ECG Blog #438 — A Paramedic Diagnosis ...

The ECG in Figure-1 was obtained from a previously healthy middle-aged woman — who was awakened by new-onset CP (Chest Pain) that began ~3 hours before this ECG was obtained. She was stable hemodynamically — but still with CP at the time ECG #1 was recorded.

• The patient reports 3 shorter episodes of CP the day before.

QUESTIONS:

• Given this history — How would YOU interpret this ECG?
• Should the cath lab be activated?

Figure-1: The initial ECG in today's case (See text).

MY Thoughts on Today’s ECG:

In view of the above history — the initial ECG in today's case is clearly of concern. The rhythm is sinus at 70-75/minute — with normal intervals (PR,QRS, QTc) — normal axis — and no chamber enlargement.

• My "eye" was immediately attracted to leads V2 and V3 (within the RED rectangle in Figure-2). There is early transition in these chest leads (with surprisingly tall R waves in leads V1,V2 — and the R becoming taller than the S wave is deep by lead V3).
• The ST segment in leads V2 and V3 is inappropriately straightened (as often emphasized in this ECG Blog — there should normally be slight, gently upsloping ST elevation in these leads).
• Continuing wth neighboring leads V4, V5 and V6 — the T waves in these leads look hyperacute (BLUE arrows) — in that their ST segment takeoff is straightened, with these T waves being larger-than-expected in size with a widened base.
• PEARL #1: By itself — the appearance of the T wave in lead V4 does not necessarily look abnormal. However, in the context of the clearly abnormal ST-T wave findings in leads V2,V3 — and the more acute-looking appearance of the T waves in leads V5 and V6 — I interpreted the T wave in lead V4 as representing the beginning of this hyperacute change.

MY Impression of ECG #1: Given the history of new-onset CP in this middle-aged woman — this initial prehospital ECG in Figure-2 suggests posterior OMI beginning and/or ongoing over the past day that this patient has had symptoms.

• Given her new episode of CP that awakened her from sleep just 3 hours earlier (and which is still ongoing) — the cath lab should be activated! 
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• PEARL #2: Admittedly — the ECG findings in this initial ECG are subtle. But abnormalities are present in each of the chest leads in this patient with new CP. In this clinical context — this ECG is diagnostic of acute posterior OMI. 
• It should be appreciated that the reason for the lack of clear ST depression in leads V2,V3 — and the lack of ST elevation in leads V4,V5,V6 — may be the ongoing clinical course in this patient, that includes multiple CP episodes over the past day (ie, There could be spontaneous opening and reclosing of the "culprit" vessel over this period of time). It may be that the ECG in Figure-2 represents some pseudo-normalization of what might have be more prominent ST-T wave changes on an earlier ECG.
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• PEARL #3: In addition to posterior involvement — the hyperacute T waves in the lateral chest leads suggest there is acute postero-lateral OMI, which in the absence of obvious inferior lead changes — points to the LCx (Left Circumflex) as the most likely "culprit" artery.
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• PEARL #4: The unexpectedly tall R waves in leads V1,V2 lend support to concern that there may be completed posterior infarction (See ECG Blog #354) — as the mirror-image reflection of deepening Q waves is increasing amplitude of the R wave in anterior leads. Unexpectedly tall anterior R waves is especially likely to signal completed posterior infarction IF this finding is new compared to prior ECGs.

Figure-2: I've labeled KEY findings in the initial ECG.

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The CASE Continues:

Serial ECGs were obtained by the prehospital team. Figure-3 offers a comparison between one of these repeat ECGs — and the original prehospital ECG (with ~30 minutes separating the time between the recording of these 2 tracings).

• WHAT do you learn from the repeat ECG in Figure-3?

Figure-3: Comparison of the initial ECG — with the repeat ECG done in the field ~30 minutes after the initial ECG.

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What We Learn from the Repeat ECG:

IF there was any doubt after seeing ECG #1 about the need for prompt cath lab activation — that doubt should be removed by the "dynamic" ST-T wave changes that are evident in virtually all leads in the repeat ECG.

