62 year old male presents to the emergency department complaining of chest discomfort.
Past medical history is significant for dyslipidemia and ulcerative colitis. Also prior history of significant tobacco use.
Maternal history of CAD. Maternal and paternal history of stroke.
The patient’s only medication is Lipitor but he took an aspinin en route to the hospital.
- Onset: Patient states the pain started that morning and became progressively worse since lunch time
- Provoke: Nothing makes the pain better or worse
- Quality: Sharp and nonpleuritic
- Radiate: The pain radiates down the right arm to the bicep
- Severity: 7/10
- Time: Patient states he experienced a similar pain in his right upper chest several days prior while playing tennis. He stopped exercising and the pain resolved.
The pain makes the patient feel “a little clammy.” He denies shortness of breath. He states that he feels “a little dizzy” but denies palpitations. He had a negative stress test 3-4 years ago.
He has a known history of left bundle branch block.
The patient’s skin is warm and dry.
Breath sounds clear bilaterally. No JVD. Neuro exam normal.
- Resp: 18
- Pulse: 60
- BP: 140/72
- SpO2: 98 on RA
A 12-lead ECG is captured and presented to the ED physician within 5 minutes of arrival.
An “old” ECG is pulled from the computer system for comparison.
What is your impression?
*** UPDATE ***
After oxygen and nitroglycerin the patient reports a significant decrease in pain.
An additional 12-lead ECG is captured.
There is now slightly less ST-elevation in leads V3 and V4.
Remember that a secondary ST-segment abnormality (as opposed to a primary ST-segment abnormality) should not “improve” with oxygen and nitroglycerin!
In other words, if this ST-elevation was caused just by the LBBB, it shouldn’t be “getting better”. Changing ST-segments suggest the dynamic supply vs. demand characteristics of ACS!
Now, let’s go back to the initial 12-lead ECG. Is the ST-elevation in the anterior leads cause for concern?
Go back and read Identifying AMI in the presence of left bundle branch block (or paced rhythm).
Remember, discordant ST-elevation = or > 5 mm is the least specific of Sgarbossa’s criteria! That’s why we use the modified rule that I learned from Dr. Stephen Smith of Dr. Smith’s ECG Blog.
That criterion states that discordant ST-elevation should not be more than 0.2 (or 20%) the depth of the S-wave in the setting of left bundle branch block (ST/QRS ratio).
Using that criterion, how does this ECG measure up? Let’s take a look.
The patient was ultimately cathed and angiography revealed 100% occlusion of the LAD.
* Note: Stephen Smith, M.D. ultimately published this paper and used a QRS/ST ratio of 0.25. In other words, it’s a STEMI if the ST-elevation (measured at the J-point) is greater than 25% the depth of the S-wave. I use this simple rule of thumb (for field use). I allow 1 mm of ST-elevation for every large block (5 mm) of S-wave depth. I also round up. So if there are 4 and a half large blocks of S-wave depth I would allow 5 mm of ST-elevation (but not 6 mm).