Patients whose heart rates remain elevated after exercise testing are more than twice as likely to die within 6 years as patients whose heart rates recover normally, according to an article in the September 3rd issue of the Journal of the American College of Cardiology. The findings imply that heart rate recovery is an independent predictor of death comparable with severity of coronary artery disease as measured by angiography.

"If anything, heart rate recovery is a stronger predictor of risk than the severity of coronary disease. What we are measuring is something which is completely different from coronary disease. What we think we are measuring is autonomic nervous system function, which is something which is very different from how much blockage there is in a coronary artery. That's probably why this is working independently of coronary disease, because we are really measuring something else," said Michael S. Lauer, MD, senior author of the study.

It is not known whether interventions to improve heart rate recovery would change the risk of death, Lauer said. At present, he believes that the greatest value of heart rate recovery testing may be to identify low-risk patients, thus sparing them from unnecessary tests or treatments.

"And I think that is extremely important, because we see a lot of patients who are being inappropriately labeled as being at uncertain risk and who are going through unnecessary tests, unnecessary procedures, or being put on medications that they probably don't need to take, because their physicians are overestimating their risk. If you have a normal heart rate recovery, and particularly in conjunction with preserved functional capacity, that combination, with great confidence, can identify a patient as being at low risk," Lauer said.

The American researchers studied 2,935 consecutive patients who underwent exercise testing for suspected coronary artery disease and then had a coronary angiogram within 90 days. Heart rate recovery was considered abnormal if it dropped by only 12 beats per minute or less during the first minute after exercise cessation (18 beats per minute or less for patients who underwent an immediate ultrasound examination and did not get a cool down period).

Within 6 years after testing, 336 (11 percent) of the study participants had died. The hazard ratio for those with an abnormal heart rate recovery versus normal recovery was 2.5 (95 percent confidence interval 2.0 to 3.1; p<0.0001). For patients with severe coronary artery disease as determined by angiography, the hazard ratio was 2.0 (95 percent confidence interval 1.6 to 2.6; p<0.0001).

Lauer noted that there are still many unanswered questions about the causes and mechanisms of abnormal heart rate recovery. He and his colleagues previously reported that abnormal heart rate recovery was also independent of ischemia and left ventricular function. He said, "The field is still in its infancy, and we do not know whether or not this is a treatable risk factor."

Bernard R. Chaitman MD, who wrote an editorial in the same issue, said the current study and a separate article in the journal by Abdou Elhendy, MD, and his colleagues contribute to the growing body of literature demonstrating lower long-term survival rates in patients with abnormal heart rate responses during or immediately following an exercise test: "Both studies indicate that abnormalities of the heart-rate response to an exercise stress predict increased mortality regardless of left ventricular function, magnitude of exercise-induced ischemic responses, and in the Vivekananthan study (the current study), coronary disease extent. What remains unknown is why some patients go on to develop an abnormal heart-rate response in the presence of predisposing risk factors, and the mechanism whereby the abnormality triggers subsequent mortality in susceptible individuals, in many cases, years after the abnormal heart rate response becomes manifest."