ORD, so Illinois. This is what the law says on the subject of self-defense in IL:

"Use of Force in Defense of Person: A person is justified in the use of force against another when and to the extent that he reasonably believes that such conduct is necessary to defend himself or another against such other's imminent use of unlawful force. However, he is justified in the use of force which is intended or likely to cause death or great bodily harm only if he reasonably believes that such force is necessary to prevent imminent death or great bodily harm to himself or another, or the commission of a forcible felony."

http://pages.prodigy.net/fhattys/page10.html

Deadly force is justified IF AND ONLY IF you reasonably believe that your life was in imminent danger. Hence "reasonable fear for your life."

Three conditions for justifiable self-defense:
1) The force used must seem necessary to prevent the attack; (The TSA agent was approaching OP with a potentially lethal "weapon," the pacemaker could be affected by the wand and such, the agent, despite being warned multiple times of the danger, decided to knowingly, willingly and recklessly approach the OP with said wand; the use of lethal/non-lethal force was necessary to stop the TSA agent from approaching him with the wand in question)
2) The force used must have been proportional to the gravity of the attack; (assume the attack was approaching the OP with the wand, which may have been deadly. This was potentially lethal, justifying the use of deadly force. Wand activated, pacemaker screwed up, OP possibly dead. Any jury with a brain can see this.)
3) The threat of force by the attacker must have been immediate and imminent. (TSA agent was 5 feet away. He was the push of a button away from potentially screwing up the pacemaker, which is KNOWN to cause problems when it comes in close contact with the wand. If that's not imminent and immediate, I don't know what is.)

I'm not a lawyer, so see a real lawyer, but if you were to have shot the TSA agent in the face, as a jury, I would have found that you were acting in self-defense.