Differential Diagnosis of Wide Complex Tachycardias – Part 5

Let’s switch gears a little bit and discuss irregular or polymorphic wide complex tachycardias.

First I need to tell you a story.

A few years ago I was teaching ACLS to a group of mostly nurses at the local community hospital. I volunteered to teach Bradycardias, Tachycardias, and the Hypotension/Shock/Acute Pulmonary Edema algorithm.

At first the education coordinator was thrilled! Apparently not many ACLS instructors feel comfortable teaching the Hypotension/Shock/Acute Pulmonary Edema alogrithm.

Keep in mind, I was following along with the AHA ACLS PowerPoint slide set. I wasn’t freelancing. I was explaining and elaborating, but I wasn’t introducing material that is outside the scope of the ACLS objectives.

I arrived at Irregular (or Polymorphic) Wide Complex Tachycardias.

I had just written on the board the differential diagnosis, which included:

  • Atrial fibrillation/flutter or (multifocal atrial tachycardia) with bundle branch block
  • Polymorphic VT
  • Torsades de Pointes
  • Atrial fibrillation with Wolff-Parkinson-White Syndrome (WPW)

When suddenly, the education coordinator yelled out from the side of the room, “You’re scaring the hell out of them!”

I was struck dumb!

I didn’t know what to say. I looked back at the screen, and I looked at the dry erase board where I had just written the differential diagnosis, and then I looked back at the education coordinator, shrugged my shoulders, and said, “What do you want me to do?”

To be honest, this wasn’t the first run-in I had had with this particular education coordinator.

A couple of years prior, I was a student in one of her ACLS classes. She handed out a cardiac rhythm strip test. I identified one of the heart rhythms on the test as 2:1 atrial tachycardia. She marked it wrong. When I asked about it, she said the correct answer was sinus tachycardia with 2°AVB and 2:1 conduction.

I laughed and said, “Is the atrial rate > 100?”

She said yes.

“And you agree there is 2:1 conduction?”

She agreed that there was.

“So you acknowledge that 2:1 atrial tachycardia is technically correct?”

She gave me look of utter contempt, leaned forward, and said quietly, “What do you think you are? A cardiologist?”

I’m not entirely sure this person likes firefighters. Let’s just say she used to be married to one, and leave it at that.

All of this to say, the differential diagnosis of irregular (or polymorhpic) wide complex tachycardias is a very neglected subject, both in paramedic school, and in ACLS class! But you have to know the differential diagnosis to select the correct treatment modality!

You can kill a patient who presents with an irregular (or polymorphic) wide complex tachycardia if you select the wrong drug!

That should “scare the hell out of you” far more than the differential diagnosis written out on a dry erase board.

Let’s start with atrial fibrillation.

Atrial fibrillation with intraventricular conduction defect (including right and left bundle branch block) can be considered a VT mimic at high rates, because the higher the heart rate, the more difficult it is to pick up on the irregularity that is normally the hallmark of atrial fibrillation!

In training (using the heart rhythm simulator) I sometimes give paramedics a scenario like this:

89 year old female contacts 9-1-1 complaining of chest pain and shortness of breath

On arrival, respirations are 36 and labored

Skin is pale and diaphoretic

Begin your assessment!

When they attach the monitor, they see atrial fibrillation with a nonspecific intraventricular conduction defect at a rate of 160.

I take that back. What they see when they attach the monitor is a wide complex tachycardia.

This example from Wide Complex Tachycardia: ECG Differential Diagnosis. Am J Emerg Med 1999; 17:376-381 should give you an idea what it looked like when printed out (which is different from how it looks on the monitor).


When they assess the BP (if they assess the BP) it comes back 160/110.

When they asses breath sounds (if they assess breath sounds) I say “wheezes with a poor tidal volume”.

When they assess the SpO2 (if they assess the SpO2) I say “72”.

Can you guess what’s wrong with this patient?

If you said “heart failure” move to the head of the class!

You would be frightened amazed to know how many paramedics immediately lie the patient flat and prepare her for immediate synchronized cardioversion!

In the debriefing that follows, when I ask why the decision was made to start shocking the patient, the ones that have clear rationale will say, “Because she was in unstable VT!” or “Because she was in unstable AF with RVR”.

When I asked what made the patient unstable, they will say, “the chest pain!” Some will say “the shortness of breath!”

Others will want to say the BP, but then they realize they never assessed it.

There’s a fine line between symptomatic and hemodynamically unstable.

For any patient who presents with a tachycardia, one of the most important and difficult questions you have to answer is:

Is the tachycardia causing the signs and symptoms, or are the signs and symptoms causing the tachycardia?

To put it another way:

Is this some type of compensatory tachycardia?

For the heart failure patient, atrial fibrillation and bundle branch block are extremely common. Have you ever seen acute, decompensated heart failure patient that did not present with tachycardia?

This is just my opinion, but I would try oxygen (CPAP if possible) and nitroglycerin before lying a heart failure patient flat and proceeding directly to synchronized cardioversion.

The next question you need to answer is:

Does the risk/benefit analysis favor treating this tachycardia in the field?

Choose wisely!

If you read the AHA ECC 2005 guidelines, you will see this statement featured prominently in the irregular (or polymorphic) wide complex tachycardia section.

“We recommend a 12-lead ECG and expert consultation if the patient is stable.”

Was the patient in this example “stable”? No!

Was the instability cased by the atrial fibrillation and rapid ventricular response?

In my opinion, no.

The BP of 160/110 gives you “room to play” so to speak. Nitroglycerin is a potent vasodilator. Why not give it, along with supplemental oxygen, and take some preload off the heart?

The heart rate will probably come down on its own when the SpO2 is back > 90.

You can always simultaneously prepare for cardioversion!

See also

Differential diagnosis of wide complex tachycardias – Part 1

Differential diagnosis of wide complex tachycardias – Part 2

Differential diagnosis of wide complex tachycardias – Part 3

Differential diagnosis of wide complex tachycardias – Part 4

Differential diagnosis of wide complex tachycardias – Part 5

Differential diagnosis of wide complex tachycardias – Part 6

4 Comments

  • SoCal Medic says:

    Picking the symptomatic vs non-symptomatic is always a unique debate at times. Easy to get tunnel vision on the things you do not see very often because we dont train enough on them. Great piece and a friendly reminder to consider the entire assessment before chosing a treatment modality.

  • Tom B says:

    Christopher – I would argue that EMS doesn’t pick up patients who aren’t symptomatic.In my mind, the relevant questions are:Is the patient stable?Is the instability being caused by the tachycardia?Having said that, reasonable people can sometimes disagree as to what constitutes instability!In addition, it’s sometimes difficult to tell whether or not the tachycardia is causing the instability or the instability is causing the tachycardia! I’m just encouraging anyone who treats a tachycardia in the field to consider these questions.In the interest of “first doing no harm” I like to start out with the basics and see if my patient starts heading the right direction! Tom

  • Bob Jester says:

    A wise old paramedic once told me to try the simple fix first. If it works, you’re golden, if not, all doubt as to stability will be removed.This has been a great refresher Tom, thanks for the mental calisthenics.I’ve been talking up you blog to the folks I work with, I hope more of them tune in.My word verification was endeper, which sounds (to me) like “in deeper” the irony was not lost.

  • Tom B says:

    Ah yes…. irony! The thinking man’s crack.There are times I don’t mind being endeeper, but with a crashing patient, you don’t want to be in too deep! :)Thanks for the positive feedback!Word verification: buscesol

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