Diagnosing Hidden Atrial Flutter

Introduction:

Ever given a patient adenosine to cure their SVT with a flourish?

Uncertain tachycardia? Let's give some adenosine!

Uncertain tachycardia? Let’s give some adenosine!

 *PUSH* – *FLUSH* – “You’re gonna feel funny,” ¹

Nailed it.

Nailed it.

…only to see the tell-tale saw tooth waves of atrial flutter marching across the screen? While you may have performed a successful diagnostic test, your patient has been given a sneak peek of the day their heart quits beating with nothing to show for it. Well you need not make this mistake again because I’ve put together a rough list of (almost) every tip out there for diagnosing subtle atrial-flutter with 2:1 conduction. In the end you’ll be talented enough to recognize this arrhythmia with your screen upside-down (hint)!

Pathophysiology:

2:1 conduction is the most common manifestation of untreated (i.e. new-onset) atrial flutter, making it doubly difficult to diagnose because the patient will often have no history. This post was originally going to include a primer on the pathophys of atrial flutter, but even when I gutted the extemporaneous info it was too much. Instead, all you need to do is look at the atrial flutter section of this animation from blaufuss.org. It’s simply the best resource I’ve come across for visualizing the phenomena behind most forms of narrow-complex tachycardia. Onto the tricks…

 Tips:

0 – Be systematic.

This flutter is almost suspiciously easy to spot...

This flutter is almost suspiciously easy to spot…

This one doesn’t pertain specifically to flutter, but develop a systematic way of approaching every ECG. It may seem redundant for easy tracings, but the simple tracing above is the exception, not the rule, when it comes to atrial flutter. You’ll never see subtle findings if you don’t look. Additionally, it will prove necessary to be well-practiced if you want to dissect very complicated cases. Here’s a good method for general 12-leads interpretation from my heroes at EMS 12-Lead, but I’ll have to do a post on specifically how to approach rhythm diagnosis since they don’t have one (yet).

 

1 – In anyone with a heart rate of 100-200 bpm, consider the possibility of atrial flutter.

It’s going out on a limb, but I’m going to boldly state that you’ll never come to the correct diagnosis unless you think of it first. Atrial flutter is often said to be relatively rare when compared to sinus tachycardia and atrial fibrillation, but my personal experience begs to differ. It is indeed less common than those other two entities, but I encounter a couple of cases of atrial flutter in the emergency department every week so it’s still very common. It may seem like overkill to think about it almost every time you encounter a tachycardic patient, but I GUARANTEE it’s an easy habit to pick up. You’ll look like a rock-star picking up flutter that otherwise would have been missed. Now a lot of things can cause a rate in that range, including sinus tach and a-fib, so that brings us to trick #2:

 

2 – The rate WILL NOT BUDGE from 147 bpm (or whatever half of that person’s particular atrial rate is).

Graph showing the heart rate of a patient in 2:1 atrial flutter. The nearly horizontal line shows the patient’s HR didn’t change from approx. 130 bpm for almost two hours.

Atrial fibrillation is usually fairly easy to identify because it is truly irregularly-irregular, but both a-flutter with uniform conduction and sinus tach are usually described as being regularly-regular. While this may be true if you’re feeling a manual pulse, watch the heart rate generated by the monitor and a sinus rhythm will almost always show at least some variation over the course of a few minutes. If the patient is experiencing atrial flutter with fixed conduction, while the rate displayed may occasionally vary by a beat or two, it will hardly move. I’ve been able to identify flutter without an ECG by simply placing the patient on a portable pulse ox, noting the rate was 153, getting a very cursory history, stepping aside for a couple of minutes to arrange further care, then returning to note that even after resting, the patient’s rate was still exactly 153 bpm. Sinus tach won’t do that. Every rule has an exception, and there are plenty of times when the rate will vary with a-flutter, leading to tip #3:

 

3 – Look for breaks in the regular rhythm.

At the start of the EKG there is a small break in the otherwise regular tachycardia, revealing underlying atrial flutter.

