Pacemakers do not necessarily produce pacing pulses all the time. They monitor the heart's performance and apply pacing pulses when necessary. Thus stopping the pacemaker today could easily not produce any effects until days or even weeks later, depending on the exact reason for the pacemaker being fitted and the problems the heart gets.
Hopefully, the pacemaker could be restarted externally in this case - modern pacers can generally be communciated with, either by radio or an external inductive system.
I agree with sallyanne and peterwe - this is too serious a matter for just a letter to airport management. See a lawyer. How about a complaint to the police of ABH? After all, security give PAX enough aggrovation - time for them to get some back!