Cardiac Arrhythmias for USMLE Step 2 & COMLEX-USA Level 2

• Abnormal Automaticity:
• Non-pacemaker cells spontaneously depolarize, generating ectopic electrical impulses.
• Example: Premature atrial or ventricular beats.

• Triggered Activity:
• Occurs due to early or delayed afterdepolarizations, leading to unplanned contractions.
• Example: Torsades de Pointes in long QT syndrome.

• Re-Entry Circuits:
• Electrical impulses re-enter previously excited tissues, perpetuating tachyarrhythmias.
• Example: Atrioventricular Reentrant Tachycardia (AVRT) in Wolff-Parkinson-White syndrome.

• Atrial Fibrillation (AF):
• Irregularly irregular rhythm with absent P waves.
• Risks: Stroke from thromboembolism (commonly managed with anticoagulation).

• Atrial Flutter:
• "Sawtooth" pattern on ECG due to rapid atrial activity.
• May require rate control and cardioversion for acute management.

• Paroxysmal Supraventricular Tachycardia (PSVT):
• Sudden-onset, regular tachycardia due to AV nodal re-entry.
• Treated with vagal maneuvers or adenosine for acute cases.

• Premature Ventricular Contractions (PVCs):
• Isolated, wide QRS complexes occurring early without a preceding P wave.
• Generally benign but frequent PVCs may warrant further evaluation.

• Ventricular Tachycardia (VT):
• Defined as three or more consecutive PVCs with a regular rhythm.
• Sustained VT (>30 sec) requires urgent treatment to prevent cardiac arrest.

• Ventricular Fibrillation (VF):
• Chaotic electrical activity causing loss of coordinated contraction; a cause of sudden cardiac death.
• Requires immediate defibrillation.

• Sinus Bradycardia:
• Heart rate <60 bpm, commonly seen in athletes or caused by medications (e.g., beta-blockers).
• May require atropine if symptomatic.

• Atrioventricular (AV) Blocks:
• First-Degree Block: Prolonged PR interval (>200 ms) without dropped beats.
• Second-Degree Block:
• Mobitz I (Wenckebach): Gradual PR prolongation followed by a dropped QRS.
• Mobitz II: Unexpected dropped QRS without PR lengthening, requiring pacemaker consideration.
• Third-Degree Block: Complete dissociation between atria and ventricles, necessitating a pacemaker.

• Atrial Fibrillation: Irregular QRS complexes without distinct P waves.
• Atrial Flutter: Rapid atrial activity producing a sawtooth ECG pattern.
• Ventricular Tachycardia: Wide QRS complexes with a regular rhythm.
• Ventricular Fibrillation: Irregular, chaotic waves without identifiable QRS complexes.
• Torsades de Pointes: Polymorphic VT with "twisting" QRS complexes, associated with prolonged QT.

• Rate Control vs. Rhythm Control:
• In atrial fibrillation, beta-blockers and calcium channel blockers are used for rate control.
• Rhythm control may involve antiarrhythmics (e.g., amiodarone) or cardioversion.

• Antiarrhythmic Classes:
• Class I: Sodium channel blockers (e.g., flecainide).
• Class II: Beta-blockers (e.g., metoprolol).
• Class III: Potassium channel blockers (e.g., amiodarone).
• Class IV: Calcium channel blockers (e.g., verapamil).

• Electrical Therapy:
• Defibrillation: Used for VF and pulseless VT.
• Cardioversion: Indicated for hemodynamically unstable AF or atrial flutter.

• Mechanisms: Re-entry is the most common arrhythmia mechanism.
• Atrial Fibrillation: A major cause of thromboembolic stroke, often requiring anticoagulation.
• Ventricular Arrhythmias: VF is fatal without immediate defibrillation.
• Bradyarrhythmias: Advanced AV blocks usually require pacemaker implantation.
• Management: Differentiating between rate vs. rhythm control is essential for atrial fibrillation treatment.