Final answer:
The first drug of choice for a patient in cardiac arrest with asystole is Epinephrine 1 mg IV/IO according to ACLS guidelines.
Step-by-step explanation:
In the scenario where a patient is in cardiac arrest with an asystole rhythm, the first medication of choice according to Advanced Cardiac Life Support (ACLS) guidelines is Epinephrine 1 mg IV/IO. This should be administered as soon as possible and can be repeated every 3-5 minutes during the resuscitation efforts. While Atropine was previously used in asystole and pulseless electrical activity (PEA), it is no longer recommended for these rhythms.