Friday, November 10, 2017

A middle-aged woman with chest pain and a "normal" ECG in triage

This was sent to me by a former resident from a community hospital:

A middle-aged woman complained of chest pain and was seen in triage.

She had a ECG recorded.

The computer interpreted the ECG (GE Marquette 12 SL) as:

"Sinus Bradycardia.  Normal ECG."

It was not seen by a physician.

Here it is:
Computer interpretation: 
"Sinus bradycardia. Normal ECG"

--This ECG does, at first glance, appear normal

--It is sinus rhythm.
--The QRS is normal

--There is possibly an abnormal Q-wave in lead III, and non-specific T-wave in aVL, but the computer did not see it.

--All the intervals are normal, including the PR, QRS, and QTc at 455 ms
--There is ST elevation in V2-V4, but it is within normal limits.

That is, it appears to be normal ST Elevation and the computer thinks it is normal STE.

There is one thing that is clearly abnormal, but computers are not programmed to detect it:

When there is ST Elevation in V2-V4, it is only normal when there is:
1) high R-wave voltage and 
2) a short QTc
3) relatively high QRS voltage in V2

This ECG has a relatively long QTc, low R-wave amplitude, and low QRS amplitude

That is why the formulas work.

STE60V3 = 2.5 mm, QTc = 455 ms, RAV4 = 6 mm, QRSV2 = 11
3-Variable formula = 27.9 (very high, diagnostic of LAD occlusion)
4-Variable formula = 23.05 (very high) 

To my knowledge, no computer algorithm has yet been programmed with the formulas

The ECG was not shown to a physician.

Later, the patient collapsed in triage and became unresponsive.  She was in full arrest with ventricular fibrillation.

Fortunately, she was resuscitated.

She had a 100% LAD occlusion.

She survived neurologicially intact.   I don't know what her subsequent cardiac function was, but that is not the point of this post.

But it could have been a disaster.


This paper has received some press recently:

Safety of Computer Interpretation of Normal Triage Electrocardiograms

The algorithm used was also the GE Marquette 12 SL.

It purports to show that you don't need to read the ECG if the computer says "normal".   That it saves you from pesky interruptions.   Many on Twitter seem to agree.

222 of 855 (26%) were interpreted as normal.  The confidence intervals were 97-100%.  Would you like to be 97% sure you're not missing an emergency?

Neural Networks are coming:

We compared a new deep neural network (DNN) machine learning artificial intelligence algorithm from Cardiologs technologies(DNN) to Veritas conventional algorithm in the interpretation of 1473 ED ECGs:

Veritas: Of 364 ECGs (24% of total) that it interpreted as "normal," is missed 5 emergencies.
DNN: Of 493 ECGs (33% of total) that it interpreted as "normal," it missed 2 emergencies.

As you can see, it had both fewer false positives and fewer false negatives. That is powerful, and it will only get better as it learns from more and more ECGs.
So things will get better as technology advances.

By the way, this deep neural network algorithm does calculate the 3-variable "Smith score" and displays it for the physician.  It did not use machine learning for this task; it was programmed.

Learning Points:

1. It is hazardous to trust the computer, even when it interprets "Normal"
2. I never trust a computer interpretation.  I only look at it after I have read the ECG, and only in order to see if it found something that I overlooked.
3. If the computer says "normal", it takes very little time to confirm this with visualization (at least for me, and anyone can get good at it with practice)
4. Learn to recognize LAD occlusion.  It is not always obvious.  And the computer will not help you.

Here are some previous posts in which the computer interpreted the ECG as "normal."

Chest Pain Diagnosed as Gastroesophageal Reflux

Another case of arrest:

Another case of arrest:

It is easy to be led astray by the computer....

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