A man in his 80s with chest pain and ventricular paced rhythm

 Written by Pendell Meyers, with edits by Smith

A man in his 80s presented with acute chest pain and normal vital signs. 

Here is his triage ECG at time = 0:

What do you think? (No prior ECG was available for comparison)

The ECG shows ventricular paced rhythm with findings very suspicious for posterior OMI, including inappropriately isoelectric ST segments in V2-V3 (we know by the principle of appropriate discordance that there should be appropriately discordant STE in these leads).

The last complex in V2 actually has a tiny amount of concordant depression, though not 1.0 mm. Thus, this meets one of the alternative versions of the modified Sgarbossa criteria that we studied, but not the primary definition on which  the publication focused. 

There is also excessively discordant STD in V4 (which is the transition lead in this case, but has a bigger component up than down).  The ST/R ratio in V4 is 2/5.5 = 36%.  In our derivation study in LBBB, a ratio > 30% was nearly 100% sensitive and 88% specific.  In the validation study, it remained 98% specific but was only 64% sensitive.  We did not assess it in the study on Ventricular Paced Rhythm, but there is no reason that it should not apply.

If you understand wide QRS complexes and appropriate discordance, you will understand that this ECG shows ischemic ST depression maximal in V1-V4, which is the best and simplest available feature we have studied for identifying posterior OMI. This ECG represents the equivalent finding but in ventricular paced rhythm, but without meeting the criteria of concordant STD in V1-V3.

It was read by the treating physician and the overreading cardiologist as "Paced, no STEMI."

As the patients pain was ongoing, and initial troponin positive and rising, he was diagnosed with "NSTEMI" and admitted with no plan for emergent cath.

How does the Queen of Hearts do?

Unfortunately, Version 1 does not recognize this one.  We also submitted it to Version 2, which is not yet available to the public, and version 2 also missed it.  We need more such ECGs for training but we are constantly working on the algorithm and one day it will make this diagnosis. 

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But isn't ongoing chest pain in NSTEMI a guideline indication for emergent angiography? 

Yes, but in normal practice, according to my experience and that of many others, this recommendation is very rarely obeyed. In fact, in the one study I'm aware of in which it has been studied, only 6.4% of very high risk NSTEMI patients underwent angiography in less than 2 hours in accordance with the 2014 ACC/AHA guidelines.

Lupu et al. Clinical Cardiology. 2022;1-11. Immediate and early percutaneous coronary intervention in very high risk and high risk non-ST segment elevation myocardial infarction patients.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/clc.23781

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12 hours after arrival, with ongoing pain and rising troponins, here is the next recorded ECG:

Similar findings, a bit more obvious STD in V4-V6, but still proportionally maximal in V3-V4.

As the troponin T was 1521 ng/L (peak troponin T over 1000 ng/L is typical of STEMI) and still rising, no further troponins were measured.

Finally, 60 hours after arrival, the angiogram showed an acute (at least 60 hours old) culprit occlusion of the proximal left circumflex artery, with PCI performed.

Here is the ECG several hours after PCI:  

Reconstitution of expected appropriate discordant STE in V2-V3, resolving STD in V4.

Final diagnosis: NSTEMI.

Unfortunately, no futher outcome is known (echo, survival, etc.)

The diagnosis should be OMI!  And this was a missed OMI.

Smith Modified Sgarbossa Criteria: 

1. Concordant STE of 1 mm in one or more leads

2. Left Bundle Branch Block (LBBB): concordant STD of 1 mm in V1-V3

2. Ventricular Paced Rhythm (VPR): concordant STD of 1 mm in V1-V6

3a.  Excessively proportionally discordant STE in any lead with at least 1 mm STE and an ST/S ratio of > 20-25%

or

3b. Any excessively discordant ST Depression with ST/R ratio > 30%

References:

Smith SW, Dodd KW, Henry TD, Dvorak DM, Pearce LA. Diagnosis of ST-elevation myocardial infarction in the presence of left bundle branch block with the ST-elevation to S-wave ratio in a modified Sgarbossa rule. Ann Emerg Med [Internet]. 2012;60:766–776. Available from: http://dx.doi.org/10.1016/j.annemergmed.2012.07.119

