Bradycardia: Causes, Symptoms and Treatment
Bradycardia is a slower-than-normal heart rate of fewer than 60 beats per minute. It can be harmless or may require medical treatment.
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Bradycardia is a slower-than-normal heart rate of fewer than 60 beats per minute. It can be harmless or may require medical treatment.
What is Bradycardia?
Bradycardia refers to a resting heart rate of fewer than 60 beats per minute. The term comes from the Greek words bradys (slow) and kardia (heart). In well-trained athletes, a low resting heart rate is entirely normal and reflects an efficient heart. However, in other individuals, bradycardia may indicate an underlying heart condition or a disorder of the cardiac conduction system.
Causes
Bradycardia can result from a wide range of physiological and pathological causes:
- Physiological: Endurance athletes often have resting heart rates below 60 bpm due to increased cardiac efficiency.
- Sick Sinus Syndrome: The natural pacemaker of the heart (the sinus node) fires too slowly or irregularly.
- AV Block: A disruption in the electrical conduction between the atria and the ventricles.
- Hypothyroidism: Insufficient thyroid hormone slows metabolism and reduces heart rate.
- Electrolyte imbalances: Elevated potassium levels (hyperkalemia) can reduce heart rate.
- Medications: Beta-blockers, calcium channel blockers, digoxin, and other cardiac drugs can cause bradycardia.
- Heart attack or myocarditis: Damage to cardiac tissue can affect the conduction system.
- Increased vagal tone or intracranial pressure: Strong parasympathetic activation can slow the heart.
Symptoms
Whether bradycardia causes symptoms depends on its severity and the underlying cause. Common symptoms include:
- Dizziness or lightheadedness
- Shortness of breath, especially during physical activity
- Fatigue and low energy
- Chest pain or palpitations
- Fainting or brief loss of consciousness (syncope)
- Reduced exercise tolerance
In severe cases, bradycardia can result in inadequate blood supply to vital organs and constitutes a medical emergency.
Diagnosis
The primary diagnostic tool is the electrocardiogram (ECG), which records the electrical activity of the heart and identifies rhythm abnormalities. Additional investigations may include:
- Holter monitor (ambulatory ECG): Records heart rhythm over 24 to 48 hours to detect intermittent bradycardia.
- Blood tests: Assessment of thyroid function, electrolytes, and medication levels.
- Echocardiography: Ultrasound examination of the heart to evaluate structure and function.
- Tilt table test: Used when a vasovagal cause of fainting is suspected.
Treatment
Treatment depends on the underlying cause and the severity of symptoms:
- Watchful waiting: Asymptomatic bradycardia, such as in athletes, requires no treatment.
- Medication adjustment: If a drug is causing the slow heart rate, the dose may be reduced or the medication changed.
- Treating the underlying condition: Hypothyroidism is managed with thyroid hormone replacement; electrolyte imbalances are corrected accordingly.
- Emergency medication: In acute situations, intravenous atropine can be used to increase heart rate.
- Pacemaker implantation: For persistent, symptomatic bradycardia that does not respond to other therapies, implanting a cardiac pacemaker is the treatment of choice. The device detects an abnormally slow heart rate and delivers electrical impulses to stimulate the heart.
When to See a Doctor
Anyone experiencing symptoms such as dizziness, fainting, persistent fatigue, or chest pain should seek medical attention promptly. In cases of sudden loss of consciousness or severe chest pain, emergency services should be called immediately.
References
- Kusumoto FM et al. - 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay. Journal of the American College of Cardiology, 2019.
- European Society of Cardiology (ESC): Guidelines for the diagnosis and management of syncope, 2018.
- Zipes DP et al. - ACC/AHA/ESC 2006 Guidelines for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death. Circulation, 2006.
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