MV sensor problem - solved

• by philip.thecyclist
• 2013-06-26 07:06:42
• Exercise & Sports
• 1522 views
• 0 comments

A week or so ago I asked if anyone had experienced sudden and prolongued "collapses" in MV pacing rates from 160+ to around 90 bpm. I experienced this with my new biventricular PM which I had to have due to a reduced ejaction fracion of my left ventrical. The problem occurred when climbing hills while cycling - and this "collapse" I can tell you was a bit frightening.

Yesterday I had a follow-up check-up, and a Boston Scientific rep. was present. With her help, and with advice from her her colleague back in the office, the problem has been solved. It seems that the PM was sensing T-waves, which are characteristic signals which occur during the recovery phase of ventricular pumping cycles. The PM was interpreting the T-waves as intrinsic ventricular beats, and so inhibited subsequent pacing beats. Then, in the absence of a T-wave following the inhibited beat, a paced beat would occur, thus repeating the cycle. You can see that this would have the effect of halving the paced rate - thus the collapse. In short, it's termed oversensing (NOT the same as overpacing).

The solution has been to reduce the sensitivity of the sensing voltage, but not by so much that pacing inhibition following true intrinsic beats, such as ectopics, does not occur. Why the problem occurred only during high exertion levels I don't know, Perhaps the magnitude of the T-waves are then greater.

The upshot is that today I did 3 hours cycling today with no problem and with greater ease than for some years.

On the topic of bi-ventricular pacing: Now that my LV is being paced I am finding any kind of exertion leaves me feeling far less breathless than previously, so if anyone active is a candidate for a bi-ventricular device for cardiac resynchronisation therapy, then the outlook could be good.