The 12 Rhythms of Christmas: Atrial Flutter

This article is the third in our latest series, The 12 Rhythms of Christmas, where each day we examine a new rhythm disorder. It’s a continuation of the theme behind last year’s 12 Leads of Christmas.

This is a new edit of the first article I ever published on my personal blog, so it may seem familiar to some readers.

Finally, if you were curious about the mystery rhythm in Fig. 16 of the first post on sinus tachycardia, you might be surprised to know that it shows atrial flutter with 2:1 conduction. The same tracing pops up in Fig. 23 of this article.

Atrial Flutter

Have you slammed adenosine to cure a patient’s SVT with a fluorish?

Atrial flutter with 2:1 conduction

Figure 1. Pre-adenosine.

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

Atrial flutter during adenosine bolus

Figure 2. A few seconds after the adenosine push.

…only to see the saw-tooth waves of atrial flutter marching across the monitor?

While you may have performed a successful diagnostic test, your unsuspecting patient has just been given a sneak peek of the day their heart quits beating with no relief from the arrhythmia actually causing their symptoms.

Atrial flutter with variable conduction

Figure 3. s/p adenosine.

Well, you need-not make that 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 monitor upside-down (hint)!

Electrophysiology

There’s three things you need to understand about the physiology of atrial flutter:

  1. Most flutter is caused by a re-entrant circuit that travels around the annulus of the mitral valve. The best way to visualize the mechanism is to watch the animation in the “Atrial Flutter” section of this tutorial (but it’s worth your time to run through all the other chapters).
  2. Because the flutter circuit does not utilize the AV-node, adenosine almost never has an effect on the atrial portion of the arrhythmia; it just temporarily interrupts conduction to the ventricles (and bothers the patient).
  3. New-onset or untreated atrial flutter most often presents with 2:1 conduction ratios, with two flutter waves occurring for every QRS complex.

Flutter isn’t always easy to spot

Basic dysrhythmia classes make it seem like atrial flutter is a simple arrhythmia to identify—just look for prominent saw-tooth waves.

Clockwise atrial flutter with variable conduction

Figure 4. This clockwise atrial flutter is almost suspiciously easy to spot.

That isn’t always the case. Here’s an extraordinarily subtle case of of atrial flutter with 2:1 conduction.

Subtle atrial flutter with 2:1 conduction

Figure 5. Extremely subtle atrial flutter with 2:1 conduction

Consider 2:1 flutter in anyone with a heart rate of 100–200 bpm

2:1 atrial flutter

Figure 6. 2:1 Flutter with an atrial rate of 336 /min and a ventricular rate of 168 bpm.

2:1 atrial flutter

Figure 7. 2:1 flutter with an atrial rate of 224 /min and a ventricular rate of 112 bpm.

It’s going out on a limb, but I’m going to boldly state that you’re unlikely to come to the correct diagnosis unless you think of it first. Atrial flutter is said to be fairly uncommon, but my personal experience begs to differ. It is indeed less prevalent than atrial fibrillation, but I see an example almost every day in my emergency department, so it’s still very common in its own right. 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 and 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 the next sign…

The heart rate in 2:1 flutter is extremely stable

HR trend in 2:1 flutter

Figure 8. Stable HR trend in a patient with 2:1 atrial flutter.

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 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 sinus tachycardia will almost always show at least some variation over the course of a few minutes. In atrial flutter with fixed conduction, while the rate displayed may occasionally vary by a beat or two, it will hardly move (Fig. 8). Sinus tach won’t do that. Every rule has an exception, however, and there are plenty of times when the rate will vary with a-flutter, leading to our next tip…

Look for breaks in the regular rhythm

2:! atrial flutter with PVC

Figure 9. 2:1 atrial flutter with a single PVC

Atrial flutter

Figure 10. Atrial flutter with 2:1 conduction and brief periods of 3:1 conduction.

Occasionally even untreated flutter may waver from 2:1 conduction for a beat or two, and those moments should be used to scrutinize the strip for signs of atrial activity. PVC’s in particular can provide a brief glimpse of the underlying rhythm. 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 choice. On the other hand, if the only other route is adenosine, vagal maneuvers may be easier to tolerate. Unfortunately, vagal maneuvers often fail or are not a option, and cases where the rhythm shows gaps without provocation are pretty uncommon, so knowledge and experience really are the key to identification.

Scrutinize every lead

Atrial flutter best seen in V1

Figure 11. Atrial flutter, with F-waves only visible in V1.

The standard ECG has 12-leads so quit relying on just monitoring lead II for arrhythmia identification! While flutter waves typically show up well in lead II, they tend to show up best 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.

2:1 atrial flutter

Figure 12. 2:1 atrial flutter with F-waves best visible in leads I, aVR, and V1.

The Bix rule

2:1 atrial flutter Bix rule

Figure 13. 2:1 atrial flutter demonstrating the Bix rule.

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.

Bix atrial flutter

Figure 14. “Bix” F-waves.

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.

Bix rule 2:1 flutter

Figure 15. 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. This is from the same patient as the ECG in Fig. 11.

ST or T-wave abnormalities are the norm

Atrial flutter false-positive STEMI

Figure 16. Atrial flutter triggering a false-positive STEMI interpretation.

Atrial flutter is excellent at mimicking 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, 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.

Never trust the computerized interpretation

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

Figure 17. 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.

Figure 18. 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.

It just doesn’t look right

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

Figure 19. 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.

Turn the beat around

This is probably my favorite trick of the bunch so I’m not sure why it’s buried so far down the list.

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...

Figure 20. 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...

Figure 21. 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.

Figure 22. 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.

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.

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.

Figure 23. 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.

Figure 24. 3:1 flutter with an atrial rate of 195 /min.

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

Figure 25. 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.

Figure 26. Atrial flutter with 4:1 conduction and an atrial rate of 186 /min.

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.

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.

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, 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.

Figure 27. 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.

Figure 28. 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.

Figure 29. 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.

Figure 30. Ectopic atrial tachycardia with 2:1 conduction—difficult to differentiate from 2:1 flutter.

Read a lot of ECG’s

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.

 

Check out the rest of The 12 Rhythms of Christmas (updated as new posts come out)!

The 12 Rhythms of Christmas: Sinus Tachycardia
The 12 Rhythms of Christmas: Sinus Bradycardia
The 12 Rhythms of Christmas: First Degree AV-Block
The 12 Rhythms of Christmas: Type I AV-Block

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