non-synced cardioversion during pulseless VT arrest

[Smellypaddler]

A question came up today that I didn't really know the answer to and thought some of the greater minds on here might be able to point me in the right direction.

During an unstable conscious VT rhythm we cardiovert with the monitor in "sync" mode (post sedation) so that the DCCS is delivered on the Q wave thus avoiding any chance of R on T phenomenon and subsequent deterioration into VF.

The question was: If VT is the presenting rhythm why do we not sync the defib when performing DCCS in the unconscious pulseless patient?

If their is a chance of R on T in the conscious (sedated) patient isn't there an equal chance of the same in the unconscious pulseless patient?

I hope the above questions make sense, I'll try and clarify if anyone has questions.

 

[Aprz]

This was discussed on the Resuscitation Facebook page recently.

https://www.facebook.com/groups/470212486437469/permalink/472513102874074/

ANSWER

It was to simplify the algorithm and to prevent delay of shocks when computer is unable to distinguish between R-waves and T-waves (so-called V-flutter) or when the rhythm becomes polymorphic (TdP or rhythm degrades to VF). In speaking with EPs on this topic they say, "Why not deliver the energy at the optimal moment in the cardiac cycle?" In 2014 it's because the perishock pause has become important.

 

[Smellypaddler]

I wasn't aware of that FB page so thank you for linking it.

Is there any evidence or even literature out there to support the FB post? Not because I don't believe it, it does make sense. More because I'd like to be able to refer others to a more reputable source than a random FB page.

Is it on CoSTR somewhere?

 

[Aprz]

I tried researching it more, but couldn't find anything.

More information from AHA.

https://circ.ahajournals.org/content/122/18_suppl_3/S706.full

However, they just tell you to provide synchronized shock for regular VT with a pulse, unsynchronized shock for VT without a pulse or irregular.

 

[cleanboofs]

Maybe I miss read the thread, but when you cardiovert someone, you sync on the R wave not the Q. If I remember correctly the R on T phenomenon comes from QT prolongation, or from cardioverting on the T wave (which could happen easily if the monitor interprets a peaked T wave to be an R wave by mistake).

In regard to the question when you cardiovert you are generally delivering a lower dose of electricity. Which is why you want to make sure to sync on the correct wave, because you can put an unstable, patient with pulses into cardiac arrest. And yes defibrillation can fall randomly in the cardiac cycle, however if you are defibrillating a patient then I imagine the extra energy levels will be enough to completely reset (hopefully) the heart and by default not having to worry about the R on T issue.

*Sorry for poor grammar/spelling. Typing on an iphone.

 

[Smellypaddler]

My bad, you are right re: delivering the synced shock on the R wave. Not sure why I wrote Q.

 

[Christopher]

Maybe I miss read the thread, but when you cardiovert someone, you sync on the R wave not the Q.

My bad, you are right re: delivering the synced shock on the R wave. Not sure why I wrote Q.

Myth alert! The Sync button does not just sync to R-waves.

It'll sync R-waves, Q-waves, S-waves, T-waves, whatever...it has no idea you call them these waveforms by certain "names". The computer speaks a mathematical algorithm ;-)

Most "R-wave" detectors are actually peak/slope detectors run on a heavily filtered input. Popular real-time detection usually squares the signal to remove any negative values. Algorithms then do some edge detection (up/down) and compare the slopes of these edges against "QRSy looking things" and "T-wavey looking things" (this part of the algorithm must adapt to changes in heart rate as the QT interval varies with heart rate). The previous moving-average R-R intervals are often used to try and screen out T-waves as well.

At that point the computer will gladly interpret an rS, RS, rs, qR, QR, QS, etc, as an "R-wave". Just as they will gladly interpret a large enough or symmetric enough T-wave as an "R-wave" as well.

They work best with a lead where the QRS complex is almost entirely monophasic (positive or negative) and with a magnitude at least twice that of the T-wave. If the T-wave is markedly symmetric you may find the algorithm will also fail.

The GE Marquette 12SL algorithm is notorious for this during Hyperkalemia, and this finding is known as Littmann's Sign. I've even documented a case of almost-triple counting during cardioversion of suspected VT.

* This is based off personal observation and a basic understanding of the math used in "R-wave" detectors.

 

[ExpatMedic0]

Myth alert! The Sync button does not just sync to R-waves.

It'll sync R-waves, Q-waves, S-waves, T-waves, whatever...it has no idea you call them these waveforms by certain "names". The computer speaks a mathematical algorithm ;-)

Most "R-wave" detectors are actually peak/slope detectors run on a heavily filtered input. Popular real-time detection usually squares the signal to remove any negative values. Algorithms then do some edge detection (up/down) and compare the slopes of these edges against "QRSy looking things" and "T-wavey looking things" (this part of the algorithm must adapt to changes in heart rate as the QT interval varies with heart rate). The previous moving-average R-R intervals are often used to try and screen out T-waves as well.

At that point the computer will gladly interpret an rS, RS, rs, qR, QR, QS, etc, as an "R-wave". Just as they will gladly interpret a large enough or symmetric enough T-wave as an "R-wave" as well.

They work best with a lead where the QRS complex is almost entirely monophasic (positive or negative) and with a magnitude at least twice that of the T-wave. If the T-wave is markedly symmetric you may find the algorithm will also fail.

The GE Marquette 12SL algorithm is notorious for this during Hyperkalemia, and this finding is known as Littmann's Sign. I've even documented a case of almost-triple counting during cardioversion of suspected VT.

* This is based off personal observation and a basic understanding of the math used in "R-wave" detectors.

Wow, that is some good information. I never would have guessed that being a software engineer and paramedic could overlap in someway, but here is a possible example.