Acute symptomatic sinus bradycardia usually responds to-

Sinus bradycardia: A regular but unusually slow hea beat (50 beats/minute or less at rest). Fainting can occur with sinus bradycardia if the hea slows down even more. This can occur, for example, when the vagus nerve sends a signal to the hea that suddenly drops the hea rate Ref Harrison 20th edition pg 1456