Hi All,

Re:  Pacemaker.

Can i have answers to the following questions please.

What voltage would the heart suffer if the two bare leads, or loose bolts touched and shorted out?  The battery being one year old. The device having two leads.  Also, Would this event register on the device memory?



by AgentX86 - 2019-08-24 13:45:57

The question makes no sense.  First, the leads can't "short out" and if they did "short out" the voltage across them would be zero.  That's what a short is.

Voltages, leads, etc.

by crustyg - 2019-08-24 18:17:26

Hi Wolfy:

Some of the very much older PM used unipolar leads - the voltage to initiate a contraction event in the heart was applied between the metal can of the PM box and the tip of the lead being used for pacing.  Typically somewhere around 2V.  I don't have a lot of personal experience monitoring hundreds of PMs, but I think this is a pretty typical level.  You could easily feel this if a skeletal muscle were suddenly part of the conduction pathway, and as many of us have our PM box installed just above the pectoral muscles this is possible.  One can normally see this uni-polar pacing as a big artefact on the ECG - and this can interfere with some chest strap HR monitors.

Except that these days it's uncommon to find anything other than bi-polar leads fitted - these apply the stimulating voltage between the inner core and the outer sheath.  The can of the PM isn't used for pacing (although it can be used for othe purposes, e.g. the Minute Ventilation sensor on the BostonScientific Essentio/Accolade boxes).  Bi-polar pacing is usually quite difficult to see as a pacing artefact on the ECG, and much less likely to stimulate any other muscles.  But how well the leads have connected to your heart muscle, and how the scarring process of long-term anchoring has affected this might result in a bi-polar lead having to be used in a uni-polar mode.  Not all heart muscle is great for picking up electrical stimulation.

So while the voltages are pretty small, they are big enough to feel like electric shocks should they be applied to the wrong tissues.  But something's fairly wrong if that's what's happening to you.  Time for a CXR to check lead placement.

*IF* your box has turned over in your pocket - it should have been anchored down with a strong, non-absorbable stitch to the base of the pocket - then it's possible for the leads to run against each other and wear through the outer insulating sheath.  But that should only bring the two outer conductors in touch.  A CXR should show this.

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