Hereâ€™s an ECG that I used for many years in the 12-lead ECG course for the Critical Care Transport (CCEMT-P) program.Â IÂ would show it to students right after teaching them to differentiate between right and left bundle branch block.
The patient is an 80 year old male who was out jogging when he experienced a syncopal episode.
EMS finds the man sitting down on a bike path. He is alert and oriented to person, place, time, and event; but heâ€™s cool, pale, and diaphoretic with absent radial pulses.
Past medical history: Hypertension
Medications: Aspirin, amlodipine, atorvastatin
At this point I ask them to identify the heart rhythm.
No one speaks up right away because no one wants to look stupid in front of the class (one of the things you find out about adult learners). SoÂ I prompt them.
“Do you see any P waves?”
â€œNo,â€ they all say in unison.
“Is it regular or irregular?”
“Whatâ€™s the rate?”
Someone says, â€œ32.â€
“So what is it?”
“Are the QRS complexes wide or narrow?”
“So what is it?”
â€œJunctional with left bundle branch block.â€
“Before you learned to differentiate between right and left bundle branch block what would you have called a wide and slow rhythm without P-waves?”
“Okayâ€¦. so whatâ€™s changed?”
TheÂ point is simple. Wide complex rhythms are ventricular until proven otherwise. Granted, this rule of thumb is typically used for rhythms that are wide and fast. However, the rule is equally valid for rhythms that are wide and slow.
â€œBut the computerized message at the top says itâ€™s a left bundle branch block.â€
“True but it also says undetermined rhythm.Â The computer is saying, ‘I donâ€™t know what rhythm this is, but the morphology matches left bundle branch block.'”
Is it possible that this rhythm is junctional with left bundle branch block? Yes, itâ€™s possible. But do you assume that itâ€™s junctional? No.
Then I pose a challenge to the class. Is there an experiment you could perform to help determine if the rhythm is junctional or ventricular?
What Iâ€™m looking for is a student to say, â€œYou could try o.5 mg atropine rapid IV push.â€
If the rhythm responds to atropine, thereâ€™s a good chance it’s junctional. If it doesnâ€™t respond to atropine, it really doesnâ€™t prove anything.
A few years back I asked my hypothetical question, and a hand went up in the back of the class (that should have been my first clue that I was dealing with a trouble-maker). I was hoping he was going to suggest atropine so I called on him.
With a dead-pan look on his face he says, â€œIf the lidocaine kills him it’s ventricular.â€