This was provided by our electrophysiologist at the Hennepin Heart Center.
The patient was having symptomatic atrial fibrillation and was to be cardioverted by a Zoll machine:
Notice there is a Paced Rhythm. The small white arrows show each time the machine detects a QRS. This is also the location on the QRS complex where it is programmed to cardiovert.
Notice that it is recognizing the T-wave as a QRS.
This has two effects:
1) It measures the heart rate at 110, instead of 55 (the actual heart rate)
2) It will cardiovert on the T-wave, which is highly likely to result in ventricular fibrillation.
Christopher Watford presents a case in which the inappropriate sensing was not noticed, and the shock resulted in ventricular fibrillation
Always look for these arrows to be certain you will not cardiovert at the wrong part of the cycle!!
If the algorithm is sensing wrong, change the lead that is being sensed.
The patient was having symptomatic atrial fibrillation and was to be cardioverted by a Zoll machine:
 |
Notice there is a Paced Rhythm. The small white arrows show each time the machine detects a QRS. This is also the location on the QRS complex where it is programmed to cardiovert.
Notice that it is recognizing the T-wave as a QRS.
This has two effects:
1) It measures the heart rate at 110, instead of 55 (the actual heart rate)
2) It will cardiovert on the T-wave, which is highly likely to result in ventricular fibrillation.
Christopher Watford presents a case in which the inappropriate sensing was not noticed, and the shock resulted in ventricular fibrillation
Learning Point:
Always look for these arrows to be certain you will not cardiovert at the wrong part of the cycle!!
If the algorithm is sensing wrong, change the lead that is being sensed.
This machine takes a serious responsibility to check heart rate but the precautions are always needed to be considered before its use.
ReplyDeleteHi Steve,
ReplyDeleteHope you're well. Great post with a great point!
This seems just as dangerous as not synchronizing any unstable monomorphic ventricular tachycardia. ACLS distinction between unstable V-TAC "with a pulse" & "pulseless" V-TAC has never made any sense. I presume this algorithm was just created for simplicity, as to not delay shock in a patient with polymorphic V-tac (Torsade) as the computer attempts to "synch", unsuccessfully. Surely someone's subjective finger sense of "perfusion" shouldn't be the determining factor here. Not sure if there's such scenario that if V-Tac if too fast that the machine could have the same trouble synchronizing and result in a delayed shock? It seems all monomorphic (unstable) V-tac should be treated with synchronized cardioversion, period, regardless of pulse, perfusion, or any other factor. Do you agree & practice as such? Curious your thoughts on this.
Thanks so much for your time!
Sam
Sam, I think if the patient has reasonable perfusion, it is better that way than to be shocked into v fib. But if there is no reasonable perfusion (patient unconscious, etc.), then so what if the shock results in v fib. V fib is no worse than the situation you're in. So just don't make things a lot worse. Does that make sense?
DeleteSteve
Steve, I agree by shocking a patient who is in non-perfusing vtac into vfib we have conceivably not made them worse; but we certainly have not made them better. Our main objective is to shock them out of the non-perfusing v-tac into a perfusing rhythm with ROSC--and we have now not only missed an opportunity to do so, but per ACLS cost them 2 more mins till the next opportunity to bring them back. That's why I think all unstable monomorphic v-tac should be treated with synchronized cardioversion, regardless.
ReplyDeleteSam
Sam,
DeleteI agree, except when the machine does not shock because it waits and waits and waits......
Steve
Hey Steve,
ReplyDeleteYes! The only factor I can think of that would cause this faulty machine delay is if you ask it to sync a polymorphic vtac (torsade). This is why I presume (only a guess) that ACLS decided to simplify this into "with a pulse" vs "without a pulse". I can't think of any other reason a "perfusing" monomorphic v-tac would be more likely to sync w/out delay than a "non-perfusing" monomorphic v-tac. It doesn't seem like a faster monomorphic v-tac rate would cause the machine confusion/malfunction to be more likely either.
