The 12-lead ECG shown in Figure 1 was obtained from 50-year-old
man with chest discomfort.
- Is this ECG likely to reflect acute
anterior
STEMI? – acute
pericarditis? – or ERP (Early Repolarization Pattern) without
acute process?
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| Figure 1 – 12-lead ECG from a 50-year-old man with chest discomfort. |
INTERPRETATION: Using our systematic
sequential approach (rate-rhythm-intervals-axis-hypertrophy-QRST
changes) – We interpret the
12-lead ECG in Figure 1 as follows:
- The QRS complex is narrow.
- There is slight but definite variability in the R-R
interval throughout the tracing. The rhythm is sinus arrhythmia.
- All intervals (PR,QRS,QT) are normal; the axis is
normal (approximately +70 degrees).
- There is voltage
for LVH (deepest S in V1,2 + tallest R in
V5,6 ≥35). No other sign of chamber enlargement.
- Q-R-S-T Changes: There
are small q waves in the inferior and lateral precordial leads. R wave progression is normal (ie, transition
occurs between leads V3-to-V4 ). T
waves are peaked.
There is some J-point ST segment elevation (with
upward concavity = "smiley" configuration) in multiple leads - and there is shallow symmetric T wave
inversion in lead aVL.
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IMPRESSION: There is some baseline artifact (seen most in leads I,
II, III, aVL . . . - albeit not enough to impede our interpretation).
Sinus arrhythmia. Voltage for LVH. Shallow T wave inversion in lead aVL – plus
– 1-2mm of J-point ST segment elevation with upward
concavity in a number of leads … STOP! ...
- Interpretation of the ECG in Figure 1
beyond the “STOP” depends greatly on the clinical setting.
- IF this ECG was
obtained from an otherwise healthy young adult without cardiac
symptoms – we would interpret the
isolated shallow T inversion in lead aVL as normal given the relatively vertical
QRS axis and predominantly negative
QRS complex in this lead (See Figure
2 below).
- Similarly – We would interpret the slight (but real) upward concavity (“smiley”) precordial
ST elevation as consistent with ERP (See
Figure 3 below).
HOWEVER – The situation in this case is different – because the patient whose
ECG is shown in Figure 1 is 50 years old and IS having chest discomfort ...
- Consideration therefore HAS to be given to the possibility
that the precordial lead ST elevation seen could represent an early
stage of acute anterior STEMI (ST
Elevation Myocardial Infarction) – especially given the T wave inversion in lead aVL.
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NOTE: We complete our interpretation of this case (and the ECG in Figure 1) at the bottom of this Blog post. Before doing
so – we address a number of key concepts relating to clinical assessment of
anterior lead ST elevation.
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Normal T Wave
Inversion:
Five leads (III,aVF,aVL,aVR,V1) – may normally display moderate-to-large Q waves and/or T wave inversion
in otherwise healthy adults. Thinking of a “reverse Z” (Ã la Zorro) may help recall which leads these are
(Figure 2):
- While we cannot rule out the
possibility that the shallow T wave inversion in lead aVL of Figure 1 reflects
ischemia – this T inversion is much more
likely to be normal in this patient because: i) T wave inversion is isolated (it is only seen in lead aVL); ii)
T inversion is shallow; iii) the QRS
complex in aVL is predominantly negative
in this patient with a relatively vertical QRS axis (conditions that predispose to the normal finding of some T inversion in
aVL); and iv) no acute
change is seen in other limb leads.
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| Figure 2 – Schematic tracing showing those leads that may normally manifest even large Q waves or deep T wave inversion (leads III,aVF,aVL,aVR,V1). Thinking of a “reverse Z” may facilitate recall. |
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ST Segment SHAPE:
The shape of ST elevation is more important than the amount
of elevation (Figure 3).
Acute MI may occur with only minimal
ST elevation:
- ST elevation with an upward concavity (ie, “smiley” configuration) is usually benign –
especially when seen in an otherwise healthy, asymptomatic individual (especially when seen with notching or slurring of the J point in one or more leads). This ST segment
variant is known as ERP (Early
Repolarization Pattern).
- In contrast – ST elevation with coving or a downward convexity (“frowny” ) – is much more likely to be due to acute
injury (from ischemia/MI).
- KEY POINT: History is ever
important. Although ST elevation with a “smiley”
configuration and J-point notching often reflects a normal variant – this is only
true IF the patient is asymptomatic.
An identical ST-T wave pattern from a
patient with chest pain must be
assumed acute until proven
otherwise.
- IF in doubt – Admit
the patient! Look at old tracings
to compare. Repeat the ECG.
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| Figure 3 – Schematic showing upward concavity (“smiley” ) ST elevation that is usually benign – especially when J-point notching is seen in one or more leads. In contrast – ST segment coving (“frowny” ) – is much more likely to be due to acute injury/infarction. |
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Are ST Segments Truly Elevated in Figure 1?
ST segment elevation in Figure 1 is subtle but real (Figure 4):
- We judge ST segment deviations with respect to the PR segment baseline. In Figure 4 – the blowup of leads V1,V2
shows the J-point to be clearly elevated above the PR segment baseline. We
estimate 1-2mm of upward concavity ST elevation in lead V2 (although we admit that subtle rounding of
the J-point area in this lead makes precise determination of the amount of ST
elevation difficult).
