Sunday, January 5, 2020

Atrial fibrillation? Multifocal Atrial Tachycardia? Don't look at computer read until AFTER you interpret!

This 60-something with h/o COPD and HFrEF (EF 25%) presented with SOB and chest pain.

Here is the ECG:
What do you think?
Computer interpretation is below.

Here is the computer interpretation:

The over-reading physician confirmed this diagnosis, which is incorrect.  

It is not atrial fibrillation.

The rhythm is indeed irregularly irregular, so atrial fibrillation must be considered.
There are 5 other rhythms that are irregularly irregular, though atrial fibrillation is by far the most common:

1. Multifocal Atrial Tachycardia
2. Sinus with multifocal PACs
3. Sinus with multifocal PVCs
4. Polymorphic VT (which is always wide complex, so does not apply here)
5. Atrial fibrillation with WPW (which is also wide complex)

This is NOT atrial fibrillation, as demonstrated in this annotated version:
The rate is 120

One should look for sinus beats by looking for an up-down P-wave in V1.
We find two (black arrow, and then another 2 beats later)

Then confirm that it is a sinus beat by going directly down to lead II across the bottom.
We find a corresponding typical lead II P-wave, confirming sinus rhythm (black arrow at bottom).

Then look for other similar P-waves (see red arrows).

Then notice that there are several other P-wave morphologies, and that several come early such that the QRS is aberrant, with an RBBB morphology because the right bundle usually has a longer refractory period (Green arrows).

The sinus node, when not interrupted, occurs more than 600 ms after the previous atrial beat, so sinus tachycardia is NOT present

One might call this multifocal atrial tachycardia (MAT), but since there are definite sinus beats which are not tachycardic, this is sinus with multifocal atrial premature beats.

MAT has at least 3 distinct P-wave morphologies, but there is no single dominant pacemaker (i.e., no underlying sinus rhythm)

Rhythm Diagnosis: Sinus Rhythm with Multifocal Premature Atrial Beats (PACs or PABs), many conducting aberrantly.

More Learning Points

Do not trust the computer algorithm to diagnose atrial fib or absence thereof.  It may lead to false negative or false positive diagnoses, and withholding of necessary anticoagulation, or administering or inappropriate anticoagulation.  See below how this has been documented.

Here is an example where the computer failed to diagnose atrial fibrillation, with disastrous consequences:

Computer often fails to diagnose atrial fibrillation in ventricular paced rhythm, and that can be catastrophic

Smith SW et al.  A deep neural network for 12-lead electrocardiogram interpretation

outperforms a conventional algorithm, and its physician over-read, in the diagnosis of atrial fibrillation.  IJC Heart and Vasculature 25(2019).

Here are excerpts from the article:

From the Introduction:

Among rhythm diagnoses, atrial fibrillation (AF) is particularly important for appropriate management. However, incorrect automated and physician overread interpretations are common and have been shown to adversely affect patient management [1]. A study of 2298 ECGs from 1085 patients which had a computerized interpretation of AF found that in 442 (19%) of these ECGs, from 382 patients (35%), the interpretation was incorrect, and that, in 92 of these 382 patients, the physician had failed to correct it. These errors resulted in unnecessary antiarrhythmic and anticoagulant therapy in 39 patients and unnecessary diagnostic testing in 90 patients, and an incorrect final diagnosis of paroxysmal AF in 43 patients.

From the discussion:

Unfortunately, however, computer algorithms have mediocre performance [14]. When they are accurate, they have been shown to increase the accuracy of physician overread, but when inaccurate, they have been shown to lead physicians astray. This has been shown for cardiology fellows [15], for emergency physicians [16], and also for fully trained cardiologists, for whom the presence of an automated interpretation resulted in lower accuracy because automated errors were not corrected [17].

Atrial dysrhythmias, and atrial fibrillation in particular, are frequently misdiagnosed by computer algorithms and then by the physician who overreads them. Shah and Rubin studied the computer
rhythm interpretation of 2160 12-lead ECGs, compared to 2 cardiologists [18]. Among the 2112 that the computer could interpret, the sensitivity and specificity were, respectively, 95% and 66.3% for sinus rhythm and 71% and 95% for atrial fibrillation. Taggar et al. noted computer over-interpretation (false positives) of AF in 9 to 19% of ECGs [19].  Hwan Bae et al. found computer under-diagnosis on 9.3% of 840 AF ECGs, and over-diagnosis in 11.3%, with 7.8% of misdiagnoses uncorrected
by the physician [20]. Among, 2447 ECGs, Mant et al. found 83.3% sensitivity and 99% specificity of the Biolog interpretive software; however, the reference experts only disagreed in 7 ECGs (0.27%), which suggests that only uncomplicated ECGs were included [21]. Poon et al. found 90.8% sensitivity and 98.9% specificity of the General Electric (GE) algorithm for AF, but they excluded cases with ventricular paced rhythm (VPR), in which the underlying atrial rhythm was frequently
AF;we did not exclude VPR, as accurate identification of AF in VPR is important for determination of stroke risk [22]. Thus, both overdiagnosis and underdiagnosis of AF are well-recognized problems in computer interpreted electrocardiograms, and they adversely affect patient management
with either inappropriate anticoagulation and/or antidysrhythmics or undertreatment [1,14]. In our study, even physicians' overread of the Veritas® algorithm disagreed with the reference interpretation
in 38 cases (7.6% of all cases, and 62% of Veritas® misdiagnoses).

