I posted this case for a few reasons, but not because it was difficult. So if you were looking for a zebra, I'm sorry to disappoint you!
I have noticed on many occasions that a paramedic's inability to recognize a paced rhythm can lead to incorrect interpretations of the 12-lead ECG. That's why it's important to look (and feel) for a pacemaker can when you do your physical exam!
You do perform a physical exam, right? (Say yes.)
When you completely undress your patient from the waist up, it helps with proper lead placement, reveals surgical scars and implantable medical devices, and allows you to assess breath sounds more accurately. It's just a good habit to get in to.
For this case there are a couple of big tip-offs that we're dealing with a paced rhythm.
It's a supraventricular rhythm with a wide QRS complex, left axis deviation, and LBBB morphology in lead V1. This is the most common morphology for paced rhythm and suggests that the pacing lead is in the apex of the right ventricle.
You will also note negative concordance of the QRS complexes across the precordial leads which is suggestive of a ventricular rhythm. Negative concordance of the QRS complex is not always present but it's a common feature of ventricular paced rhythms.
In addition, pacer spikes (or blips or "nubbins" since Christopher is making up his own words) are visible in a few leads, most notable of which is lead V4. This makes sense when you think about it because lead V4 is in close proximity to the apex of the right ventricle.
This case is also a nice example of appropriate T-wave discordance. Since all of the precordial leads show negative QRS complexes, let's arrange them smallest to largest and see if we notice anything.
See how the T-wave gets larger and larger as the S-wave gets deeper and deeper? The more times you look at this in a "normal" paced rhythm or left bundle branch block ECG, the easier it will be for you to identify when something looks "wrong".
I have no idea what was causing this man's chest pain but I feel confident it wasn't an acute STEMI.
Speaking of acute STEMI, I was recently made aware of another case where a computer algorithm incorrectly identified a WPW Type B pattern.
This was sent to me by Dr. Jody Griswold.
This is an interesting case in its own right and Dr. Griswold wrote a very informative paper about it which you can download here (with Dr. Griswold's permission):
WPW_Type_B_versus_STEMI (This is a Word .doc).
Just to show that the GE-Marquette 12SL interpretive algorithm gets it right sometimes, check out:
Wolf-Parkinson-White (WPW) - STEMI Mimic.