How effective is epinephrine for treating cardiac arrest?

Epinephrine: Epinephrine remains a component of the ACLS training by American Heart Association. Measuring 'how' effective it is, is difficult. It is generally considered one of the few drugs that helps in cardiac arrest from 'experience'. A controlled study isn't available. Cardiac Arrest has a very high mortality, we continue to consider epi effective while most other drugs have fallen off the chart.