ECG #413 — A Pre-Op ECG in an ASx Patient

I was sent the tracing shown in Figure-1 — told only that this was a preoperative ECG obtained from an asymptomatic older woman scheduled for non-cardiac surgery.

• How would YOU interpret this ECG?
• Would you approve her for surgery if the procedure was nonemergent?  

Figure-1: Preoperative ECG from an asymptomatic older woman scheduled for non-cardiac surgery. Would you approve her for a nonemergent surgical procedure? (To improve visualization — I've digitized the original ECG using PMcardio).

MY Initial Thoughts on Today’s CASE:

This patient should not be approved for non-emergent surgery.

• Looking first at the long-lead II rhythm strip — there is significant bradycardia, with a heart Rate just under 40/minute. The QRS complex is narrow in all 12 leads — so the rhythm is supraventricular. 
• The overall ventricular response looks Regular.
• P waves are present — but they seem to be unRelated to neighboring QRS complexes (ie, The PR interval varies — at the least, for some of the beats).
• 
  
• BOTTOM Line: Since many of the P waves in this long lead II rhythm strip occur at points within the R-R interval where they appear to have more than ample opportunity to conduct — yet still fail to do so — some form of 2nd-degree (if not, 3rd-degree) AV block is present, in association with marked bradycardia.

Comment:

• PEARL #1: I arrived at the above initial thoughts on today’s rhythm within seconds of seeing the long lead II rhythm strip. Stressing this aspect of how time-efficiency in rhythm diagnosis may facilitate rapid clinical decision-making — is one of my primary objectives in writing this ECG Blog (ie, the surgeon in today’s case may be waiting on your interpretation of this “routine” pre-op ECG before proceding). 
• PEARL #2: The KEY for optimal time-efficiency — is to use a systematic approach that addresses the 5 parameters, which are easily recalled by the phrase, “Watch your Ps, Qs and the 3Rs” (See ECG Blog #185 for review of this system). Applying the Ps,Qs,3Rs tells us within seconds that this 70-year old woman should not be approved for non-emergent surgery.

What About the 12-Lead ECG?

While our brief assessment of the rhythm in today's case is enough to merit canceling this patient's non-emergent surgery — there is more!

• The 12-lead ECG is very concerning. Although we only see 1 or 2 beats in each lead (because the heart rate is so slow) — there is ST segment straightening with slight depression, that appears to be maximal in lead V3 (especially noteworthy since normally there is slight ST elevation in this lead!). ST segment straightening is also seen in leads I,aVL; and in leads V4,V5,V6 (with a hint of ST depression in leads V5,V6). Finally — the T waves in leads V4,V5,V6 are "fatter"-at-their-peak than they should be (beyond what might be expected from superposition of P waves on these T waves). KEY Point: Although the above ST-T wave changes are admittedly subtle — the fact that they are undeniably present in so many leads (and most marked in lead V3) is real!
• 
  
• PEARL #3: 2nd- and 3rd-degree AV blocks are a common complication of inferior and/or posterior OMI. As a result — the finding of ST segment flattening in multiple leads, but being most marked in lead V3 — in a patient with bradycardia and some significant form of AV block — suggests a strong possibility of recent posterior OMI (See ECG Blog #351).
• 
  
• PEARL #4: The fact that today's elderly patient was asymptomatic does not rule out the possibility of having had an acute (or recent) MI. As discussed in ECG Blog #228 — the incidence of "Silent" MI may be as high as between 20-40% of all MIs, being especially common in older individuals.

MY Impression of Today's CASE: Despite no symptoms — I strongly suspect from the initial ECG, that this older woman had a recent LCx (Left Circumflex) occlusion with posterior MI — that resulted in bradycardia with 2nd- or 3rd-degree AV block. Given the lack of symptoms — this was a “silent" MI. The patient may need a pacemaker.

• CASE Follow-Up: Providers in today's case recognized the above abnormalities — and promptly referred the patient to a PCI center for cardiac catheterization and potential pacemaker insertion.

==========================

Looking Closer at Today's Rhythm:

The rhythm in Figure-1 has a number of complexities. As a result — I needed additional time before deciding on the precise rhythm diagnosis. I walk through my thought process below. But the point to emphasize — is that it should only take seconds to recognize that there is bradycardia from significant AV block.

======================

My Approach to Rhythm Determination:

• PEARL #5: The simple step of labeling P waves is tremendously helpful in facilitating rhythm diagnosis. I have done this with RED arrows in Figure-2.
• Prior to labeling the P waves — Did YOU Notice how much variation there is in P wave morphology?
• 
  
• Is the atrial rhythm in Figure-2 regular? If not — How does this realization complicate today's rhythm diagnosis?

Figure-2: I've labeled P waves with RED arrows.

PEARL #6: In Figure-2 — Isn't there a lot of variation in P wave morphology? This raises the question as to whether each of the RED arrow P waves is a sinus P wave? — OR — Is the underlying rhythm sinus with atrial bigeminy (ie, every-other-P-wave being a PAC?).