Meyers HP, Limkakeng AT Jr, Jaffa EJ, Patel A, Theiling BJ, Rezaie SR, Stewart T, Zhuang C, Pera VK, Smith SW. Validation of the modified Sgarbossa criteria for acute coronary occlusion in the setting of left bundle branch block: A retrospective case-control study. Am Heart J [Internet]. 2015;170:1255–1264. Available from: http://dx.doi.org/10.1016/j.ahj.2015.09.005

Dodd KW, Zvosec DL, Hart MA, Glass G 3rd, Bannister LE, Body RM, Boggust BA, Brady WJ, Chang AM, Cullen L, Gómez-Vicente R, Huis In ’t Veld MA, Karim RM, Meyers HP 3rd, Miranda DF, Mitchell GJ, Reynard C, Rice C, Salverda BJ, Stellpflug SJ, Tolia VM, Walsh BM, White JL, Smith SW, PERFECT study investigators (the complete list of PERFECT study investigators is provided in Appendix E1, available at http://www.annemergmed.com). Electrocardiographic Diagnosis of Acute Coronary Occlusion Myocardial Infarction in Ventricular Paced Rhythm Using the Modified Sgarbossa Criteria. Ann Emerg Med [Internet]. 2021;Available from: http://dx.doi.org/10.1016/j.annemergmed.2021.03.036

Other references:

Lindow T, Mokhtari A, Nyström A, Koul S, Smith SW, Ekelund U. Comparison of diagnostic accuracy of current left bundle branch block and ventricular pacing ECG criteria for detection of occlusion myocardial infarction. Int J Cardiol [Internet]. 2023;131569. Available from: http://dx.doi.org/10.1016/j.ijcard.2023.131569

Khawaja M, Thakker J, Kherallah R, Ye Y, Smith SW, Birnbaum Y. Diagnosis of Occlusion Myocardial Infarction in Patients with Left Bundle Branch Block and Paced Rhythms. Curr Cardiol Rep [Internet]. 2021;23:187. Available from: http://dx.doi.org/10.1007/s11886-021-01613-0

Do not use the Barcelona Rule:

Barcelona Rule on Left Bundle Branch Block: Lots of Issues.

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MY Comment, by KEN GRAUER, MD (7/19/2024):

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Interpretation of a paced ECG in a patient with new CP (Chest Pain) has always been challenging. That said — as we have shown in multiple posts on Dr. Smith’s ECG Blog (See My Comments in the October 5, 2020 and the October 3, 2018 posts) — there will often be clues to OMI on a paced ECG — IF you know how to look for them.

• For clarity in Figure-1 — I’ve labeled the initial ECG in today’s case. In addition to strong suspicion of acute OMI on this tracing (as per discussion above by Dr. Meyers) — I draw attention to a number of additional aspects of interpreting a paced 12-lead tracing in a patient with CP, with special focus on the challenges of today's case.
• Because of the complexity of pacemaker troubleshooting — I was happy to find the wonderful on-line “primer” (with color-coded illustrations) by Dr. Harry Mond — that outlines a user-friendly approach to — “Where Am I Pacing From?” — as can be determined based on the appearance of the 12-lead ECG (See CardioScan — May 5, 2021).

Application to Today’s Initial ECG:

I thought today's initial ECG was far from simple. Applying concepts from Dr. Mond's approach — My thought process was the following: 

• Even though there is no long lead rhythm strip in Figure-1 — we can determine that the rhythm is ventricular paced. This is because the small RED circles highlight ventricular pacing spikes that are seen just before the QRS in multiple leads.
• NOTE #1: As is often the case — pacer spikes are not seen in every lead (No pacer spike is seen before the QRS in lead aVL or lead V1). Factors such as pacemaker placement in the ventricle, as well as filter settings are among reasons why pacemakers spikes are not always seen in all leads (See My Comment at the bottom of the page in the January 13, 2024 post in Dr. Smith's ECG Blog).
• The situation is more complex in simultaneously-recorded leads I,II,III — in that there is significant baseline artifact (occurring over the dotted BLUE lines in leads II and III in Figure-1). As a result — I at first thought there was atrial pacing! It was only after finding myself unable to make out any consistency in these erratic baseline undulations — that I realized there was no atrial pacing.

KEY Point: It is at times challenging trying to answer the seemingly simple question of whether the ECG in front of us is (or is not) from a patient with a pacemaker!

