Cardiac Arrhythmias

Arrhythmia Basics & ECG - ECG Code Crackers

• Normal Conduction: SA node → AV node → Bundle of His → Bundle branches → Purkinje fibers.
• Arrhythmia: Any rhythm deviating from normal sinus rhythm.
• ECG Components:
  • P wave: Atrial depolarization.
  • PR interval: AV nodal delay; normal 0.12-0.20s.
  • QRS complex: Ventricular depolarization; normal <0.12s.
  • T wave: Ventricular repolarization.
  • U wave: Late ventricular repolarization (Purkinje fibers).
• Key Ion Channels: $Na^+$ (fast depolarization), $Ca^{2+}$ (pacemaker potential, plateau), $K^+$ (repolarization).

⭐ The U wave, when prominent, can indicate hypokalemia or effects of certain drugs like quinidine or digitalis.

Bradyarrhythmias - Slow Beat Scene

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Supraventricular Tachycardias - Atrial Rhythm Riot

⭐ WPW + AF/Flutter: AV nodal blockers (adenosine, BB, CCB, digoxin) are contraindicated; risk VF via accessory pathway.

• Key SVTs & ECG:

  SVT	Rhythm	P waves / ECG	Adenosine
  AF	Irreg. irreg.	Absent, fibrillatory	Slows rate
  Atrial Flutter	Regular (often)	Sawtooth (F)	Unmasks F waves
  AVNRT	Regular	Buried/retrograde P	Terminates
  AVRT (WPW)	Regular	Delta, short PR	Terminates
  MAT	Irregular	≥3 P types, varying PR/RR; lung dz	Variable, may slow

• Acute: Vagal → Adenosine (6mg IV, then 12mg) → CCB/BB → Cardioversion.
• Chronic: Rate/Rhythm control. AF: Anticoagulate (CHA2DS2-VASc). 📌 CHA2DS2-VASc: CHF(1), HTN(1), Age ≥75(2)/ 65-74(1), DM(1), Stroke/TIA(2), Vasc Dz(1), Sex F(1).

Ventricular Arrhythmias - Ventricle Danger Vibes

• PVCs: Wide QRS, ectopic.
• VT (Ventricular Tachycardia): Wide QRS (>0.12s).
  • Stable Monomorphic: Amiodarone 150mg IV.
  • Unstable (pulse): Sync. Cardioversion (100J).
• Pulseless VT/VF: Defibrillation (e.g., 120-200J biphasic), CPR, Amiodarone 300mg IV. (ACLS)
• TdP (Torsades de Pointes): Polymorphic VT, long QT. Mgmt: IV Mg (2g).
• Brugada Syn: Coved ST ↑ V1-V3. ICD.
• ARVD: Epsilon wave. ICD.
• 📌 H's & T's for reversible causes (cardiac arrest).

⭐ Synchronized cardioversion is used for unstable VT with a pulse, while defibrillation (unsynchronized shock) is used for pulseless VT or VF. Amiodarone is a key antiarrhythmic for both stable VT and in ACLS for refractory VT/VF.

Antiarrhythmic Drugs - Rhythm Rx Roundup

• Other:
  • Adenosine: ↓AVN; Acute SVT; SE: Flush.
  • Digoxin: ↑Vagal; AF rate ctrl; SE: GI, vision.
  • MgSO4: TdP, Dig-tox.

⭐ Beta-blockers (Class II antiarrhythmics) are contraindicated in patients with cocaine-induced myocardial ischemia/tachycardia as they can lead to unopposed alpha-adrenergic stimulation, worsening coronary vasoconstriction and hypertension.

High‑Yield Points - ⚡ Biggest Takeaways

• Atrial fibrillation: Most common sustained arrhythmia. Key is stroke prevention (CHADS-VASc).
• Ventricular tachycardia: Pulseless VT needs immediate defibrillation. Stable VT: amiodarone.
• WPW syndrome: Short PR, delta wave. Avoid AV nodal blockers (e.g., adenosine, verapamil, digoxin).
• AVNRT: Most common paroxysmal SVT. Treat with vagal maneuvers, then adenosine.
• Brugada syndrome: Coved ST elevation (V1-V3), risk of SCD. ICD is treatment.
• Torsades de Pointes: Associated with Long QT syndrome. Treat with magnesium sulfate.