Which of the following must be present to cardiovert a patient with atrial fibrillation?

In the context of cardioverting a patient with atrial fibrillation, the presence of the R wave is crucial. The R wave represents the depolarization of the ventricles in the cardiac cycle and is a key reference point for timing the delivery of the electrical shock. During cardioversion, the goal is to synchronize the shock with the R wave to avoid delivering it during the vulnerable period of the cardiac cycle, which could potentially induce ventricular fibrillation, a more dangerous rhythm.

In atrial fibrillation, where there is a lack of organized electrical activity in the atria, a patient will still show R waves on their electrocardiogram (ECG). By targeting the R wave, healthcare professionals can effectively reset the electrical rhythm of the heart. Therefore, the presence of the R wave indicates that it is safe and appropriate to proceed with the cardioversion procedure.