I was sent the ECG in Figure-1 — told only that it was from a middle-aged man who presented for acute CP (Chest Pain).
QUESTIONS:
- What is going on?
- How to approach interpreting this ECG?
- What is the rhythm?
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| Figure-1: The initial ECG in today's case. (To improve visualization — I've digitized the original ECG using PMcardio). |
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My Approach:
As always (assuming your patient is stable and not in need of immediately cardioversion) — I favor a systematic approach, beginning with a quick look at the rhythm ==> "Watch your Ps,Qs, and the 3Rs" (as reviewed in ECG Blog #185).
- I vary which of these 5 KEY parameters I look at first — depending on particularities of the rhythm (and depending on which of these 5 parameters are easiest to recognize).
- In today's case, as I looked at the long lead II rhythm strip — I was struck by the almost beat-to-beat variability in QRS morphology. That said — many of the beats look to be narrow, suggesting the underlying rhythm is supraventricular.
- P waves are present!
PEARL #1: The simple step of labeling P waves is often surprisingly helpful in figuring out what is going on. I have done this in Figure-2 (RED arrows highlighting those P waves that I can definitely identify).
- What do we learn from Figure-2?
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| Figure-2: I've labeled those P waves that I can definitely identify. |
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What We Learn from Figure-2:
- The underlying rhythm in today's tracing appears to be sinus — as upright P waves with a constant and normal PR interval are seen in front of beats #1,3,4,6,8,11,13 and 15.
- I look for 2 sinus-conducted beats in a row — since if the underlying atrial rhythm is regular, seeing 2 sinus-conducted beats in a row will suggest what the P-P interval is (We see this for beats #3 and 4). The R-R interval between beats #3 and 4 is just over 3 large boxes — suggesting the presence of an underlying sinus rhythm at ~90/minute.
- NOTE: Although we do not clearly see P waves throughout the entire tracing in Figure-2 — the constant P-P interval between consecutive RED arrow P waves that we do definitely see suggests that there probably is a regular underlying P wave rhythm.
- The underlying atrial rhythm is regular.
- In addition to the RED arrow P waves that we definitely see — the PINK arrows in Figure-3 highlight "on time" sinus P waves that partially deform some part of the QRS.
- Even though we do not see any deformation of beat #10 — it makes sense that another "on time" sinus P wave is hidden entirely within this beat ( = the WHITE arrow drawn over beat #10).
- PEARL #3: The PR interval for all of the "on time" PINK arrow P waves is too short to conduct normally. This establishes the presence of intermittent AV dissociation — and this proves that beats #2,5,7,14 and 16 must all be ventricular beats.
- The reason for slight variation in QRS morphology for these ventricular beats is that there is some degree of fusion between sinus-conducted P waves and the ventricular beats that follow so soon thereafter that they interrupt conduction of sinus-initiated impulses through the ventricles (See ECG Blog #128 — for more on fusion beats).
- Fusion is unlikely for beat #10 — because the "on time" WHITE arrow P wave occurs too late to be able to enter the ventricles in time to conduct. The fact that the WHITE arrow P wave arrives in the ventricles too late to conduct provides insight as to what PVCs will look like in lead II — and therefore also what PVCs will look like in simultaneously-recorded leads V1,V2,V3.
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| Figure-3: Using calipers — I’ve added PINK arrows and a WHITE arrow where I expect "on time" P waves to be partially or totally hiding throughout today’s long lead II rhythm strip. |
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Focus for a moment on these 4 simultaneously-recorded leads ( = leads V1,V2,V3 — and lead II in the long lead rhythm strip) For clarity — I facilitate doing this in Figure-4.
- It should now be obvious from Figure-4 — that beat #11 looks different than the 3 other beats in leads V1,V2,V3, and in the long lead II. This is because the only normal sinus-conducted impulse among these 4 beats is this beat #11.
- Beats #9,10 and 12 are ventricular (presumably with some degree of fusion for beats #9 and 12).
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| Figure-4: Focus on the 4 simultaneously-recorded leads V1,V2,V3; and on the long lead II for the purpose of highlighting QRST morphology of beats #9,10,11,12). |
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Putting It All Together:
Now that we know from Figure-4 that beat #11 in the long lead II rhythm strip manifests the QRST morphology of a normal sinus-conducted beat — We can go back to Figure-3 to figure out which of the 16 beats in today's ECG are sinus conducted without partial fusion from ventricular beats:
- Beats #1,3,4,6,8,11,13 and 15 are all purely sinus-conducted.
- PEARL #4: Assessment of ST-T wave morphology for the presence of acute ischemic changes is best done from assessment of normally conducted sinus beats.
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| Figure-5: Within each of the 4 dotted BLUE rectangles — are simultaneously recorded sinus beats from each of the 4 lead groups. |
To facilitate visualization of QRST morphology in each of the 4 lead groups — I have modified Figure-5 by shading out the other beats in Figure-6.
- Isn't it now much easier to appreciate marked acute ST elevation in the anterior leads? ( = beat #11 as it is seen in leads V1,V2,V3 in Figure-6)?
- Completing the pattern of Precordial Swirl that is diagnostic of acute proximal LAD occlusion (See ECG Blog #380 — for more on Precordial Swirl) — is ST depression in lateral chest leads V5,V6 (beat #13).
- Normal sinus-conducted beats #3 and #6 reveal large Q waves with slight ST elevation in inferior leads III and aVF — and ST depression in leads I,II,aVL. There is also some ST elevation in lead aVR.
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| Figure-6: To facilitate visualization of acute ST-T wave changes in each of the 12 leads for sinus-conducted beats — I've shaded out other beats on this tracing. |
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CASE Conclusion:
Unfortunately — I lack follow-up and the results of cardiac catheterization. Nevertheless, given the history of new CP — I feel confident in concluding the following from today's initial ECG that I have once again reproduced in Figure-7.
- The underlying rhythm in Figure-7 is sinus.
- The reason for the frequently changed QRS morphology in the long lead II rhythm strip is superimposed AIVR (Accelerated IdioVentricular Rhythm) at a rate of ~115/minute. As reviewed in ECG Blog #108 — in the setting of an acute evolving OMI, AIVR is often a "reperfusion" arrhythmia that is usually short-lived, and which usually does not require specific antiarrhythmic treatment. Instead, prompt cath with PCI is needed to prevent reocclusion of the "culprit" artery.
- The reason today's ECG is so challenging to interpret — is the frequent occurrence of fusion beats that results in constantly changing QRS morphology.
- Shading out these fusion beats (as was done in Figure-6) facilitates recognition of acute proximal LAD occlusion (Precordial "Swirl" pattern — with hyperacute anterior lead ST elevation and flattened ST depression in leads V5,V6 — as described in ECG Blog #380).
- The large inferior Q waves + ST depression in leads I,II,aVL,V5,V6 in association with ST elevation in lead aVR suggests that there may be multi-vessel disease (and/or prior inferior infarction) vs extensive LAD occlusion with "wraparound". But the message is clear ==> acute proximal LAD occlusion with immediate need for cardiac cath with PCI.
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| Figure-7: Today's ECG with "on time" P waves labeled. |
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Acknowledgment: My appreciation for the anonymous contribution of today's case.
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