At the start of the EKG there is a small break in the otherwise regular tachycardia, revealing underlying atrial flutter.

Occasionally even untreated flutter may waver from 2:1 conduction for a beat or two, and these moments should be used to scrutinize the strip for signs of atrial activity. Vagal maneuvers are an option but aren’t always successful. Additionally, flutter tends to crop up in elderly patients, a population famous for passing out if they bear-down too hard, so maybe having them Valsalva is not the slickest option. On the other hand, if the only other route is adenosine, vagal maneuvers may be easier to tolerate (noting, of course, if they are allowed in your scope of practice). Unfortunately, vagal maneuvers often fail or are not a possibility and cases where the rhythm shows gaps on its own are pretty uncommon, so knowledge and experience really are the key to identification.

 

4 – Scrutinize EVERY lead.

This atrial flutter is nearly imperceptible in every lead except V1.

This atrial flutter is nearly imperceptible in every lead except V1.

The standard ECG has 12-leads so quit relying on just monitoring lead II for arrhythmia identification! While flutter waves do typically show up well in lead II, they tend to show up better in III and aVF. Also, we’re not talking about easy cases here, so use all of the information available to you. V1 is an excellent lead for detecting atrial activity, especially flutter waves (or the “Lewis lead” if you’re monitoring), and don’t discount less common views of the heart like aVR. Flutter waves usually appear upright in V1 and aVR, sometimes making them easier to spot than the inverted F-waves in II, III, and aVF.

While I’m on the topic of rhythm monitoring, if you’re using a Lifepack-12 you should rarely trust what you see displayed on the rhythm strip. The filter used in monitor-mode grossly distorts the ST-segments and T-waves, making tricky rhythm analysis even more difficult. I’m sure there are other brands and models that do it, that’s just the only product I’ve ever used on a regular basis that can make even simple rhythm analysis downright difficult. The company assumes that we are willing to sacrifice accurate accurate morphology for the sake of eliminating artifact on the road, but I’ve yet to see a case where an LP-12 rhythm strip was any more useful than the diagnostic (and noisier) 12-lead. Instead, I’m consistently hindered by the distortion that occurs when the rhythm is recorded in “monitor mode,” wishing that a diagnostic filter had been used instead.

Thankfully even ACLS has started to encourage folks to obtain a 12-lead for rhythm identification unless the patient is in extremis, so don’t be slower to evolve than the AHA.

 

4.5 – UPDATE – Really try the “Lewis Lead”

In tip #4 I mentioned using the “Lewis lead” for detecting hidden atrial activity, but I just wanted to share a case that reinforces the utility of this lead when searching for hidden atrial flutter.

Standard Electrode Placement – Lead II
At a glance this looks like atrial fibrillation, but there appears to be some regularity to the complexes with shorter R-R intervals, suggesting 2:1 atrial flutter. Can we prove this is the case?

Lewis Electrode Placement – Lead I
It is now obvious that there were indeed flutter waves being missed on the initial rhythm strip.

 

5 – The Bix rule.

There are signs of atrial activity located almost exact half-way between the QRS complexes, suggesting there could be more buried within.

There are signs of atrial activity located almost exactly half-way between the QRS complexes, suggesting there could be more buried within.

Harold Bix, a cardiologist from Vienna, noted that if a P-wave is located halfway between two QRS complexes, there’s a good chance there is also a P-wave buried inside the QRS as well. Since flutter waves tend to be somewhat wide and rarely fall perfectly inside a narrow QRS complex, you can often find signs of buried waves as slurring in the upstroke or downstroke of the QRS. In the EKG above there is a slight “notch” or “slur” at the tail end of each QRS complex, confirming that there is indeed atrial activity hidden there.

Lead III of the above EKG.

Lead III of the above EKG.

Not all tracings are going to give you a hint of the buried activity. In those instances all you can rely on is Bix’s suggestion, your clinical suspicion, and the other tips presented here.

