Computerized interpretive statements and bundle branch blocks

Here’s an ECG that I used for many years in the 12-lead ECG course for the Critical Care Transport (CCEMT-P) program. I 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 he’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). So I prompt them.

“Do you see any P waves?”

“No,” they all say in unison.

“Is it regular or irregular?”

“It’s regular.”

“What’s the rate?”

Someone says, “32.”

“So what is it?”


“Are the QRS complexes wide or narrow?”


“So what is it?”

“Junctional with left bundle branch block.”

“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?”

“Idioventricular rhythm.”

“Okay…. so what’s changed?”

The 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.

“But the computerized message at the top says it’s a left bundle branch block.”

“True but it also says undetermined rhythm. The computer is saying, ‘I don’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, it’s possible. But do you assume that it’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 I’m looking for is a student to say, “You could try o.5 mg atropine rapid IV push.”

If the rhythm responds to atropine, there’s a good chance it’s junctional. If it doesn’t respond to atropine, it really doesn’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, “If the lidocaine kills him it’s ventricular.”



  • people always forget the first criterion of BBB is it has to be supraventricular.

    it’s no coincidence that when teaching an organized approach to EKG interpretation the first thing they always teach is to look for P waves.

  • Art says:

    I’ve had similar discussions with my cardiology students. I’ve had to remind them on several occasions that the computerized interpretive information is useful, but it shouldn’t be accepted “verbatim” until it’s confirmed by human interpretation.

    Great post! 🙂

  • Slayer says:

    It also supports the fact we should always run a six second strip to interpret. Not try and do it in a 12-lead.

  • Medic-Minx says:

    AMEN!!! Art!!! I commend you and couldn’t say it better! I argue with so many people at work that RELY TO A TEE on the monitor interpretation. As soon as my 12-L prints I rip it off and make my own judgement call; the only thing I keep is the Qtc, QRS-Int & PR-Int for validity. When I’m confident on my decision I’ll glance at the interpretation. Half of my print-outs tell me it’s an ****ACUTE MI***** when it’s not. And there are so many people that STEMI-Alerts based on the monitor telling them that.

    I had a girl tell me today that she had a STEMI yesterday and she told me that she couldn’t really read the rhythm because there were so many PVCs and the HR was about 38. She says that she noted some nice STE in II, III, avF and called a STEMI; she says the patient had a BP of 81/42 however only complaint was feeling dizzy (denies any chest pain) and only dyspnea upon being supine due to history of COPD and CHF (lungs clear). She tells me that she didn’t do a right-sided 12-L but she knew there was involvement and that he was also a posterior MI. I asked her what made her consider a posterior? I said, “did he have STD in the V-leads?” and the answer I got just stopped MY heart dead…”I don’t know what was in the v-leads because the monitor told me there was posterior involvement. And I go by what it says.”

    This also comes from the same person that told me you CANNOT read a V-Paced rhythm or a LBBB. My arguments were futile; she says the QRS is machine-generated in a V-pacer and it’s next to impossible to read them, let alone determine if the patient is having an MI and that LBBB mimic that of an MI and you can’t call because it always looks like there is STE.

  • Mario says:

    In my opinion is complete heart block (third degree A-V block) with underlying AF and junctional escape rhythm.

  • Ludwig Abaunza says:

    If you check AVR it should always be negative but if it is positive for sure is coming from the ventricles. Remember in V-tach electricity will travel up and make AVR positive. Also for the person that states that paced rhythms can not be analyzed, remember that with demand settings only when the heart is not pacing is that the electrical battery will carry the impulse. Otherwise the heart is doing its own pacing. For LBB tell her to look at the SGARBOSSA criteria which is controversial but can help you determine if you are dealing with a STEMI pt. Also LBBB with L axis deviation have a high incidence of LAD occlusion by statistics.

  • Iliyas says:

    Idioventricular rhythm
    T wave looks hyperacute in v2, v3, v4, and inf leads
    Pt is in infraction

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