# How accurate are the LifePak/Zoll Defibs at Identifying Rhythms?



## MMiz (Jan 1, 2012)

This thread got me thinking.  Based on your experiences, how accurate are current defibrillators at identifying rhythms?

Would you trust a BLS provider to treat a patient based on the defibrillators interpretation alone?


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## abckidsmom (Jan 1, 2012)

As an AED?  In my experience, yes.  They are fine.


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## silver (Jan 1, 2012)

"A total of 3,448 AED rhythms were available for interpretation. Sensitivity and specificity for appropriate AED management of a shockable (VF or VT) rhythm were 81.0% (95% CI 77.9% to 83.8%) and 99.9% (95% CI 99.7% to 100%), respectively. Positive and negative predictive values were 99.6% (95% CI 98.7% to 99.9%) and 95.5% (95% CI 94.7% to 96.2%), respectively. There were 132 errors associated with AED management. Two errors resulted in delivery of an inappropriate shock. In the remaining 130 errors, a shockable rhythm was not shocked. Fifty-five (42.3%) errors were AED dependent, 70 (53.9%) were operator dependent, and 5 (3.9%) were unclassified."

http://www.ncbi.nlm.nih.gov/pubmed/11524645

Potential limitations of this study: technology used is currently 10+ years old and that is with AEDs only. Obviously the manual defibs used today have better algorithms. 


Edit: Oh, another experience/opinion thread. I'm just going to take my science elsewhere... :sad:


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## bstone (Jan 2, 2012)

silver said:


> "A total of 3,448 AED rhythms were available for interpretation. Sensitivity and specificity for appropriate AED management of a shockable (VF or VT) rhythm were 81.0% (95% CI 77.9% to 83.8%) and 99.9% (95% CI 99.7% to 100%), respectively. Positive and negative predictive values were 99.6% (95% CI 98.7% to 99.9%) and 95.5% (95% CI 94.7% to 96.2%), respectively. There were 132 errors associated with AED management. Two errors resulted in delivery of an inappropriate shock. In the remaining 130 errors, a shockable rhythm was not shocked. Fifty-five (42.3%) errors were AED dependent, 70 (53.9%) were operator dependent, and 5 (3.9%) were unclassified."
> 
> http://www.ncbi.nlm.nih.gov/pubmed/11524645
> 
> ...



From Ann Emerg Med. 2001. Anything newer? Hopefully things have improved in the 10+ years since this study came out.


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## MMiz (Jan 2, 2012)

I'm thinking not about the AED function, but when using the monitor as a monitor during a cardiac code. I remember that there was a code review/interpretation feature. I'm wondering if they were accurate.


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## EMT PR (Jan 2, 2012)

*don't count on those...*

According to my experience (with LP and PROTOCOL) don't trust on those… some time they wrong- but most of the time they are pretty accurate.
You can use them- but don't relate on them as your only diagnosis


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## Handsome Robb (Jan 2, 2012)

Are you talking about basic rhythm interp or 12-lead interp?

If you are letting the monitor tell you what's going on in a 12-lead you have serious issues.


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## EMT PR (Jan 2, 2012)

*both*

both- but the self interpretation  of 12 lead  is more offten incorrect then the monitor interpretation.


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## silver (Jan 2, 2012)

bstone said:


> From Ann Emerg Med. 2001. Anything newer? Hopefully things have improved in the 10+ years since this study came out.



Okay I found the Glasgow (U of Glasgow does the majority of this type of research) analysis for Lifepak 15's diagnostic accuracy.

http://www.physio-control.com/uploa...ment of Validation and Accuracy 3302436.A.pdf


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## TomB (Jan 2, 2012)

The GE-Marquette 12SL interpretive algorithm does a fairly decent job identifying conduction abnormalities like bundle branch blocks and has a fairly high specificity when it gives the ***ACUTE MI SUSPECTED*** or ***ACUTE MI*** message. However, it does not do particularly well at basic rhythm analysis. One of the reasons the sensitivity for acute STEMI is somewhat low is that the STEMI criterion (1 mm of ST-elevation in 2 or more anatomically continguous leads -- 2 mm for leads V2 and V3) is problematic because it does not take into account the rule of proportionality. In other words, it does not consider the depth of the S-wave. If you're programming a computer it's easy to make it follow rules. It's hard to program it to sometimes ignore the rules. It's also important to point out that computerized interpretive algorithms are very susceptible to errors from poor data quality.


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## Flight-LP (Jan 2, 2012)

MMiz said:


> I'm thinking not about the AED function, but when using the monitor as a monitor during a cardiac code. I remember that there was a code review/interpretation feature. I'm wondering if they were accurate.



My question, again, is why is it necessary?

The EMT-B has no business even attempting to interpret a rhythm. If the pulse is missing, hook them up to the computer who will interpret if a shock is needed or not. It really is that simple. The AED was not designed to be used in an ALS environment. Now Zoll has created an "all in one unit" in their "M" series, that is fine. The unit was designed to allow integration at a reduced cost so one unit could be used by different level personnel. It was not designed to allow a non-trained BLS provider to have a screen for an interpretation that they are not trained or qualified to perform.