Believe it or not, and despite the cardiologist's official interpretation at the top, this is actually 2:1 atrial flutter (proven after giving diltiazem). The ONLY hint on this tracing that there might be hidden atrial activity is the Bix rule.

Believe it or not, and despite the cardiologist’s official interpretation at the top, this is actually 2:1 atrial flutter (proven after giving diltiazem). The only hint that there might be hidden atrial activity on this tracing is the Bix rule.

 

6 – ST or T-wave abnormalities are the norm.

False-positive computerized reading of inferior STEMI

False-positive computerized reading of inferior STEMI due to atrial flutter.

Atrial flutter is excellent at mimicking the ST-depression and ST-elevation. It can also leave the T-wave totally unidentifiable in some leads. This is because flutter waves are relentless and will barrel through everything on a tracing. QRS complexes are relatively large deflections and not easily affected (except as noted in #5), but ST-segments and T-waves end up being fairly susceptible to distortion. Because of the timing and slope of the F-waves in 2:1 flutter, this most often manifests as apparent ST-depression in the inferior leads. Any unusual ST-depression, T-wave shapes, or unexpectedly biphasic T-waves should tip you off to search for signs of more buried deflections approximately 200 ms later (1 large box, corresponding to the usual atrial rate of 300 bpm).

The presence of atrial flutter should also make you question the diagnosis of STEMI. The two can be present at the same time but it is a pretty rare occurrence and most computer-generated statements of STEMI in the setting of flutter are false-positives. Acute MI can sometimes trigger atrial fibrillation but it’s rather unusual for it to present with new-onset flutter. That said, flutter + STEMI is not impossible, especially if the patient has a history of the former, and if the EKG shows a clear STEMI then it’s a STEMI.

 

7 – Never trust the computerized interpretation.

2:1 atrial flutter, misdiagnosed as sinus tach by the GE Marquette algorithm.

2:1 atrial flutter, misdiagnosed as sinus tach by the GE Marquette algorithm.

2:1 atrial flutter, misdiagnosed as "SVT" by the Mortara VERITAS algorithm.

2:1 atrial flutter, misdiagnosed as “SVT” by the Mortara VERITAS algorithm.

It’s fairly well-known that the GE Marquette 12-lead algorithm is a poor diagnostician of rhythm abnormalities, but when it comes to 2:1 atrial flutter it is especially flawed. In my experience an incorrect interpretation is the norm. The Mortara VERITAS algorithm is much better at considering the possibility of flutter (though it has plenty of other flaws), but it’s still not perfect.

 

8 – It just doesn’t look right.

This funny-looking-tachycardia is actually 2:1 atrial flutter.

This funny-looking-tachycardia is actually 2:1 atrial flutter.

When it comes to odd-looking rhythms with very wide complexes, hyperkalemia should always pop into your mind. In the same vein, if you see a tachycardia that just doesn’t look like a typical sinus tach, AVNRT, or AVRT (“SVT” if you prefer the vernacular for the latter two), consider atrial flutter.

 

9 – Turn the beat around.

This is probably my favorite trick of the bunch so I’m not sure why it’s buried way down at #9.

Most people don’t realize this, but disco singer Vicki Sue Robinson was not an actual electrophysiologist. Lacking an MD or DO, her rendition of the hit song “Turn the Beat Around,” which instructed cardiologists to, “turn the beat around, turn it upside-down,” still managed to make waves in the diagnosis of atrial flutter.

Flutter waves tend to show up best as negative deflections in the inferior leads (II, III, aVF), so if you’re considering the diagnosis, flip the ECG upside down and look at these leads. You’ll be amazed how much easier it is to identify the regular F-waves of flutter once they’re upright. It also makes it easier to see how those ST and T-wave distortions mentioned in #6 really are the predictable result of atrial activity.

 

It looks like an ectopic atrial rhythm, but the Bix Rule tells us to consider buried atrial activity here...

It looks like an ectopic atrial rhythm, but the Bix Rule tells us to consider buried atrial activity here…

Zooming in on the leads with the most clear atrial activity…

Those S-waves look a little wide, but not markedly abnormal...

