12 Lead STEMI Mimics

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12 Lead STEMI Mimics
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Objectives

• Identify ECG findings that imitate or conceal
  STEMI
• Significance of bundle branch blocks (BBB) in the
  acute coronary syndrome patient
• Cardiac conditions that can cause ST
  abnormalities in the absence of ACS

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Bundle Branch Blocks

• Produce ECG changes that can imitate or conceal
  the ECG changes that are associated with Acute
  Coronary Syndromes (ACS)

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Bundle Branch Anatomy
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Bundle Branch Block Significance

• In cases where an acute MI produces a BBB the
  mortality rate is higher then in patients without
  a BBB
• It is not the presence of the BBB that increases
  mortality but the fact that the necrosis is more
  widespread
• In an ACS patient with a new or presumed new BBB
  acute reperfusion therapy is indicated

Important to know When a bundle branch block
is present on the 12 lead ECG try to obtain a
copy of an old 12 lead ECG if possible in order
to determine if the BBB is old or new
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Recognition of BBB

• Wide QRS (greater then 0.12 seconds or 3 small
  squares)
• Supraventricular rhythm
• If both of the above criteria are met suspect a
  BBB

gt 3 small squares
P wave
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Right or Left BBB?

• Look at V1 (this method only works in V1)
• Does the QRS meet the criteria for BBB?
• If it does follow the steps below
• Find the J point
• Draw a line into the centre of the QRS
• Draw a line back towards complex point
• Shade the area in
• If the arrow points up it is a right BBB, if the
  arrow points down it is a left BBB

Left BBB
Right BBB
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Practice ECG 1

• Look for signs of a BBB (wide QRS with P waves
  present)
• Determine if the BBB is a left BBB or a right BBB
• Are there signs of ST elevation present?

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Answer ECG 1
QRS gt 0.12s
P wave

• QRS gt 0.12 seconds
• P waves present
• In V1 arrow points down
• Left BBB
• No ST elevation present

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Practice ECG 2

• Look for signs of a BBB (wide QRS with P waves
  present)
• Determine if the BBB is a left BBB or a right BBB
• Are there signs of ST elevation present?

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Answer ECG 2

• QRS is wide
• No P waves present (this is a ventricular rhythm)
• Not a bundle branch block
• No signs of ST elevation
• This is ventricular tachycardia

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Practice ECG 3

• Look for signs of a BBB (wide QRS with P waves
  present)
• Determine if the BBB is a left BBB or a right BBB
• Are there signs of ST elevation present?

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Answer ECG 3

• Wide QRS and P waves are present
• Arrow in V1 points up
• No ST elevation
• This is a right BBB

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Other conditions that can mimic or conceal ST
elevation

• Ventricular rhythms (will not be covered here)
• Paced rhythms
• Idioventricular rhythms
• Ventricular tachycardia
• Premature ventricular complexes
• Other conditions
• Left ventricular hypertrophy
• Ventricular aneurysm
• Benign early repolarization
• Pericarditis
• Hyperkalemia

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Left Ventricular Hypertrophy (LVH)

• Enlargement of the left ventricle often caused by
  uncontrolled hypertension
• Recognized by an increase in the amplitude of the
  QRS complex
• In LVH the QRS is narrow but has a much greater
  amplitude then QRS complexes of a normal heart
• Can cause the ST segment to appear elevated in
  some leads and to down slope in other leads

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When to Suspect LVH

• To determine if LVH is a possibility do the
  following
• Pick the deepest QRS from V1 or V2, in this ECG
  it is V2
• Pick the tallest QRS from V5 or V6, in this ECG
  it is V5
• Count the small boxes for both V2 QRS and V5 QRS
  (V2 30, V5 35)
• Add the number together, if it is greater then 35
  suspect LVH (65 for this ECG therefore LVH is
  suspected)

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Ventricular Aneurysm

• May cause ST elevation in leads V1 through V4 in
  the absence of an acute cardiac condition
• Generally result from an area of necrosis due to
  an old infarct which causes the ventricle to
  bulge out during ventricular contraction

Ventricular Aneurysm
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Benign Early Repolarization

• This is a normal ECG variation
• Completely healthy people can have an ECG that
  shows ST elevation and tall T waves
• This condition typically occurs in young healthy
  males
• The J point and ST segment are elevated and
  usually have a fish hook appearance
• Tall upright T waves may also be present

Important to know presence of a fish hook J
point and ST segment does not rule out ACS as
some ACS patients will also have a fish hook
Fish hook
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Pericarditis

• An inflammation of the pericardial sac caused by
  a bacterial or viral infection or a metabolic
  condition
• Causes diffuse ST segment changes and may also
  have a fish hook appearance as in early
  repolarization
• Different pain pattern then in ACS patients
  (classic pericarditis pain pattern)
• Sharp knife like
• Very localized
• May radiate to base of neck or between shoulder
  blades
• Affected by movement, respiration etc
• Often pain improves when patient leans forward
• Pain worsens when supine or semi-fowlers

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Hyperkalemia

• Changes to ECG vary depending on potassium level
• Tall peaked T waves are present throughout the
  ECG in mild cases
• With higher potassium levels the QRS will be wide
  and the ST segment will disappear P waves will
  also begin to flatten
• In severe cases of hyperkalemia P waves will
  disappear entirely and the QRS will widen and
  join the T wave to form a Sine wave

Tall peaked T wave
Sine wave
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For More Information on 12 Leads

• For more information on ST abnormalities
  http//www.madsci.com/manu/ekg_st-t.htm
• For more information on 12 lead ECG and patient
  presentations
• http//www.madsci.com/manu/indexekg.htm
• ECG Learning Centre
• http//library.med.utah.edu/kw/ecg/index.html

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