I'm on propranolol daily for svt from wolff-parkinson-white & my pulse drops to 45 or lower at night. doc said it's ok and just stay on it?

Probably: Not significant if you don't have any other symptoms, such as fainting or dizziness. Consult with a cardiologist to make sure.

Good advice: At your age with wpw, i would also recommend an electrical study of your heart to help evaluate your risk for developing serious heart rhythm problems that could lead to fainting or sudden collapse. http://www.hrsonline.org/practice-guidance/clinical-guidelines-documents/2012-management-of-the-asymptomatic-young-patient-with-a-wolff-parkinson-white#axzz2td6p9v5a.

Probably: With that story, i would not expect you to have any symptoms, ; i would not be concerned unless you had symptoms. Of course, at your age, i would typically recommend an electrophysiology study and possible ablation to attempt to cure the condition.