Which intervention is synchronized to the cardiac cycle when treating a hemodynamically unstable tachyarrhythmia?

• A. Synchronized electrical cardioversion
• B. Defibrillation
• C. Vagal maneuvers
• D. Adenosine administration

Answer: (A)

When a tachyarrhythmia causes poor perfusion or shock, the priority is to restore a stable rhythm quickly. Delivering a synchronized electrical shock means the defibrillator times the shock to the R-wave, aligning with ventricular depolarization and avoiding delivery during the vulnerable T-wave. This minimizes the risk of provoking ventricular fibrillation and provides prompt restoration of circulation in an unstable patient.

Using defibrillation (unsynchronized) is reserved for cardiac arrest with pulseless VT or VF, not for a patient who still has a pulse. Vagal maneuvers and adenosine can help some stable narrow-complex tachycardias, but they are too slow and inappropriate when the patient is hemodynamically unstable, where immediate synchronized cardioversion is indicated.