MY Comment by KEN GRAUER, MD (1/5/2020):
This case illustrates a number of important teaching points. I address these sequentially in the series of Questions below:
  • For clarity — I’ve reproduced and labeled the ECG in this case in Figure-1.

Figure-1: The ECG shown in this case (See text).

QUESTION: Is it the “fault” of the Computer that the correct rhythm diagnosis was overlooked by the overseeing clinician?

MANSWER  The issue of whether Computerized ECG Interpretations are “at fault” for an inaccurate ECG diagnosis has been addressed numerous times on this blog.
  • PEARL #1: It is not the “fault” of the computer that an ECG diagnosis is missed. Instead — it is the fault of the provider who accepts the computer interpretation without independently interpreting the ECG before looking at what the computer said (CLICK HERE for “My Take” on how to optimally use the computerized report).
  • My views may differ from others — in that as an Attending charged with overreading ECGs for numerous providers — I loved the computerized interpretation once I learned to appreciate what the computer can and cannot do. That’s because the computer saved me LOTS of time (!) by greatly speeding up my interpretation, when I would be confronted with a large stack of ECGs in front of me to interpret. But for anyone who has read less than many thousands of tracings — it is imperative not to even look at the computer interpretation until after YOU have independently interpreted the ECG yourself. Failure to follow this advice will undoubtedly lead to overlooking subtle acute MIs — and, it will especially lead to misdiagnosing many cardiac arrhythmias (as was done in this case). BOTTOM LINE: Don’t blame the computer for YOUR mistakes! Don't look at the computer interpretation until after you yourself have interpreted the tracing!

QUESTION: Why is MAT (Multifocal Atrial Tachycardia) so commonly overlooked?
  • How can you avoid overlooking this arrhythmia?

MANSWER  In my experience, MAT is the 2nd-most commonly overlooked cardiac arrhythmia (surpassed only by Atrial Flutter). The reasons for overlooking this arrhythmia are simple:
  • True MAT is not a common rhythm. AFib is the irregularly irregular rhythm that is most commonly confused with MAT — and, AFib is much, much, much more common than true MAT.
  • Clearly identifiable P waves will not always be seen in each of the 12 leads on an ECG. Therefore — IF the single-lead rhythm strip that you are using for cardiac monitoring does not clearly show identifiable P waves — it will be EASY to mistake this rhythm for AFib. PEARL #2  Remember that, 12 Leads are Better than One. Many arrhythmias will prove uninterpretable — IF only 1 or a few leads are used. GET a 12-lead!
  • Providers FORGET to Use the Odds”. MAT almost always occurs in one of 2 common clinical scenarios: iSevere pulmonary disease (ie, COPD, long-term asthma; pulmonary hypertension); or, ii) Acutely ill patients with multisystem disease (ie, patients with sepsis; shock; electrolyte and/or acid-base disorders).
  • PEARL #3  IF your patient has either of these 2 clinical scenarios (in the above bullet) — and the cardiac rhythm is irregular — then LOOK CAREFULLY for possible MAT! You will not miss MAT — IF you are looking for it!
  • Because of all the baseline artifact in ECG #1 — it was not immediately apparent to me that multiple different P waves were present! That said — I had NO doubt that the upright deflections in front of beats #4, 6, 9, 14, 16 and 18 were all most definitely P waves (BLUE arrows in front of these beats in Figure-1). Closer scrutiny in front of the remaining QRS complexes then strongly suggested that all beats in this tracing were preceded by P waves (especially since P wave morphology and the PR interval preceding beats #2, 11, 13, 15 and 17 were all identical).
  • Support that we were dealing with an MAT-like arrhythmia in this case came from the History (ie, known COPD+ additional ECG findings consistent with pulmonary disease (ie, persistent S waves through to lead V6 + the finding of tall and peaked inferior lead P waves for many of the P waves in the long lead II rhythm strip).

QUESTION: Is there a difference between sinus rhythm with multiple PACs vs MAT?

