EKG of the Week #1

click for larger view

Pretty classic example of failure to sense and failure to capture.

As you can see, the pacer is firing but there is no response from the heart.  No P-waves, no QRS complexes, just lone pacer spikes hanging out.  This is classic failure to capture.  Possible causes of this can be a fractured or dislodged lead, battery failure or electrolyte abnormalities among others.  Luckily in this case the patient has an intrinsic rhythm that is probably perfusing them.

The second item shown is failure to sense.  Notable for this is the pacer spikes in the ST-segments.  Failure to sense is exactly what is says, the pacer is failing to sense the cardiac cycle and inappropriately pacing.  Again, luckily in this case the pacer is not capturing so the inappropriate pacing is not causing issues.  The biggest problem with this failure is inappropriate firing when the heart is not quite yet refractory possibly initiating ventricular arrhythmias.  Causes of failure to sense include lead issues (dislodgement, fracture or poor positioning) or sensitivity issues requires a change to sensitivity.

In this particular case, it appears the patient is in atrial fibrillation, which may be causing issues with both capture and sensitivity.  The erratic electrical signals emanating from the atria may be throwing off the pacer, but many times they are programmed with this in mind.  For nurses the important things to remember is to check on the patient when the pacer is acting up and ensure they are stable.  Past that, with permanent pacemakers, we need to get the cardiolosit involved.  If it the nurse who is running a temporary pacer at the bedside, adjustments to both output and sensitivity may be required to ensure adequate sensitivity and capture (but that’s a whole other ball-game!).

Here’s what a pacer strip should look like:

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Each spike has a corresponding activity, just like it should.

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