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| Figure 4 – Second look at the ECG shown in Figure 1 from this 50 year-old man with chest discomfort. Blowup of leads V1,V2 illustrates subtle but real upward concavity ST elevation above the PR segment baseline (See text). |
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Putting It All
Together:
As stated earlier – the ECG in Figure 1
shows sinus arrhythmia; voltage for LVH; shallow
T wave inversion in lead aVL – plus
– 1-2mm of J-point ST segment elevation with upward
concavity in a number of leads … Our impression is probable ERP (and not
anterior STEMI or pericarditis) because:
- ST elevation manifests and upward concavity (“smiley” ) configuration (albeit
no J-point notching is seen).
- ST elevation is seen (at least in
small amount) in all precordial
leads. IF acute anterior STEMI was evolving – one would expect additional ST-T wave abnormality
elsewhere on this tracing given the extent of ST elevation.
- The shallow T wave inversion in lead aVL is isolated and probably normal given the patient’s relatively vertical
QRS axis and predominantly negative QRS in lead aVL.
- The q waves seen on this tracing are small and narrow. They most
probably are normal septal q waves (which
are typically seen in lateral leads and sometimes also in inferior leads in
patients with a vertical axis).
- The ECG picture in Figure 1 is not suggestive of acute pericarditis (it lacks sinus tachycardia; ST elevation is
absent in the limb leads; there is no PR depression).
We conclude our interpretation of the ECG in Figure 1 with the statement: “Urge clinical correlation”.
The point to emphasize is that although we would be relatively comfortable that the ECG shown in Figure 1 is unlikely to represent early acute anterior STEMI
– We can not rule out this
possibility on the basis of this single tracing! How to proceed with only a ~90% comfort level that the ECG in
Figure 1 is benign would depend:
- IF this patient presented to the office with a history of chest
discomfort that was relatively unconvincing
for ischemic pain – we would probably manage the case on an ambulatory basis. We would
be that much more inclined to do so IF history and physical exam suggested a non-cardiac cause (peptic ulcer disease; musculoskeletal chest pain, etc.).
- Access to a prior ECG on this patient might prove invaluable (especially if it confirmed baseline anterior
ST elevation and T wave inversion in aVL of similar nature to that seen in
Figure 1).
- On the other hand – IF this 50-year-old man presented to the ED
(Emergency Department)
with new-onset chest discomfort (and no prior tracing available) – he
would almost certainly be admitted to the hospital. One simply can’t rule out the possibility of early
anterior STEMI on the basis of this single tracing… (In our experience – such patients with new-onset chest discomfort are
not sent home from the ED).
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Should the Cath Lab
Be Activated?
Taking the 2nd scenario presented above (ie, that this 50-year-old man presented to the ED with the ECG in Figure 1
and a history of new-onset chest discomfort) – the question arises as to
whether the cath lab should be activated for possible acute reperfusion on the basis of this tracing? IF Figure 1 in fact represents an early stage of
anterior STEMI – then prompt reperfusion becomes a critical determinant of
optimal prognosis.
- At what point to activate the cath lab is difficult to say
from the comfort of our home computer as we view this tracing …. Sometimes – “Ya just gotta be there …”. That said –
We most probably would not
activate the cath lab on the basis of what we see in Figure 1.
- Access to a prior ECG on this patient might be revealing (if a prior tracing can be found…).
- Repeating the ECG in short
order may establish the diagnosis. With acute evolving infarction – significant change may be evident on ECG in as little as 20-to-30 minutes.
- Obtaining an Echo at the bedside in the ED while the patient is having chest discomfort may provide invaluable assistance in determining the likelihood of an acute event. If an anterior wall motion abnormality is seen during symptoms — this becomes highly suggestive of an acute event. On the other hand, if during chest discomfort the Echo is entirely normal — this makes an acute event much less likely. (NOTE: We emphasize 2 points regarding ED use of Echo for this purpose: i) these Echos may be challenging to read, so expertise is needed to KNOW whether wall motion abnormality is or is not present; and ii) an Echo is only helpful IF obtained during chest discomfort. If chest discomfort has resolved and the Echo is normal — unfortunately nothing can be ruled out!)
- STAT troponin values may confirm acute infarction (though even high-sensitivity troponins would
not rule this possibility out if they were normal).
- IF still in doubt after reexamining the patient and the above series of
steps – Consider consulting the Cardiologist-On-Call to assist in the
decision-making process. There are times when acute cath may be performed even without definitive diagnosis – although
in this case, careful observation with close serial follow-up will almost
certainly tell the tale over the next few hours. But at least the cardiologist is aware in the event a surprise occurs
and the ECG evolves ...
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FINAL Thoughts: Is
there Help in the Literature?
Smith et al have developed a multivariate equation to assist in acute
evaluation of the patient with anterior ST elevation (Ann Emerg Med 60:45, 2012). Findings from their retrospective
analysis of a large data set are insightful in this case – and further support
our suspicion that the ECG in Figure 1 is most probably benign. These
include relatively taller R wave amplitude and a QT interval that is not
prolonged in Figure 1. That said – overlap exists in the parameters used in
the calculated Smith equation, such that we are still left with being unable to exclude an acute process on
the basis of the number score reported. – END OF CASE –
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Please click on the icon below for a pdf Link to Section 09.0 (from our ECG-2014-ePub) on assessment of ST-T waves. The part on Early Repolarization begins in Section 09.14 in this pdf:
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