Low Pulse Rate (Bradycardia): Causes and Implications

Introduction

A low pulse rate, also known as bradycardia, is typically defined as a heart rate lower than 60 beats per minute (bpm) in adults. While bradycardia can sometimes be normal (for example, in well-trained athletes), it may also indicate an underlying health issue that requires medical attention.

Common Causes of Bradycardia

1. Physiological Causes

• Athletes' heart: Well-conditioned athletes often have a lower resting heart rate due to increased cardiac efficiency.
• Sleep: Heart rate naturally slows down during sleep as part of normal physiological processes.

2. Medical Conditions

• Sick sinus syndrome (SSS): A dysfunction of the sinoatrial (SA) node, the heart’s natural pacemaker.
• Heart block: A problem with the electrical conduction system of the heart, slowing down impulses from the atria to the ventricles.
• Hypothyroidism: An underactive thyroid gland can slow down metabolism, including heart rate.
• Electrolyte imbalances: Low potassium or calcium levels can disturb the heart’s electrical activity.
• Sleep apnea: Repeated drops in oxygen levels during sleep can affect heart rate regulation.

3. Medication-Related Causes

• Beta-blockers (e.g., metoprolol, atenolol) slow the heart rate by blocking adrenaline effects.
• Calcium channel blockers (e.g., diltiazem, verapamil) can reduce heart rate by affecting electrical conduction.
• Antiarrhythmic drugs used for heart rhythm disorders may sometimes cause excessive slowing.

4. Other Causes

• Aging: The SA node tends to degenerate over time, leading to a slower heart rate.
• Severe infections (e.g., sepsis): Systemic infections can sometimes interfere with heart function.

When to Seek Medical Help

Bradycardia can be asymptomatic in some individuals, but medical evaluation is necessary if you experience: - Dizziness or fainting (syncope) - Severe fatigue or weakness - Shortness of breath - Chest pain - Cognitive issues (confusion, memory lapses)

Diagnostic Approaches

Doctors typically use the following tests: - Electrocardiogram (ECG): Records the electrical activity of the heart. - Holter monitoring: 24-48 hour continuous ECG recording to detect intermittent slow heart rhythms. - Blood tests: To assess for electrolyte imbalances, thyroid function, or infections.

Treatment Options

• Lifestyle changes (if applicable, such as adjusting medications or treating underlying conditions).
• Pacemaker implantation if bradycardia is severe and symptomatic.
• Medication adjustments (if drugs are causing bradycardia).

Conclusion

Bradycardia can be harmless or a sign of an underlying condition that requires attention. If you experience symptoms, consult a doctor for proper evaluation and treatment.

Source recommendations

1. American College of Cardiology/American Heart Association ECG & Arrhythmia Guidelines

1. https://www.acc.org/Guidelines
2. https://www.ahajournals.org/doi/10.1161/CIR.0000000000001193
3. https://pubmed.ncbi.nlm.nih.gov/17322457/
4. https://www.ahajournals.org/doi/10.1161/01.cir.100.8.886
5. https://pubmed.ncbi.nlm.nih.gov/10483977/

2. European Society of Cardiology Guidelines on Cardiac Pacing and Resynchronization Therapy

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Cardiac-Pacing-and-Cardiac-Resynchronization-Therapy
2. https://academic.oup.com/eurheartj/article/42/35/3427/6358547
3. https://pubmed.ncbi.nlm.nih.gov/34455430/
4. https://academic.oup.com/eurheartj/article/34/29/2281/401445
5. https://pubmed.ncbi.nlm.nih.gov/23801827/