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Cardiac Arrhythmias for the Physician Assistant Licensing Exam

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Mechanisms of Arrhythmias
  • Abnormal Automaticity:
    • Non-pacemaker cells generate spontaneous impulses, disrupting normal heart rhythms.
    • Example: Atrial or ventricular ectopic beats.
  • Triggered Activity:
    • Afterdepolarizations (early or delayed) induce abnormal contractions.
    • Example: Torsades de Pointes, seen with prolonged QT syndrome.
  • Re-Entry Circuits:
    • Electrical impulses re-enter previously activated tissues, leading to continuous arrhythmic cycles.
    • Example: AV Nodal Reentrant Tachycardia (AVNRT) in PSVT.
Supraventricular Arrhythmias
  • Atrial Fibrillation (AF):
    • Irregularly irregular rhythm without identifiable P waves.
    • Increases thromboembolic risk, requiring anticoagulation with warfarin or DOACs.
    • Rate Control: Beta-blockers (e.g., metoprolol) or calcium channel blockers (e.g., diltiazem).
    • Rhythm Control: Amiodarone or electrical cardioversion if unstable.
  • Atrial Flutter:
    • Rapid atrial contractions with a "sawtooth" pattern on ECG.
    • Managed similarly to AF with focus on rate control and anticoagulation.
  • Paroxysmal Supraventricular Tachycardia (PSVT):
    • Sudden-onset tachycardia caused by re-entrant circuits through the AV node.
    • Acute management: Vagal maneuvers or adenosine; chronic management may involve ablation.
Ventricular Arrhythmias
  • Premature Ventricular Contractions (PVCs):
    • Wide QRS complexes without a preceding P wave, occurring early.
    • Typically benign, but frequent PVCs may indicate underlying heart disease.
  • Ventricular Tachycardia (VT):
    • Three or more consecutive PVCs with a heart rate >100 bpm.
    • Sustained VT (>30 sec): Requires immediate cardioversion if unstable.
    • Chronic management: Antiarrhythmics (e.g., amiodarone) or ICD in structural heart disease.
  • Ventricular Fibrillation (VF):
    • Chaotic ventricular activity resulting in cardiac arrest.
    • Immediate defibrillation and CPR required.
Bradyarrhythmias
  • Sinus Bradycardia:
    • HR <60 bpm; may be due to high vagal tone or medications.
    • Managed with atropine if symptomatic; pacing may be needed in refractory cases.
  • Atrioventricular (AV) Blocks:
    • First-Degree Block: PR interval >200 ms without missed beats.
    • Second-Degree Block:
    • Mobitz I (Wenckebach): Progressive PR lengthening followed by a dropped QRS.
    • Mobitz II: Sudden dropped QRS, often requiring pacemaker placement.
    • Third-Degree Block: Complete dissociation between atrial and ventricular activity; treated with a pacemaker.
Management of Life-Threatening Arrhythmias
  • Advanced Cardiac Life Support (ACLS):
    • VF or Pulseless VT: Immediate defibrillation and epinephrine.
    • Bradycardia with Hypotension: Atropine and transcutaneous pacing if needed.
  • Torsades de Pointes:
    • Polymorphic VT linked to prolonged QT; treated with magnesium sulfate and defibrillation if unstable.
Key Points
  • Atrial Fibrillation: Focus on anticoagulation, rate control, and rhythm management.
  • Ventricular Tachycardia/Fibrillation: Require urgent cardioversion or defibrillation.
  • Torsades de Pointes: Treated with magnesium sulfate due to its association with prolonged QT.
  • Bradyarrhythmias: Severe AV blocks often necessitate pacemaker implantation.
  • ACLS Protocols: Essential for handling cardiac arrest and unstable arrhythmias.