Rate Recovery After Exercise
Summary: Recent research in the U.S. found that a delayed decrease in the heart rate during the first minute after graded exercise is a powerful predictor of overall mortality.
Norman Swan: Welcome to the program.
Now I don't know about you but I'm always seeing joggers stopping to take their pulses and I'm never sure why; they probably have some esoteric knowledge about their fitness level which escapes me. But research published last week in the United States may one day give them a very good reason.
In a six-year follow-up study, researchers showed that in a group of men and women aged around 57, the heart rate one minute after peak exercise strongly predicted their likelihood of dying in the following few years.
It's a dramatic finding which could have an impact on the way people with serious coronary risk are screened or indeed whether you need to go on to have fancier tests like nuclear heart scans of angiography where your coronary blood vessels are catheterised and X-rayed.
And if the findings are repeated outside the laboratory in real life, for example in pulse-taking joggers, it could have wide public health ramifications.
The person who led the research team was Dr Michael Lauer, a cardiologist at the prestigious Cleveland Clinic in Cleveland, Ohio.
Michael Lauer: We looked at something very simple; we looked at the heart rate at the end of exercise, in people undergoing exercise testing, and then we looked at their heart rate one minute after they finished exercise. We took the difference between the heart rate at peak exercise and the heart rate one minute later, and we measured the heart rate recovery. We followed 2,400 patients for about six years, during which time 213 of them died. And what we found was that this change in heart rate during the first minute after exercise was an extremely powerful predictor of mortality, in fact it was the most powerful predictor of mortality that we've looked at; it was a more powerful predictor of mortality than nuclear tests, which look at blood flow abnormality to the heart, and it was a much more powerful predictor of mortality than the electrocardiogram we physically looked at during exercise.
Norman Swan: Or during the stress test. So give me an idea of peak exercise in the stress test; how far do you take people in the stress test to get to this peak level?
Michael Lauer: Well typically we will exercise people for about 8-12 minutes, that's how long it usually takes to get somebody going very quickly and getting them to the point of maximal exhaustion. Let's say for a typical 50-year-old man, you'd expect the heart rate to rise from about 70 at rest to about 170 at peak exercise. And then what we'd like to see is the heart rate fall by at least 20 beats per minute during that first minute after exercise. That would take us down to 150. People with an abnormal heart rate recovery, the heart rate only falls by a little bit during that first minute after exercise. They were the ones who were at really high risk for subsequent death.
Norman Swan: I think in the paper you defined the heart beat reduction as 12 beats per minute or less.
Michael Lauer: Twelve beats a minute, that's correct.
Norman Swan: As a reduction. Can you apply this knowledge, or is there any other research which suggests if you go for your average jog, measure your pulse at the end of it and your pulse a minute later, that's got any measure worth considering here?
Michael Lauer: That's a very good question, because an average jog typically is not maximal exercise. We are looking at people who underwent some maximal exercise, and we're going to look at that as well. My guess is that it will work, but that's something that will require some further research.
Norman Swan: What is it about the heart, what is it about the cardiovascular system that you're measuring here? Is it some sort of holistic measure that you can't pin it down to one thing, in other words you're getting a kind of global snapshot of the health of the cardiovascular system, or is it something specific?
Michael Lauer: What we're actually measuring is something called the autonomic nervous system, that part of the nervous system that regulates heart rate and blood pressure and breathing. It's been known for a long time that abnormalities of the autonomic nervous system are correlated with death risk, but the problem is that the way in which these abnormalities are measured are very difficult. They require sophisticated equipment and they require the kind of tests which simply have not entered the realm of normal clinical practice. What we find is that these very, very simple measures that are obtained as part of regular routine exercise testing deflect what happens to the autonomic nervous system and provides us with just as powerful predictors of risk of death.
Norman Swan: So what you're saying is you're not finding necessarily blocked coronary arteries; in other words you couldn't replace the stress test or some of these nuclear scans with this simple test, because it's not picking up a blocked artery which then you can go on and do an angioplasty on.
Michael Lauer: Well we may very well; we are looking at something different than blocked coronary arteries. But what we can say is this: people have a normal heart rate recovery are at extremely low risk, and because they are at extremely low risk, it makes a lot more sense to manage them conservatively, and not project them to essentially risky procedures. If you know that somebody has a death risk of less than 1% per year then it really doesn't make very much sense to refer them for a procedure which carries with it a 1%-2% chance of death within 30 days.
Norman Swan: So in other words, it's almost a negative message that you get from it from the positive result.
Michael Lauer: Well yes. I would say right now the immediate practical use of this is that if a patient has a normal heart rate recovery, that identifies them as a low risk, therefore we don't really need to send them for further testing unless they're having for example refractory symptoms. But if their symptoms are easily controlled by medicines, or they're not having any symptoms at all, you know they're at very low risk and so we know that we can comfortably manage them conservatively without going on to any further testing.
Norman Swan: Now this paper is interesting in that you don't actually commit yourselves to saying that these people died of heart attacks or sudden coronary death. It's overall death. Now commonsense would say that they karked it from their hearts, but you're not sure; why is that?
Michael Lauer: We're not sure why they died, that's something which is going to have to require further research. What the exact mechanism is between this and death is not known. The current most popular theory is that if there's problems with the autonomic nervous system, people are more vulnerable to developing fatal heart arrhythmias, like sudden cardiac death and that's the most likely cause of death but that's going to require more work.
Norman Swan: So just in summary: the next challenge with this is to see whether without bringing somebody into the laboratory, there is a way of predicting, with just regular exercise, whether or not your recovery is adequate?
Michael Lauer: Right. And other things that we need to look at is how well this is working in other populations. We also need to look at how best to incorporate this with the rest of the exercise test result. And then of course one big question is what do you do about people who have an abnormal heart rate recovery beyond things that we already know about, like smoking cessation, cholesterol reduction and blood pressure reduction. Are there other things that we could specifically do to treat this abnormality, and that's something which will have to await further work.
Norman Swan: Let's say for a moment you had somebody who has an abnormal heart rate recovery one minute after the stress test, but the stress test doesn't show any ischaemic changes, there's no changes due to shortage of blood supply, therefore nothing that otherwise would make you suggest there's a blocked coronary artery. If it was you, would you ask the doctor to send you off for an angiogram to see whether or not you've got a blocked coronary artery?
Michael Lauer: I would be very worried. That would be an occasion I would be worried about. What I would do next is an imaging test; I would do like a nuclear test, or an echocardiogram to see if there's evidence of a blockage there, then I would go from there. I would only get a coronary angiogram if the imaging test showed that there is a problem.
Norman Swan: Michael Lauer, thanks for joining us on the Health Report.
Michael Lauer: Great, thank you so much for your interest in our work.
Norman Swan: Dr Michael Lauer is a cardiologist at the Cleveland Clinic and that study was published in the current edition of The New England Journal of Medicine.
Cole et al. Heart-rate recovery immediately after exercise as a predictor of mortality. New England Journal of Medicine 1999;341:1351-1357
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