Final answer:
The immediate action for a patient with witnessed loss of consciousness and polymorphic ventricular tachycardia on an ECG is to perform synchronized cardioversion or defibrillation, depending on the patient's stability and presence of a pulse.
Step-by-step explanation:
When a patient experiences a witnessed loss of consciousness and their Lead II ECG reveals polymorphic ventricular tachycardia, the immediate action should be to perform synchronized cardioversion if the patient is stable and has a pulse, or unsynchronized defibrillation (also known simply as defibrillation) if the patient is pulseless. This is because polymorphic ventricular tachycardia, which can degenerate into ventricular fibrillation, is a life-threatening arrhythmia that needs to be corrected immediately to prevent further deterioration of the patient's condition. Defibrillation uses special paddles or pads to apply an electric charge to the heart in an attempt to reset the heart's rhythm back to normal. It is crucial in the event of ventricular fibrillation. While administering magnesium sulfate can be appropriate in cases of torsades de pointes (a specific type of polymorphic ventricular tachycardia), it is not the first-line immediate action and should not precede attempts at cardioversion or defibrillation.