• NOTE: A certain amount of variation in P wave morphology is common in sinus rhythms — be this from patient (or electrode lead) movement — from artifact — or — from more complex factors that may include variation in the exit site of atrial depolarization from the SA node — variation in the impulse path through the atria and/or in the degree of intra-atrial conduction block (Qin et al: Circulation 139:1225-1227, 2019 — Pezzuto et al: EP Europace 20, 2018 — Platonov: Ann Noninvasive Electrocardiol 17(3):161-169, 2012).
• While acknowledging that a certain amount of variation in P wave morphology is often seen with sinus rhythms — there usually is not as much variation as is seen in Figure-2 (ie, from the fairly tall and pointed P wave before beat #5 — compared to the tiny, flat P wave in front of beat #6).
• 
  
• BOTTOM Line: The above said — I strongly suspect that despite marked variability in P wave morphology in today's tarcing — that all of the RED arrow P waves in Figure-2 are sinus P waves! I say this because of the PR and R-R intervals that I will measure momentarily in Figure-3 (ie, The PR interval continually varies — whereas it should be constant if the rhythm was sinus with atrial bigeminy).

PEARL #7: As is evident for many of the examples of AV block that have appeared in this ECG Blog — it is common to see a "ventriculophasic" sinus arrhythmia in association with 2nd or 3rd degree AV block. Much of the time (as is the case in Figure-2) — the shorter P-P interval is the one that “sandwiches” a QRS complex (the theory being that perfusion improves following ventricular contraction — with resultant shortening by a slight amount of the P-P interval that contains a QRS).

=============================

Measuring Intervals:

I needed calipers to "solve" today's rhythm.

• PEARL #8: My favorite PEARL for distinguishing 2nd-degree from 3rd-degree AV block is knowing that in the presence of an underlying sinus rhythm — a QRS complex that occurs earlier-than-expected is probably conducted (therefore the rhythm is unlikely to be complete AV block!).
• In contrast — the escape rhythm with complete AV block will usually be regular (or at least, almost regular). This is why careful measurement of both PR and R-R intervals is essential for solving today's rhythm (See Figure-3).

Figure-3: I have carefully measured PR and R-R intervals.

Applying the Measurements in Figure-3:

• Note in Figure-3 that the ventricular rhythm is completely regular! (ie, all R-R intervals = 1680 msec.).
• Note also that despite "looking" similar — there is slight-but-definite variation in the PR interval from one beat to the next. This rules out the possibility of sinus rhythm with atrial bigeminy — because the PR interval varies from beat-to-beat (whereas it should be constant if the rhythm was sinus).
• As per PEARL #8 — None of the 6 beats in Figure-3 occur earlier-than-expected. This strongly suggests that none of the RED arrow P waves are being conducted — and that the rhythm probably is complete ( = 3rd-degree) AV block.
• As noted in PEARL #6 — despite marked variation in P wave morphology, I suspect that all RED arrow P waves are sinus impulses. In view of the likelihood of complete AV block — it would seem highly unlikely for the same pattern of P wave rhythmicity (ie, shorter-than-longer P-P intervals) — to be seen if the multiple variations in P wave shape were all originating from different atrial foci.
• 
  
• Advanced Point (Beyond-the-Core): Technically, the rhythm strip in today's tracing is too short to prove that the rhythm is complete AV block. This is because we do not see P waves occurring at all points within the R-R interval (ie, There are no P waves occurring near the middle of the R-R interval). That said, this does not matter clinically — because regardless of the degree of AV block, prompt referral to a PCI center is indicated given likely recent posterior OMI with marked bradycardia and at least 2nd-degree AV block.

LADDERGRAM:

I conclude my comments with a laddergram for the rhythm in today's case. At the least — there is no conduction of any of the RED arrow P waves because: i) The ventricular rhythm is regular (here, at a rate just under 40/minute); — and, ii) The PR interval continually varies.

• The QRS complex is narrow. This defines the escape rhythm focus as either arising in the AV node or from the Bundle of His (with the rate of less than 40/minute being a bit slow for an AV nodal escape rhythm).

Figure-4: My laddergram for today's case.

Take-Home POINTS:

• Today's case conveys a number of advanced concepts. My goal is to challenge experienced interpreters through discussion of these advanced concepts. As always — Your comments are welcome! 
• Recognition of the subtle ECG findings I point out regarding the 12-lead tracing in today's case are important details to be aware of! To Emphasize: As soon as I recognize significant bradycardia with some form of AV block — I actively look for recent evidence of acute OMI. By appreciating the need to look for subtle signs of recent inferior and/or posterior OMI — you greatly increase the chance that you will find it!
• 
  
• The above said — Today's case conveys important information for any level interpreter. Less experienced providers will hopefully appreciate how application of the Ps,Qs,3R approach allows you within seconds to recognize the essentials of today's rhythm enough to tell us to cancel non-emergent surgery, and to promptly refer this patient to a catheterization-capable center.

