Online ACLS Course

Chapter 14 : Bradycardia

Bradycardia is when the heart rate or rhythm is too slow (<50 beats/min) and can cause sudden death due decreased oxygen to the heart.  Causes of bradycardia include:

  • Hypertension
  • Congenital heart defect
  • Tissue damage due to aging, heart disease or heart attack
  • Myocarditis
  • Hypothyroidism
  • Imbalance of electrolytes
  • Obstructive sleep apnea
  • Inflammatory diseases
  • Medications

Symptoms of bradycardia include:

  • Dizziness
  • Shortness of breath
  • Feeling tired
  • Chest pain or fluttering of heart
  • Confused and trouble concentrating
  • Drop in blood pressure causing the person to faint
  • Presyncope – lightheadedness
  • Syncope – loss of consciousness

Signs of bracycardia include:

  • Hypotension – low blood pressure
  • Orthostatic hypotension – a drop in blood pressure due to change in position (example: sitting or standing)
  • Diaphoresis – sweating
  • Pulmonary congestion or edema – increase of fluid in the lungs
  • Congestive heart failure – heart does not pump enough blood
  • Premature Ventricular contractions (PVCs) – Ventricle produces abnormal heart beats
Video Demonstration


There are 4 types of ECG rhythms associated with bradycardia:

  1. Sinus bradycardia
  2. First-degree AV block
  3. Second-degree AV block: Type I (Mobitz 1) and Type II (Mobitz II)
  4. Third-degree AV block

Sinus bradycardia starts in the SA node with decreased rate (<60 beats/min).

sinus bradycardia

First degree AV block is when the PR interval is prolonged (> 0.20 seconds).

first-degree av block

2nd Degree AV block type I (Wenckebach-Mobitz I) is when the PR intervals are prolonged, R-R intervals are shortened and finally one beat drops.