The old LP-300 was a prime example. It had a manual override feature that was misused and gave a false sense of BLS autonomy. 

This is an excellent example of the age old issue in EMS, a BLS provider does not need any additional tools that they are not prepared, nor trained to use. Remember the KISS principle, if we as an industry actually followed it, we probably wouldn't be worried about such trivial issues.

Now on the manual monitor / defibrillator side, personally I could care less what the interpretation says on the strip in the 12 lead or code review mode. I do not function like LaCo, I for one will actually print a strip, measure out my waves and complexes, and do a manual interpretation. It is my sincerest hope that other medics do as well. 

I like how Tom put it, its easy for the computer to follow the rules, but hard to deviate. For the layperson and BLS level, this is a fine way to deliver resuscitative care. At the ALS level though, a little critical thinking and creativity needs to come into play, hence why we need to move away from the computer.

So Matt, yes I would trust the computer for a BLS provider, a lot more than I would trust a manual interpretation.


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## Flight-LP (Jan 2, 2012)

EMT PR said:


> both- but the self interpretation  of 12 lead  is more offten incorrect then the monitor interpretation.



Not if you have a medic who actually knows what they are doing. If a self interpretation is "more offten incorrect", then your QA and clinical department has some work ahead.....


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## mikie (Jan 2, 2012)

*on a side note...*



TomB said:


> The GE-Marquette 12SL interpretive algorithm...



Is that what is standard across all the models? LP, Zoll, Phillips?

Can you point me in the direction of finding more information on the actual 'algorithm' for how the EKG interpretation does occur throughout the various machines (LifePak mostly)?  Google-ing wasn't so helpful..

Thanks


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## TomB (Jan 2, 2012)

Yes for LP12 and ZOLL M-series. No for Philips MRx. Not sure about LP15.

Tom



mikie said:


> Is that what is standard across all the models? LP, Zoll, Phillips?
> 
> Can you point me in the direction of finding more information on the actual 'algorithm' for how the EKG interpretation does occur throughout the various machines (LifePak mostly)?  Google-ing wasn't so helpful..
> 
> Thanks


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## TheGodfather (Jan 2, 2012)

Flight-LP said:


> I for one will actually print a strip, measure out my waves and complexes, and do a manual interpretation. It is my sincerest hope that other medics do as well.



I completely agree with this statement. I keep a pocket ECG ruler in the back pouch of my monitor. :beerchug:


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## EMSrush (Jan 2, 2012)

I was just wondering about this myself not too long ago... I was wondering if the LP-12 is able to differentiate between an acute STEMI and an imposter? Will it interpret all elevation as a STEMI even if the elevation is benign?


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## TheGodfather (Jan 2, 2012)

LP-12 has a 98% specifity... IE, if it says **acute mi suspected** , 98% of the time it is right... however, along with that, it has approx a 52% sensitivity, IE; 48% of the time, it overlooks the problem... 

moral, if it says **acute mi suspected** STONGLY consider it... however, do not count on it finding it approx 1/2 of the time... measure, measure, measure!


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## Brandon O (Jan 2, 2012)

Zoll is switching to an in-house algorithm for their new Propaqs. The M and E will still use the Marquette.

Marquette is surprisingly good at sussing out STEMI mimics but not perfect. Specificity numbers vary by study but are 90%-100% with good data. However pretest probability affects this significantly. (Can't get into Bayesianism on my phone keyboard!) In sum, good tool, needs overall clinical and electrical context like all tools. We shouldn't be reliant on nor ignore it but understand and use it appropriately.

via Droid


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## tacitblue (Jan 2, 2012)

MMiz said:


> This thread got me thinking.  Based on your experiences, how accurate are current defibrillators at identifying rhythms?
> 
> Would you trust a BLS provider to treat a patient based on the defibrillators interpretation alone?



I use Phillips MRx at my company, and I never trust its interpretation of the 3 or 12 lead. Why? The VF alarm comes on when my patients move. The extreme brady alarm goes off with paced patients with good mechanical capture and normal perfusion. When interpreting rhythms, I almost always print a strip, calculate the rate and measure the intervals myself. On 12 leads I interpret axis and R wave progression, measure ST deviations, and look for BBBs myself as well. These are good habits and every medic worth his salt should be very good at this.

As for EMTs on a cardiac arrest deciding to defibrillate or not, I would actually rather the EMT make the decision on whether it was VF/VT vs asystole or PEA him/herself. It isn't that hard and if trained, they could probably do better than the machine. This isn't in their scope of practice in my area nor do they have the education to do so, so its moot. As an aside, I have told my EMT partner that if I am not around and we are holding the wall at the ED or what not, she is to use the AED function on the monitor.


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## rmabrey (Jan 2, 2012)

EMT PR said:


> both- but the self interpretation  of 12 lead  is more offten incorrect then the monitor interpretation.



A cardiologists at a local specialty hospital called us to pick up a patient having an MI cause the monitor interpreted MI. Needless to say nobody else saw MI when interpreting the 12-lead, and our LP15's didn't even kick MI. 

