fjrboomer,
I work for a pacemaker/defibrillator manufacturer, and I would be happy to shed some clarity on the topic. Please keep in mind that you should always follow the direction of your physician. I can tell you how these devices work, but ultimately your doc is responsible for your care, and you are responsible for compliance.
All modern pacemakers operate on a beat to beat basis (commonlycalled "demand"). This means that they have an internal countdown clock (which is programmable) and will deliver a small electric current to your heart to induce a contraction should it not do so on its own by the programmed time delay. If your heart is beating faster than the programmed rate, it will stand by (or more technically accurate, inhibit) and start the countdown again.
Pacemakers by all manufacturers (Boston Scientific (Guidant), Medtronic, St. Jude Medical, ELA, Biotronik) will respond to magnetic flux by changing their rate and mode. This is called a magnet response. The rate & mode is manufacturer and model dependent, and is likely a rate that indicates battery status (for example 100 beats per minute with a good battery, 85 with one that needs replacement). That is one of the things that is identified on your trans-telephonic phone check. The mode is also likely asynchronous, meaning the pacemaker will deliver pacing stimuli independent of your heart's own activity. Therefore, in the presence of a magnet, your rate could be faster and your heart could beat somewhat erratically (pacemaker and intrinsic beats occuring at almost the same time).
Generally speaking, this rarely poses a safety risk, and the rate & mode reverts to normal as soon as the magnet is removed. It would be extremely unlikely that exposure to the magnet would cause your pacemaker to stop working or your heart rate to slow or stop causing you lightheadedness, etc., and you may not even feel anything. Do you notice anything when you put the magnet over your device for your trans-telephonic checks?
Pacemakers and ICDs (defibrillators) need a very strong magnet, placed within a few centimeters of the device in order for it to trigger its magnet response. Therefore, unless the tankbag's magnets are held within a few inches of your chest, it should not trigger. In the normal use of a tankbag, I sincerely believe that you should be OK. Sit up normally and do not lean over it. Given that, and the unliklihood of experiencing any ill effects if the magnet response were tripped, the safety of using a tankbag is relatively high. If you are really concerned, use a strap-down type.
Some other comments: ICDs (defibrillators) and Bi-V or CRT-D defibrillators do not have the same magnet response that pacemakers do. In the presence of a magnet, they will not deliver shock therapy as they normally would, but their pacing rate and mode remain unchanged. Also, a pacemaker or ICD patient can walk through the metal detector at the airport without concern. You may set off the alarm (especially ICDs), but it will not cause any ill effects if you walk through normally. Things to avoid are close proximity to anything that emits electromagnetic interference (motors, etc.). As a rule of thumb, if it has a fat power cord hanging out of it, keep it 12 inches or more away from your chest. Anti-pilfering antennas (security sensors) near the doors of retail stores should be avoided by walking through them normally as well.
By all means, if anyone has any questions or concerns on this topic, you can respond here or send me a PM. I will try to help as best I can.
-BD
