DALLAS, Oct. 13 -- A new test that measures swings in heart rate during the day may help identify individuals with congestive heart failure who are at the highest risk of dying from the condition within a year, according to a study in today's Circulation: Journal of the American Heart Association. Congestive heart failure (CHF) occurs when the heart muscle becomes unable to pump enough blood to meet the needs of the body's other organs. The test measures heart rate variability (HRV), the amount by which the heart rate changes from slow rates to fast rates in one 24-hour period. "The less the heart rate varies over 24 hours, the more likely a person will die of congestive heart failure," says the study's lead author James Nolan, M.D., consultant cardiologist at the Cardiology Center, North Staffordshire Hospital in Staffordshire, England.
In the study, people with the lowest HRV whose fastest heart rate was not much different from their slowest heart rate were three times more likely to die than individuals with the highest HRV. The annual death rate of people with the lowest HRV was 51.4 percent compared to 5.5 percent for those with the highest HRV. People whose HRV was between the two extremes had an annual death rate of 12.7 percent. The test can offer physicians a warning when people are at risk for early death and need intense treatment to save their lives, he says. "The take-home message to doctors is to measure the HRV in their patients with congestive heart failure. If it's high, the person is going to do well. If it's low, he or she is quite likely to die soon and the doctor should adjust treatment to try to prevent that," says Nolan.
"The HRV test will allow physicians to target extra treatment to the 40 percent of patients most likely to benefit. The money saved by not treating low-risk patients can then be allocated to other areas of health care," he says. The report is a follow-up investigation to previous studies indicating that a low HRV soon after a heart attack reduces a person's chance of survival. "There were reasons to think that if HRV is predictive following a heart attack, it might be even more valuable for heart failure patients," Nolan says.
For the study, the scientists selected 433 people in the United Kingdom Heart Failure Evaluation and Assessment of Risk Trial (UK-HEART) with symptoms of severe heart disease. The participants' average age was 62. Heart electrical activity was recorded by a small portable electrocardiograph (ECG) worn by each participant for a full day. Participants were able to continue with their normal daily activities throughout the recording period. The taped ECGs were run through an automatic analyzer that excluded abnormal beats and determined the variability in the 24-hour recording period. Participants were followed for an average of 482 days after their monitoring. Fifty-four deaths occurred during this time, with a total death rate of 9.5 percent.
The HRV is a good way to identify patients who are more likely to die of congestive heart failure. It can be used in conjunction with other measurements such as chest x-ray, blood tests or heart ultrasound examinations, says Nolan. Low HRV may be due to a defect in the autonomic nervous system -- the part of the nervous system that regulates "involuntary" body functions such as breathing and the beating of the heart, says Nolan. "The autonomic nervous system is constantly adjusting the rate at which the heart beats. Those people with the sickest hearts can't do that, so they have very little variability in their heart rate," says Nolan.
"If part of your heart is damaged and functioning inadequately, quality of life is maintained at the expense of overworking the surviving parts of your heart. There are no 'down' times where the heartbeat can slow down, allowing the heart to rest," he says. "And that may lead to a downward spiral of declining heart function and death from congestive heart failure. "Drugs like beta blockers, digoxin, and scopolamine -- a drug used to treat travel sickness that affects the autonomic nervous system -- and simple things like exercise training improve heart rate variability," Nolan says. "These beneficial effects may prevent heart function from deteriorating and keep individuals alive for longer."
Nolan and his colleagues have planned more studies to test the effectiveness of various treatments in prolonging the lives of people with congestive heart failure with low HRV. CHF, which is increasing dramatically in the U.S. population, can be caused by conditions including, but not limited to, high blood pressure, scar tissue from prior heart attacks and coronary heart disease that narrows the vessels that supply blood to the heart muscle. About 4.9 million Americans have CHF. Co-authors are Phillip Batin, M.D.; Steven Lindsay, M.R.C.P.; Richard Andrews, M.R.C.P.; Paul Brooksby, M.D.; Michael Mullen, M.R.C.P.; Wazir Baig, M.D.; Andrew Flapan, M.D.; Alan Cowley, F.R.C.P.; Robin Prescott, Ph.D.; James Neilson, Ph.D.; and Keith Fox, F.R.C.P.
Materials provided by American Heart Association. Note: Content may be edited for style and length.
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