Questions about pacemakers

[LukaLR]

Hi. I'm a french researcher in computer sciences and I hope you won't mind me posting here for some help. Right now I'm working on a paper involving a pacemaker as a case study for model checking. It's a dual-chamber one. Some specifications were provided and I browsed the web for more but now I start feeling confused about some points.

First I'd like to check if I got triggered modes (XXT) right ... As far as I understand, it answers a sensing in a chamber by an immediate pacing. Specifications are quite clear about it but I don't get why you'd want to do that and would like to make sure.

Then, it's not clear to me what happens if an event is sensed too "early" (according to specified parameters like refractory periods or lower beat rate). For example in VVT mode, what happens if there's an early ventricular sensing? Does the cycle reset? Is there a pacing? What about VVI?

During the magnet test (XOO mode), what is the usual fixed beat rate? The specifications I got sets it at 100ppm (assuming BOL), sounds high to me.

Sorry if this all post sounds stupid, me not being a native english speaker nor a student/doctor doesn't help. Answers would be much appreciated!

Luka

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[itceps]

Triggered mode is seldom used. It was initially developed to solve the problem of "oversensing" in patients who did not have any intrinsic rhythm. In the early days, the oversensing problem was a common one. Pacemaker would be inhibited by noise and often the discrimination between noise and intrinsic rhythm was no so sophisticated. Hence, triggered mode was designed for safety at the expense of draining the battery and unnecessary pacing. In addition, triggered mode can be used in non invasive electrophysiological studies. For instance, chest stimulation can trigger pacing so one effectively can do a full EP study without putting the catheters in the body. A partial trigger mode is used today in BIV pacing. For instance, sensed RV event triggers LV pacing. This is especially useful in atrial fibrillation where the rhythm is irregular or in patients with frequent PVC. The goal is to maximize pacing with RV and LV synchrony.

As far as the second part of the question, any sensed (in I mode) or paced beat (in T or I mode) inhibits the pacing. Otherwise you can end up with rapid non physiological pacing. So , some minimum has to be set. In VVI mode refractory period is set to avoid seeing the T wave. After the refractory period, any sensed event starts the new cycle.

As far as the magnet rates , every company has its own rates. You have to call them and give them the specific model. Depending on optimal, effective replacement time or end of life battery the magnet rate is different.

Hope this helps.