Implanted Defibrillator Helps Spot Death Risk
It tracks trouble with daily heart rhythms, study finds
MONDAY, March 7, 2005 (HealthDay News) -- A type of implanted defibrillator that automatically resets a distressed heart may have a second benefit: It may suggest whether a patient is at especially high risk of dying from heart failure.
The implanted device could alert doctors to patients requiring special treatment, North Carolina researchers reported Monday at the American College of Cardiology's scientific sessions in Orlando, Fla.
Data issued by the device "provide us with an unbiased -- distinct from the patient's perception -- look at how the patient is truly doing. It is an objective finding that you can look at and easily understand," Duke University cardiologist and study co-author Dr. Roosevelt Gilliam said in a prepared statement.
The device, cardiac resynchronization therapy with defibrillation (CRT-D), is implanted in patients with heart failure and automatically zaps the heart when it enters a potentially dangerous rhythm. In addition to guarding against heart trouble, the device continuously monitors something known as heart rate variability.
Heart failure affects an estimated 4.7 million Americans, and 400,000 new cases are reported each year. The hearts of those affected become weak and can't effectively pump blood and oxygen throughout the body. The condition is potentially deadly, and half of those diagnosed die within five years.
Like the defibrillator machines now found in many airports and schools, CRT-D devices zap the heart with an electric shock to stop irregular heart rhythm. The devices also stimulate both sides of the heart, allowing it to beat with less effort.
The Duke researchers examined the medical records of more than 1,400 heart failure patients -- more than three-quarters men -- who received an implanted CRT-D device.
Out-of-control heart rates known as arrhythmias can lead to death. But another kind of variability -- a continuous, natural adjustment from beat to beat -- is good, experts say, and the more of it the better. In fact, in this study the researchers found that patients with the least variation in their normal 24-hour heart rates were 2.4 times more likely to die within a year.
Better control of heart rhythm means less overexertion on the part of the heart, one expert explained.
"If the heart is healthy, and each beat of the heart is very effective, the brain can send signals to the heart, telling it that it can take it easy and doesn't have to exert a lot," said Dr. Alan Kadish, associate director of Northwestern University's Cardiovascular Institute. "If the heart is not healthy and the body is not getting enough oxygen from the blood, the brain sends signals to the heart that it needs to do more. As part of its signaling, it is putting more stress on the heart."
Kadish said earlier studies have confirmed that heart rate variability is a good indication of how well a patient is doing. The new study shows the CRT-D device provides helpful measurements of that variability, he said.
But he cautioned that at this point in time there's still no consensus on how doctors can best help patients with poor heart rate variability.
"There's no clear direction on what one should do to improve the situation," Kadish said, especially considering that it's not clear the role played by heart rate variability in heart failure.
"If you improve something and the heart rate variability improves, does that mean the outcome is now better? We don't know that yet," he said.
In other findings presented Sunday at the cardiology meeting, four different trials compared various brand of stents, the thin mesh cylinders used by doctors to prop open dangerously narrowed arteries, usually after angioplasty.
As reported by the New York Times, the studies argue for increased use of these devices, especially the newest generation of "drug-eluting" stents, which carry a polymer coating that slowly releases drugs into the artery that help prevent re-closure.
Learn more about heart failure from the American Heart Association.