**Core Concept**
Asynchronous cardioversion refers to the delivery of an electrical shock during the cardiac cycle, specifically during the T wave, to convert an abnormal heart rhythm back to a normal sinus rhythm. This technique is used in specific situations to avoid certain complications.

**Why the Correct Answer is Right**
Asynchronous cardioversion is given when a patient is experiencing a ventricular tachycardia (VT) or ventricular fibrillation (VF) and is unresponsive. Delivering a shock during the T wave can help to reset the cardiac cycle and restore a normal rhythm. This is particularly useful in emergency situations where immediate intervention is required. The T wave is a specific phase of the cardiac cycle when the ventricles are depolarized, and a shock during this phase can be more effective in terminating VT or VF.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because synchronous cardioversion is typically used for atrial fibrillation or atrial flutter, not VT or VF.
**Option B:** This option is incorrect because antitachycardia pacing (ATP) is a technique used to terminate VT or VF, but it involves pacing the heart rather than delivering a shock.
**Option C:** This option is incorrect because biphasic cardioversion is a type of defibrillator waveform, not a specific indication for cardioversion.

**Clinical Pearl / High-Yield Fact**
Remember that asynchronous cardioversion is typically reserved for emergency situations where the patient is unresponsive and VT or VF is suspected. Always prioritize synchronous cardioversion or other treatment options when possible.

**Correct Answer: C. Biphasic cardioversion is often used for asynchronous cardioversion.**