New predictor for sudden death from heart failure
Low heart rate variability means high risk
American heart failure experts are cautiously optimistic that a simple test may be a powerful new tool to recognize congestive heart failure patients at high risk of death within a year and to give physicians an opportunity to provide the intensive treatment that may save their lives.
The effectiveness of the 24-hour heart rate variability test (HRV) in identifying patients at high risk of death within a year was studied by British researchers and reported in the Oct. 13 issue of the journal Circulation. (See related story on methods, p. 84.)
The results: CHF patients with a low variability rate were at ten times the risk of death as those with high swings in heart rate.
In fact, of 433 patients in the study, ages 18 to 80, all with congestive heart failure for at least three months, half of those with low heart rate variability died during the study follow-up period (+/-482 days), and of those with normal variability rates, only 5.5% died during the study.
Those patients whose HRVs were between the extremes had an annual death rate of 12.7%.
At this point, says David A. Meyerson, MD, a national spokesman for the Dallas-based American Heart Association (AHA) and senior cardiologist at Johns Hopkins University in Baltimore, "It is an excellent research tool that we can use to help design interventions that will help people live longer with congestive heart failure." The HRV test is already in limited use in the United States "as an investigative tool," Meyerson says.
Should all CHF patients get HRV tests?
In a press release issued at the time the study was made public, lead author James Nolan, MD, of St. James’s University Hospital in Leeds, England, recommended HRV tests for all CHF patients.
Meyerson and his colleagues think it’s not yet time for the HRV test to be in routine use in the United States.
"But physicians can be aware that literature now exists and HRV is helpful in predicting who is at high risk," Meyerson said. "We will all look forward to the next meetings of the AHA where interventions will have been developed that will minimize this variability and hopefully help predict who we can help do better."
Lee Dykstra, MD, director of the congestive heart failure unit at the Kaiser Permanente Foundation Hospital in Bellflower, CA, thinks CHF patients who are reasonably healthy and can reasonably expect to survive another five years or so can benefit most from an early predictor like the HRV.
"If true, then this is a piece of information that is likely to help us focus our efforts on those patients who are likely to benefit. We have therapy that will help them, but until now we have not been able to identify who can benefit," he says.
"I couldn’t tell you that I think we’re going to improve outcomes by 5%, 10%, 20%. I really don’t know, but I think it’s the right thing to do," Dykstra says. "Whether it’s going to help all that much, we’ll have to wait and see."
Like many of his colleagues, Dykstra stresses the accomplishments of angiotensin-converting enzyme (ACE) inhibitors. "We are just coming out of the Dark Ages in congestive heart failure. ACE inhibitors have reduced mortality by 30% in the past five years because they prevent the condition from worsening by lowering the blood pressure. And best of all, the more you take, the more benefits you get."
He says there is a "general feeling" among American cardiologists that many patients on ACE inhibitors would do better with higher dosages. "General practitioners, family practitioners, and internists may not be as aggressive in this as they should be."
"I sympathize with the primary care physicians that they have to worry about cholesterol screening, cancer, blood pressure, and remember everything else and try to do some education, all in the course of a 15-minute visit," Dykstra added.
Test can help 40% of patients
Nolan estimates that the early predictor HRV test can benefit 40% of CHF patients with extra treatment. His study is an evaluation of results of the UK-Heart (Heart-Failure Evaluation and Assessment of Risk Trial) that showed that patients with a low HRV following a heart attack had a lower chance of survival.
"Our aim was to recruit a wide spectrum of ambulant outpatients with mild to moderate symptoms treated with optimal contemporary drug therapy and characterized according to simple, widely available clinical techniques," Nolan wrote.
Patients from four hospitals were analyzed between December 1993 and April 1995. All subjects had diagnosed CHF, and those with confounding factors or comorbid diseases such as diabetes, chronic renal failure, history of alcohol abuse, clinical evidence of autonomic neuropathy or a recent myocardial infarction, and a variety of other cardiac factors were eliminated.
Baseline data were collected for each patient, including chest X-rays, electrocardiograms, left ventricular functions, and cardiothoracic ratios. Electrolytic concentrations and renal and liver functions were also measured. In addition, left ventricular ejection fraction and fractional shortening indices were calculated according to standard formulas.
The majority of patients (76%) were diagnosed with ischemic heart disease and were being treated with diuretics (97%) and ACE inhibitors (82%).
All patients were registered with the UK national death reporting system, which notified researchers of all deaths. Death certificates, autopsy findings, and hospital and physician records were reviewed by independent researchers at the University of Edinburgh in Scotland.
Better understanding of death
Nolan concluded, "Our data relating to mode of death are based on relatively small numbers of events, and many deaths in heart failure patients are difficult to classify. The results should therefore be viewed with caution, but they do provide insights into the relationship between autonomic activity and mode of death in CHF."
Finally, the study states, "Data in relation to mode of death suggest that 24-hour ambulatory ECG may be useful in guiding the prescription of additional therapy for patients with symptomatic CHF who are already established on a diuretic and ACE inhibitor."
For more information, contact: David Meyerson, MD, Johns Hopkins University, Baltimore. Telephone: (410) 750-5555.