Can you tell me if throughout asystole, is adrenaline injected directly into the heart?

Not any more: That was part of the older protocol - makes for very dramatic television! The modern approach is to inject it into a running IV - central line is best but peripheral IV is acceptable. There were too many lacerated coronary arteries and right ventricles with tamponade when direct injections were used. (especially while CPR is going on).

No: this is in the museum of history of medicine. No need to do that. Appropriate compressions and IV adrenaline are now being used. Direct injection may injure the main left heart artery LAD. Not a good idea.