==============================

Acknowledgment: My appreciation to Mohamed Salah (from Muscat, Oman) for the case and this tracing.

==================================

 

 Related ECG Blog Posts to Today’s Case:

• ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
• ECG Blog #185 — Review of the Ps, Qs, 3R Approach for systematic rhythm interpretation.
• ECG Blog #188 — Reviews how to read and draw Laddergrams (with LINKS to more than 100 laddergram cases — many with step-by-step sequential illustration).

• ECG Blog #351 — reviews the diagnosis of acute posterior OMI. To see this illustrative case presented as an ECG Video — Please check out ECG Blog #406 (For a LINKED Contents to this ECG Video — Click on MORE in the Description under the video on YouTube).
• 
  
• ECG Blog #405 — ECG Video presentation that reviews the distinction between AV Dissociation vs Complete (3rd-degree) AV Block (For a LINKED Contents to this ECG Video — Click on MORE in the Description under the video on YouTube).
•  
• ECG Blog #164 — Which reviews step-by-step the diagnosis of a Mobitz I 2nd-degree AV block (with sequential laddergram illustration).
• 
  
• ECG Blog #258 — How to "Date" an Infarction based on the initial ECG.
• ECG Blog #294 — Reviews how to tell IF the "culprit" artery has reperfused.
• ECG Blog #230 — Reviews how to compare Serial ECGs.
• ECG Blog #115 — Shows how dramatic ST-T changes can occur in as short as an 8-minute period.
• ECG Blog #268 — Shows an example of reperfusion T waves.

• Diagnosis of an OMI from the initial ECG — Serial tracings with spontaneous reperfusion — then reocclusion! — See My Comment at the bottom of the page in the October 14, 2020 post on Dr. Smith's ECG Blog.
• Acute OMI that wasn’t accepted by the Attending — See My Comment at the bottom of the page in the November 21, 2020 post on Dr. Smith’s ECG Blog.
• Another overlooked OMI (Cardiologist limited by STEMI Definition — OMI evident by Mirror Test) — See My Comment at the bottom of the page in the September 21, 2020 post on Dr. Smith’s ECG Blog.
• Recognizing hyperacute T waves — patterns of leads — an OMI (though not a STEMI) — See My Comment at the bottom of the page in the November 8, 2020 post on Dr. Smith's ECG Blog.

ADDENDUM (1/20/2024): 

• Included below is a series of additional material relevant to today's case. 

 

Free PDF Downloads from relevant Sections in my ECG-2014-ePub:

• PDF File: Overview on the Cardiac Circulation and the “Culprit” Artery in Acute MI —
• PDF File: Posterior MI and the “Mirror Test” —

 

Figure-5: ECG findings to look for when your patient with new-onset cardiac symptoms does not manifest STEMI-criteria ST elevation on ECG. For more on this subject — SEE the September 3, 2020 post in Dr. Smith’s ECG Blog with 20-minute video talk by Dr. Meyers on The OMI Manifesto. For my clarifying Figure illustrating T-QRS-D (2nd bullet) — See My Comment at the bottom of the page in Dr. Smith’s November 14, 2019 post.

 

Figure-6: KEY points in the recognition of isolated posterior MI (This figure is taken from ECG Blog #193 — in which I review the "Basics" for predicting the "culprit" artery). 

—  — 

ECG Media PEARL #60 (8:30 minutes Audio) — Reviews use of the "Mirror Test" to facilitate recognition of: i) Acute Posterior MI; ii) Acute High-Lateral or Inferior MI (ie, the "magical" reciprocal relationship between leads III and aVL); and, iii) Anterior ST elevation due to LVH (that is not indicative of anterior MI).

 

—  —

ECG Media PEARL #10 (10 minutes Audio) — reviews the concept of why the term “OMI” ( = Occlusion-based MI) should replace the more familiar term STEMI — and — reviews the basics on how to predict the "culprit" artery.

—  —

ECG Media PEARL #11 (6 minutes Audio) — Reviews how to tell IF the “culprit” (ie, acutely occluded) artery has reperfused, using clinical and ECG criteria.

==================================

Additional Material on Today's CASE:

—  —

ECG Media PEARL #4 (4:30 minutes Audio): — takes a brief look at the AV Blocks — and focuses on WHEN to suspect Mobitz I.

ECG Media Pearl #8 (8:20 minutes Video) — ECG Blog #191 — Distinguishing between AV Dissociation vs Complete AV Block (2/6/2021).

ECG Media Pearl #9 (5:40 minutes Video) — ECG Blog #192 — Reviews the 3 Causes of AV Dissociation (2/9/2021).

• Section 2F (6 pages = the "short" Answer) from my ECG-2014 Pocket Brain book provides quick written review of the AV Blocks (This is a free download).
• Section 20 (54 pages = the "long" Answer) from my ACLS-2013-Arrhythmias Expanded Version provides detailed discussion of WHAT the AV Blocks are — and what they are not! (This is a free download).