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79 year old, atrial fib, one pacemaker leads is high impedance, developed Vtac in 4 months. Anything to do with pacemaker ?

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Cardiologist, Interventional
Practicing since : 1996
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Pretty Healthy 79 year old - Develops Vtac in 4 months ? :

I just wondered about the likelihood of my mother developing vtac episodes in 4 months.
Last check at cardiologist, she was fine. Some atrial fib, but the same amount for years.
Followed very closely by cardiologist for at least 10 years. No mention of vtac episodes.
On the other hand, one of her pacemaker leads is high impedance. 2 visits ago, the "capture test"
was inconclusive (ie didn't really pass that well) - they decided not to replace the lead.
That lead has been suspect in other pacemaker tests. Her most recent pacemaker check - they
enabled a new "capture parameter" - something she never had before. And is it a co-incidence -
4 months later she ends up in hospital with vtac - which she has never had before.
Pacemaker tech said that bad capture can certainly cause the pacemaker to trigger when
it isn't supposed to - and put a heart into vtac. This sounds like a pacemaker investigation
is needed ? Doc (young guy) wants to do angiography first - his background is imaging.
I get that, but there is no family history of coronary disease. And there is a history of stuff going
on with the pacemaker. It makes sense to me to look at the pacemaker. I've told them so.
What do you think ?
Posted Wed, 18 Apr 2012 in Heart Rate and Rhythm Disorders
Answered by Dr. Raja Sekhar Varma 11 hours later
Thank you for the query.

Before I can give you any concrete advice, I would like certain clarifications from you.

1) What type of pacemaker was put (Single chamber/dual chamber/triple chamber/ICD/Combo device etc), when was the implant done and what was the indication for the pacemaker?
2) What brand/model of pacemaker was used (the programming parameters and facilities available depend on the model)
3) Which lead was defective - atrial or ventricular?
4) Is it possible to upload the exact programming data ?
5) If there are relevant ECGs, you could upload that also to this website (including the ECGs of the VT)
6) What does the echocardiogram show about the LV function?

The reason for the pacemaker implantation is important because, the changes in the heart rate can be due to ischemia also, in addition to degenerative changes in the conduction system. Ischemia is also an important cause for VT.

Elderly individuals can develop blockages in the coronary arteries that can result in ischemia to the cardiac muscle. Hence, a coronary angiogram may be indicated in the complete evaluation of an elderly patient with VT.

As you rightly said, in a patient who has a pacemaker implanted, abnormalities in pacemaker function and/or lead issues can trigger arrhythmias. Many pacemaker models have inbuilt mechanisms to prevent arrhythmias. Also, these devices can be interrogated to see the data recorded which can help in understanding the arrhythmia. Some parameters can also be programmed, in certain types of pacemakers, to respond to extra systoles and prevent a major arrhythmia.

A high impedance usually indicates that the lead tip is not in an ideal position, or has had a micro-dislodgement from its original position, or chronic inflammation and fibrosis has developed at the contact point. This will mean that higher currents are needed to capture the myocardium. Beyond a particular limit, the pacemaker may not be able to produce that high a current, and this can result in "failure to capture". Failure to capture results in loss of pacing and bradycardia rather than tachycardia.

If there is failure to sense as well, there is a possibility of mistimed pacemaker impulses triggering a tachycardia.

However, the need for replacing the lead/repositioning the lead will also depend on the lead's role. For example, an atrial lead, which is usually involved in sensing, and less often in pacing, may continue to sense well despite a high pacing threshold. Thus, it may not need any intervention. Of course, if it has to play a role in pacing as well, it may need to be replaced/repositioned.

I hope this resolves some of your doubts. I can give you a more specific answer and further recommendations after you clarify the questions that I have raised.

With regards,
Dr RS Varma
Above answer was peer-reviewed by
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