Those S-waves look a little wide, but not markedly abnormal…

When flipped…

Flipping the leads vertically (and horizontally so it still reads left-to-right), those wide S-waves look a bit more like they're hiding something. This was confirmed to be markedly slow atrial flutter in a patient on carvedilol.

Flipping the leads vertically (so it still reads left-to-right), it becomes a bit more suggestive that those wide S-waves are hiding something. With the P-waves now upright, it is easier to see that the terminal portion of the S-waves look very similar to the tail end of the P-waves. This was confirmed to be markedly slow atrial flutter in a patient on carvedilol.

 

10 – Faster paper speeds are your friend

[edit 2014/6/27: I have decided to remove this as a tip because I no longer believe faster paper speeds are useful for the non-electrophysiologist. While EP’s are comfortable reading ECG’s at 50mm/s, other providers (in the U.S. at least) are not and setting the paper speed faster will not help you unlock hidden information or buried waves. All it will do is cause confusion and possibly lead you astray.]

 

11 – If it’s less than 150 bpm, it still might be 2:1 flutter.

Many anti-arrhythmic medications (I’ve always thought mostly class I and III, but apparently at least some, if not all beta-blockers as well) can slow down the rate of the circus movement of the atria, consequently slowing down ventricular response. Of note, this can lead to a very dangerous state if the atrial rate slows down enough for the AV node to begin conducting 1:1 rather than the default 2:1. This becomes a big concern with the use of class I antiarrhythmics, which have a tendency to slow down the rate of  the flutter circuit without actually breaking the rhythm. 300 /min is too fast for the AV-node to conduct, but slow the atrial rate to 220 /min without also blocking the AV-node and the patient’s ventricular rate can suddenly jump from a rate of 150 bpm with 2:1 conduction to 220 bpm with 1:1 conduction.

The EKG in tip #9 showed 2:1 conduction with a ventricular rate of only 96 bpm, meaning the atria have slowed from their typical rate of 300 /min to 192 /min. Below are some more examples. I’ve included a bunch because I think it’s important to recognize just how subtle this can present and how slow the atrial rate can drop and still be in flutter.

I missed this one but the Mortara VERITAS algorithm somehow picked it up. Very slow 2:1 atrial flutter with an atrial rate of 206 /min.

I missed this one but the Mortara VERITAS algorithm somehow picked it up. Very slow 2:1 atrial flutter with an atrial rate of 206 /min.

3:1 flutter with an atrial rate of 195 /min.

3:1 flutter with an atrial rate of 195 /min.

Atrial flutter with variable conduction and an atrial rate of 225 /min.

Atrial flutter with variable conduction and an atrial rate of 225 /min.

Atrial flutter with 4:1 conduction and an atrial rate of 186 /min.

Atrial flutter with 4:1 conduction and an atrial rate of 186 /min.

 

12 – A saw-tooth pattern is not necessary to seal the diagnosis

Very few of the EKG’s I’ve shown so far have demonstrated the clear, classic “saw-tooth” pattern that is touted as being representative of atrial flutter. The F-waves of flutter can take a variety of morphologies, but most often the bulk of the wave is negative in the inferior leads and upright in V1. Also, as the atrial rate slows with the use of medications, there is a loss of F-wave amplitude and the morphology can become incredibly subtle. This makes slow atrial flutter, at rates that often causes us to omit flutter from our differential, very difficult to identify (see the examples in #11).

There’s no easy way to get around these tough cases and your best tool will be keen observation. Keep an eye open for repeating patterns in the baseline with a consistent relationship to the QRS complexes that could easily be written off as artifact.

