The relationship between sinus bradycardia and physical exercise is well known. Sinus bradycardia is defined as a heart rhythm that has a normal origin (the sinus node) and a heart rate of less than 60 beats per minute (bpm). The heart rate depends on the discharge rate of the sinus node. This rhythm is conditioned by the nervous stimulus (the balance between the sympathetic and vagus nerves) and circulating hormones (mainly catecholamines). There are people without pathology who have a slow heart rate by nature. In the case of people who practice physical exercise or sport regularly, their heart rate may be slow due to adaptation to training.
Sinus bradycardia is therefore common in athletes. The slow heart rate in them is primarily caused by increased vagal tone secondary to physical conditioning and is therefore considered physiological. The response of heart rate to training depends on the individual. Most athletes have mild sinus bradycardia (greater than 40 bpm). Some may have lower heart rates, even 30-40 bpm at rest. This is usually seen in highly trained athletes. In them, it is possible to find heart rates lower than 30 bpm during sleep.
Sinus bradycardia is considered a normal response to training in most athletes. Some athletes have significant pauses that typically end with escape beats from the atrioventricular node or the lower parts of the atria. Although this could have pathological significance in a non-athletic individual, it is considered a normal phenomenon in athletes with marked sinus bradycardia. These athletes usually have no difficulty increasing their heart rate during exercise.
Evaluation of the athlete with bradycardia
The evaluation of an athlete with sinus bradycardia should include an assessment to rule out the presence of underlying structural heart disease. The following is recommended:
- Medical history. This begins with an assessment of family and personal history. It should also determine whether the athlete has symptoms related to bradycardia (especially dizziness, loss of consciousness, shortness of breath, and/or weakness).
- Physical examination. A general physical examination should be performed, focusing on cardiovascular disease.
- Electrocardiogram. Recommended for all athletes.
- Echocardiogram. This should be performed if any abnormality is suspected with what was discussed in the previous points.
- Stress test. Necessary in certain cases, especially in athletes who engage in intense physical activity.
Other procedures:
If the aforementioned evaluation reveals heart disease, the athlete must undergo the appropriate examinations and treatment. Likewise, the corresponding attitude towards sports will be taken according to the severity of the disease. If no heart disease is detected, the athlete may continue his or her sporting activity as normal. If the athlete reports physical limitations during exercise, a stress test may be indicated to assess the heart rate response to exercise. A 24-hour Holter monitor may also be useful to check changes in heart rate during the day and night.
Many people, whether they are athletes or not, go to the cardiologist for sinus bradycardia. It is common to perform a Holter monitor to check their heart rate throughout the day. In athletes, the most common thing is to find an average heart rate below 60 bpm, with momentary increases in heart rate in response to physical activity or due to situations of stress or nervousness. It is also normal to find a slower heart rate when the individual is relaxed and, above all, when they are sleeping. Likewise, it is common to observe “sinus arrhythmia” in athletes, which has no pathological significance.
An athlete’s Holter monitor may show pauses longer than 2 seconds, although they are usually less than 3 seconds, and are considered a physiological response to sports conditioning. Longer pauses may also be secondary to training but should be monitored more closely. However, if sinus bradycardia or pauses produce symptoms, they should be considered abnormal and may require further investigation. In these cases, athletes should have an electrocardiogram, 24-hour Holter monitor, echocardiogram, and exercise stress test. These studies should also be performed in asymptomatic athletes who have a resting heart rate less than 30 bpm or pauses of more than 3 seconds.
In exceptional situations, athletes must undergo other types of tests. Magnetic resonance imaging, computed tomography, electrophysiological study or coronary angiography may be necessary. These techniques are reserved for those who present symptoms of extreme bradycardia or very long pauses, and show pathological data that require it in the electrocardiogram, Holter, echocardiogram or stress test.
Management of sinus bradycardia in athletes
- The vast majority of athletes who present sinus bradycardia do not require specific treatment. They should not be limited in their physical training or participation in competitions. It should be considered that a well-trained athlete presents sinus bradycardia as a normal response to physical conditioning and does not represent any type of pathology or limitation.
- Athletes with symptoms related to sinus bradycardia secondary to physical conditioning should decrease their training level to assess response. It is common for the heart rate to increase when training is reduced, and the symptoms disappear. If this is the case, no further testing or further restriction is required. If bradycardia and symptoms persist despite reduced training, the athlete should undergo further testing, as discussed in the previous section.
- If the studies reveal a pathology, the corresponding diagnostic and therapeutic measures must be applied. In addition, appropriate recommendations regarding exercise should be given. This all depends on the pathology in question. In any case, if no correctable cause is found and the athlete continues to have symptoms of bradycardia or significant pauses despite reducing or even suspending training, it may be advisable to implant a permanent pacemaker. This is rarely necessary. The athlete with a pacemaker can return to training normally, with the minor limitations that the pacemaker requires.
