A 1st degree block means the electrical impulse passing through the heart is moving more slowly than normal. With a normal heart rate and rhythm, nothing is considered 'wrong' with the heart and no treatment is needed.
Septal infarct, age undetermined means you might have had a mild heart attack but they don't know when it happened. It might also mean the tech didn't connect the wires correctly! ECGs are notoriously inaccurate
for this type of infarct. Septal refers to the septum, the wall between the right and left chambers of the heart.
"Normal sinus rhythm . . ." means your heart is working fine now, whatever did or didn't happen.
Keep in mind I'm not a doctor, nurse or medical professional of anykind. I'm just a "professional patient" with time on my hands and a search engine addiction.
Good luck with your appt on Monday . . .