CAUTION – MATH! – If there is variable conduction to the ventricles, atrial fibrillation becomes a common misdiagnosis. Measure a bunch of R-R intervals and look for a lowest-common-denominator. For example, if the atria are contracting at 300 bpm, meaning F-waves are 200 ms apart (1 large box), even with variable conduction every RR interval should be a multiple of 200. This means that 2:1 conduction would result in R-waves exactly 2 large boxes apart (400 ms); 3:1 conduction leads to R-waves 3 large boxes apart (600 ms); and 4:1 conduction would exhibit 4 large boxes between R-waves (800 ms). It’s minutiae for a diagnosis that probably won’t change the treatment plan, but who cares about patient outcomes when you can prove to everyone that you’re smarter than them.²

 

13 – F-waves are not exclusive to flutter.

If you see what appear to be F-waves at a rate exceeding 350 bpm, they’re probably “f-waves” associated with atrial fibrillation (note the clever use of lower-case in this case). The key to this distinction is that in atrial flutter with regular conduction (be it 2:1, 4:1, or 7:1), the QRS complex will typically appear at a regular interval in relation to the F-waves. In fibrillation the QRS will vary its relationship to the f-waves. The morphology of fibrillatory f-waves will often vary as well, sometimes by a very small degree, though I have also seen cases of very regular appearing fibrillatory waves.

There’s also a rare form of atrial flutter (type II) that can generate flutter waves at 340-440 bpm, but in contrast to a-fib, this should still present with a fairly fixed relationship between the F-waves and QRS complexes.

Confusing things further (especially after tips #11 and 12), if the rate is less than 250 bpm it may be an entity known as “atrial tachycardia.” In A-tach you will see distinct P-waves of abnormal morphology at a rate exceeding the normal physiological rate of sinus rhythm, often with similar conduction ratios to a-flutter, except they don’t have the saw-tooth pattern of flutter waves and are slower. As I stated in #9, there can be some overlap with slow a-flutter and atrial tach, leaving a diagnostic grey-zone. Thankfully they’re still treated the same acutely.

Small fibrillatory waves with a changing morphology in V1 and a irregularly-irregular ventricular response confirms this is atrial fibrillation.

Small fibrillatory waves with a changing morphology in V1 and a irregularly-irregular ventricular response confirms this is atrial fibrillation.

There are large waves in V1 that very closely resemble atrial flutter. There is a slight variation to their morphology and peak-peak interval which, combined with the irregularly-irregular ventricular response confirms atrial fibrillation.

There are large waves in V1 that very closely resemble atrial flutter. There is a slight variation to their morphology and peak-peak interval which, combined with the irregularly-irregular ventricular response confirms this is actually atrial fibrillation.

Again, this looks like atrial flutter at first glance, but there is a changing morphology to the atrial waves and the ventricular rhythm is irregularly-irregular. This is atrial fibrillation.

Again, this looks like atrial flutter at first glance, but there is a changing morphology to the atrial waves and the ventricular rhythm is irregularly-irregular. This is atrial fibrillation.

Ectopic atrial tachycardia with 2:1 conduction—difficult to differentiate from 2:1 flutter.

Ectopic atrial tachycardia with 2:1 conduction—difficult to differentiate from 2:1 flutter.

 

14 – Too fast to be possible is not impossible.

(To deter accusations of being unsafe [What?! Baseless accusations on the internet?! Never!!], I have to note the obvious: My whole blog, and this section in particular, in no way endorses trying to get fancy and pull out a zebra to diagnose an unstable patient; just follow ACLS. It is simply intended to act as water for your mind-grapes.³)

I noted in the pathophys section (before it was gutted) that if you combine a rapid atrial rate with Wolff-Parkinson White syndrome (WPW), you can get some truly astounding ventricular rates. If you encounter a wide-complex tachycardia faster than 220 bpm, it may be worth considering the existence of either atrial fibrillation or flutter with WPW. The key to distinguishing the two is that in flutter you will see a (mostly) regular, (mostly) consistent QRS morphology – as you should expect by now, at around 300 bpm. If the patient has a-fib, the rhythm will be irregularly irregular (as in normal a-fib, but extra fast) and the QRS morphology may vary wildly. Actual study of this topic would require a couple of posts unto itself, but I figured it was at least worth a cursory mention.

