Understanding Bradycardia: Causes and Risk Factors

Introduction

Bradycardia refers to a slow heart rate, typically defined as fewer than 60 beats per minute (bpm) in adults. While a lower heart rate can be normal in athletes and during sleep, abnormally slow heart rates can indicate an underlying health problem. Let's explore its causes, risk factors, and when it might be a concern.

Causes of Bradycardia

1. Intrinsic Cardiac Causes (Issues Within the Heart)

  • Sick Sinus Syndrome (SSS): A malfunction of the sinoatrial (SA) node, the heart's natural pacemaker.
  • Heart Block: A delay or blockage in the electrical signals from the atria to the ventricles.
  • Myocardial Infarction (Heart Attack): Damage to cardiac tissue can impact electrical conduction.
  • Cardiomyopathies: Diseases of the heart muscle leading to electrical dysfunction.
  • Congenital Heart Defects: Structural heart abnormalities present from birth.

2. Extrinsic Causes (External Factors Affecting the Heart)

  • Electrolyte Imbalances: Especially abnormal levels of potassium, calcium, and magnesium.
  • Hypothyroidism: A slow metabolism due to reduced thyroid hormone levels can lower heart rate.
  • Medications: Beta-blockers, calcium channel blockers, certain antiarrhythmics, and digoxin can slow the heart rate.
  • Sleep Apnea: Intermittent oxygen deprivation can affect heart rhythm.
  • Hypothermia: Cold temperatures slow down the body's metabolic and cardiac activity.

3. Neurological and Autonomic Nervous System Disorders

  • Vasovagal Syncope: An overreaction of the vagus nerve leading to sudden heart rate drops.
  • Increased Intracranial Pressure (ICP): Conditions like brain injury or tumors affecting brainstem function.

4. Aging and Degenerative Conditions

  • Fibrosis of the Conduction System: Age-related degeneration of the heart’s electrical pathways.

When to Seek Medical Attention

  • Symptoms such as dizziness, fainting, fatigue, confusion, or shortness of breath.
  • An unexplained persistent heart rate below 50 bpm.
  • Presence of underlying heart disease or risk factors like diabetes and high blood pressure.

Conclusion

Bradycardia can be benign or indicate a serious underlying condition. A thorough clinical evaluation, including ECG and blood tests, helps identify the cause and determine if treatment is necessary, such as medication adjustment, pacemaker placement, or addressing underlying health issues.

Source recommendations

1. American Heart Association Guidelines on Bradycardia

  1. https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia/bradycardia--slow-heart-rate
  2. https://cpr.heart.org/-/media/cpr-files/cpr-guidelines-files/algorithms/algorithmacls_bradycardia_200612.pdf
  3. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000628
  4. https://cpr.heart.org/en/resuscitation-science/cpr-and-ecc-guidelines/algorithms
  5. https://pubmed.ncbi.nlm.nih.gov/30412710/

2. European Society of Cardiology Guidelines on Cardiac Arrhythmias

  1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Ventricular-Arrhythmias-and-the-Prevention-of-Sudden-Cardiac-Death
  2. https://academic.oup.com/eurheartj/article/43/40/3997/6675633
  3. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Supraventricular-Tachycardia
  4. https://pubmed.ncbi.nlm.nih.gov/36017572/
  5. https://www.ahajournals.org/doi/10.1161/01.cir.0000091380.04100.84

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