Understanding Cardiac Arrhythmias

Aug 28, 2024

Cardiac Arrhythmias

Classification by Site of Origin

  • Sinus Rhythms: Originate from the sinoatrial node (SA node)
  • Atrial Rhythms: Originate from the atria
  • Ventricular Rhythms: Originate from the ventricles

Sinus Rhythm

  • Normal heart rhythm set by the SA node
  • Heart Rate: 60 to 100 beats per minute

Variations of Sinus Rhythm

  • Sinus Bradycardia:
    • SA node fires less than 60 times per minute
    • Heart rate less than 60 beats per minute
    • Normal during sleep
  • Sinus Tachycardia:
    • SA node fires more than 100 times per minute
    • Heart rate greater than 100 beats per minute
    • Normal during physical exercise

Atrial Rhythms

  • Always Clinical
  • Includes atrial flutter, atrial fibrillation, and AV nodal re-entrant tachycardia
  • Forms of supraventricular tachycardia (SVT)

Atrial Flutter (A-flutter)

  • Caused by a self-perpetuating loop (re-entrant pathway) in the right atrium
  • Atrial Rate: 250 to 400 beats per minute
  • Ventricular Rate:
    • Slower due to AV node's refractory properties
    • Example: "3 to 1 heart block"
  • ECG Characteristics:
    • Absence of normal P wave
    • Presence of flutter waves (f-waves) in saw-tooth patterns

Atrial Fibrillation (A-fib)

  • Caused by multiple random electrical impulses from ectopic sites
  • Atrial Rate: Extremely high
  • Ventricular Rate: Irregular, can range from less than 60 to more than 100 beats per minute
  • ECG Characteristics:
    • Absence of P-waves
    • Irregular narrow QRS complexes
    • Baseline may appear undulating or flat

AV Nodal Re-entrant Tachycardia (AVNRT)

  • Small re-entrant pathway involving the AV node
  • Heart Rate: Regular and fast, 150 to 250 beats per minute

Ventricular Rhythms

  • Considered lethal

Ventricular Tachycardia (V-tach)

  • Caused by a single strong firing site in the ventricles
  • Associated with structural heart problems
  • Ventricular Rate: 100 to 250 beats per minute
  • ECG Characteristics:
    • Wide and bizarre QRS complexes
    • Absence of P wave
  • Can occur in short episodes or be sustained (more than 30 seconds requiring immediate treatment)
  • May progress to ventricular fibrillation

Ventricular Fibrillation (V-fib)

  • Caused by multiple weak ectopic sites
  • Effect: Ventricles quiver, leading to little or no blood pumping
  • Can quickly lead to cardiac arrest
  • ECG Characteristics:
    • Irregular random waveforms
    • No identifiable P wave, QRS complex, or T wave
    • Amplitude decreases over time, leading to flatline