More about herat block

Does this mean that if you are pacing at 100% in your top chamber that there is no electrical pulse between the upper and lower chambers does that constitute a thied degree heart block?

I am pacing at 75% in top atrium due to dual lead out pacing afib which is intermitent but now controlled at under 1% by beta blockers
Does this mean I will go on to 100% top atrium pacing dependancy and if so will that lead to a heart block and then require a defibrillator?

7 Comments

Heart Block

by SMITTY - 2008-03-27 01:03:52

More on this subject.

The heart's "natural" pacemaker is the sinus node. This is a small mass of specialized cells in the top of the heart's right atrium (upper chamber) is where the electrical impulses that cause your heart to beat are generated. Since our heart actually has two areas which can generate an electrical impulse to make the heart chamber(s) contract, I will call this one the primary natural pacemaker.

A chamber of the heart contracts when it is stimulated by an electrical impulse. For the heart to beat properly, the electrical impulse generated in the sinus node must travel down a specific path to reach the ventricles, which are the heart's pumping chambers that send the life-sustaining blood to all parts of our body.

Our heart’s natural pacemaker may be defective, causing the heartbeat to be too fast, too slow or irregular. Or the heart's electrical pathways may become blocked and this is what we hear referred to as heat block.

When the electrical impulse from the heart's upper chambers (atria) does make it to the ventricle for anyone of a number of reasons, this is called heart block. This does not mean that blood flow or blood vessels are blocked. It simply means the electrical impulse is not completing its journey and there are three degrees of heart block.

A first-degree heart block means the electrical impulse moves through the atria more slowly than normal. Heart rate and rhythm are normal, and there may be nothing wrong with the heart as some heart medicines such as digitalis can slow conduction of the impulse from the atria to the ventricles and cause what is known as first-degree heart block.

A second-degree heart block occurs when some signals from the atria don't reach the ventricles. This result in what we usually call "skip-beats."
Third-degree or complete heart block means that the heart's electrical impulse does not pass from the heart's upper to lower chambers. When this occurs, bradycardia (slow heartbeat) may result. In such cases, secondary natural pacemaker cells in the lower chambers take over. The impulses from the secondary natural pacemaker cause the ventricles to contract and pump blood. But the pumping is at a slower rate than if it were getting an impulse from the primary natural pacemaker. Complete heart block is most often caused in adults by heart disease or as a side effect of drug toxicity. Heart block also can be present at or even before birth (congenital heart block). An injury to the electrical conduction system during heart surgery also may cause heart block.

Those of us that have a problem in our heart’s natural pacemaker are fortunate to live in a time when we can get a manmade pacemaker to assist or completely takeover the electrical impulse generating job and keep our heart beating.

Most pacemakers in use today are demand pacemakers. A demand pacemaker means that the pacemaker contains a sensing device. This sensor constantly checks our heart rate and when the heart rate drops below the low-set point on the pacemaker, that pacemaker will bring the heart rate up to the number of the low-set point. Since the pacemaker will also have a high set point, it turns the signal off when the heartbeat is above that.

For those of us that have a pacemaker that is working100% of the time that just means our natural heart rate would be below the low-set point on the pacemaker. The fact that is working100% of the time does not mean our heart’s natural pacemaker is no longer working.

When I get a pacemaker checkup I always ask what my unassisted heart rate is as I know at one point during the checkup that will be determined/ The last time I was told it was 45. Since the low setting on my pacemaker is 70, I can understand why my PM is working 100% of the time. At one point in my life when I was on a hefty exercise program, my natural heart rate was in the low 40’s with an ejection fraction of 60%+ and I got along just fine. But time, medicines and Mother Nature can change things so I’m thankful for my little electronic buddy most of the time.

Smitty

So Smitty...

by axg9504 - 2008-03-27 02:03:09

Let's say that in an interval there were 100 heart beats. If your interrogation says that during that interval you were paced 75% of the time in the upper and say 10% in the lower, what does that mean? (1) Can the two numbers add up to greater than 100 (2) Does it mean that 75 beats were initiated in the upper and 10 in the lower.. I don't think that's right at all, doesn't sound right.

I don't understand what '... of the time' refers to. What time interval is that? Thanks.

Total Percentage

by SMITTY - 2008-03-27 06:03:03

AXG9504,

I never thought of it that way. But my thought is that the total number could be 100 X the number of leads from your pacemaker. So my answer is yes, the total number could be greater than 100.

