What is there to read through if you don't have an understanding of the clinical information let alone pre-clinical foundation? If you try to read something "introductory" you will only end up having a superficial understanding and most likely forget the information anyways.
I definitely approve of your EM positive attitude, but you do need to slow (and know) your role. You're going to be doing this stuff for the next 10-50 years, you can wait one more to get started.
If you are absolutely DYING to get started on something clinical, you could get a good resource on ECGs, such as ECG academy which walks you through the basics and gets progressively more advanced. Knowing ECGs would be relevant to multiple specialties as well.