• PEARL #5: The BEST way to compare one serial ECG with another — is to put both tracings side-by-side — and to then go lead-by-lead, always comparing one lead area to the corresponding lead area in the 2nd ECG.
• Instead — it is all-to-common for clinicians to ignore this important procedural point. Instead, the tendency is to try to "gain time" by looking at 1 tracing in its entirety — and then the 2nd tracing in its entirety without taking the time to directly compare each lead area with the corresponding lead area in the 2nd tracing. The reality is that unless you compare the 2 tracings by going lead-by-lead — it is all-too-easy to overlook subtle but important findings.
• Along the way — it is also important to ensure that our lead-by-lead comparison is "comparing apples with apples, and not with oranges". By this I mean — that we want to ensure that any changes in ST-T wave morphology are not the result of a significant frontal plane axis shift or due to a change in chest lead electrode placement.

Applying this Comparison Technique in Figure-4:

Although there is a slight frontal plane axis shift (from about +40 degrees in ECG #1 — to +60 degrees in ECG #2) — this small change is unlikely to alter our assessment of comparative limb lead ST-T wave appearance. Chest lead QRS morphology appearance is essentially the same in both tracings. Therefore — any ST-T wave changes that we note between these 2 ECGs are likely to be "real".

• In the Limb leads of ECG #2 — there now is subtle-but-real ST elevation in each of the inferior leads (as seen by respect to the dotted RED line baseline in each of these leads). 
• ST-T waves in these inferior leads have a more acute appearance than they did in ECG #1 (ie, there is more straightening of the elevated ST segment takeoff) — and we may be seeing the beginning of small inferior lead Q waves.
• The BLUE arrow in lead aVL — highlights ST segment straightening that was not present in ECG #1. I interpreted this as a reciprocal change to the new inferior lead ST elevation.

In Chest Leads:

• BLUE arrows in leads V2 and V3 — highlight an increase in ST depression.
• In leads V5 and V6 — there should be no doubt that there is a more acute appearance with straightening of the ST segment takeoff and increased ST elevation (with respect to the dotted RED lines in these leads).

MY Impression of ECG #2: In this patient with ongoing CP — the repeat ECG in Figure-4 confirms "dynamic" ST-T wave changes. 

• Prompt cath is indicated! — in this symptomatic patient with acute ongoing infero-postero-lateral OMI.

Figure-4: I've labeled findings in the repeat ECG.

CASE Follow-Up:

• Serial troponin values were markedly elevated.
• Cardiac cath revealed normal left main and LAD branches — and, a small but non-obstructed RCA. The main trunk of the LCx (Left Circumflex) showed a 50% lesion in the middle of this vessel — with severe narrowing proximally in the 1st Obtuse Marginal branch of the LCx, which was felt to be the "culprit" artery. Angioplasty was successfully performed.

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Acknowledgment: My appreciation to Konstantin Тихонов (from Moscow, Russia) for the case and this tracing.

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Related ECG Blog Posts to Today’s Case:

• ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
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• ECG Blog #193 — Reviews the basics for predicting the "culprit" artery (as well as reviewing why the term "STEMI" — should be replaced by "OMI" = an acute coronary Occlusion MI).

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• CLICK HERE — for my 6 new ECG Videos (on Rhythm interpretation — 12-lead interpretation with Case Studies for ECG diagnosis of acute OMI).
• CLICK HERE — for my 2 new ECG Podcasts (on ECG & Rhythm interpretation Errors — and — Errors in assessing for acute OMI).

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• 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.
• Recognizing ECG signs of Precordial Swirl (from acute OMI of LAD Septal Perforators) — See My Comment at the bottom of the page in the March 22, 2024 post on Dr. Smith's ECG Blog. 
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• 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.
• ECG Blog #400 — Reviews the concept of "dynamic" ST-T wave changes.
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• ECG Blog #337 — A "NSTEMI" that was really an ongoing OMI of uncertain duration (presenting with inferior lead reperfusion T waves).