Listen to the beat: Can heart rate recovery predict death?

 

What if I told you I could make a better-than-average prediction of your lifespan over the next eight years just by calculating how fast your heart recovers after exercise?  What if I also told you that even if you fail this quick calculation test, it is not an immediate death sentence, but rather a fantastic warning system that alerts you to a problem and gives you a chance to make amends?  Would you be interested in learning more?  Well, if avoiding death is on your list of 2015 New Year’s resolutions, you are going to love this information.

We have all experienced the familiar increase in heart rate after going up a few flights of stairs or running to catch a plane at the airport.  A simple yet amazing process occurs.  The brain senses a change and cues the cardiovascular system to increase the heart rate, respiration rate, and blood pressure to supply the body with the oxygen it will need for the extra effort.  But have you ever considered the mechanisms behind the opposite side of this coin?  How do our bodies put the brakes on this ramp-up system and reestablish homeostasis; and can this process tell us anything about our risk of heart disease or death?

Heart rate recovery (HRR) is the term we use to describe the drop in heart rate following physical exertion.  Generally speaking, we assume the faster the drop after exertion the better the health of the cardiovascular system.  We have long known of accelerated HRR in athletes as compared to the general population.  This accelerated recovery is thought to be the result of improved vagal tone.  The vagus nerve has many functions, but one of the primary ones is to slow down the heart rate for the parasympathetic aspect of the autonomic nervous system.  For our simplistic purposes, think of the role of the vagus nerve as the equivalent of brakes on your car, except in this case it’s a brake for your heart.  If you have good brake pads and the system is maintained, you can smoothly decelerate your car and avoid problems.  If, on the other hand, your brakes are worn or ineffective for some reason, you will have a harder time slowing down and preventing a serious problem.  In the same manner, the interplay between the accelerator pedal (sympathetic nervous system) and the brake (parasympathetic nervous system) and the effectiveness of the brake to slow down the heart rate after exertion might be critical in the body’s ability to avoid a crash.

In 1999 researchers examined the relationship between heart rate recovery from exercise and mortality. For six years they followed 2,428 adults without a history of heart failure or coronary revascularization and without pacemakers.1 It is important to note these patients did not have a history of heart disease.  Of the total patients, 639, or 26%, had abnormally low HRR after one minute following cessation of exercise.  An abnormally low value was considered to be a drop of 12 or fewer beats per minute after the first minute of recovery. 

After six years, 213 patients had died from various causes.  Of these 213 patients, 56% had abnormally low values for heart rate recovery.  This equated to a relative risk of 19% for those with an abnormal recovery versus 5% for all others.  This was one of the first studies to clearly show heart rate recovery as a powerful independent predictor of death.

Since the investigation back in 1999, researchers have continued to clarify the association between HRR and mortality.2,4,5 One key finding in the last ten years has been that cardiac rehab can improve heart rate recovery in patients with heart disease, and this improvement is linked to a decrease in mortality from all causes.3,4  A retrospective study published in the journal Circulation in 2011 demonstrated once again the strong association between abnormal heart rate recovery and all-cause mortality. Not only that, but it also showed that individuals who normalized their HRR after phase two cardiac rehab returned their relative risk to that of patients with baseline normal HRR.3

Let’s assume you are buying into the well-supported argument that heart rate recovery can be an important predictor of your health and mortality, and you want to use this information to test yourself.  How would you go about doing it?  All you really need is a stopwatch, a step, and the ability to find your pulse. 

1)    Begin by finding your target heart rate range by subtracting your age from 220  (For example: 220 – 50 years old = 170 beats per minute).  Now multiply this by 85%  (170 x .85 = 145 beats per minute).  A fifty-year-old individual would want to get her heart rate over 145 beats per minute for the test.

2)    The next step is to figure out how to measure your pulse.  To find your pulse, press lightly on the carotid artery in your neck located just toward either side and directly below the jaw bone; or you can use the radial artery in your wrist, which is located just below your thumb.  Got it?  Great! 

