Heart Health for Endurance Athletes: Athlete’s Heart vs. Pathological Heart Disease

Introduction: Exercise is Medicine, But the Heart Has Limits

Regular exercise is undoubtedly one of the most effective ways to prevent cardiovascular disease. However, when training volume reaches the level of an endurance athlete—cycling 15-20 hours per week or running over 100 kilometers—the load on the heart far exceeds that of the average person. Over time, the heart undergoes structural adaptations known medically as “Athlete’s Heart”.

The issue is: these changes on an ECG and echocardiogram can sometimes be extremely similar to pathological heart diseases such as Hypertrophic Cardiomyopathy (HCM) or Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC). The latter is a primary cause of sudden death in young athletes.

Normal Adaptations in Athlete’s Heart

Mechanism of Cardiac Remodeling

Endurance exercise (such as cycling, marathon running, swimming) primarily produces volume overload. To meet the high cardiac output demands during each exercise session, the heart undergoes the following adaptations:

• Left Ventricular Dilation: End-diastolic dimension can reach 55-65mm (normal upper limit approx. 56mm)
• Moderate Left Ventricular Wall Thickening: Typically between 12-15mm
• Right Ventricular Dilation: Due to increased pulmonary circulation pressure, the right ventricle also dilates
• Increased Stroke Volume: Resting heart rate drops to 40-50 bpm or even lower
• ECG Changes: Sinus bradycardia, early repolarization, increased voltage

These changes are physiological, symmetrical, and reversible. Once training stops for 3-6 months, cardiac structure usually returns to the normal range.

The Grey Area Between Normal and Abnormal

According to the 2020 International Consensus on ECG Interpretation in Athletes by the European Society of Cardiology (ESC), the following changes are considered normal (no further examination needed):

• Sinus bradycardia (≥30 bpm)
• First-degree AV block
• Incomplete right bundle branch block
• Early repolarization
• Left ventricular voltage elevation (meeting LVH voltage criteria but without other abnormalities)

Pathological Heart Diseases to Watch Out For

Hypertrophic Cardiomyopathy (HCM)

HCM is the most common cause of sudden death in athletes under 35, with a prevalence of approx. 1/500. Its characteristics include:

• Asymmetric ventricular wall thickening (typically ≥15mm)
• Left ventricular cavity not dilated or even small
• Abnormal diastolic function
• Possible left ventricular outflow tract obstruction

Key points for differentiation from Athlete’s Heart: In Athlete’s Heart, wall thickening is symmetrical and accompanied by chamber dilation; in HCM, thickening is typically asymmetrical and the chamber is small. The “grey area” of wall thickness between 13-15mm requires further examination.

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)

ARVC is particularly concerning in endurance athletes, as studies indicate that high-intensity endurance exercise may accelerate the expression and progression of ARVC. Characteristics include:

• Right ventricular dilation and dysfunction
• Myocardium replaced by fibrofatty tissue
• Ventricular arrhythmias (especially during exercise)
• T-wave inversion in ECG leads V1-V3

A study published in European Heart Journal in 2023 indicated that long-term high-intensity endurance training (accumulating over 2000 hours) is associated with an increased risk of right ventricular fibrosis, even in athletes without gene mutations.

Exercise-Induced Atrial Fibrillation

This is a relatively new understanding: the risk of developing atrial fibrillation (AF) in long-term endurance athletes is 2-5 times that of the general population. Possible mechanisms include:

• Atrial dilation and fibrosis
• Autonomic nervous system changes (increased vagal tone)
• Repeated atrial wall stretching

Male endurance athletes over 40 years old with more than 10 years of training history are at the highest risk. If palpitations, worsening shortness of breath during exercise, or a sudden drop in exercise tolerance occur, AF should be considered.

Screening Recommendations: Current Situation and Advice in Taiwan

International Guidelines

• American Heart Association (AHA): Recommends a 14-item questionnaire screening (medical history + family history + physical examination); does not routinely recommend ECG
• European Society of Cardiology (ESC): Recommends a 12-lead ECG as a routine screening item
• International Olympic Committee (IOC): Supports ECG screening and recommends regular follow-up

Practical Advice for Taiwanese Athletes

1. Initial Screening: It is recommended that everyone starting high-intensity endurance training undergo a cardiac screening including a 12-lead ECG. In Taiwan, most medical centers’ sports medicine departments or cardiology departments can arrange this, costing approx. NT$500-1,500 out-of-pocket.

2. Timing for Advanced Examination:

   • Abnormal findings on ECG
   • Syncope or near-syncope during exercise
   • Family history of sudden cardiac death in a first-degree relative before age 50
   • Unusual chest pain or shortness of breath during exercise

3. Advanced Examination Items:

   • Echocardiogram: Assesses structure and function (out-of-pocket approx. NT$2,000-4,000)
   • Cardiac MRI: Gold standard, can detect myocardial fibrosis (out-of-pocket approx. NT$15,000-25,000)
   • 24-hour Holter monitoring: Assesses arrhythmias
   • Exercise ECG (Treadmill test): Assesses exercise-induced arrhythmias

4. Regular Follow-up: For high-training-volume athletes over 35 years old, it is recommended to undergo echocardiogram follow-up every 2-3 years.

Warning Signs: When to Stop Exercise and Seek Medical Attention

If the following symptoms occur, please stop exercise immediately and seek medical attention as soon as possible:

• Chest pain, tightness, or abnormal pressure sensation during exercise
• Syncope or near-syncope during or immediately after exercise
• Feeling of abnormal rapid, irregular heartbeat or “skipped beats” during exercise
• Unexplained sudden drop in exercise tolerance
• Abnormal shortness of breath during exercise (disproportionate to usual performance)

Conclusion: Train Smart, and Screen Smart

Athlete’s heart is a wonderful adaptation of the human body to long-term training; the cardiac changes in the vast majority of endurance athletes are benign. However, recognizing risks, undergoing appropriate screening, and paying attention to warning signs are manifestations of taking responsibility for your own health.

Your heart is your most important engine. Just as you regularly maintain your carbon fiber frame and ceramic bearings, please treat your heart with the same attitude.

References

• Sharma S, et al. International recommendations for electrocardiographic interpretation in athletes. Eur Heart J. 2018;39(16):1466-1480.
• La Gerche A, et al. Exercise-induced right ventricular dysfunction and structural remodelling in endurance athletes. Eur Heart J. 2012;33(8):998-1006.
• Maron BJ, et al. Eligibility and Disqualification Recommendations for Competitive Athletes With Cardiovascular Abnormalities. JACC. 2015;66(21):2343-2349.
• Related clinical guidelines from the Taiwan Sports Medicine Society

Related Topics

• Runner’s Cardiac Hypertrophy and Arrhythmia: Long-Term Effects of Endurance Training
• Endurance Exercise and the Heart: Positive and Negative Effects of Long-Term Training
• Cardiac Remodeling in Long-Term Endurance Training: A Longitudinal Comparison Study Using Echocardiography
• Athlete’s Heart vs. Pathological Hypertrophy: How to Understand the Deadly “Gray Zone”