My friends at Endurance Corner recently circulated an abstract about atrial arrhythmias in endurance athletes and I thought this would be a great topic for the blog. At the outset, let me say that entire books have been written on the topic of atrial arrhythmias, so anything here will necessarily be the story “in a nutshell.”
What is Atrial Fibrillation?
In the normal situation, the electrical activity of the heart is highly organized, starting as a self-initiating impulse in the sinus node located in the upper chamber on the right side of the heart (right atrium) and proceeding through the right and left atrium, then down into the lower chambers of the heart, the ventricles. In medical terms, the normal situation is a called a sinus rhythm. And when the heart rate is between 60 and 100 beats per minute, we call this a “normal sinus rhythm”. Any time the heart’s electrical activity is NOT a normal sinus rhythm, the situation is called an arrhythmia….and there are many different types. I realize that many athletes have a sinus rhythm at less than 60 beats per minute at rest—and ordinarily we’d call this a “sinus bradycardia”—but this is quite normal for the well trained athlete.
Today, we’re talking about atrial fibrillation (AF), the most common sustained arrhythmia. In this situation, the electrical activity in the upper chambers of the heart is highly disorganized. You might picture many circular electrical circuits all firing in disarray. The result is that the atria, the upper chambers of the heart, do not contract properly and electrical impulses reach the ventricles, the lower chambers of the heart, in an irregular sequence and often at a fast rate. The result is an irregular pulse (when you feel the pulse at the wrist, for example), a reduction in the cardiac output (the amount of blood the heart pumps each minute), and stagnation of blood within the atria. AF may be constant (or persistent or chronic) or intermittent (paroxysmal).
Thinking for a moment about the general population, the chance of having AF increases with age, The overall incidence is less than 0.5%, but that rate increases to more than 8% at age 80. This arrhythmia commonly accompanies other forms of heart disease such as mitral valve prolapse, rheumatic heart disease, or hyperthyroidism, but it may also occur alone. When it occurs alone, in the absence of other heart disease, we call it “lone atrial fibrillation.” In the United States, it is estimated than more than 2 million individuals are affected. And importantly, AF is associated with a variety of poor outcomes over the long-term, including stroke, heart failure, and even death. In fact, the mortality rate for individuals with AF is nearly twice that for individuals without AF.
AF can produce a variety of symptoms….and sometimes, no symptoms at all. The symptoms are usually due to a fast heart rate and include: palpitations, chest discomfort, shortness of breath, sweating (diaphoresis), and even syncope (blacking out). Palpitations are probably the most common symptom in athletes and, in fact, recent studies have shown that as many as 70% of athletes in some sports will report having palpitations during exercise. Most palpitations are benign, are not associated with any underlying heart disease, and require no treatment. But if palpitations are bothersome, the problem should be investigated.
Atrial Fibrillation in Athletes
Back to athletes…. What’s interesting is that athletes are much more likely than non-athletes to be bothered by AF. Not only is AF the most commonly encountered arrhythmia in athletes but also a variety of cohort studies have shown that the prevalence of AF in athletes is probably 2 to 3 times that of the general population. The reasons are not entirely clear, but there are several likely explanations. First, it is likely that the cardiovascular stresses placed on the athlete’s heart over the long term result in structural changes to the muscle tissue of the atria that foster irregular electrical activity. And it’s probably the case that not all sports are created equal in this regard (eg, the changes resulting from a career of golf might be different from those resulting from a career as a marathoner). Second, there is increased firing of various autonomic nerves that supply the heart might promote a disruption in the normal electrical activity. And lastly, low level chronic inflammation that accompanies exercise has been proposed as a possible explanation.
In athletes, intermittent AF is much more common than persistent AF, but either form can impair the athlete’s performance. Af can limit peak performance and can also become bothersome to the point that the amount of training which is possible is reduced.
Diagnosis of Atrial Fibrillation
How do we make the diagnosis of AF? Most patients will report 1 or more of the symptoms listed above and their physician will do an electrocardiogram (ECG). The ECG will clearly show the AF if the arrhythmia is constant, but may be completely normal if the AF is intermittent. A Holter monitor (a tape recorder of sort, with chest electrodes) can be worn for 1-3 days to “capture” any intermittent AF on tape. The Holter monitor can also be worn during treadmill or other monitored exercise to help “capture” the arrhythmia on tape.
Treatment of Atrial Fibrillation
Medical treatment. Medical treatment is focused on 2 alternative approaches: 1) rate control, where medicines are prescribed that keep the heart rate relatively low in spite of having the arrhythmia and 2) rhythm control, where medicines are prescribed to try to convert and keep the electrical activity in a sinus rhythm rather than AF. The typical rate control medications include: beta-blockers (propranolol, atenolol) and calcium channel blockers (diltiazem, Verapamil). The typical rhythm control medications include Amiodarone and Sotalol, among others. Unfortunately, most long-term studies (primarily in non-athletes) show that all of these medications are often ineffective (
A second medical consideration is blood thinning, or anticoagulation, to help prevent small blood clots from forming in the atria during AF and breaking loose and causing stroke. There are guidelines published by the American Heart Association and American College of Cardiology (ACC) that address this problem. For athletes with no other form of heart disease other than AF, a daily aspirin is probably prudent. For those with other forms of heart disease in addition to AF, a stronger anticoagulant such as Warfarin (Coumadin) may be recommended to reduce the long-term risk of stroke. Unfortunately for the athlete, blood thinning with Coumadin also carries a risk of severe bleeding if bodily injury occurs during sports activities.
Ablation treatment. Another option for individuals affected by AF is ablation, performed either as a catheter-based procedure or as a surgical procedure. In the catheter-based procedure, catheters are threaded up to the heart, often starting in the arteries or veins of the groin, and electrical energy is used to ablate (think “kill”) the tissue in the heart that is responsible for starting or propagating the abnormal electrical activity of AF. In the surgical version, a series of small port incisions are made in the chest wall on both sides, and using video assistance, tiny surgical surgical instruments are inserted into the chest to ablate the heart tissue, again using electrical energy. Both of these procedures can be very straightforward for patients with intermittent AF and can be much more difficult for patients with persistent AF. Regardless, the risks associated with these procedures are relatively small, and I would encourage athletes bothered by AF to give strong consideration to these options.
Guidelines for Participation in Sports
Athletes with AF whose heart rate is controlled (no higher than the typical sinus heart rate associated with exercise) can participate fully. Those athletes who require anticoagulation with Coumadin should avoid sports in which the risk of bodily injury is high (because of the higher risk of internal bleeding with injury).