Saturday, April 17, 2021

Blog #215 (ECG-MP-32) — At Least 4 Notable Findings


The ECG shown in Figure-1 was obtained from a 60-ish year old man who presented with new-onset chest pain.

  • HOW would you interpret this ECG?
  • HINT: There are at least 4 remarkable findings that should be noted ...

 

Figure-1: ECG obtained from a 60-ish year old man with new-onset chest pain (See text).


 

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NOTE #2: Some readers may prefer at this point to listen to the 7:30 minute ECG Audio PEARL before reading My Thoughts regarding the ECG in Figure-1. Feel free at any time to review to My Thoughts on this tracing (that appear below ECG MP-29).

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Today’s ECG Media PEARL #32 (7:30 minutes Audio) — reviews the Cabrera ECG Format — and doing ECGs at a recording speed of 50 mm/second.

 

 

The First 2 Findings that should be Noted:

Depending on where you live and work — the ECG in Figure-1 may have appeared unusual. The first 2 findings that should be noted relate to technical aspects of the ECG format used.

  • The recording speed for each of the leads in the 12-lead tracing was 50 mm/second — or twice as fast as the standard (25 mm/second) recording speed used in the United States, and throughout much of the world. Germany, Sweden, and some other countries favor the faster 50 mm/second speed. 
  • DID YOU NOTICE the notation of “50 mm/sec” that appeared in the upper left of the 12-lead tracing in Figure-1(enclosed within the RED rectangle in Figure-2).
  • The other technical finding that should be noted in Figure-1 — is the difference in limb lead sequencing (compared to the standard lead sequencing format used in the United States, and throughout much of the world). The ECG in Figure-1 was recorded in Germany — and it was recorded using the Cabrera Lead Format (Figure-2).

 

Figure-2: I’ve labeled the technical findings from Figure-1 that should be noted. These are: i) A recording speed of 50 mm/second for leads in the 12-lead tracing (within the RED rectangle in the upper left corner); and, ii) The Cabrera Format for limb lead sequencing (See text).


 



Editorial NOTE:

As an American-trained physician who practiced exclusively in the United States — I had not been exposed to ECG formats other than the standard format used in the United States. This changed for me in 2010 — at which time I began active participation in multiple ECG internet forums, many with a huge international audience. 

  • Even for those clinicians not participating in internet ECG forums — the internet has changed the world. Because of international travel — the chances are that all clinicians at one time or another will encounter in medical records or elsewhere, different ECG formats from countries other than their own.
  • Two of these differences are seen in today’s case: i) Use of the Cabrera Format for limb lead sequencing; andii) Use of a 50 mm/second recording speed.

 

 

The Cabrera Format:

Figure-2 highlights the difference in limb lead sequencing with the Cabrera Format:

  • Instead of beginning the limb lead display with standard lead I — the Cabrera format begins with the highest lateral lead ( = lead aVLcorresponding to an electrical viewpoint perspective obtained from -30 degrees).
  • The right augmented lead is displayed using reversed polarity ( = -aVRcorresponding to an electrical viewpoint perspective obtained from +30 degrees).
  • As suggested by the Axis Insert in Figure-2 — the Cabrera Format offers a more logical display of limb lead sequencing, in that there is a gradual progression of equally spaced (at increments of 30 degrees) limb leads, beginning with lead aVL (at -30 degrees) — and continuing until the most rightward frontal plane lead = lead III (at +120 degrees).
  • In contrast, the standard U.S. format is not sequential — it views the right augmented lead from the remote perspective of the right shoulder — and it uses unequal spacing between neighboring leads.
  • NOTE: The chest leads are unchanged with the Cabrera format.

 

 

Potential Advantages of the Cabrera Format:

The more logical limb lead sequencing used in the Cabrera Format offers a number of potential advantages:

  • It simplifies calculation of the frontal plane axis. One can tell at a glance which of the 6 limb leads manifests the greatest net QRS deflection.
  • The addition of lead -aVR provides a transition lead between lateral and inferior frontal plane location. Having 6 equally spaced frontal plane viewpoints facilitates appreciation of the location and relative amounts of ST segment elevation and reciprocal ST depression in the 6 limb leads, making it easier to assess acute ischemia and/or infarction in these infero-lateral leads.
  • Availability of 6 equally-spaced, sequential limb leads renders comparison of serial tracings easier and more accurate.

