I would suggest you look up the website of the manufacturer of the pacemaker your father gets. They have sections on their websites with detailed information on living and traveling with a pace maker.

You will probably see that the card you are given concerns the fact that your pacemaker may cause an alarm with a WTMD rather than that the pacemaker will be affected by the WTMD.

Its all a matter of choice by the pacemaker user whether to go through the WTMD or not. Also most cardiologists will tell pacemaker users to avoid going through WTMD. Unfortunately the alternative is usually a pat down search!