Cardiac Arrhythmias

Cardiac Arrhythmias

Normal Sinus Rhythm

  • P before every QRS & QRS after every P
  • P:QRS = 1
  • Upright P wave in Leads II, III, AVF (Inferior Leads)
  • Equal intervals between identical waves
  • P-P interval
  • QRS-QRS interval

Sinus Arrhythmia

  • Respirophasic variation of sinus rate
  • Sinus rate increases during inspiration (withdrawal of parasympathetic tone), decreases with expiration

Sinus Pause

  • Sinus node dysfunction, often due to age or medications
  • No escape rhythm in the pacemaker hierarchy
  • May pass out ("syncope")

Atrial Rhythm

  • Atrial pacemaker rate is similar to sinus

Junctional Rhythm

  • Atrial impulse starts near the AV node and uses the His-Purkinje system
  • Based on the location, P waves may be right before, within, or after the QRS
  • QRS duration usually normal
  • Junctional rhythm 40-60 bpm
  • Accelerated junctional rhythm 60-100 bpm
  • Junctional tachycardia >100 bpm
  • Junctional bradycardia < 40 bpm

Ventricular Rhythm

  • Ventricular escape rhythm 20-40 bpm
  • Accelerated idioventricular rhythm 40-100 bpm
  • Ventricular tachycardia >100 bpm

Premature Atrial Complex (PAC)

  • A complex that occurs before the next expected P wave ("premature") and that originates in the atria (P wave of different morphology than sinus P wave, "atrial complex")

Premature Junctional Complex/Junctional Escape Complex

  • Premature Junctional Complex
  • Junctional Escape Beat

Premature Ventricular Complex (PVC)

  • Wide QRS (> 0.120 sec) with abnormal polarity
  • No preceding P wave
  • Unifocal or Multifocal

Patterns:

  • Isolated
  • Bigeminy → every second complex is PVC
  • Trigeminy → every third complex is PVC
  • Quadrigeminy → every fourth complex is PVC

General Approach to Tachyarrhythmias

  • Is the QRS complex narrow or wide?
  • Is the rhythm regular or irregular?
  • Where are the P waves and how do they look?

Narrow-Complex Tachycardia

Regular rhythm

  • Morphology same as sinus. Seen in leads II, III, aVF, and V1
  • P waves just after the QRS (pseudo R' in lead V1) or no P waves
  • Short RP interval

Irregular rhythm

  • Flutter waves
  • Irregular baseline with no P waves
  • At least three different P wave morphologies
[h3]Wide-Complex Tachycardia[/h3]
  • Pre-excited tachycardia (antidromic AVRT)
  • Supraventricular tachycardia (SVT) with aberrant conduction
  • Ventricular tachycardia

    Atrial Fibrillation 
  • Irregularly irregular rhythm
  • Extremely fast atrial rate with sporadic conduction through AV node
  • No obvious P waves; irregular baseline
  • A. Fib with rapid ventricular response (RVR): Rate > 100
Abnormal P Waves: Atrial Flutter 
  • Atria depolarizing at ~300 bpm
  • Saw-tooth appearance
  • AV node controls ventricular conduction, often 2:1, 3:1, 4:1 or variable conduction
  • Usually regular, irregular if variable conduction
Multifocal Atrial Tachycardia 
  • Three or more P wave morphologies
  • Common in patients with lung disease
[h2]Supraventricular Tachycardias (SVT)[/h2]
  • Generally a narrow complex tachyarrhythmia that is not sinus tachycardia/atrial fibrillation/atrial flutter
  • Re-entry is the mechanism of most SVT