3)    Now press the start button on the stopwatch and begin by stepping up and down on a step at a cadence of at least 96 beats per minute.  Those individuals in good condition will probably need to raise this cadence up to 120 beats per minute or greater to achieve 85% of their predicted maximal heart rate.  Whatever cadence you choose, you can easily download a cadence app on your smart phone to guide you.  Your goal is to reach your 85% or greater target after about 2–3 minutes of stepping. 

4)    After two minutes of stepping, find your pulse and begin counting for ten seconds, then multiply by six to get your pulse rate.  If you have not yet reached 85% of your predicted maximal heart rate then continue stepping at a faster cadence for another minute.  Once you reach your target, stop exercising, walk slowly around the room, and take your pulse again for ten seconds, then multiply by six. 

5)    At the end of one minute, take your pulse again for ten seconds and multiply by six.  Subtract the first measurement from the second measurement to calculate your heart rate recovery.  If you dropped more than 12 beats per minute, congratulations, you passed the test.  (You can also take your HR at the end of two minutes with a passing score being a drop of more than 42 beats during recovery). 

If you failed, should you go see about a grave plot?  No.  But it is darn sure time to stop screwing around and think about some serious interventions to improve your health and fitness.

Action plan following the test:

1)    If you failed to achieve a 12 bpm drop during the first minute after exercise (or 42 in the first two minutes) then the first step in your action plan is to go and see your physician.  You need a full medical exam from a qualified physician BEFORE we can suggest an intervention plan.

2)    Once you have been cleared by your physician, you should establish a regular aerobic exercise routine of at least 4x per week for 30 minutes at 50–70% of your heart rate max and a resistance training plan 2x per week.

3)    Once you have been cleared by your physician and become accustomed to your new exercise routine (about 6–12 weeks) it is time to begin working high intensity interval training (HIIT) into your routine 2–3 times per week.  HIIT is simply the act of alternating periods of very high heart rate (80–95% of max) with periods of recovery. 

The benefits of HIIT to cardiovascular endurance, blood sugar regulation, body fat loss, and mitochondrial function, as well as central hemodynamic variables, are widely published.  It is also exciting to note that these benefits are extending to at-risk populations such as patients with known cardiovascular disease, prior cardiovascular surgery, heart transplants, diabetes, and even certain autoimmune diseases.

For me, however, the real benefit of HIIT for the topic at hand comes from my—as yet unproven—hypothesis. I believe we will eventually find the vigorous alternating actions of acceleration and deceleration on the heart, which are so prevalent in HIIT as compared to moderate intensity cardiovascular exercise, will lead to increased vagal tone and improved heart rate recovery.  I believe this benefit of HIIT will yield tremendous outcomes as far as decreases in mortality and overall cardiovascular health benefits.  I believe these benefits will exceed those associated with continuous moderate intensity cardiovascular exercise, thus extending the reach and breadth of impact HIIT has on the health and fitness of both general and at-risk populations.     

Simply put, I believe (though, at least to my knowledge, it is in no way proven) that if your heart is regularly and systematically exposed to accelerating and recovering phases along the entire spectrum of its potential range, your health and fitness outcomes will be superior to those of other training methods or inaction. 

1.      Cole, C. R., Blackstone, E. H., Pashkow, F. J., Snader, C. E., & Lauer, M. S. (1999). Heart-rate recovery immediately after exercise as a predictor of mortality. New England Journal of Medicine, 341(18), 1351-1357.

2.      Cole, C. R., Foody, J. M., Blackstone, E. H., Lauer, M. S. (2000). Heart rate recovery after submaximal exercise testing as a predictor of mortality in cardiovascularly healthy cohorts. Annals of Internal Medicine, 132:552-555. 

3.      Jolly, M. A., Brennan, D. M., & Cho, L. (2011). Impact of exercise on heart rate recovery. Circulation, 124(14), 1520-1526.

4.      MacMillan, Davis, Durham, and Matteson (2006). Exercise and heart rate recovery. Heart and Lung, 35(6), 383-390.

5.      Watanabe, J., Thamilarasan, M., Blackstone, E. H., Thomas, J. D., & Lauer, M. S. (2001). Heart rate recovery immediately after treadmill exercise and left ventricular systolic dysfunction as predictors of mortality: The case of stress echocardiography. Circulation, 104(16), 1911-1916.