains static for prolonged periods of time, or as a result of turbulent blood flow, both of which are likely to occur during the erratic and disorganized heart beat of atrial fibrillation.
Researchers estimate that about 35 percent of patients with AF will suffer a stroke at some point if the condition is left untreated.
Strokes caused by AF tend to be worse than other strokes. Half of all strokes associated with atrial fibrillation are major and disabling, according to Dr. Bryan D. Loftus of Texas.
About 23 percent of AF stroke patients die, and 44 percent suffer significant neurological damage. This compares to only an 8 percent mortality rate from other causes of stroke, according to a 2006 report in Circulation.
About 15 to 20 percent of all strokes are the result of AF, according to the
American Heart Association. Sometimes such strokes can be manifested at first as TIAs or transient ischemic attacks, also known as "mini-strokes." These do not result in lasting damage but serve as warning signs.
If left untreated, AF can eventually result in a major stroke, Dr. Haffajee said.
In a paper published in 2004, Dr. Jonathan S. Steinberg of St. Luke's-Roosevelt Hospital Center said effective use of preventative treatment is available but underutilized.
"(Coumadin) has been proven to reduce stroke incidence by about two thirds in high risk AF patients, yet surveys repeatedly indicate that many patients who should be anticoagulated are not," he said.
"There is no disputing that chronic treatment with (Coumadin®) is a practical challenge, but clearly a much higher proportion of eligible patients should be treated," he said.
Dr. Haffajee said this problem should be reduced when a new type of blood thinner known as a direct thrombin inhibitor comes on the market. Such drugs are expected to be easier to take as they will not require blood testing for assessing therapeutic effect and are not interfered by green vegetables or antibiotics.
"The consequences of this effort will likely be fewer strokes," Steinberg said.