Does injury in the vegus nerve cause baseline hr to be 120 bpm? what else suddenly change the baseline hr?

Tachcar: Irregular heart rhythm such as atrial tachycardia, atrial fibrillation or flutter are most likely. Even if you had a surgery within one inch of the vagal nerve, irregular rhythm would still be most likely. If all abnormal heart rhythms are ruled out then it might be inappropriate sinus tachycardia. This diagnosis is a mystery to doctors.

Autonomic imbalance : The reduced vegus nervous output will cause the balance to shift to increases sympathetic output, thus faster heart rate. There are other consequences from the injury itself depending on the extend.