Pacemakers

Hi Everyone.

Haven't posted for ages but please can someone verify for me the concern I have with a pacemaker.

My pacemaker works when my pulse drops below 50 which is if I am sitting in the evening or asleep at night. Other than that my heart's own pacemaker works for me.

My question is does a pacemaker actually weaken your heart muscle over a period of time when it takes over your heart rhythm. I have asked my cardiologist here in France but as usual the answer is very vague. This now is my only concern so I have learnt to accept it now, and am running and keeping quite fit.

Hope someone can just clear this one up and I can get out of this stress area.

Thanks in advance.

Julie

9 Comments

Weaker contraction

by Terry - 2008-08-16 04:08:32

According to the scientific studies, the heart doesn't pump as efficeintly with a paced pulse that starts in muscle where the electrode resides. In the long term, esoecially when the pacemaker paces more than 40% of the time, the heart remodels and can lead to heart failure, See the following studies about the penelty to be paid by bypassing the heart's conduction system (Google cardiac conduction system.) Fortunately, there are EPs who have started to pace the heart's conduction system at the bundle of His. The MOST Study - Dr, Sweeney:

http://content.onlinejacc.org/cgi/content/abstract/47/2/282?ck=nck

The DAVID Study:

http://jama.ama-assn.org/cgi/content/abstract/288/24/3115?ijkey=fc54101eeb36560b8f5865583bbdd2a50bd26de4&keytype2=tf_ipsecsha

Questions? Send a private message if you like.

Terry

PM Making Heart Weaker

by SMITTY - 2008-08-16 07:08:00


Hello Jules,

I doubt that you will get a much more clear answer to your question here. I've seen it asked before and there are varying opinions. My opinion is that it will not significantly weaken the heart.

All the pacemaker does is replace the electrical impulse that is not being supplied by the heart's natural pacemaker. I can see no way that should weaken the heart. To the contrary, because the heart is getting more uniform flow of blood the pacemaker should make the heart healthier at least, if not stronger.

It seems that I have seen something about single lead pacemakers that pace only the ventricle can cause a weakening of that chamber of the heart over a long period of time, and that is one reason single lead units are being implanted less frequently. Now I may be all wet on this, but I'm pretty sure it was something along this line.

After writing the above I saw Terry's comment and I have seen a little of this study and I think I understand the reasoning behind what is said. I'll try to pass on my interpretation of how this may or may not happen.

First, let's take a look at how the heart's natural pacemaker works. Your heartbeat is triggered by electrical impulses that travel down a special pathway through your heart. The impulse starts in a small bundle of specialized cells located in the right atrium, called the SA node (sinoatrial node). The electrical activity spreads through the walls of the atria and causes them to contract.

The AV node (atrioventricular node) is a cluster of cells in the center of the heart between the atria and ventricles, and acts like a gate that slows the electrical signal originally generated in the ASA node before it enters the ventricles. This delay gives the atria time to contract before the ventricles do.

Notice the above talks about how the electrical impulse generated by the heart's natural pacemaker "spreads" out to make the heart beat. To me what this is saying is that when the electrical charge from the heart's pacemaker arrives it is not strong enough to cause the heart chamber to contract, but continues to increase in intensity and spread out over the heart muscle until muscle contraction is achieved. So you have a heart beat that is the result of an electrical charge that goes from zero to whatever amount it takes to make the heart muscle contract.

On the other hand look at what happens when that pacemaker sends an electrical charge. It arrives at one point (wherever the tip of the lead is touching the heart wall) with full voltage, at a little less than 186,000 miles/second and its wham o the heart chamber contracts. (For a complete understand of what I'm talking about, try touching a spark plug on a running engine.)

That is not the gentle heart beat generated by the heart's natural PM. In fact the heart muscle may be receiving a bigger electrical charge than really necessary to make the heart muscle contract and over a long, long period of time I can see where it may weaken the heart muscle. But because the intensity of the electrical charge from a manmade pacemaker is adjustable the voltage can be increased as necessary.

So, considering the difference in the strength and speed of the electrical charge being received by the heart muscle from the heart's natural pacemaker and the manmade pacemaker, it seem reasonable to expect changes in the heart over long periods of time.

Now, if I’m wrong in my understanding of what goes on, remember they tell us ignorance make bliss, so you can just figure Old Smitty is one happy soul.

