A Pacer Puzzler

Sometimes we see things on the monitor that while they look like things aren’t working correctly they actually are doing what they should.  Case in point from awhile ago.

The tech calls me and says, “Your patient in 75, they keep alarming for missing beats and pacer not pacing.  You going to call the doc?” as he hands me the following strips:

#1#2

I looked down, double checked and said, “Nope.  It’s working perfectly.”

In both strips you can see spots where it appears that the pacemaker is failing to pace, after 1st and 7th QRS complexes in strip #1 and after the 4th QRS in strip #2.  In each case you have a spike then a p-wave and nothing until a odd appearing PVC-like beat.  The tech pointed these out and I further reiterated that, “Yes, it’s working just fine.

But I had a cheat, I had read the interrogation report from when the patient had been admitted and knew what mode the device was set for, the tech hadn’t.  This is a pretty good example of a mode known as MVP, or managed ventricular pacing.  Basically this is a mode designed to reduce ventricular dysynchrony by allowing the heart’s natural conduction system to function while providing back-up in case of failure.  Excessive right ventricular pacing has been shown in studies to lead to congestive heart failure, increased incidence of atrial fibrillation, increased left atrial diameter and changes to hemodynamics and ventricular remodeling all of which can have detrimental effect on the patient and their quality of life.

In MVP pacing the pacemaker operates in AAI/R mode, as shown in both strips, with a set duration of time to allow for a ventricular beat.  If no beat arrives in the programmed time span the device will initiate a ventricular beat then return to the AAI/R.  If a beats are frequently dropped, usually 2 out of 4 complexes, the device shifts to DDD/R mode.  It will continue this way for a minute then attempt to return to AAI/R to detect AV conduction.  If beats are still dropped it will remain in DDD/R mode for increasing amounts of time, periodically checking for the return of AV conduction, at which point it will switch back to AAI/R mode.

Let’s break each strip down.

Strip #1:  starts with normal AV conduction in AAI/R mode and almost immediately, a beat is dropped and the device iniates the rescue beat.  It continues for 5 more QRS complexes until there is another dropped beat.  There is normal AV conduction for one more QRS then another dropped beat after which the device switches to DDD/R mode (it was too long to scan).

Strip #2: a little simpler.  4 normal QRS complexes then a dropped beat followed by a PVC, then another dropped beat.  Here you can see the device then switch into DDD/R mode due to dropping 2 out of 4 beats.

So, yes, the pacer was working exactly as it was supposed to.  I explained this to the tech and went on my merry way.  The next time he sees this he’ll stop to ask if they are set to MVP from now on.  Good learning moments come when you least expect them!

Sources:

Sweeney, M., Ellenbogen, K., Casavant, D., Betzold, R., Sheldon, T., Tang, F., & … Lingle, J. (2005). Multicenter, prospective, randomized safety and efficacy study of a new atrial-based managed ventricular pacing mode (MVP) in dual chamber ICDs. Journal of Cardiovascular Electrophysiology, 16(8), 811-817. Retrieved from EBSCOhost.

 Gillis, A., Purerfellner, H., Israel, C., Sunthorn, H., Kacet, S., Anelli-Monti, M., & … Boriani, G. (2006). Reducing unnecessary right ventricular pacing with the managed ventricular pacing mode in patients with sinus node disease and AV block. Pacing & Clinical Electrophysiology, 29(7), 697-705. Retrieved from EBSCOhost.

 

 

 

 

 

Advertisements

3 Comments

  1. Ironically I had a somewhat-similar query at work the other day about paced beats / rescue beats / AICD vs Pacer.
    Thanks for the info!
    Gewd stuff.

    Reply

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s