Atrial fibrillation is the most common irregular heartbeat. It occurs in 1.5 to 2 percent of the general population and risk increases with age. It affects 10 percent of 75-year-olds and 20 percent of those over 85, because aging increases the risk factors for atrial fibrillation such as blocked arteries, high blood pressure or diabetes.

In a healthy heart, each heartbeat starts when a "battery" in the upper heart (atrium) sends an electrical impulse through the upper heart to make it contract to squeeze blood toward the lower heart (ventricle). Then the electrical impulse reaches another "battery" in the lower heart to make the lower heart squeeze blood forward. Atrial fibrillation means that the upper heart quivers and does not push blood forward, while the lower heart beats independently.

Some people with these irregular heartbeats have no symptoms and do not even know that they have atrial fibrillation until it is discovered during a routine physical examination. Common symptoms can include fatigue, palpitations, shortness of breath, lightheadedness, dizziness, fainting, and chest pain or discomfort. These symptoms are usually harmless, but when a person has an upper (atrial) heart that is fluttering, a clot can collect there and pass to the brain to cause a stroke, or to the lungs to block blood flow through the lungs. This is so dangerous that most doctors prescribe anti-clotting drugs to everyone with atrial fibrillation. They may also prescribe:
• drugs to slow heart rate,
• a pacemaker to change the maximum heart rate, and
• sometimes, a treatment called cardioversion, where electrical waves are used to restore a normal heart rhythm.

Risk Factors for Atrial Fibrillation
• High blood pressure, greater than 140/90 (Hypertension, Feb 2012;59(2):198-204; J Am Soc Hypertens, Mar 2015;9(3):191-6)
• Diabetes
• Overweight (J Am Coll Cardiol, Jul 7, 2015)
• Alcohol
• Smoking
• An over-active thyroid
• A very low heart rate, below 50 beats per minute (Circ Arrhythm Electrophysiol, Aug 2013;6(4):726-31)
• Abnormal coronary artery calcium score, even with no heart symptoms (Am J Cardiol, 2014 Dec 1;114(11):1707-12)
• Lack of exercise (Am J Cardiol, 2012 Aug 1;110(3):425-32)
• Aging
• Possibly extreme ultra-endurance exercise

Irregular Heartbeats in Older Athletes and Exercisers
Most researchers believe that exercise helps to strengthen the heart and protect it from disease, but about twenty years ago, researchers noted that some men over 80 who competed in cross country ski races longer than 100 kilometers (60 miles) were at increased risk for atrial fibrillation (BMJ, 1998 Jun 13; 316(7147):1784–1785). Extensive studies have since confirmed this increased incidence of atrial fibrillation in healthy older world-class endurance athletes (Scan J Med & Sci in Sports, Nov 21, 2013;24(4)). However, most of these people were healthy athletes and had no obvious problems with their hearts.

Fit people are less likely to suffer atrial fibrillation, and a regular exercise program reduces a person's chances of developing atrial fibrillation (Circulation, April 22, 2015). More than 36,000 middle-aged women were followed for 10 years, and those who exercised regularly were far less likely to develop atrial fibrillation (Heart, May 27, 2015).

Extreme Endurance Exercise May Increase Risk for Atrial Fibrillation
Two studies raised the concern about extreme amounts of exercise in older athletes. In the first study, 29 elite athletes were given MRIs to look for heart muscle scarring that increases risk of atrial fibrillation. They were Olympic or national team runners and rowers who had competed throughout their lives, including some who had completed more than 100 marathons. In the older group of 12 athletes ages 50 to 67, half showed some heart muscle scarring (J Appl Physiol, June 2011;110(6):1622-6). Those who had trained the longest and hardest had the most scarring. None of the 17 younger athletes (20-42) or the control group of 20 older non-athletes showed this heart muscle scarring.

In the second study, on rats, a 16-week program of daily one-hour treadmill running caused widening of the upper part of their hearts and scarring in the heart muscle that could increase risk for irregular heartbeats (J Am Coll Cardiol, July 2013;62(1):68-77). The scars in the upper heart remained after the rats stopped exercising.

Articles about these studies in the Wall Street Journal, The New York Times and other popular media suggested that athletes who continue to do extensive fast mileage or train for extreme endurance events in later life may be doing more harm than good. I feel that these articles caused a tremendous amount of harm in the exercising community.

Studies Explaining the Signs of Heart Damage in Endurance Athletes
Forty athletes were tested immediately after a 3-to-11-hour cross-country ski race and were found to have right ventricular abnormalities that returned to normal afterwards (Eur Heart J, 2012 Apr;33(8), 998-1006). This is what you expect when you exercise any muscle vigorously. Your skeletal muscles are supposed to feel sore after vigorous exercise because all muscles in your body show signs of damage after being vigorously exercised, and that can include your heart muscle. To make a muscle stronger, you have to exercise so intensely that you damage the z-lines that join the sarcomeres in muscle fibers. You can tell you are doing this when you feel a burning in muscles during exercise and delayed onset muscle soreness (DOMS) several hours afterwards. Then when the z-lines heal, your muscle become stronger. The fibers of heart muscle have the same z-lines that skeletal muscles have, but we do not have any good evidence to show that the same damage occurs to your heart muscle during exercise.

A newer study found no evidence of irregular heartbeats from damage to the right ventricular heart chamber in elite lifetime-endurance athletes (Circulation, May 17, 2016;133(20):1927-35). Thirty-three world-class endurance athletes, 30 to 60 years old, training for more than 15 hours per week, received extensive heart function tests that were compared to the same number of healthy men who did not have a regular exercise program. Of course, the athletes had larger and stronger heart right ventricles, but they had no evidence of damage or potentially harmful effects. Their hearts pumped more blood, beat at a much slower resting rate, and had no evidence of atrial fibrillation. Athletes with lifelong high training volumes seem to be very unlikely to suffer from heart disease.

My Recommendations
In my opinion, athletes with atrial fibrillation are far less likely to suffer clots that cause strokes than non-athletes with atrial fibrillation, but I have not seen any studies to support my belief. Healthy athletes can have occasional irregular heartbeats that may not harm them, but at this time, most doctors treat atrial fibrillation in athletes the same way they treat their other patients.

I believe that virtually everyone should try to exercise every day. Older athletes can and should continue to compete into their later years, but they need to remember that preventing heart problems involves more than just exercising. You can help to prevent atrial fibrillation with an anti-inflammatory lifestyle:
• Eat lots of fruits, vegetables, nuts and beans
• Avoid sugared drinks, sugar-added foods, red meat, processed meats and fried foods
• Lose excess weight if overweight
• Keep hydroxy Vitamin D levels above 20 ng/ml (Current Atherosclerosis Reports, Jan 23, 2017)
• Exercise regularly