Working Diagnosis:
Complete Heart Block (Third Degree Atrioventricular Block)

Treatment:
He was placed on activity rest until placement of the dual chamber pacemaker. He was advised to start a gradual return to baseline cycling activity 10 days after pacemaker placement with electrophysiologist clearance.

Outcome:
The patient returned to the clinic one year later and was doing well with regards to his exercise capacity. He continued to bicycle quite vigorously and had noted improvements in his stamina and exercise performance.

Author's Comments:
A low resting heart rate is a common finding seen in athletes due to increased parasympathetic stimulation at baseline. Patients presenting with asymptomatic bradycardia should be worked up with an in office EKG to detect potentially underlying conduction disorders. Early detection of a conduction block can lead to early intervention and improve survival in adults with conduction blocks. It is rare to see an avid cyclist in his 60's present with a complete heart block with mild chest pressure without any previous episodes of lightheadedness or syncope. It is worth investigating the cost benefit analysis to assess outcomes in screening asymptomatic bradycardia in the primary care setting

Editor's Comments:
Atrioventricular block occurs when electrical signals in the heart are delayed or do not reach the ventricles. This can be a physiological adaptation to training but may also be due to coronary artery disease, myocardial infarction, certain medication use, and cardiomyopathy, among other causes. While it was previously thought that atrioventricular dysfunction occurred due to increased vagal tone in athletes, newer studies have suggested that it may be related to electrical remodeling of the heart.

Atrioventricular block leads to bradycardia and patients may present with complaints of chest pain, dizziness, shortness of breathing, palpitations, lightheadedness, and fatigue. In more severe cases of atrioventricular block, patients may present with episodes of syncope. Diagnosis includes an ECG, and may also include a electrophysiology study, Holter monitor, echo, exercise stress test and other lab/imaging studies depending on the possible causes of atrioventricular block.

Asymptomatic patients with first degree or Mobitz Type I second degree atrioventricular block may not require treatment. These types are considered physiologic changes of the athletic heart and findings typically resolve with the onset of exercise. Symptomatic patients or those with higher degree heart block, such as the patient in this case, are generally treated with a pacemaker. Participation in competitive athletics is a decision best made between an athlete and their cardiologist.

References:
1. Mesirca P, Nakao S, Nissen SD, et al. Intrinsic Electrical Remodeling Underlies Atrioventricular Block in Athletes. Circulation Research. 2021;129(1).
2. D'Souza A, Trussell T, Morris GM, Dobrzynski H, Boyett MR. Supraventricular Arrhythmias in Athletes: Basic Mechanisms and New Directions. Physiology. 2019;34(5):314-326.
3. Drezner JA, Sharma S, Baggish A, et al. International criteria for electrocardiographic interpretation in athletes: Consensus statement. British Journal of Sports Medicine 2017(51):704-731.

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