SVT, or SupraVentricular Tachycardia, is not usually considered dangerous rhythm, though it is frightening. Supra means above. SupraVentricular is a rhythm that originates above the ventricles.
Tachycardias that originate on the ventricles are of significant concern, fortunately this isn't the case for you.
I've taken benzodiazepines in one form, or another, modestly, for 30 years now. I use Klonopin now, it has a long half life, but you'd need to be careful with the dose as it can lower the blood pressure. It has never caused problems with my heart rhythm, in fact it helps me get through times when my arrhythmia acts up.
I've had short bouts with PSVT, Paroxysmal SVT, it's scary, but it's been relatively short.