• If I did not have access to the chest leads — I would not have thought today's patient had a pacemaker from the appearance of the limb leads alone.
• It is only because I know from the chest leads that the small RED circles in Figure-1 are ventricular pacing spikes — that I can deduce that the small WHITE circles highlight ventricular pacing spikes in leads I,II,III.
• Note that the QRS complex in lead II looks deceptively narrow! As shown by the vertical dotted RED line (which is timed to the onset of the QRS in simultaneously-recorded leads I and III) — the initial part of the QRS complex in lead II lies on the baseline. This highlights the importance of using more than a single lead for various ECG determinations such as QRS "width" that may be off if only a single lead is used.

NOTE #2: I always like to look for the presence of an underlying rhythm in pacemaker tracings. Did YOU Notice that the underlying rhythm in Figure-1 appears to be atrial tachycardia? (regularly occurring BLUE arrows in lead V1 at a rate of ~190/minute). At the least, there appears to be high-grade AV block — which may be the reason the pacemaker was inserted.

• It is of interest that underlying atrial activity is only seen in lead V1. That said — I believe this is "real" atrial activity, because of how precise the P-P interval is for the limited number of beats that we see in lead V1. 

Figure-1: For ease of comparison — I’ve put today's initial ECG on top of my labeled version of this tracing.

From Where in the Ventricles is the Rhythm Paced? 

As per Dr. Mond's primer — the bundle branch block configuration tells us which ventricle is paced first.

• IF there is a LBBB configuration (determined by predominant negativity in lead V1) — then the RV is being paced first.
• In contrast, if there is a RBBB configuration (determined by a positive QRS in lead V1) — then the LV is being paced first. The most common reason for pacing the LV first is biventricular pacing (which typically manifests a rightward frontal axis).
• 
  
• Terminology: The reason the term, "configuration" is used (and not bundle branch block) — is that despite the ECG appearance, when there is ventricular pacing — depolarization is not via the conduction system.

In the past — the traditional site for RV pacing had been from the RV apex. For physiologic reasons, recent years have seen a tendency to favor RV pacing from a higher site in the right ventricle. 

• KEY Point: With RV pacing — Whether or not lateral chest leads do or do not have R waves indicates where the pacing catheter is positioned within the right ventricular chamber.
• With pacing from the RV apex — there will be a LBBB configuration (ie, with a negative QRS in lead V1) — in which the QRS remains negative through to lead V6.
• With pacing from the RVOT (Right Ventricular Outflow Track) — there will be a LBBB configuration with a more typical LBBB pattern in the chest leads (ie, negative QRS in anterior leads — but with a positive QRS in lateral chest leads beginning by lead V4 or V5 — and staying positive in V6). The frontal plane axis is rightward.
• With pacing from the mid-RV — there will be a LBBB configuration, with a more typical LBBB pattern in the chest leads. The frontal plane axis tends to be normal or leftward (depending on how high the pacing lead is).

With Regard to Today's CASE: 

QRS morphology of the ventricular-paced beats in Figure-1 manifests a conduction pattern very similar to that of LBBB conduction (ie, negative QRS in anterior chest leads — positive QRS in lateral chest leads). The frontal plane axis is leftward (all upright in lead I — negative in lead aVF). 

• This QRS morphology described for the ECG in Figure-1 is consistent with RV pacing from the mid-RV wall. The importance of recognizing this pattern — is that it helps us appreciate an ST-T wave appearance that may or may not be appropriate considering QRS morphology of paced beats.
• I favor a qualitative approach for ST-T wave assessment of paced beats. In a patient with QRS widening from pacing and new CP — I become suspicious of an acute cardiac event when ST-T wave changes look like they should not be there.
• The most abnormal lead in Figure-1 is lead V4 (within the RED rectangle). Given the relatively small size of the R wave in lead V4 — there is no way the amount of J-point ST depression and the downsloping ST segment shape in this lead are normal.
• In the context of the ST-T wave in lead V4 being definitely abnormal — the ST coving and amount of J-point ST depression in lead V5 are disproportionate (within the BLUE rectangle). Similarly — the ST coving in lead V6 appears to be a continuation of the abnormalities seen in neighboring leads V4,V5.
• Finally — the slender, symmetric T wave peaking with narrow base in leads V2 and V3 (within the BLUE rectangles) — are definitely not normal. Assuming serum K+ is normal — in a patient with new CP, these peaked T waves in leads V2,V3 may represent posterior reperfusion. 
• 
  
• BOTTOM Line: In this older man with new CP and a paced ECG — the 5 abnormal leads (within the colored rectangles in Figure-1) have to be assumed to indicate acute OMI until proven otherwise.