i dont know how fast it would be effective or how to covertly administer it but Glaucine from yellow horned poppy is a calcium channel blocker.  Encainide is an  antiarrhythmic  that is also a sodium channel blocker and Amiodarone as a potasium channel blocker. possibly an atomized powder mix of those three could only effect the sinus or where it contacted neurons temopratly blocking the signal across the board.