Smitty

it is what it is

by Tracey_E - 2008-08-16 07:08:43

The scientists can argue over it all they want but I'd be dead without it... so whether it makes the heart weaker or stronger is irrelevant in my opinion. YMMV, of course :o)

Have a pm allows me to work out, that makes my heart stronger.

Stronger

by chiliman - 2008-08-16 07:08:56

In my case, and often (but not always) in the case of others with biventricular 3-lead CRT/ICD pacemakers, there is an INCREASE in the hearts' overall strength that is quite significant.

Prior to my being switched from a standard 2 lead Guidant to my new 3-lead St. Judes CR/ICD 3 months ago, my ejection fraction was at 16%. (Normal heart ejection fraction is in the 50~60% level.) Simply put, the ejection fraction is a measure of the power output of your heart; it's overall efficiency at pumping blood.

According to the stats that I've seen, (and I won't know exactly until my next echocardiogram in 2 months) ejection fractions typically rise considerably with cardiac-resynchronization, and I know from how much better I feel and the dramatic gain in endurance and stamina, that mine has risen significantly from its low of 16%.

I do know that my heart has already shrunk nearly 18% (chest x-ray overlay) since my new implant as it is working more efficiently and not having to pump so hard and consequently grow larger.

Again as in most things, your mileage will vary :)

Comment

by ElectricFrank - 2008-08-17 01:08:22

Jules,
As I remember when I looked into the studies a year or so ago, the problem with lowered ejection fraction happened in people who already had congestive heart failure. This leads to the question of whether the lower EF was due to the pacemaker or would have happened anyway.

In my case the thing I am watching is the slow over time increase in the pacing voltage required. I don't know whether this is a local effect and could be corrected at some point in the future by installing a new lead at a different location or not. At some point it theoretically reach a level where the pacemaker can't put out enough to pace the ventricles. I don't know how well I can get along with an ejection fraction of 0. LOL At 78 I'm not worried YET.

frank

WEAKENING HEART

by pete - 2008-08-17 03:08:04

We have pacemakers for a great variety of reasons. If we did not get them we would most likely die. In order to die your heart has to stop. In order to stop it needs to weaken. Your pacemaker keeps you heart going for longer than it otherwise would. So the logical answer to yuor question is definately "NO".
I cant put it simpler than that.
Cheers pete

Thanks all

by Jules - 2008-08-17 04:08:42

Well what a wonderful response from all and the explanations are great. Difficult to understand without reading once or twice but great all the same.

Hey, I am due another check in September and hopefully some sort of read-out. I have not had one yet. Until then I am going to try and relax and follow everyone's example.

Cheers guys.

Luv Me X

Hi Jules,

by Gellia2 - 2008-08-17 12:08:39

Everything they say, plus, I've been right paced for third degree block for over 33 years. EF is still the same (55%).
Now that doesn't mean that it won't change in the future, but I'm still ticking along fine.
I don't think everyone that right paces 100% (I do) of the time always gets CHF. It, like everything else with a PM should be watched. I have periodic echos done.
Best to you, and don't worry. Pace with NO FEAR.
Gellia

A Natural Paced Contraction

by Terry - 2008-08-18 03:08:40

When a pacemaker paced it directly activates only a few cells at the electrode site. Then, cell-to-cell conduction takes over. The problem with that is that as the slow contraction propigates through heart muscle (cell gap junction to gap junction) muiscle fibers away form the electrode site are stretched, according to Prinzen, resulting in a more vigerous contraction in muscle away from the electrode. This is what apparently leads to heart failure. According to Karpawich, after a few months the heart developes myofibrilar dissaray and mitocondrial abnormalities. You can see the slow long-term depolarization by looking at the QRS on the ECG.

The only device that can depolarize all the heart at one time, at the speed of light, is a defibrilator, and it takes hundreda of volts to effectivly do that.

There are now hundreds of patients who's pacemaker paces the hear's natural conduction system for a healthy long life. Biventricular pacing can help - two electoreds are better than one, but the purkinje system has many hundreds of terminations of fibers to provied a natural synchronous contraction.

Terry

You know you're wired when...

The mortgage on your device is more than your house.

Member Quotes

A properly implanted and adjusted pacemaker will not even be noticeable after you get over the surgery.