Medical Associates Clinic

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GETTYSBURG MEDICAL NEWS
The Clinical View
by P.E. Hoffsten, MD
20 March 2002

HOW FAST SHOULD YOUR HEART BEAT?

    In this age of fancy CAT scans, and echocardiograms and electrocardiograms and many other fancy studies that cardiologists do, one of the most useful pieces of information about a person’s heart still comes from simply measuring how fast the heart is beating.  In a normal adult male, the average heart rate is 68 beats per minute and in a female it is around 74 beats per minute.  The textbooks list a normal heart rate as between 60 and 100 per minute.

       But under certain conditions, these numbers can change substantially.  For example, a very skilled athlete may have a resting heart beat of only 40-45 beats per minute.  Classically, competitive swimmers will have a relatively slow heartbeat in this area.  John Landy, who was the first man to run the 4 minute mile had a resting heartbeat of 32 beats per minute and yet he was as healthy as a man could be.  For a trained athlete, a slow heartbeat is not abnormal. However, for an elderly individual who is used to a resting heartbeat in the 70’s, it is usually an ominous and dangerous sign when the heartbeat drops into the 50’s, 40’s and finally into the 30’s.  This is usually the result of something called “sick sinus syndrome”;  this is a condition in which the clock that runs the heart simply gets too tired and runs slower and slower.  These people frequently need to have a pacemaker in order to get their heart beating fast enough to be comfortable.  Alternatively, certain drugs such as Digitalis, Amiodarone, beta blockers (Atenolol, Metoprolol), or calcium channel blockers such as Verapamil or Diltiazem can all cause the heart to beat too slowly.  Sometimes simply stopping these drugs is enough to get a heartbeat back into the normal range and avoid the need for a pacemaker.

       What about the opposite problem of a heart going too fast?  The predicted maximum heart rate is age related.   A person’s maximum heart rate is equal to 220 minus the person’s age. Thus a 60 year old individual would have a predicted maximum heart  rate of 160 beats per minute whereas an 80 year old individual would have a predicted  maximum heart rate of 140 beats per minute.  This formula for deriving a person’s maximum heart rate has some remarkable predictive values.  For instance if a person can exercise to the point of reaching 85% of their predicted maximal heart rate, there risk of heart attack is markedly  decreased compared to people who can not do this.  Another simple marker of heart health has to do with how fast the heart slows after peak exercise.  For instance, if a 60 year old man were  to exercise to 85% of predicted maximum heart rate, his heart would be beating 136 times per minute.  A measure of heart health is how quickly the heart slows down after the exercise is  completed.  It should be at least 12 beats decreased in the first minute of rest.  In other words,  one minute after resting from maximum exercise, his heart rate should be under 124 or less.  In  general, the greater the rate of drop of the heart beat after exercise, the healthier the person’s heart is.

     As a last consideration, it has been shown that a fast resting heart rate is basically an unhealthy situation.  Ideally a resting heart rate should be in the 60-80 beats per minute range.  A heart rate faster than this has been shown to be associated with an increased incidence of heart attack.

       As a final point of interest, one might consider the case of world class mountain climbers.These individuals are in excellent physical condition with resting heart rates in the 50’s when at sea level. As they climb higher and higher up in a mountain, the amount of oxygen in the air decreases progressively and it takes an increased heart rate to deliver the necessary oxygen to the body’s parts.  But as the climber goes higher and higher up in the mountains, their resting  heartbeat becomes higher also so that above 26,000 feet, a climber’s resting heartbeat may be 130 beats per minutes.  While at sea level, the mountain climber may be able to increase their heart rate from 50 to 150 beats per minute in response to heavy, vigorous exercise.  When the climber reaches 26,000 feet or higher, their maximum heart rate may be very near their resting  heart rate.  In mountain climbing  jargon, this is called the death zone because the climber is virtually running out of air and asking their heart to go faster than a heart can go on sustained  basis.

       The point of this story is that the same type of thing happens to individuals in our community when their heart begins to fail from high blood pressure, diabetes, or other causes. Asking the heart to go too fast, too long, simply wears it out and mortal outcome is predictable.  Your car maybe able to go 100 miles an hour but it can’t do it for very long without wearing out.  The same is true for the human heart.  There needs to be rest periods and appropriate maintenance by avoiding high blood pressure, diabetes, cigarette smoking, and excess cholesterol.  When one puts continuous stress upon a heart over a long period of time, it is the same as climbing mountains in the death zone and hearts wear.

       As a final note, it should be known that exercise for brief periods on a daily basis is highly beneficial for overall health and heart function.  Getting the heart rate into the training zone, of 60-80% of the maximum age adjusted heart rate is highly beneficial.  Trying to run a heart for longer periods of time at much higher rates wears the heart out.