The synchronizer switch must be turned on when cardioversion is planned. The synchronize circuit in the defibrillator is programmed to deliver a shock on the R wave of the QRS complex on the electrocardiogram (ECG). This allows the unit to sense this client's rhythm and time the shock to avoid having it occur during the T wave. A shock delivered during the T wave could cause this client to go into a more lethal rhythm (eg, ventricular tachycardia, ventricular fibrillation). If this client becomes pulseless, the synchronize function should be turned off and the nurse should proceed with defibrillation.