ECG Blog #537 — What is the Rhythm?

The ECG in Figure-1 was obtained from an older woman with diabetes — who presented with acute dyspnea.

QUESTIONS:

• What is the rhythm?
• Is there an underlying RBBB (Right Bundle Branch Block) or aberrant conduction?

Figure-1: The initial ECG in today's case — obtained from an older woman with acute dyspnea. (To improve visualization — I've digitized the original ECG using PMcardio).

MY Thoughts on Today's CASE:

The above questions were contemplated by initial providers in today's case. As to the rhythm in Figure-1 — the KEY is to avoid being sidetracked, and instead to remain systematic in our approach to today's tracing.

• PEARL #1: Whenever I am confronted by a challenging 12-lead ECG in association with a challenging arrhythmia — I always favor first at least taking a brief look at the rhythm in the long lead rhythm strip. This is because many of the questions we might have about the 12-lead — will often be answered once we appreciate what the underlying rhythm is.

PEARL #2: When confronted with an arrhythmia that contains 2 or more different elements — Begin with the easier-to-interpret element(s). Doing so often renders interpretation of the more difficult elements much simpler to understand. Often, the 1st "easier-to-interpret" element that I address will be to determine IF there is an underlying rhythm?

• For example, in Figure-1 — the muliple different QRS shapes (that we see in the long lead II rhythm strip at the bottom of the tracing) are difficult to assess.
• As a result, I defer looking at QRS morphology in the long lead II — and instead, I begin my interpretation by looking to see IF there is an underlying rhythm? In other words — Do we see P waves in the long lead II?

What do YOU think?

• Do we see P waves in the long lead II?

• NOTE: The answer appears below in Figure-2.

 

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Answer:

At 1st glance, on looking at the long lead II — I found it difficult to identify P waves until I arrived near the end of the rhythm strip.

• Then I saw the unmistakeable upright P wave in front of beat #17 (3rd RED arrow in Figure-2).
• And, once I saw this 1st upright P wave with a normal PR interval in front of beat #17 — it became easy to recognize the upright P wave in front of the next beat, albeit with a shorter PR interval (4th RED arrow in Figure-2).
• Now returning toward the front of the long lead II in Figure-2 — I was able to recognize the upright P waves (albeit with short PR intervals) in front of beats #7 and 8 (1st and 2nd RED arrows).

Figure-2: RED arrows in the long lead II rhythm strip highlight upright sinus P waves that I can readily identify.

Now take another LOOK at the long lead II in Figure-2. Can you identify any more P waves in this long lead rhythm strip?

• HINT: Use calipers! (Set your calipers to the P-P interval between any 2 consecutive P waves that we can readily identify = the P-P interval between either the first 2 — or the 3rd and 4th RED arrows in Figure-2).

• NOTE: The answer appears below in Figure-3.

 

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Answer:

I've highlighted with PINK arrows in Figure-3 — a series of small, upright (partially hidden) deflections that represent underlying "on time" sinus P waves at an atrial rate of slightly more than 100/minute. 

• Isn't it logical for there to be additional "on time" sinus P waves that I've not yet labeled in Figure-3?

• NOTE: The answer appears below in Figure-4.

Figure-3: I've labeled with PINK arrows a series of additional partially hidden upright sinus P waves.

 

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Answer:

It should now be apparent that an underlying rhythm of regular sinus P waves at a rate just over 100/minute is present throughout the entire long lead rhythm strip! My "color coding" in Figure-4 is as follows:

• The original 4 RED arrows represent the first 4 sinus P waves that were easiest to identify.
• PINK arrows in Figure-4 represent additional sinus P waves that I was able to identify by "walking out" the P-P interval that I had set my calipers to (Note partially hidden "on time" deflections highlighting the P waves under each of these PINK arrows).
• WHITE arrows in Figure-4 represent underlying "on time" sinus P waves that are all-but-certain to be present, albeit "hidden" by their simultaneous occurrence with either the QRS or T wave.
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• PEARL #3: Note that we have just established the presence of an underlying sinus P wave rhythm that for the most part is not related to neighboring QRS complexes. This is the definition of AV dissociation! — and the presence of AV dissociation during a regular wide tachycardia is virtually diagnostic of VT (See ECG Blog #133, among many other posts regarding the diagnostic value of AV dissociation). 