MANSWER  In my opinion — it is both academic and clinically unimportant (as well as often impossible) to attempt to distinguish between sinus rhythm with multiple different-looking PACs vs MAT. This is because: i) The same clinical scenarios (that I just cited above) are the common causes of both of these arrhythmias; andii) Clinical treatment (ie, identify and treat the underlying cause of the arrhythmia) is THE SAME for both conditions.
  • PEARL #4  In “real life” — there is often NO distinct “cut-off” for differentiating between sinus tachycardia with multiple different-looking PACs vs MAT. Instead — there is a SPECTRUM of rhythm disorders in this “family”, in which many possibilities exist for middle-ground” irregular SVT rhythms that manifest variable P wave morphology. For example — rhythms otherwise suggestive of being “MAT” are not always “tachycardic”. Moreover — the point of transition between sinus rhythm with multiple different-shaped PACs into “MAT” is often elusive. (CLICK HERE for more on “My Take” about the spectrum” for MAT).
  • In my opinion — the rhythm in Figure-1 represents one of these middle-ground” irregular SVT rhythms that for all practical purposes functions as MAT. This is because despite a number of P waves that do suggest an underlying sinus mechanism (ie, similar, sinus-looking P wave morphologies for the P waves preceding beats #2, 11, 13, 15 and 17): i) I count at least 9 different P wave morphologies in ECG #1; and, ii) The average RATE of the P waves for the 10-second rhythm strip in ECG #1 is over 115/minute (and the atrial rate is much faster than this for the 8 different-looking P waves that occur in-a-row from beat #3-thru-beat #9).
  • NOTE (Beyond-the-Core):  It is possible that the presumed sinus beats in ECG #1 (ie, beats #2, 11, 13, 15 and 17) are not necessarily as slow as they appear to be in this tracing. Given the amount of baseline artifact present on this tracing — and the absence of ever seeing 2 sinus-conducted beats in a row — we simply do not know what a “normal ST-T wave” would look like. When there are numerous PACs (many of which are aberrantly conducted) — there often will also be non-conducted PACs — and it is impossible with this much artifact to adequately assess ST-T wave morphology for those beats at the onset of each relative pause for the possibility of a hidden non-conducted P wave. The fact that the R-R interval preceding each of these 5 presumed sinus beats is different supports the premise that something else (ie, perhaps one or more blocked PACs) may account for these variable preceding R-R intervals. IF this were the case — then we truly would have completely irregularly irregular + constantly varying + tachycardic atrial activity. We just cannot determine this with certainty from this artifact-laden tracing.
  • That said — NONE of this matters clinically! The patient in this case presented with dyspnea and chest pain. Given the significant tachycardia and this “middle-ground” irregular SVT rhythm (regardless of what you call it) — acute pulmonary disease is virtually certain to be an important contributing (if not the sole) cause of this tachyarrhythmia. The KEY to getting this patient better will doubtlessly include optimizing pulmonary function. Chances are great that whatever this interesting irregular SVT rhythm happens to be — it will go away once you improve pulmonary status!

QUESTION: HOW CERTAIN are YOU that the wide beats in ECG #1 are aberrantly conducted (and not PVCs)? Are YOU — 50% — 75% — 90% or 100% certain?
  • IF you are 100% certain — HOW can you be so sure?

MANSWER  I am 1,000% certain that all of the wider (more abnormal-looking) beats in ECG #1 are aberrantly conducted supraventricular beats. PEARL #5  In addition to looking at the long lead II rhythm strip — Reference to each of the 12-leads on this tracing is needed for identification of these abnormal beats and their etiology. Sequentially — this was my approach:
  • It is easiest to identify beats #12 and 14 in lead V1 as wider (ie, more abnormal-looking). These beats are clearly aberrantly conducted because: i) There is a completely typical rSR’ (taller right-rabbit-ear + S wave in V1 that descends below the baselineRBBB-morphology for beats #12 and 14; ii) Both of these beats are clearly preceded by early-occurring P waves (so there is a “reason” for aberrancy); iii) If we follow beats #12 and 14 in lead V1 vertically down to beats #12 and 14 in the long lead II rhythm strip — the smaller r wave + deeper S wave of beats #12 and 14 in this long lead II are perfectly consistent with LAHB aberration (so there is bifascicular block = RBBB/LAHB aberration); iv) The slope and initial direction of the first portion of the QRS complex in virtually all leads is virtually identical for the wider beats and the normally conducted beats (and that does not happen with PVCs); and, vThe Ashman Phenomenon (in which aberrant conduction occurs for the beats after the relative pause) holds true throughout this long lead II rhythm strip.
  • Once we have identified with certainty that the smaller r wave + deeper S wave of beats #12 and 14 in the long lead II are aberrantly conducted — we KNOW that all other beats that look like this in lead II must also be aberrantly conducted ( = beats #4, 6, 7, 12, 14, 16 and 18).
  • We can confirm that beats #16 and 18 are conducted with RBBB aberration as well as LAHB aberration — because the S wave of these 2 beats in lead V6 is clearly wider than other S waves in V6 (as should be the case with RBBB aberration). BOTTOM LINE  Recognition of a completely typical conduction defect (ie, such as RBBB/LBBB that we see here) + clear identification of early-occurring P waves + virtually identical initial slope and direction of the initial portion of the QRS for both wider beats and normally-conducted beats + strict adherence to the Ashman phenomenon throughout this long lead II rhythm strip confirms aberrant conduction as the cause for all different-looking QRS complexes in this tracing.
  • CLICK HERE for detailed illustration and explanation of the Ashman Phenomenon.
  • CLICK HERE and listen to the next few minutes of this ECG Video for explanation on the Basics of Aberrant ConductionCLICK HERE for an illustrative case in which there are different forms of aberrancy.

Out THANKS to Dr. Smith for presenting this case.

1 comment:

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