 

 

Correcting for the 5mm/second Recording Speed:

The format used in recording the ECG shown in Figure-2 provides a single complex in each of the 12 leads(recorded at 5mm/second) — and a long lead II rhythm strip at the bottom of the tracing (recorded at 25 mm/second).

  • Confession — My brain is “programmed” to interpreting 12-lead ECGs and rhythm strips at the 25 mm/second speed that is standard in the United States. After 4+ decades of interpreting tens of thousands of tracings — there is an instant (automatic) process of “pattern recognition” that I find takes place in my brain, even before I begin systematic interpretation of any given tracing. This process is invalidated by the unfamiliar appearance of wider-than-expected complexes that are produced when a 50 mm/second recording speed is used.


PEARL #1: For readers like me who find themselves “visually challenged” by the sight of an ECG recorded at 50 mm/second speed — I will offer the quick and easy way I’ve developed for “visually correcting” the wider appearance produced by a doubling of recording speed to 50 mm/second.

  • To compensate for a 50 mm/second recording speed — I upload the ECG to Power Point and perform these 2 Steps: i) Reduce the width of the ECG by 50% (ie, from 10 inches to 5 inches); andii) Make SURE that I uncheck the “Keep Proportions” ( = “Lock aspect ratio” box) in the Format Pane under Size options in Power Point before reducing the tracing’s width. Carrying out these 2 Steps narrows the width of the ECG by 50% without affecting the height. 
  • NOTE: When you perform these 2 Steps — each R-R interval on ECG paper will contain twice as many little boxes (which must be considered when assessing rates and interval duration) — but QRS complexes and ST-T waves will now "look normal" to my eye.

 

 

Figure-3 shows the result of applying the procedure I describe in Pearl #1 — with end result of reducing the width of QRST complexes by 50% (but not affecting the height of QRST complexes) for the 12-lead ECG shown in Figure-2.

  • For clarity — I have added an insert of Cabrera limb lead sequencing to the upper left part of Figure-3.
  • Visually — QRST complexes in Figure-3 now “look normal” to my eye (although you’ll note the reduced width of little boxes, compared to the wider small boxes in the long lead II rhythm strip that was recorded at 25 mm/second).

 

Figure-3: Application of the procedure described in Pearl #1 results in a 50% reduction in QRST complex width — with end result that QRST complexes in the 12-lead ECG now “look normal” to my eye (See text).


 

 

Interpreting the 12-Lead ECG in Figure-3:

I now found it much easier to interpret the ECG in today’s case. Assessment of QRST complexes in the 12-lead tracing shown in Figure-3 suggests acute RCA (Right Coronary Artery) Occlusion. I noted the following findings:

  • There is marked ST segment elevation with hyperacute T waves in each of the inferior leads.
  • Inferior lead Q waves are seen. Although small in size — given dramatic ST-T wave changes in each of these leads with Q waves — it is likely that these Q waves reflect ongoing infarction.
  • There is terminal QRS distortion (T-QRS-D) in each of the leads that manifest acute ST-T wave changes. By this, I mean that none of the 4 inferior leads with ST elevation have either J-point notching or an S wave. Although usually reported as a finding supportive of acute infarction when seen in anterior leads — the impressive T-QRS-D seen in Figure-3 is clearly an additional manifestation of ongoing acute RCA occlusion.
  • High lateral leads I and aVL show marked reciprocal ST depression.
  • PEARL #2: Note how nicely the Cabrera limb lead sequencing seen in Figure-3 displays gradual progression of ST elevation that begins with transitional lead -aVR (at +30 degrees) — and then maximizes in leads IIaVF and III. As expected from the Cabrera limb lead insert in this Figure — maximal ST elevation in leads II, aVF and III is countered by maximal reciprocal ST depression in lead aVL (much more so than the modest ST depression seen in lead I)Cabrera sequencing localizes the vector of maximal ST elevation “rightward” (ie, to about +90 degrees) — which supports our suspicion of the RCA (rather than the Left Circumflex) as the “culprit” artery.
  • In addition to acute inferior infarction — maximal ST depression in leads V2V3 and V4 strongly suggests associated acute posterior MI. Presumption of posterior MI is supported by the finding of taller-than-expected anterior R waves (with a dominant R wave already seen by lead V3).
  • NOTE: ST depression extends across the entire precordium. How much of this ST depression that extends to leads V5 and V6 is a result of extensive posterior MI — vs lateral ischemia — vs LV “strain” is uncertain from this single tracing (NOTEAlthough subtle due to overlap of QRS complexes — R wave amplitude in lead V5 is very large, therefore consistent with LVH).
  • In Addition — there is terminal T wave positivity in leads V2-thru-V5. This is one more finding consistent with acute ongoing/evolving infarction.
  • Finally — there are small and narrow q waves in leads V5 and V6. These are of uncertain significance.