Figure-4: Colored arrows represent the underlying regular sinus rhythm that is present throughout today's tracing.

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Putting It All Together ...

Now that we've established the presence of a regular underlying sinus P wave rhythm with some element of AV dissociation — We can take another look at the multiple QRS shapes in the long lead II rhythm strip.

• Note in Figure-5 that there are 4 upright QRS complexes (albeit with slight variation in shape between beats #6,7; and #16,17) — and that the remaining 15 beats manifest negative QRS complexes. 
• Note also that I've added the labels, "C" and "F" to the long lead II rhythm strip in Figure-5.
• The KEY is beat #17. The QRS complex of this beat #17 is the most narrow beat, as well as the beat that is preceded by the most normal PR interval. This suggests that beat #17 is being conducted!
• And, if beat #17 is sinus-conducted — whereas beats #1-thru-5; #8-thru-15; and #18,19 all look very different (all being predominantly negative) with AV dissociation — this must mean that these predominantly negative beats represent an ongoing, underlying ventricular rhythm, occurring here at a rate of ~115/minute.

PEARL #4: As discussed in a number of blog posts (See ECG Blog #108, among others) — an independent ventricular rhythm at a rate of less than 120-130/minute is probably best classified as AIVR (Accelerated IdioVentriclar Rhythm) rather than "VT" (Ventricular Tachycardia). This is important clinically — because AIVR is often a consequence of other ongoing events, such that AIVR does not necessarily mandate immediate treatment with cardioversion.

• PEARL #5: The reason today's rhythm is "tricky" — is that the 15 predominantly negative QRS complexes in the long lead II rhythm strip do not "look" wide! But if we look directly upward at simultaneously-recorded leads V1,V2,V3 — the all-upright monophasic R wave in lead V1 for beats #11-thru-14 clearly looks to be ventricular in etiology.
• Thus, this is not RBBB and not aberrant conduction. Instead — there is underlying AIVR at ~115/minute. We prove this by the presence of AV dissociation. 
• Beat #17 is a "Capture" beat (labeled "C" in Figure-5).
• The reason the QRS morphology of beats #6,7 and 16 all look slightly different than that of beat #17 — is that these other upright QRS complexes all manifest different degrees of "Fusion" (labeled "F" in Figure-5) — with the concept of fusion beats explained in ECG Blog #128.
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• PEARL #6: The importance of recognizing Fusion and Capture beats — is that in association with underlying AV dissociation, this proves beyond doubt that the 15 predominantly negative QRS complexes in Figure-5 are ventricular beats!

Figure-5: I've labeled "Capture" and "Fusion" beats.

CASE Conclusion:

Today's patient was an older woman with diabetes — who presented with acute dyspnea. And although I do not have the specific details of what happened — I advised the following regarding clinical management:

• AIVR is often a well tolerated rhythm that does not necessarily mandate antiarrhythmic treatment or immediate cardioversion IF the patient is hemodynamically stable.
• Thus, if the reason for this patient's acute dyspnea is something "fixable" (ie, acute heart failure) — it may be reasonable to treat the heart failure. This may be all that is needed for the AIVR to resolve on its own.
• I do not see evidence of an ongoing acute infarction in Figure-5. To assess this — I focused on ST-T wave morphology of the more normally conducted beats (ie, the capture and fusion beats #16,17 in simultaneously-recorded leads V5,V6 — and the fusion beats #6,7 in simultaneously-recorded lead aVF). These complexes suggested marked LVH (greatly increased R wave amplitude for beat #17 in leads V5,V6) with ischemic symmetric T wave inversion in beats #6,7 and 16,17 in simultaneously-recorded leads aVF,V5,V6 — but no ST elevation.
• BOTTOM Line: If this patient remained hemodynamically stable — it may be reasonable to treat her heart failure (or other treatable cause of her acute dyspnea) to see if normal sinus rhythm returned. Depending on how the patient did, as well as depending on serial ECG and Troponin results — a decision can be made as the patient stabilized as to whether cardiac catheterization or other intervention will be needed. 

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Acknowledgment: My appreciation to Bashiruddin Sayeem  (from Chittagong, Bangladesh) for the case and this tracing.

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