ECG Solution: The court's verdict?
Do the math to detect subtle changes in an AMI
Editor's note: We asked columnist Tom Bouthillet to pick a winner to this month's challenge and he wrote: "I selected Jameson McIntosh as having the best response. His first name corresponds with my favorite whiskey and his last name corresponds with my favorite computer (ba dum bump). Seriously, though, Jameson isn't my favorite whiskey. At any rate, he picked up on the very subtle reciprocal changes in lead aVF and correctly identified that the T-waves in the anterior leads were hyperacute based on the low voltage QRS complexes, poor R-wave progression, and fragmentation of the QRS complex in lead V2. In addition he compared the S-wave depth to the T-wave amplitude (rule of proportionality). He was absolutely correct in predicting LAD occlusion and wisely suggested serial ECGs. I don't know Mr. McIntosh but he seem to be a clever fellow when it comes to 12-lead ECG interpretation. Thanks for participating and I hope you gained something useful from this interesting case!"
Haven't read the initial case presentation? Read: ECG Challenge: The court's verdict?
This is the conclusion to the current ECG Challenge. You may want to go back and review the initial history and clinical presentation.
Let’s take another look at the 12-lead ECG.
This is a suspicious ECG for several reasons.
• Anterior R-wave progression is poor. There should be a gradual increase in the amplitude of the R-wave between lead V1 and lead V4.
• There are (very) tiny Q-waves in lead V2.
• The T-waves in leads V1-V4 don’t look particularly large, but they are disproportionately large when one considers the relatively small size of the QRS complexes. This is referred to as the “rule of proportionality” which states that repolarization (the ST/T-waves) should be proportional to depolarization (the QRS complex).
Having said that, most paramedics, ED physicians and cardiologists would not consider the initial 12-lead ECG to be diagnostic of acute anterior STEMI.
I say most ED physicians because Stephen Smith, M.D. of Dr. Smith’s ECG Blog has a formula to distinguish early repolarization from acute anterior STEMI when the diagnosis is not obvious.
(You can download the full text of Dr. Smith’s article in the Annals of Emergency Medicine.)
Here is the equation:
(1.196 x STE at 60 ms after the J-point in V3 in mm) + (0.059 x computerized QTc) - (0.326 x R-wave Amplitude in V4 in mm).
A value of 23.4 or greater is both sensitive and specific for LAD occlusion.
In Dr. Smith’s opinion features that should make the diagnosis obvious include:
• ST-elevation > 5 mm
• Reciprocal changes in the inferior leads
• Straight or upwardly convex ST-segments
• Terminal T-wave inversion
• Terminal distortion of the QRS complex
• The presence of Q-waves in leads V2-V4
If we ignore the tiny Q-wave in lead V2 and use the equation with these values:
• ST-elevation at 60 ms after the J-point in lead V3: 1.5 mm
• QTc: 407 ms
• R-wave amplitude in lead V4: 5 mm
The result is 24.17 which is positive for acute anterior STEMI.
Since most of us work under specific protocols that would preclude us from calling a Code STEMI based on the patient’s initial ECG, what should we do?
Obtain serial 12-leads!
You will almost always see changes on serially obtained 12-lead ECGs due to dynamic myocardial oxygen supply versus demand characteristics of true ACS.
By 10:03 the patient’s 12-lead ECG looked like this.
Now we can see obvious anterior ST-elevation with reciprocal changes in the inferior leads. (Note: Lead V4 is in the position of V4R).
Again, while these T-waves aren’t huge, they are very large considering the very small size of the QRS complex. We also now have the *** ACUTE MI SUSPECTED *** message at the top of the ECG.
A total of four 12-lead ECGs were captured on the call. Let’s look at just the right precordial leads (V1-V3) in series:
Now let’s look at leads III and aVF to see how the reciprocal changes emerge between the first and last 12-lead ECG taken in the field.
I used to be somewhat ambivalent about continuous ST-segment trending for prehospital 12-lead ECGs. I mean, it’s not like we’re taking care of multiple patients, right? Why not just trust the paramedics to perform serial ECGs?
Well, it’s nice to have the computer print out ECGs automatically when there are changes just in case the treating paramedic gets distracted! After all, time is muscle. We can all use a little help sometimes!
As a final thought, patients who take drugs for erectile dysfunction should not receive nitroglycerin! You might wish to specifically ask male patients about erectile dysfunction as they may not volunteer the information.