I say contact the PM maker to be certain.

Smitty

Degree of pacing

by axg9504 - 2008-03-27 10:03:10

in each chamber I believe (Smitty where are you?) refers to the extent to which pacing was initiated in that chamber. I know it's not good (or perhaps preferable not to) have a large degree of pacing in the lower chamber. Early pacemakers paced the lower chamber all the time and apparently unncecessary lower chamber pacing can lead to heart problems. Like you I have a dual chamber pacer and am on a mild blocker. The blocker is to control my upper chamber arrhythmia which causes my bradycardia and it seems to be helping. Anyway my last reading at 6 weeks post PM was 75% paced in the upper and practically zero in the lower (my natural conduction does work most of the time, it has problems when I exercise). This was regarded by the doc as very good, so I take it that it is good to have the pacing in the upper chamber.

I think the percentage is referring to the situation 'when you are paced by the PM' (Smitty?). So 100% paced in the top chamber may not mean being paced 100% of the time. It might just mean that the PM supplied 100% of its pacing at the top. (I am not sure).

If it does mean that you slowly become PM dependent, I don't think that's necessarily bad. After all there are many here who have that problem because they don't have a working conduction system either due to surgery or otherwise.

A defibrillator is to prevent ventricular fibrillation. It shocks your heart when it detects this condition. Sorry but I don't know unde what conditions VF can arise. Some people are predisposed to it and can have it in anotherwise normal heart so it's not in any way related to heart block.

For instance, I have had problems with a junctional rhythm where because my sinus node was not working properly, a lower level mechanism stepped in and kept my ventricles going. Most of the time this lower level pacing was lower than 60 bpm. Sometimes it was accelerated at 90 bpm (when I was walking fast-which was good, it helped me get some exercise). But the junctional rhythm never ran at rates higher than 90. I put up with this for nearly 5 years without any other problems. My docs recommended a PM which I finally got, but they never said I had to absolutely have it.

Percentage of Pacing

by TwoCents - 2008-03-27 12:03:23

Being paced 100% of the time in the upper chamber means just that...that chamber is pacing all of the time. However, that doesn't mean the bottom chamber is also pacing at 100%. In a dual lead pacemaker, a pm interrogation, will reveal what percentage of the time EACH chamber is pacing.

Heart Block

by TwoCents - 2008-03-27 12:03:51

Heart block refers to various degrees of problems with the AV node which is between your upper and lower heart chambers. When the problem originates with your sinus node, an area in the upper chambers, it is called sinus node dysfunction. You can have problems with both nodes. I, for example, have sinus node dysfunction and pace 100% of the time in the the upper right chamber. I have "sinus arrest" or "atria standstill". I also pace 40% of the time in the right ventricle (lower chamber). There are other ways that the heart can generate a "heart beat" even though the sinus node is not operating. Generally, this would be called an "escape rhythm". A "junctional rhythm" is when the heartbeat generates from the AV node because the sinus node is not functioning properly. A "junctional rhythm", in general, is a slower rhythm that that originating from the sinus node. The sinus node is also referred to as the "heart's natural pacemaker". Also, "heart block" (problems with AV node) does not constitute a need for an inplantable difibrillator. Other problems must be present to justify an ICD. Hope this helps. I hope this helps. TwoCents

Understanding percent of pacing

by Vai - 2008-03-28 12:03:23

I asked the PM tech to explain this pacing percentage measurement and this is her explanation
- the percentage is measured over time, not number of heart beats.
- the duration of time is the time logged on the interrogation report usually the total time from the last check-up to the current check-up (= T hours)
- the pacing time is the total time (in minutes or hours) that the PM assisted or supported your heart during this duration of time ( = p hours)
- then it is only arithmetic calculation to calculate the percentage pace which is 100 X p/T %
- The pacing in the upper chamber and the lower chamber is measured independently. It is not meant to be added together. It makes no sense to add them up.
- For PM, being paced in the upper chamber is normal. This is one of the objectives of the PM implant. Being paced from 20% to 90% is quite within the range, although I thought such a wide range seems odd to be called "within range".
- For PM, being paced in the lower chamber is not good news. Being paced at < 1% is very good news. Being paced on the lower chamber leads to undesirable side effects like cardiomyopathy (thickening of heart walls), heart block, heart failure etc

I trust this helps.

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