Several years ago I told a group of paramedics that while not relaying on the computer interpretation in the case of STEMI, they should consider it as a fellow paramedic offering his opinion. I told them that the studies showed a 60% sensitivity and a 90% specificity in identifying STEMI. In other words, the computer would only identify 60% of the STEMIs, but if it identified a STEMI, it was going to be right about 90% of the time. I based this on several older studies I had read.
I can tell you as a paramedic when I suspect a patient may be having a STEMI and the computer agrees and the tracing meets criteria, I feel much better about calling a STEMI alert. I confess once when I had a patient with an ECG suggesting a small elevation in I and AVL. I did 9 ECGs en route to the hospital, and finally on the 5th one, the computer came around and agreed with my suspicion that the patient was possibly having a STEMI, giving me the maniless to call in the alert (I know I was being a wimp). Though the computer reversed course again on the 6th and 9th ECG, the patient was in fact having a lateral STEMI. He coded in the ED, was revived and successfully had his 100% occlusion in his circumflex artery stented.
Conversely when the computer calls it a STEMI, but I disagree with the reading, I recheck my lead placement and do another. Some make me doubt my reading ability, others make me want to put a dunce cap on the monitor and put in the corner of the ambulance facing the wall. You weren’t paying attention in paramedic school obviously, bad monitor!
A new study in the April-June 2013 Prehospital Emergency Care, Prehospital Electrocardiographic Computer Identification of ST-segment Elevation Myocardial Infarction, reports a 58% sensitivity and a 100% specificity for computer interpretation.
They reviewed the transmitted 12-leads of a 100 consecutive STEMIs and found 58 of them had the interpretation “Acute MI Suspected” on the 12-lead. Then to determine specificity, they analyzed 100 random 12-leads from non STEMI patients and found none of them incorrectly said “Acute MI Suspected.”
I must ask: Does this high specificity match anyone’s experience? Or even come close?
How often do you do a 12-lead and it says ***Acute MI Suspected*** or “Consider Acute MI” depending on the monitor you use, and you can look at the 12-lead and say No. Not even close.
In my hospital I receive an email each time a 12-lead is transmitted. I enjoy reading the strip. Our medical director and I play a STEMI game where we immediately email each other with our vote STEMI or no STEMI assuming the patient always to be symptomatic. I can tell you the number of 12-leads transmitted that say “Consider Acute MI” is way more than the number that actually are STEMIs.
The computer seems particularly inaccurate in wide complex and tachycardic strips.
I have had to go back to the medics and say the studies are wrong. Don’t put as much stock in the computer interpretation as I suggested you should. It is not close to 90% accurate.
An informal tally using the same criteria as the 2012 study for sensitivity shows the Life Pack 15 is about 60%. It properly identifies 60% of STEMIs, but misses 40%.
But then when I analyze specificity, I admittedly use a different criteria, which will yield a markedly different, but more telling conclusion. I ask, what percentage of the time when the computer reads “Meets ST Elevation Criteria” and “Consider Acute Infarct,” is it actually a STEMI? And the answer in this small sample (50 cases) is 32%. Not 100%.
Note: The published study cited above used the Life Pack 12, my figures are for the LifePack 15, which uses a different software.
The computer seems to consistently misread tachycardic rhythms and wide complex rhythms.
These, in my mind, are the proper questions we should be asking if we are going to incorporate the machine reading into our decisions:
What percent of the time is it a STEMI and the machine missed it? Seems to run about 60%
When the machine does call it a STEMI, what percentage of the time is it right? That answer is clearly not 100%, or even close.
Obviously, this should be confirmed in formal studies, which can be easily done at any PCI facility.
Does this mean I would be in favor of removing the interpretation from the machines? No, I think they can be valuable. I am just saying we shouldn’t be misleading others and ourselves by claiming the machines are better than they are.
When making policy that incorporates the computer reading into the decision making, we need to understand its limitations.
We need to make certain that paramedics are not relaying on the computer alone to call, and that if the machine does read STEMI, the medic makes agrees with the interpretation.
And we need to continue to work to improve basic paramedic interpretation, as well as proper placement and technique of ECG aquisition.
This will help limit false activations for services that cannot transmit.
Note: In our state we use the following to help determine diversion to a PCI center:
1. Active chest pain or equivalent symptoms (nausea, SOB)
2. 12-Lead ECG of good quality showing STEMI
i. > or = 2mm in 2 contiguous leads (V1-V4), and/or
ii. > or = 1 mm in 2 contiguous leads (limb, lateral)
b. QRS duration < or = 12 seconds
c. ***ACUTE MI*** or equivalent prints on 12-lead ECG; paramedic agrees