My checkup today

Today was checkup day for me. As NASA would put it all was nominal. The only change we made was to reduce my ventricle pacing voltage from 3.75V to 2.5V. This is where it was before my problem back in November when I was losing capture of ventricle pacing intermittently. At that time we turned the voltage up to 5.0V to assure that I would remain one of the living! Both the cardiologist and the Medtronic rep agree that I probably had a virus that was causing irritation of my heart tissue. During this period I was also running in excess of 2000 PVC's/week. Now it is back down to about 30/week.

Something interesting about the voltage adjustments. For me they have a marked effect on how pacing and my heart beat feels to me. At 5V it was like someone was in there with a hammer pounding on my heart to get it to beat. After we reduced the voltage to 3.75V it felt much better. I was aware of my heart beat, but it wasn't uncomfortable. Today since reducing it to 2.5V I have hardly noticed by heart beat. It is like a smooth running machine. I think there is a good reason for the effect. With our natural pacing system the right and left bundles conduct small electrical pulse to the heart wall where it smoothly spreads out into a powerful contraction. The pacemaker is attempting to imitate this system by applying an electrical pulse through the leads and electrodes into the heart wall. With just enough voltage to get the tissue around the electrode to respond the contraction spreads in a natural way. If we apply a large electrical pulse into the heart wall it is conducted through the surrounding tissue and instantaneously stimulates a larger area. The contraction starts with a larger than normal force and spreads rapidly causing an uncomfortable heart sensation. I'm wondering if this isn't the cause of heart failure that has been reported. My sense is that few EP's take the time to fine tune the pacing voltages.

Keep in mind that the voltages I mentioned above are optimized for me. They can vary greatly depending on the condition of the heart. When I had the virus my heart required the higher voltage just to work and how it felt was secondary.

Enough for this one.

frank

4 Comments

Explain Capture...

by Pacing13 - 2008-04-10 09:04:26

ElectricFrank - I had my check up today and wow, alot of the comments you talk about were mentioned todat at my check up!
One thing I was wondering...what does CAPTURE mean? My nurse was telling me that my upper lead is not capturing and my volts were turned up. This all because I was having troubles with fluttering and feeling the need to catch my breath.

Can you explain???

THANKS,
Tracie

Checkup Report

by SMITTY - 2008-04-10 10:04:24

Hello Frank,

Thank you for the excellent report and for the explanations of some of the things that can take place with our pacemakers. I do have a couple of comments I would like to add.

I have always visualized the impulse from the hearts natural pacemaker as being weak when it arrives at the heart chamber and continues to increase in strength over the next few milliseconds until it reaches significant strength to cause the heart chamber to contract. With a pacemaker that impulse arrives at full strength and the contraction of the heart chamber is much more abrupt that the contraction from the hearts pacemaker. While the results are the same, this difference in strength of the impulse on arrival causes some of us to be more likely to feel the contraction imitated by the pacemaker than the one imitated by the heart’s pacemaker. This especially so if the voltage setting from the pacemaker is slightly higher than necessary. And I think that may be a portion of the problem for many of us.

While I’m by no stretch of the imagination an expert on this subject, I have the idea that our hearts natural pacemaker can usually makes adjustments in impulse strength to meet our needs, while our man made PM sends out the same strength impulse each time, needed or not. This is one of the reasons that, while our man made pacemaker keeps many of alive, we can never enjoy the comfort of having our heart beats initiated by a man made device that we have from natures PM.

Furthermore, I think therein is also one reason an E.P., or technician can ever take the time to get the perfect setting for many of us. I’ll bet that if I were to plot the impulse strength form my man made PM I would have a very straight line. However, if I plotted the strength of the impulse strength from my natural PM I would see many peaks and valleys.

Come to think of it, isn’t an Electrocardiogram a plot of electrical impulse strength, timing and electrical conductance of our heart’s electrical system. Stupid question I know, for you learned folks, but I had never thought about just what an ECG was telling the doctors.
Anyway, these are some of the reasons that while I know pacemakers are one of the greatest medical inventions we have seen in our time, the efforts of experts like you are still needed to make them more perfect

Smitty

Responses

by ElectricFrank - 2008-04-10 11:04:24

To Pacing13:
Capture means the electrical impluse from the pacer creates a contraction of the chamber it is connected to. In a case like yours since the voltage is turned up it could be that the lead has detached, is broken, or that the particular area of your heart wall where the electrode is attached isn't sensitive to pacing. As far as broken or detached lead it should show up on the Impedance reading when they interrogated the pacer. What are they suggesting doing at this point?

To Smitty:
Your comments on the natural pacemaker are right on. As I understand it fibers from the bundle actually fan out over an area which makes the nature of the pacing different. I need to find someone who is only pacing part of the time and collect ECG data using my system. Then we could look at the difference in paced and non paced contractions. I use a much higher sampling rate and filter bandwidth than the usual ECG's. The ECG waveform comes from the contraction of the heart muscle. The QRS waveform comes from the successive contractions of the various muscles of the heart. (I need to find my old physiology book). I don't think we can see the electrical activity in the bundles. They are too small and contained.
All this does have an impact on how it feels to be paced. The Medtronic rep today told me that the new units just coming on the market actually calibrate themselves in real time, rather than once a day, etc. I was asking him why in my case where I was losing capture intermittently the pacer didn't sense it and increase the voltage on the next pulse.
I kind of got him on this one. He said he could program mine to test capture threshold every 15 minutes if I liked. I told him that since I was pretty much totally dependent that all that would do is increase the voltage to my dead heart 14 minutes later. I'm not sure he thought it was funny.

frank

Electric Frank and Smitty

by Blueaustralia - 2008-04-11 02:04:03



Please, please never disappear out of our lives we need your explanations you guys are gems.

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