“Cardiac arrhythmias are common and can present as dizziness, palpitations, syncope, or sudden death. Arrhythmias can be caused by a primary cardiac event, such as ischemia, by a genetic abnormality of the conduction system, or as a result of a vast number of pathologic processes, including sepsis, metabolic derangements, toxicologic, or traumatic.”1


Being able to confidently interpret an ECG in the setting of an arrhythmia is key to the initial diagnosis and treatment approach for many common emergency room presentations. (ECG Basics & ECG Library) Having a basic understanding of the pathophysiology of the slow (brady-) and fast (tachy-) arrhythmias can help with this. Patients with pacemakers are frequently encountered in the ED and having a basic approach to these devices can be beneficial in emergent settings. 



  • Mechanisms of Bradyarrhythmias:
    • “Bradyarrhythmias can be caused by two mechanisms: depression a sinus normal activity or conduction system blocks.”1
  • Types of Bradyarrhythmias:1
    • Supraventricular bradyarrhythmias
      • Sinus bradycardia
      • Sick sinus syndrome
    • Conduction disturbances
      • Sinoatrial Block
      • Sinus arrest (pause)
      • Atrioventricular Block 
        • First-degree atrioventricular block
        • Second degree Mobitz 1 (Wenckebach) atrioventricular block
        • Second-degree Mobitz 2 atrioventricular block
        • Third degree (complete) atrioventricular block
  • Treatment of Unstable Bradycardia 



  • Mechanisms of Tachyarrhythmias:
    • “There are three excepted mechanisms for tachyarrhythmias: (1) increased automaticity in a normal or ectopic site, (2) re-entry in a normal or accessory pathway, and (3) after depolarization causing triggered rhythms.”1
  • Types of Tachyarrhythmias:1
    • Supraventricular tachyarrhythmias
      • Narrow complex regular arrhythmias
        • Sinus tachycardia
        • Supraventricular tachycardia (Modified Valsalva Maneuver)
          • Atrioventricular nodal re-entrant tachycardia
          • Atrioventricular re-entrant tachycardia
        • Atrial flutter
      • Narrow complex irregular arrhythmias
      • Ventricular tachyarrhythmias:
        • Accelerated idioventricular rhythm
        • Ventricular fibrillation (Torsades de Pointes)
        • Ventricular tachycardia
        • SVT with aberrancy versus ventricular tachyarrhythmia


In addition, there are also subsets of “conduction abnormalities that can cause rhythm disturbances”1:

  • Brugada syndrome
  • Long QT syndrome
  • Pre-terminal rhythms


Click HERE for a list of all mentioned FOAM resources.


  1. Piktel, JS. Chapter 22, “Cardiac Rhythm Disturbances”. Tintinalli’s Emergency Medicine – A Comprehensive Study Guide. J Tintinalli. 7th ed. McGraw-Hill Education, 2010. 129. Print.


Prepared by Alex Mungham PGY1 FM – University of Ottawa