ECG Blog #158 (STEMI – OMI – Ischemia – ST depression – not acute)

Imagine the ECG in Figure-1 was obtained from a previously healthy, middle-aged man who presented to an ambulatory clinic for “indigestion”.

• How would you interpret this ECG in light of the above history?
• Are there acute changes?

Figure-1: Imagine this ECG was obtained from a previously healthy, middle-aged man with “indigestion”. How would you interpret this tracing? NOTE— Enlarge by clicking on the Figure.

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Interpretation: The rhythm for the ECG shown in Figure-1 is sinus at a rate of ~70/minute. All intervals are normal. The mean QRS axis is normal (about +30 degrees — as judged by the upright QRS in leads I and aVF, with greater net positivity in lead in lead I). There is no chamber enlargement. Regarding assessment of Q-R-S-T Changes:

• A large Q wave is seen in lead III — and small q waves are present in leads II and aVF.
• Transition is normal (occurs between V3-to-V4).
• There is coved ST elevation in leads III and aVF — with a hint of early T wave inversion in these leads. There also appears to be slight-but-real ST elevation in lead II (See below).
• ST depression is seen in lead I (slightly), and in lead aVL (more definite) — and probably also in lead V2.
• The T wave is relatively flat in leads V5 and V6 (normally the T wave is clearly upright in these lateral chest leads).

IMPRESSION: The combination of findings described above suggests we should assume inferior MI (Myocardial Infarction) has occurred at some point, most probably in the recent past — at least, until proven otherwise. The challenge is to determine the probable age of this MI. We highlight the following points:

• PEARL #1: I like using the concept of “patterns of leads” — especially when assessing the ECG of a patient suspected of acute ischemic heart disease. To apply this concept — Look at all leads that view a given area of the heart at the same time. Thus, we look here at the 3 inferior leads (II,III,aVF) at the same time (Figure-2). Given that 2 of these leads (ie, leads III and aVF) clearly show Q waves + ST elevation + beginning T wave inversion — it becomes exceedingly likely that the much more subtle findings in lead II are also real. These findings in lead II consist of ST elevation (RED arrow pointing to the ST segment which lies above the RED horizontal baseline in this lead) — and — and the small q wave (within the RED circle).
• PEARL #2: With acute coronary disease — an almost “magical” reciprocal (= mirror-image) relationship will usually be seen between ST-T wave deviations in leads III and aVL. To illustrate this concept — I have placed the mirror-image of the first 2 beats in lead III just over the complexes in lead aVL — and, the mirror-image of the first 2 beats in lead aVL just over the complexes in lead III. Recognition of this “almost magical” reciprocal relationship (as we see here in Figure-2) virtually confirms acute (or at least recent) changes of MI.
• Reciprocal ST flattening/depression is also seen in leads I and V2 in Figure-2 — albeit quite modest in degree. In the setting of acute or recent inferior MI — ST depression in anterior leads (ie, V1, V2 and/or V3) typically indicates posterior wall involvement — so we suspect infero-postero MI in this case.
• PEARL #3: It is uncommon for the amplitude of a positive T wave in lead V1 to be greater than the amplitude of the positive T wave in lead V6. When this relationship is seen in a patient with potentially acute symptoms (as is the case in Figure-2) — acute ischemia is likely.
• NOTE — There may also be RV (right ventricular) involvement in this case. Lead V1 is both an anterior, as well right-sided lead. Proximal RCA (Right Coronary Artery) occlusion often results in acute infarction of the 3 areas of the heart supplied by the RCA, which are the inferior and posterior wall of the LV (left ventricle), and the RV (right ventricle). Diagnosis of acute RV MI is often challenging on a standard 12-lead ECG — because the expected right-sided ST elevation is frequently cancelled out by anterior ST depression from associated posterior MI. While we might suspect this as the reason for the modest amount of anterior ST depression and the upright T wave in lead V1 of Figure-2 — the only way to know if there is RV involvement in this case would be with right-sided leads (ie, leads V1R-thru at least V4R).

Figure-2: We have labeled Figure-1 to highlight subtle changes in lead II — and the “magic” reciprocal (mirror-image) relationship with acute or recent coronary disease between leads III and aVL (See text).

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BOTTOM Line: The ECG in Figure-2 strongly suggests that there has been an Infero-Postero MI (possibly also with RV involvement). But the question remains as to whether this is acute (ie, within the last couple of hours) — recent (within the past day or two or three … ) — or more remote than just a few days ago?

• Treatment recommendations for this patient will vary dramatically depending on the acuity of the MI. For example, immediate cardiac catheterization and/or thrombolytic therapy are less likely to be helpful if much time has passed since the acute event.
• The History in this case is very important. Because the area of the heart viewed by the inferior leads (especially leads III and aVF) lies on top of the diaphragm — it is not at all uncommon for patients with inferior MI to present with GI symptoms. If this is in fact the case here — it will be important to try to elicit from the history WHEN this patient’s “indigestion” began.
• ECG findings in Figure-1 that suggest a more acute STEMI (= ST Elevation MI ) are: i) that there is ST elevation in each of the inferior leads; ii) that there is reciprocal ST depression, including that “magical” mirror-image picture for the ST-T waves in leads III and aVL; and, iii) that T wave inversion looks like it might only be beginning ...
• On the other hand, ECG findings that suggest a LESS acute picture include: i) that the overall amount of ST elevation is relatively modest; ii) that a very large Q wave has already formed in lead III; iii) that the amount of reciprocal ST depression is also extremely modest; and, iv) that the patient presented to an ambulatory clinic instead of to an ED (Emergency Department). While it certainly occurs that patients with acute MI can present to an ambulatory clinic — I’ve observed over the years a “self-selection” process, whereby statistical likelihood of an acute event seems greatly enhanced when patients call 911 and present with their symptoms to the ED instead of to an outpatient clinic.

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My BEST Guess: Pending additional historical information — the seemingly uncertain onset of GI complaints + outpatient presentation + an ECG with a very large Q wave in lead III + relatively modest amount of ST elevation and depression all suggest a less acute onset for this MI. Whether this dates the infarct as having occurred 12-24 hours ago, or even longer ago than that — is uncertain from the information available.

• That above said, one can not rule out a more acute onset — especially if the reason for relatively little ST elevation is spontaneous reperfusion (in which case, the risk of potential reocclusion may be considerable).
• To emphasize — clinical priorities and the treatment approach would be very different IF the history suggested a recent and/or ongoing onset. For example, prompt cath to define the anatomy would be indicated if the patient had called 911 and/or presented to the ED with new-onset chest pain ... Sometimes, "Ya gotta be there" to fully appreciate the clinical situation.
• In Summary — prompt assessment and more information is needed to determine true risk of this patient.

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• NOTE: For more on our approach to dating an infarct — Please see our ECG Blog #142.