12 Lead STEMI Mimics

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

Bundle Branch Blocks

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

Bundle Branch Anatomy

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

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

> 3 small squares

P wave

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

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?

Answer ECG # 1

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

QRS > 0.12s

P wave

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?

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

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?

Answer ECG # 3

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

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

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

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)

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

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

Fish hook

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”

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

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

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

Thank You for participating in Sunnybrook – Osler Centre for

Prehospital Care online education!

If you have any questions please bring them with you to class!