help with pacing percentage

I've not felt well since having a dual chamber pacemaker 4 months ago. Yesterday I was told the PM is pacing at 0.2%. That seems incredibly low and I wonder of the PM is collecting data properly. It also recorded zero events and one of my problems is I believe I am still getting events.

Does the pacing percentage include the following?

Before the operation my heart rate was typically 50. It is now set at 64 and seems to be doing that reasonably well. I would assume that's nearly 20% pacing (64/50 -1)

My heart rate at night was as low as 25 per minute. To get to 64 is over 100% pacing.

Is it correct, do people think, that I'm only 0.2% pacing or does sound like a recording fault? I'm not sure what is factored into the pacing. Is it just when the heart fails/skips a beat?

I expressed surprise with the cardiologist but he dismissed it.

6 Comments

Atrial and ventricular pacing

by golden_snitch - 2013-10-01 02:10:17

Hi!

With a dual chamber pacemaker, you have two pacing percentages: atrial and ventricular. If you suffered from sinus bradycardia before the implant - sounds like it as you don't mention any pauses or passing out, "just" low heart rates -, the atrial pacing percentage is what's most important. The 0.2% you mention sound more like your ventricular pacing percentage. With sinus bradycardia you should not pace in the ventricles at all or, if you do, not much, so the 0.2% sounds just fine.

You're absolutely right with heart rates of 25bpm at night, and 50 at daytime, and with the pacemaker now set at around 60bpm, you should have a much higher percentage. So, my guess is that what the doctor told you was this ventricular percentage only. If there had been anything wrong, for instance with the leads, he would have seen that during interrogation. What he also sees are heart rate histograms, so in case your heart rate had still been too slow, the doctor would have seen that. But apparently everything was fine.

What do you mean by "events"? If you feel the same as before the implant, if there really is no improvement at all, you should contact your doctor again.

Best wishes
Inga

Comment on % Pacing

by donr - 2013-10-01 03:10:37

To understand % Pacing, you need to know how it works & how the heart works.

The is no Santa Claus; no Easter Bunny; no tooth Fairy; no Jack Frost; NO HEART RATE.

The heart rate (HR) is a fiction of historical origin. Man has known for a long time how to determine a HR - the Dr. takes out his pocket watch w/ the second hand , gropes around to find the HR at the patient's wrist, starts counting & timing at the same time. Counts fr 15 seconds & multiplies by 4 - gets a HR. At that time no one knew how the heart worked. They all thought there was some master timer that ran the heart at whatever rate was needed - sorta like a sine wave of a fixed frequency or a square wave that created the rate.

Nope - the heart is run by the Sinus Node (SA) that somehow times individual events in cooperation w/ the A-T Node. I do not think anyone knows if it is a digital timer or an analog timer, but it is a timer that takes cues from events. Your PM times things the same way, using the same reference events as the nodes - but we know the PM is a digital timer (Whoopee!).

This sorta gets to the question "Which came first, the chicken or the egg?" WE do not know how the heart starts, but we know what it counts FROM.

Look at a cy of your ECG. The first reference point is that little pimple called the P Wave -that's the Atria contracting & is started by the SA node by it giving a signal. The SA node starts a count. Meanwhile, the signal is traveling down the heart to the Atrio-Ventricular Node (AV), but is purposely delayed so the Ventricles can fill w/blood. AFter the delay, which is counted out by the AV, the Ventricles contract.That's the BIG squiggle called the QRS Complex. Meanwhile the AV is still counting, just in case the ventricles don't contract - this is so that it can act as a fail-safe & take over from the SA. (You'll read about people talking about an "Escape Rhythm. that's this). The QRS completes its course & there are two more critical events to take place. The stretch after the QRS has a purpose in the recharging of all the electrical tissues, leading up to the little speed bump, the T Wave, where the tissues do their work getting ready for the next beat. So what's the SA doing all this time? Still counting. The nature of the heart is that the SA cannot start the next beat till AFTER the functions of the T wave are complete. A so-called Refratory period keeps it from doing so. If the SA gives the signal for the Atria to contract while the T wave exists, confusion can result, leading to V-Fib - not a good result. So the SA timer can vary a bit from beat to beat.

Your PM follows all this activity, keeping track of times between actual events & comparing them to the times stored in its memory. Simplified, the PM stores a time equal to that from P to P that corresponds to the "Heart Rate" given for your lower limit. It also has a stored time for the P-QRS DESIRED elapsed time. Now the stored times are a bit longer than what the heart would really do, so the PM can allow the heart to do its thing naturally. The PM sits there, sensing what the heart is doing through it's two leads, counting along w/ the nodes. If the natural signals come w/i the correct interval, the PM does nothing. If the signal is NOT there before the PM counts to its stored time, it gives the old high sign & fires off a pacing pulse.

So how does it figure % pacing? It's a great counter that's its main purpose - to count things. So it counts every beat of your heart. It counts the number of times it paces you. % Paced is a simple ratio: Number of paces (P) divided by total number of beats (T). % Paced = P/T. To complete the data, we need one other number - % unpaced (They call it S, for sensed, meaning that the PM did nothing) %Sensed = T-P/T Add the two up & they equal 1 as well they should!

Now your PM really gives you more than that; it gives you FOUR %ages. Called Atrial sensed, Ventrical sensed (AsVs); Atria sensed Ventricle paced (AsVp); Atria Paced-Ventricle sensed (ApVs): & Atria Paced-Ventricle Paced (ApVp). That tells you everything you need to know about how much you are paced.

When the PM calculates these percentages, it cares NOT what the HR is - it calculates them for the beats COUNTED w/o reference to the rates.

Thanks

by davidjb - 2013-10-02 03:10:55

These were both very comprehensive and useful replies. I phoned the technician today and you are bot correct - it is Ventricle Pacing they are quoting. That makes a lot of sense now. I also understand what Atrial Pacing is about.

Brilliant guys and thanks

% pacing

by HK - 2013-10-12 12:10:25

All true words! I have 0% Atrial pacing and 100% ventricular pacing. Without the PM nobody would be typing this.
HK

?

by davidjb - 2013-10-13 05:10:07

So which is best to have? I guess 100? Atrial and 0% Ventricular? Does it matter. i guess not and as HK says, the important thing is we are still going. My dad had sick sinus syndrome 3 years older than I am now, and he died after the Op due to septicaemia.

Best to have?

by donr - 2013-10-13 09:10:57

Why ZERO for both parts, Atria & Ventricular, of course.

But those of us writing these notes have to face the simple fact that all the alternatives to hosting the PM are infinitely worse.

For me, I'm third generation hosting a PM. My maternal GM hosted one; two of her three sons did likewise, & now me. I did not learn till after her death that my mother had an arrhythmia & took Flecainide, just like I do. She died at age 94 because everything just wore out & quit one night while she was asleep.

Don

You know you're wired when...

You always have something close to your heart.

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