Athletes with Bradycardia: How Slow Is Too Slow?

Educational Objectives

Distinguish between physiologic bradycardia (caused by autonomic conditions or athletic training) and inappropriate bradycardia that requires permanent cardiac pacing.

Summary

• In athletes, a normal electrocardiogram (ECG) is the exception; the vast majority of athletes show some ECG changes that are most likely attributable to physiologic adaptation of the cardiac autonomic nervous system to athletic conditioning.
• Resting sinus bradycardia, as defined by a heart rate <60 bpm, is the most common ECG pattern in athletes. In highly trained athletes marked bradycardia <30 bpm is not uncommon, particularly during sleep.
• It is crucial to distinguish between physiologic bradycardia (caused by autonomic conditions or training effects) and inappropriate bradycardia that requires permanent cardiac pacing.

In athletes, a normal electrocardiogram (ECG) is the anomaly. In Italy, where there is a nationwide screening program for conditions that can cause sudden cardiac death, the proportion of individuals 14 to 35 years of age with a completely normal ECG was 42.5% in nonathletes but only 2.6% in athletes (p < 0.001).¹ The paper by Raju and colleagues, published in JACC, demonstrated that trained athletes show ECG changes such as sinus bradycardia, first-degree atrioventricular block, and early repolarization, all of which can result from physiologic adaptation of the cardiac autonomic nervous system to athletic conditioning (e.g., increased vagal tone and/or withdrawal of sympathetic activity).

The ECGs of trained athletes often exhibit pure voltage criteria (i.e., based only on QRS amplitude measurements) for LVH that reflect physiologic LV remodeling with increased LV wall thickness and chamber size (as discussed immediately above).

Resting sinus bradycardia, as defined by a heart rate <60 bpm, is the most common ECG pattern in athletes, occurring in 57.6% of the 4,081 athletes versus 26.1% of the 7,764 nonathletes evaluated in the aforementioned Italian study. Prevalence did vary depending on the type of sport and the level of training/competition. Participation in sports that require high endurance, such as cycling, cross-country skiing, and rowing/canoeing, is significantly associated with a greater rate and extent of physiologic ECG changes compared with participation in sports that require more strength and speed but relatively less endurance.

In highly trained athletes, Pelliccia and others have noted² that marked bradycardia <30 bpm and asymptomatic sinus pauses >2 seconds are not uncommon during 24-hour ECG, particularly during sleep.

When the Abnormal Is Normal

When Dr. Raju and his associates reported their large analysis in JACC in 2014, they demonstrated that 1 in 5 young people have group 2 ECG patterns, meaning ECG patterns suggestive of cardiomyopathy or structural cardiac abnormality.¹ The low incidence of sudden cardiac death in young people suggests that, in most instances, such patterns are nonspecific. That is important to know, given that the European guidelines recommend transthoracic echocardiography in individuals with group 2 ECG patterns.

According to Dr. Raju, their findings have significant implications for the feasibility and cost effectiveness of nationwide screening programs for CVD in young nonathletes and athletes alike, on the basis of current guidelines.

What advice do the current guidelines offer? As Pelliccia and others noted in their recommendations for interpreting a 12-lead ECG in the athlete,² only profound sinus bradycardia and/or marked sinus arrhythmia (heart rate <30 bpm and/or pauses ≥3 seconds during waking hours) need to be distinguished from sinus node disease. Sinoatrial node dysfunction can be reasonably excluded by demonstrating that: 1) symptoms such as dizziness or syncope are absent; 2) sinus bradycardia is easily overcome with exercise, suggesting that high vagal tone causes slowing of the sinoatrial node; and 3) bradycardia reverses with reduction or discontinuation of training. (Note: it’s not just exercise: heart rate also normalizes during sympathetic maneuvers or with drugs, with preservation of maximal heart rate.)

The ESC pacing guidelines also address this issue,³ noting that “it is crucial” to distinguish between physiologic bradycardia, due to autonomic conditions or training effects, and inappropriate bradycardia that requires permanent cardiac pacing. For example, sinus bradycardia, even when it is 40 to 50 bpm while at rest or as slow as 30 bpm while sleeping, does not require cardiac pacing in trained athletes.

In brief, according to Hariharan Raju, MBChB, St. George’s University of London, United Kingdom, if the patient is not symptomatic, there is no such thing as “too slow.” Having said that, he reminds clinicians not to forget the differential diagnosis, considering that there are other potential reasons for bradycardia such as Lyme disease, an inherited disease, and structural heart disease.

Readings

1. Chandra N, Bastiaenen R, Papadakis M, et al. Prevalence of electrocardiographic anomalies in young individuals: relevance to a nationwide cardiac screening program. J Am Coll Cardiol 2014;63:2028-34. http://content.onlinejacc.org/article.aspx?articleID=1838317

2. Corrado D, Pelliccia A, Heidbuchel H, et al. Recommendations for interpretation of 12-lead electrocardiogram in the athlete. Eur Heart J 2010;31:243-59.

3. Brignole M, Auricchio A, Baron-Esquivias G, et al. 2013 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy: the task force on cardiac pacing and resynchronization therapy of the European Society of Cardiology (ESC). Developed in collaboration with the European Heart Rhythm Association (EHRA). Eur Heart J 2013;34:2281-329.

Disclosures

Hariharan Raju, MBChB
This author has nothing to disclose.

Interviewer: Freek W.A. Verheugt, MD, FACC
This author has nothing to disclose.

The planning committee reported noting to disclose.

A = Advisory panel B = Speakers’ bureau C = Consultant fees/honoraria D = Data and Safety Monitoring Board E = Equity interests/stock options F = Fellowship support G = Grant support L = Licensing Agreement O = Other relationship R = Royalties S = Salary W = Expert witness

Acknowledgements

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