Sent from my Desire HD using Tapatalk


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## medicdan (Jan 2, 2012)

Are there rural systems that place 12-lead capable monitors on BLS trucks for early ECG measurement/serial assessments, and automatically send the tracing to the ED for interpretation? I can imagine that could be a valuable tool if no ALS is available... for the ED to determine whether to activate a cath team. BLS would, of course, be trained on electrode placement, and the monitor would be used only for the 12-leads, and of course AED mode.


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## Brandon O (Jan 2, 2012)

emt.dan said:


> Are there rural systems that place 12-lead capable monitors on BLS trucks for early ECG measurement/serial assessments, and automatically send the tracing to the ED for interpretation? I can imagine that could be a valuable tool if no ALS is available... for the ED to determine whether to activate a cath team. BLS would, of course, be trained on electrode placement, and the monitor would be used only for the 12-leads, and of course AED mode.



Los Angeles has played with this, and Physio is making a standalone "monitor" for such services now (hook it up, get a diagnostic-quality 12-lead, transmit it -- no interventions, can't print, just electrodes and a modem).

http://www.physio-control.com/ProductDetail.aspx?id=2147484151


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## medicdan (Jan 2, 2012)

Brandon Oto said:


> Los Angeles has played with this, and Physio is making a standalone "monitor" for such services now (hook it up, get a diagnostic-quality 12-lead, transmit it -- no interventions, can't print, just electrodes and a modem).
> 
> http://www.physio-control.com/ProductDetail.aspx?id=2147484151



Interesting. Thanks for sharing.


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## DrParasite (Jan 3, 2012)

rmabrey said:


> A cardiologists at a local specialty hospital called us to pick up a patient having an MI cause the monitor interpreted MI. Needless to say nobody else saw MI when interpreting the 12-lead, and our LP15's didn't even kick MI.


was the patient actually having an MI, or was it a false positive?


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## rmabrey (Jan 3, 2012)

They weren't having an MI. He read the words at the top "acute MI" or whatever it says. They were in NSR.

Sent from my Desire HD using Tapatalk


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## VFlutter (Jan 9, 2012)

I work with Telemetry monitors so it is kind of off topic but I always laugh when every patient in perfect A Flutter is labeled as Sinus Rhythm. They can never seem to get that right.


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## Physio Control (Jan 11, 2012)

_My name is Erik and I'm the communications program manager at Physio-Control. I came across this discussion and thought it would be a good opportunity to check in with Physio's research and clinical departments for their perspective, with the hope that it would be helpful to forum members. Here's what they had to say..._
"TomB is correct about the importance of good ECG quality, with correct location of electrodes and with minimization of baseline wander and muscle artifact. The algorithms in the Physio-Control devices all do signal averaging of the dominant P-QRS-T complexes to reduce artifact, but if there is too much artifact, the averaging cannot remove it all using only ten seconds of ECG. If excessive artifact causes measurement errors, those can lead to interpretation errors. If ECG artifact makes it challenging for you to measure the ECG, it is best to capture another, cleaner ECG. To reduce muscle artifact, make sure that the patient’s limbs are supported and that their muscles are relaxed during the 12-lead. If respiration is causing baseline wander, have the patient exhale half of their air and then stop breathing during the ten seconds it takes for a repeat ECG.

The algorithms in the Physio-Control devices all attempt to identify the STEMI imposters, and when identified they give statements like pericarditis, early repolarization, LVH, LBBB, or ventricular pacing rather than ACUTE MI or STEMI. With LBBB, the Glasgow algorithm will still give the STEMI statement if the Sgarbossa criteria are met for LBBB with STEMI. The algorithms have fairly sophisticated rules for STEMI, taking into account measurements such as QRS duration and R, S, and T amplitudes. The Glasgow program takes age and gender into account for STEMI. In general, the ST elevation thresholds are lowest for women and highest for young men (for example, see the current AHA recommendations for STEMI criteria).

One advantage that experienced physicians and experienced paramedics have over the automated algorithms is in taking into account the patient’s description of symptoms. A cardiologist may call it STEMI for a patient with typical symptoms but slightly short on ST elevation when they say, “It feels like an elephant is stepping on my chest.” A cardiologist may not activate the cath lab for a patient who has marginal ST elevation but vague symptoms with an alternate explanation for those symptoms. The automated algorithms do not have a way of accepting such information about symptoms.

Operating instructions for these devices recommend that 12-lead ECG interpretations be over-read by a qualified person before making treatment decisions."​


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## OrlandoRMAMedic (Jan 11, 2012)

Physio Control said:


> _My name is Erik and I'm the communications program manager at Physio-Control. I came across this discussion and thought it would be a good opportunity to check in with Physio's research and clinical departments for their perspective, with the hope that it would be helpful to forum members. Here's what they had to say..._



I wish more people, from the companies that we get equipment from, would pop their heads in here more often.  This is awesome and thank you for the explanation.


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## Fish (Jan 12, 2012)

At proper 12-Lead diagnosis they are something in the 60 percent, well atleast according to the Cardiology conference that came to town in San Diego.


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## EMT PR (Jan 12, 2012)

THANK YOU Erik!!! and as fish say- we wish there will be more like you!


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