What does a PM record?

Hi, Can a Pacemaker tell the differents between a drop below it's lowest setting & an AV Block event? I ask this because I want to ask the Cardio Tech about how much my PM has paced, and more important to me, for what reason it has paced. Thank you.

4 Comments

pacing

by Tracey_E - 2011-11-02 06:11:59

If I understand your question, yes it can tell the difference. The minimum rate is the atrial rate, the rate set by the sinus node. When you are in block, you will be pacing ventricle. If all you have is av block, odds are good your atrial rate is perfectly normal and you rarely pace atrial making the lower limit irrelevant.

The SA node in the atria is the "brains" of the heart. It senses the oxygen level in the blood and raises/lowers the hr accordingly. The ventricles are the "brawn", they make the strong contraction we feel as our pulse. With av block, the SA node works as it should but this signal is blocked all or some of the time and never makes it to the AV node in the ventricles.

The pm has two leads, one in the atria and one in the ventricles. The atrial lead makes sure the rate doesn't drop below the minimum, it paces only when the rate drops too low. The ventricular lead watches to see when the atria beats. It gives the heart a fraction of a second to beat on its own then steps in and paces if it doesn't. So with av block our own SA node sets the pace most if not all the time and the pm works primarily to keep the heart in sync.

Ask to see a copy of the report when you go for a check. If they don't explain it clearly you can bring it back here and we have some members who can help decipher it. All docs/reps are different but in my experience as soon as they saw I wanted to know, they started telling me automatically and explaining any changes. You'll be looking for Atrial Sensing/Atrial Pacing and Ventricular Sensing/Ventricular Pacing. The pm is always either sensing (watching) or pacing so the sensing + pacing = 100%. I have 3rd degree av block and I atrial pace about 2%, ventricular pace 99.9%.

TraceyE

by climber - 2011-11-02 07:11:57

Hi TraceyE, Very good info. I've asked to see the print-out of my check-up's, was told 'no' by the tech. I'm in the UK under the NHS.
My lower setting is at 40 and upper is at 150. My lower is at 40 as I've always been fit & active and at rest my HR is in the low 40's.
I just wanted to know as my setting is at 40 & my pulse goes below 40 and is not in av block would the PM know the difference? I think your reply covered this.
One thing I do remember about when I got my PM is that I thought I was only going to have one lead fitted, but after the op the doctor said he used two as he said it may help me in older life.

second lead

by Tracey_E - 2011-11-02 10:11:45

If the tech says no, can you ask the dr? I've noticed they are easier about it in the States but we've had UK members sweet talk their way to a copy of the report.

How much under 40 have you found your rate? Because the pm doesn't work in beats per minute. We discuss it that way because it's easier to understand but it is set for the delay between beats. If you are at 60 bpm, it won't let you go more than one second without beating so it won't always work out to exactly 40 bpm. Also, sometimes there are small beats we don't feel when we count so the number is a bit higher. If you're getting 37-38, that's close enough to 40 not to worry. If you're getting 25, something isn't right.

The pm will pace ventricular every time the atria beats, whatever that rate is as long as it's under 150 when it maxes out. It will only pace you atrial if your natural sinus rate drops under 40 bpm. The pm doesn't think if you are in block or not, it only makes sure the atria doesn't go too slowly and the ventricle beats whenever the atria does. Does that make sense? It doesn't care what causes your heart to slow down, only that it doesn't go too slowly (atrial lead) and that it stays in sync (ventricular lead).

Upper limit is how high the ventricle will pace, so if you are working out and your atria gets to 170, the pm will only pace you to 150, or whatever your upper limit is. Upper limit should be 10-20 above wherever your rate tends to be when you are active.

And yes, it's good to have both leads. As long as they're already in there might as well get all the goodies! It provides more information so the pm can work more efficiently, and you never know when you might need it. Even though I don't use my second lead often- less than 2% of the time- if you add up the beats over the course of a week it's a lot. Those times it kicks in make a big difference, esp when I'm active. I had a secondary problem we didn't know about because my bigger problem- av block- masked it. Sometimes during workouts, my rate will suddenly plummet. Well, it used to, now the pm kicks in when that happens so I never know the difference, I work out hard and feel great.

TraceyE

by climber - 2011-11-02 12:11:15

On my 6 month check-up the tech raised my upper limit to 150 b/m although on a treadmill test I was maxing out at over 170 b/m. It can get that high when I run/jog. Looks like it should be set higher. Something for me to ask about next visit. The UK NHS are full of red-tape. I would have to put in a formal written request for detailed info.

As for the lower level set at 40 b/m, I've never been under 40 b/m, that I know of. I do check my pulse rate & never known it to drop below the low 40's, which is my at rest rate normally.

I'm asking these questions because since the PM was fitted I've been so ill (12 months), I wasn't ill before it was fitted:( It's got to the point where I've been told the PM must come out to see if the troubles stop. The top Doc's seem to think that's ok for me to do. I want to have a better understanding of av block before my next visit to the hospital.

Your info has been far better than anything I've had from my Doc. Thank you.

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