Seems to be a lot of contradictory info on the web. Several sites say things like this...
Pacemaker Frequently Asked Questions
Can security equipment in Airports and Shop entrance damage or interfere with my pacemaker? ....snip...
Your pacemaker will not be affected by the security system. However the metal case around your pacemaker could set off the alarm.
Pacemakers: Generating regular heartbeats - MayoClinic.com
Security Systems. Passing through an airport metal detector won't interfere with your pacemeker, although the metal may sound an alarm
I suspect you may have a battle for compensation if the effect wasn't instant. Proving it was the security scanner might be difficult unless the pacemaker has some kind of data logging built in.