During a cardiopulmonary resuscitation (CPR) class, a participant asks about the difference between cardioversion and defibrillation. What would be the instructor's best response?

The key distinction between cardioversion and defibrillation lies in the timing of electrical current delivery. Cardioversion is synchronized to the patient's cardiac cycle — specifically, the current is delivered in coordination with the R wave (during the QRS complex) to avoid triggering ventricular fibrillation. It is used for organized but unstable dysrhythmias such as atrial flutter, atrial fibrillation, or supraventricular tachycardia. Defibrillation, by contrast, delivers an unsynchronized shock at any point in the cardiac cycle and is used in life-threatening, disorganized rhythms like ventricular fibrillation or pulseless ventricular tachycardia where there is no meaningful organized electrical activity to synchronize with. The statement about the difference being the timing of electrical current delivery is therefore accurate and complete. The option stating cardioversion is always attempted before defibrillation is incorrect — the choice depends on the specific rhythm, not a fixed sequence. The option suggesting defibrillation is synchronized and cardioversion is not reverses the definitions. The option saying cardioversion is done on a beating heart while defibrillation is not is partially misleading — defibrillation can also be used when the heart has some electrical activity, and the beating-heart distinction alone does not capture the critical synchronization concept that defines each technique.