From the Research
The usual initial energy setting for synchronized cardioversion in unstable wide complex tachycardia is 100 joules, as demonstrated by a case of electrical cardioversion used to treat a hemodynamically unstable wide complex tachycardia (WCT) where the patient returned to normal sinus rhythm after being cardioverted with 100 joules (J) on the first attempt 1. This is the recommended starting point for monophasic defibrillators, while for biphasic defibrillators, the initial energy setting is typically 100-120 joules. If the first shock is unsuccessful, the energy level should be escalated in a stepwise manner for subsequent attempts.
Before performing cardioversion, ensure the patient receives appropriate sedation if they are conscious. It's crucial to confirm that the defibrillator is in synchronized mode before delivering the shock to avoid inadvertently triggering ventricular fibrillation by delivering energy during the vulnerable period of the cardiac cycle. The synchronization ensures that the electrical discharge is timed to coincide with the R wave of the QRS complex, avoiding the relative refractory period represented by the T wave.
For patients who are hemodynamically unstable with symptoms such as hypotension, altered mental status, chest pain, or heart failure, immediate cardioversion is indicated rather than pharmacological management. Some studies suggest that the optimal initial energy setting may vary depending on the type and duration of the arrhythmia, but for unstable wide complex tachycardia, 100 joules is a commonly recommended starting point 2.
Key considerations for cardioversion include:
- Ensuring the patient is properly sedated if conscious
- Confirming the defibrillator is in synchronized mode
- Starting with an initial energy setting of 100 joules for monophasic defibrillators and 100-120 joules for biphasic defibrillators
- Escalating energy levels in a stepwise manner if the first shock is unsuccessful
- Prioritizing immediate cardioversion for hemodynamically unstable patients over pharmacological management.