Monday, February 1, 2016

Nine Interesting Facts About the Athlete’s Heart

by Larry Creswell, M.D.

  1. The Beat Goes On. Medical folks define the normal heart rate to be 60 to 100 beats per minute. Anything slower is called bradycardia and anything faster is called tachycardia. A slow heart rate is an adaptation to chronic exercise, though, so it’s typical for a well-trained endurance athlete to have bradycardia at rest. This is healthy.

  2. How Many Heartbeats? The human heart starts beating during the fourth week of gestation and beats more than 50 million times before birth. A typical human may have as many as 3 billion heartbeats during a lifetime. In general, longer life-expectancy is associated with a slower heart rate -- a good thing for athletes with bradycardia at rest! Use this calculator to estimate your life expectancy and lifetime total heartbeats based on your resting heart rate.

  3. Gear Up! In a recent blog post, Alan Couzens described the anatomical and physiological characteristics of a Kona Monster -- the ideal Kona triathlete. He reminded us of the cardiovascular demands: cardiac output of 34 liters per minute at a heart rate of 180 beats per minute. Well-trained athletes have a tremendous reserve. At rest, the cardiac output can be 5-6 liters per minute, but can ramp up seven (or more)-fold when needed. Next time you’re at the grocery store, take a look at seventeen 2-liter soda bottles. At full exertion, the heart pumps that much every minute!

  4. Big heart. I’m reminded of the children’s story, The Grinch Who Stole Christmas. You’ll recall as the story heads to its conclusion, “[T]hat the Grinch’s small heart grew 3 sizes that day!” For the endurance athlete, it takes more than a single day, but there is tremendous adaptation over time to exercise. For endurance athletes, the walls of the left ventricle (the pumping chamber) increase in thickness by 20-30% and the cavity of the left ventricle increases in volume by as much as 50%. This is how the heart can generate such a large cardiac output.

  5. Sudden Cardiac Death (SCD). Undoubtedly, the most dramatic heart problem for athletes is sudden cardiac death (SCD). A sudden arrhythmia -- ventricular tachycardia or fibrillation -- causes the heart to stop pumping blood. Although exercise is healthy for the heart over the long term, SCD is much more common during (and immediately after) exercise. Recent studies show the risk of SCD to be: 1 per 44,000 NCAA athletes per year; 1 per 370,000 half marathon participants; 1 per 101,000 marathon participants; and 1 per 75,000 triathlon participants.

  6. A Bright Spot. Historically, there have been few survivors from out-of-hospital SCD. In one recent study, though, as many as 29% of athlete victims of cardiac arrest during marathon or half marathon events were successfully resuscitated. Credit goes to prompt bystander CPR and early defibrillation. This is good motivation for athletes and their cheering sections to attend an American Heart Association (AHA) CPR course.

  7. A Skipped Beat? Sometimes there really is a skipped beat, but more often there are extra beats. We feel these “extra” beats as palpitations. Although there are many different arrhythmias, the most common for athletes are atrial arrhythmias -- those that originate in the upper (non-pumping) chambers of the heart. If we include everything on the spectrum, from simple extra atrial beats to sustained atrial arrhythmias, more than one third of endurance athletes are probably affected.

  8. Watch Out! One fascinating -- and thankfully, uncommon -- cause of SCD in athletes is a blow to the chest. One example is a baseball hit directly back at the pitcher or the hitter struck with a fastball. That sudden blow can instantaneously produce a fatal arrhythmia and the athlete collapses. We call this situation commotio cordis, from the Latin, “agitation of the heart.”

  9. Oh, baby. There are variety of forms of inherited heart disease. The most common congenital heart problems that manifest in athletes during adulthood are: hypertrophic cardiomyopathy (HCM), 0.5% in the general population; anomalies of the coronary arteries, 1% in the general population; and valve or aortic problems related to bicuspid aortic valve (BAV), 1% in the general population. A careful history and physical examination can sometimes identify these problems before any harm occurs.

Larry Creswell, M.D., is a cardiac surgeon and Associate Professor of Surgery at the University of Mississippi Medical Center in Jackson, Mississippi. In addition to his regular column on Endurance Corner, he maintains The Athlete's Heart blog to offer information about athletes and heart disease in an informal way and to encourage exchange and discussion that will help athletes build a heart-healthier lifestyle. You can contact him at lcreswell@umc.edu.
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