This patient's heart is absolutely tearing along at approximately 270 bpm. Probably some form of atrial flutter with one or maybe two accessory pathways. This patient presented ambulatory complaining only of palpitations.

This patient’s heart is absolutely tearing along at approximately 270 bpm. This is probably some form of atrial flutter with one or maybe two accessory pathways. This patient presented ambulatory complaining only of palpitations and minor lightheadedness.

Atrial fibrillation in a patient with WPW. Click image for source. Courtesy of LifeintheFastLane.com.

 

15 – Read a lot of ECGs.

If you’ve spent any time studying ECGs beyond the simplistic introduction to arrhythmias we all start with, it has probably become apparent that there is a lot of gray surrounding the many distinct electrophysiologic abnormalities recognizable on a 12-lead. This post is not intended to act as a hard framework for making the diagnosis of atrial flutter, but is merely a collection of the thoughts that cross my mind when I’m dissecting a difficult tracing. In these cases there will always be a lot of overlap with atrial fibrillation, AVNRT, atrial tachycardia, and several other dysrhythmias. The best advice I can offer is just to read LOTS of ECGs. There are scores of algorithms and diagnostic criteria to aid in making an electrocardiographic diagnosis, and while they have their place and can be of some utility (e.g. the aVR algorithm for ruling-in V-Tach, or the Sgarbossa criteria for recognizing STEMI w/ LBBB), the most useful tool is a well-trained eye capable of noticing when something on a tracing just doesn’t fit.

 

Conclusion:

Well congratulations if you’ve made it all the way through. If you have any ideas of your own please let me know and I’ll be glad to include them, with due credit of course.

 

Notes:

1. Don’t do this.

2. Sarcasm, don’t fight me please.

3.“Jack Welch has such unparalleled management skills they named Welch’s Grape Juice after him, because he squeezes the sweetest juice out of his workers’ mind grapes.” — Jack Donaghy

Last modified: 2014.11.10

10 thoughts on “Diagnosing Hidden Atrial Flutter

  1. ekgpress says:

    Nice post that totally supports my observation over the year that by far, the most commonly overlooked diagnosis is atrial flutter! – which becomes unlikely to happen IF your readers can assimilate your pearls of wisdom. KEY: Not to miss flutter because one hasn’t thought of this possibility. NICE JOB – : ) Ken Grauer, MD (ekgpress@mac.com)

    • Ken Grauer, MD says:

      UPDATE: Vince has just revised his post on AFlutter that I commented on in January, 2012. CONGRATS to Vince – as his new piece has greatly enhanced his work on this subject. I LIKE the new organization that I believe is more user-friendly. If ever you’ve had questions about how to diagnose AFlutter – the answer is probably here within Vince’s discussion – HIGHLY recommended! – :)

  2. Alexis Doreski, MD says:

    Very useful, I found your post clarifying, thank you very much for your contribution.
    Alexis Doreski, MD. Argentina.

  3. Great post and topic review– the most extensive summary of a-flutter diagnostic “tricks” I have yet seen in one place! I particularly appreciated your reference to the Bix Rule; I was unaware of this entity and I am very glad to have it on my radar. Keep up the good work!

  4. […] more tips to becoming an Atrial Flutter Rock Star, check out our friend Vince DiGiulio's blog post "Diagnosing Hidden Atrial Flutter". Posted by Christopher Watford on September 21, 2012 • Filed under: ems-topics, […]

  5. Andy Neill says:

    nice post. though last time i gave the adenosine it revealed the flutter waves for about 5 secs then the QRS kicked in and the flutter terminated – diagnosis AND treatment all in one! I have a nice little trace of it i must post.

    • Vince D says:

      Thanks! And that sounds like an awesome strip, so I would love to get a sneak peak if you get the chance. My email’s in the “about” section if you need it.

  6. […] first post on 2:1 atrial flutter turned out to be one of my most popular and successful contributions to the FOAM world over the […]

Leave a Reply