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Atrial & Ventricular Arrhythmias for USMLE Step 1

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Atrial & Ventricular Arrhythmias for the USMLE Step 1 Exam
Supraventricular Arrhythmias
Supraventricular arrhythmias originate above the ventricles and are generally less life-threatening than ventricular arrhythmias, though they can cause significant symptoms and complications.
Atrial Fibrillation (AF)
  • Mechanism: Caused by rapid, irregular electrical activity in the atria, leading to uncoordinated atrial contraction.
  • ECG Findings: Absence of distinct P waves and “irregularly irregular” QRS complexes.
  • Clinical Significance: AF is the most common sustained arrhythmia, associated with an increased risk of thromboembolic stroke.
  • Management:
    • Rate Control: Beta-blockers or calcium channel blockers (e.g., metoprolol, diltiazem).
    • Anticoagulation: Used based on CHA₂DS₂-VASc score to reduce stroke risk.
atrial fibrillation
Atrial Flutter
  • Mechanism: Typically caused by a reentrant circuit around the tricuspid annulus, leading to rapid, regular atrial contractions.
  • ECG Findings: “Sawtooth” P-wave pattern, often with 2:1 atrial to ventricular conduction.
  • Management:
    • Rate Control: Beta-blockers or calcium channel blockers.
    • Anticoagulation: Recommended due to stroke risk similar to AF.
Paroxysmal Supraventricular Tachycardia (PSVT)
  • Mechanism: Often caused by AV nodal reentry or accessory pathway reentry (e.g., Wolff-Parkinson-White syndrome).
  • ECG Findings: Narrow QRS tachycardia with a regular rhythm; P waves may be hidden in the QRS complex.
  • Management:
    • Acute Termination: Vagal maneuvers (Valsalva) or adenosine administration.
    • Chronic Management: Beta-blockers or calcium channel blockers; catheter ablation for recurrent cases.
Ventricular Arrhythmias
Ventricular arrhythmias arise in the ventricles and are more serious due to their potential to cause hemodynamic instability and sudden death.
Premature Ventricular Contractions (PVCs)
  • Mechanism: Ectopic beats originating from the ventricles, often due to abnormal automaticity.
  • ECG Findings: Wide QRS complex occurring early, followed by a compensatory pause.
  • Management: Often benign; beta-blockers may be used if symptoms are significant.
Ventricular Tachycardia (VT)
  • Mechanism: Series of rapid, consecutive ventricular beats, often due to reentry in the setting of structural heart disease.
  • ECG Findings: Regular, wide QRS complexes with a rate of 100–250 bpm; monomorphic VT has a uniform QRS morphology, while polymorphic VT varies.
  • Management:
    • Unstable VT: Immediate synchronized cardioversion.
    • Stable VT: Antiarrhythmic drugs (e.g., amiodarone); ICD placement is indicated in high-risk patients.
Torsades de Pointes (TdP)
  • Mechanism: A polymorphic VT associated with QT prolongation, often triggered by electrolyte imbalances or drugs.
  • ECG Findings: “Twisting” QRS complexes that change in amplitude and axis.
  • Management:
    • Acute Treatment: IV magnesium sulfate is first-line.
    • Prevention: Correct electrolyte imbalances and avoid QT-prolonging drugs.
Ventricular Fibrillation (VF)
  • Mechanism: Chaotic, disorganized ventricular electrical activity resulting in ineffective contraction.
  • ECG Findings: Irregular, erratic waveform without identifiable P waves, QRS complexes, or T waves.
  • Management:
    • Immediate Defibrillation: Required to restore a stable rhythm.
    • Post-Resuscitation: ICD placement for secondary prevention.
Key Points
  • Supraventricular Arrhythmias:
    • AF: Irregular QRS rhythm without P waves; treated with rate control and anticoagulation.
    • Atrial Flutter: Regular, “sawtooth” P waves; managed with rate control and anticoagulation.
    • PSVT: Narrow QRS tachycardia, often responsive to vagal maneuvers or adenosine.
  • Ventricular Arrhythmias:
    • PVCs: Wide, early QRS complexes; often benign.
    • Ventricular Tachycardia: Wide QRS tachycardia; requires cardioversion if unstable.
    • Torsades de Pointes: Polymorphic VT with QT prolongation; treated with IV magnesium.
    • Ventricular Fibrillation: Life-threatening, chaotic rhythm requiring immediate defibrillation.
  • Management:
    • Stable Arrhythmias: Often treated with beta-blockers or antiarrhythmics, with ablation in refractory cases.
    • Unstable Arrhythmias: Require immediate cardioversion or defibrillation.

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