Interestingly, if we do the math assuming 10-30 milliseconds for vulnerable period with a heart rate of 60 bpm (cardiac cycle of 1000 milliseconds): 1-3% chance. This math also assumes the vulnerable period changes proportionally with increasing heart rate (V-tac rates). I'm not sure if it does. But the risk is something to consider.
The other interesting thing it that it seems the vulnerable period is during the ascending phase of the t-wave. If this is true, then the above example where the machine is counting the T's as QRS, it may in fact not be a problem to shock at this point(since the point the machine is confusing is after the peak of the T) , and changing leads may not be necessary?
Interesting stuff! As always, love discussing this stuff with you.
-Sam
Sam,
DeleteIt never occurred to me that they thought the machine would be able to sync better with a perfusing than non-perfusing rhythm. I always just assumed that the rule went that way so that you would not leave someone in a non-perfusing state for any longer than necessary.
I would bet, but do not know, that was the rationale.
Steve
i agree with all of you but still i think this machine is not reliable so we can't trust on it, we must have some percaution related to that.
ReplyDeleteI agree and except that when the machine does not shock because it waiting.
ReplyDeleteRegarding points by Sam Ghali — My understanding of why ACLS decided to recommended synchronized cardioversion for VT+Pulse, but NOT for VT without a pulse (from back in the days when I was National ACLS Affiliate Faculty) — was to simplify the protocols — since they were writing ACLS Guidelines for many thousands of providers of all degrees of training and experience. The “thought” was that IF you had monomorphic VT with a pulse — that the rate of that VT would not be as fast — and therefore both YOU (AND the machine) would be much more likely to clearly distinguish between QRS complex and ST-T wave. Therefore synch cardioversion of VT+Pulse in theory should be “safer”. In contrast, if their was monomorphic VT without a pulse — then the rate of this VT would be much more likely to be FASTER — and much more likely to evolve, if not already constitute a VFlutter form in which you (and also the machine) would NOT be able to distinguish the QRS from the ST-T wave. Therefore, VT without a pulse would seemingly (in more cases) pose much greater risk that synchronization might occur on an ST-T wave (on perhaps on the “vulnerable period”) instead of the QRS … My understanding from conversations at the time (in the 80s) with higher-up ACLS “gurus” — would be that this recommendation of VT with vs without a pulse was for “less experienced providers” — and that more experienced providers (ie, experienced ED physicians) could (and SHOULD) judge for themselves based on the appearance of the ECG waveform (and sensing by the defibrillator) whether an attempt at synch cardioversion should be made (IF you could clearly distinguish in the VT between QRS vs ST-T wave) — or whether unsynch DeFib should be the initial form of shock delivery — with the thought that if an experienced clinician could not distinguish between QRS vs ST-T wave, that the machine will do no better. Subsequent ACLS Guidelines (I believe circa 2000 … ) finally evolved to allowing MORE discrepancy in their recommendations, so that experienced clinicians might deviate from ACLS Recs that were written. However, many EMT/Paramedic personnel worked primarily from “the Guidelines” — in which case, those individuals continued to adhere to VT with or without a pulse for providing indication of how to respond. BOTTOM LINE ( = My Synthesis) — “Ya Gotta Be There”. Medicine is an ART that applies the Science to the case at hand. Our own experience and comfort level often “colors” the approach we take — but there IS indeed more than 1 correct answer. FINAL THOUGHT: Synchronized Cardioversion is NOT perfect — so the KEY premise remains that IF you attempt to synch but for WHATever reason are unsuccessful — unsynchronized Defibrillation without further delay is advised (and will USUALLY work fine!) — :)
ReplyDeleteGood one
ReplyDeletei agree with all of you but still i think this machine is not reliable so we can't trust on it, we must have some percaution related to that.
ReplyDelete@ Super Celeb — I agree.
Delete