 

 

Interpreting the Long Lead II Rhythm Strip:

For facility of discussion — I intentionally deferred assessment of the rhythm in today’s case until last (Figure-4).

  • Unfortunately — the tracing in today’s case is curved, and therefore somewhat distorted. That said — accurate interpretation of the rhythm in Figure-4 is clearly possible.
  • Note that the recording speed for the long lead II rhythm strip is 25 mm/second — so no adjustment in tracing width was made.
  • The QRS complex is narrow — therefore the rhythm originates within the conduction system.
  • Although curvature of the long lead II rhythm strip makes precise measurement and comparison of intervals problematic — I believe the ventricular rhythm is regular (or at least, almost regular) — with an R-R interval of ~6 large boxes, corresponding to a ventricular rate of ~50/minute.
  • RED arrows in the long lead II rhythm strip highlight sinus P waves that we know are present.
  • I strongly suspect additional P waves are present under the YELLOW arrows because: i) Given how regular the RED arrows seem to be — we would logically expect P waves to also be present under the YELLOW arrows (ie, there would have to be a highly unusual form of SA block if you didn’t postulate regular sinus P waves continuing throughout the tracing); andii) I believe there is a slight deformity under each of the YELLOW arrows, corresponding to partially hidden P waves.
  • Note that none of the PR intervals repeat in this 9-beat rhythm strip. This suggests there is complete AV dissociation. But despite the slow ventricular rate (ie, of ~50/minute) — and despite P waves having more than adequate opportunity to conduct, yet failing to do so (ie, P waves occur at virtually all points in the cardiac cycle) — there is no indication that any of the P waves conduct. Therefore — there is complete AV block.

 

Figure-4: I’ve labeled P waves in today’s case with colored arrows (See text).


 


 

Putting It All Together:

In summary — the notable findings for the ECG in today’s case include the following:

  • Use of the Cabrera Format.
  • A recording speed of 50 mm/second for the 12-lead ECG.
  • Strong suggestion of acute RCA occlusion in this 60-ish year old man with new-onset chest pain — with an ongoing, acute infero-postero STEMI.
  • Complete AV Block — with an AV nodal escape rhythm at ~50/minute.
  • LVH and strain and/or ischemia.

 

 

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Acknowledgment: My appreciation to Tim Hellmann (from Wörth am Rhein, Germany) for the case and this tracing.

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REFERENCES: 

  • ECG Blog #114 — Reviews another case using the Cabrera format (from Romania) — and explores a bit more potential advantages of this more logical anatomical sequencing.
  • The September 26, 2018 post in Dr. Smith’s ECG Blog (Please scroll down to the BOTTOM of the page for My Comment regarding this interesting ECG submitted from Sweden).
  • The October 26, 2020 post by Dr. Pendell Meyers, in Dr. Smith’s ECG Blog (Please scroll down to the BOTTOM of the page for My Comment regarding this fascinating ECG case of dynamic shark fin” morphology, submitted from Norway).
  • The November 14, 2019 post in Dr. Smith’s ECG Blog (Please scroll down to the BOTTOM of the page for My Comment and illustration of the phenomenon of T-QRS-D = Terminal QRS Distortion).






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