Chapter 7. Cardioversion and Defibrillation

Sabrina Tsao, MD; Barbara J. Deal, MD

• Rapid termination of tachycardia that is either unresponsive to medications or pacing interventions or is hemodynamically compromising, necessitating more urgent intervention.

Cardioversion

• Tachycardia, either supraventricular or ventricular, with regular ventricular response with mild to moderate hypotension.
• Mechanisms of supraventricular tachycardia include the following:
- • Atrial reentry tachycardia.
  • Reciprocating tachycardia utilizing an accessory connection.
  • Atrial flutter.
  • Atrioventricular nodal reentry tachycardia.

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• Cardioversion: Can be performed using medications, electrical pacing, or electrical direct current shock synchronized to QRS complex to correct an abnormal rapid cardiac rhythm.

• Benefits of cardioversion are restoration of a sinus or slower rhythm, improving cardiac output and function, and decreasing the risk of thromboembolism, cardiac dysfunction, and sudden death associated with the tachycardia.

Defibrillation

• The most effective treatment for ventricular fibrillation and pulseless ventricular tachycardia (Table 7–1).
• Its effectiveness diminishes rapidly over time; therefore, early defibrillation is recommended in patients who have suffered cardiac arrest.
• Atrial fibrillation.
• Supraventricular tachycardia with rapid conduction via an accessory connection.
• Ventricular fibrillation.
• Torsades de pointes.

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• Defibrillation: Uses electrical energy delivered transthoracically, nonsynchronously, and in a random fashion during the cardiac cycle to correct a very rapid rhythm.

Table 7–1. Treating tachycardia.

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Table 7–1. Treating tachycardia.

Tachycardia

Specific rhythm

Treatment

Narrow QRS complex

Sinus tachycardia

Treat underlying cause

Narrow QRS complex

Supraventricular tachycardia

Medications

Vagal maneuvers

Pacing

Cardioversion

Wide QRS complex

Ventricular tachycardia

SVT with aberrant conduction

SVT with antegrade conduction over an accessory connection

Medications

Cardioversion

Pulseless rhythm

Very rapid atrial or ventricular tachycardia

Atrial or ventricular fibrillation

Torsades de pointes

Defibrillation

Absolute

• A patient directive regarding resuscitation.

Relative

• Cardioversion of a rhythm known to be automatic in origin is not indicated.
• Digoxin toxicity-induced arrhythmia.
- • With digoxin toxicity, there is a high incidence of post-cardioversion ventricular tachycardia and fibrillation.
• Elective cardioversion of a hemodynamically stable patient with a known atrial thrombus; however, the likelihood of impending cardiovascular compromise can outweigh the risk of thromboembolism.
• Repeated cardioversion of a rhythm where the predisposing cause is not eliminated.

• External defibrillator, either manual or semi-automated (Figure 7–1).

• Skin electrode patches, wires to connect to defibrillator.
• Heart rhythm monitor.
• Equipment to protect the airway as well as resuscitation medications to support blood pressure.
• Do not delay cardioversion or defibrillation in a hemodynamically unstable patient while waiting for additional monitoring equipment or personnel.