• Review of the normal Q and ST segments
• The EKG of myocardial infarction
• How to locate an MI
• The EKG of ischemia --stress testing

Normal EKG: Insignificant Q wave ST is isoelectric QRS and T angle normal

The EKG of acute myocardial infarction: Significant Q 1/3 QRS amplitude or .04 sec duration

Evolution of the EKG in MI:

When acute: Q waves, ST elevation, T wave inversion

When old (after 1 year): Significant Q wave persists

Let’s review coronary artery anatomy again...

Now let’s think “left ventricle”!

Lateral MI:

• Q’s in I and AVL (Dubin); also V5, V6
• Left circumflex ?

Anterior MI:

• Q’s in V1, V2; also V3, V4
• LAD?

Inferior MI:

• Q in II, III, AVF
• Blood supply varies (may be R or L, usually right)

Posterior MI:(won't be on test)

• Large R w/ ST depression in V1, V2 (mirror of anterior)
• Right coronary artery

Acute inferior MI

Old inferior MI

Acute anterior MI

The EKG below shows a HUGE MI! You can see evidence anterior, inferior, and lateral!

ST segment significantly depressed from baseline. Diagnostic criteria for a ‘positive’ test: Electrically positive: 1 mm or greater ST depression @ 2 mm past J point. Clinically positive: Angina pectoris and severe SOB

 Make sure when you summarize the results of a test you distinguish those TWO features. Clinical and electrical!

Ischemia isn't the only cause of ST depression! Others include: subendocardial infarction, LBBB, strain pattern seen on ventricual hypertrophy, reciprocal changes in the anterior leads when a posterior MI is present. Some times ST depression is 'false positive' for ischemia.

Correctly measuring ST depression

• Find baseline (PQ junction)
• Find the ‘J’ point
• Measure depth of depression @ 2 mm past J point

I handed out review sheets. Please look 'em over for Friday. Lab reports are due Friday.