Ischemia Injury Infarction Module

Ischemia, Injury & Infarction

Tech Series
ECG Interpretation

Thomas E. O'Brien
AS CCT CRAT RMA

Learning Objectives

Upon completion of the accompanying narrative and practice the student will be able to:

Associate the views of a 12-Lead ECG with specific surfaces and the primary artery to that region of the heart
Know the difference between indicative and reciprocal views
Measure and recognize electrocardiographic changes caused by STEMI (EKG changes MI)

ischemia
injury
infarction

12-Lead ECG

People may choose to analyze ECG’s in a number of different ways. The sequence doesn’t necessarily matter as long as you gather and report the proper information each time. I read from left to right as much as possible (in anatomic groupings).
If your protocols are different, always follow them.
The following slides will review the leads, surfaces, and associated coronary arteries which commonly supply that portion of the heart.

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Lessons

Lesson #1: Views 323

Illustration

This file is licensed under the Creative Commons Attribution-Share Alike 3.0
Author: Patrick J. Lynch, medical illustrator

II, III & aVF

Inferior wall of left ventricle
Right Coronary Artery
Marginal branch

V1 & V2

Septum
Left Coronary
Septal branch

V3 & V4

Anterior
Left Coronary
Anterior Descending and Diagonal arteries

I, aVL, V5 & V6

Lateral
Left Coronary
Circumflex & Obtuse marginal

Labeled Views

Lesson #2: Quick Check 1 323

Question 1

Name the inferior view leads.

Answer

II, III & aVF

Question 2

Name the main coronary artery that supplies this artery.

Answer

Right Main Coronary artery

Lesson #3: Quick Check 2 323

Question 1

Name the septal view leads.

Answer

V1 & V2

Question 2

Name the artery that supplies the septal wall.

Answer

Left Main Coronary artery

Lesson #4: Quick Check 3 323

Question 1

Name the anterior view leads.

Answer

V3 & V4

Question 2

Name the arteries that supply the anterior wall.

Answer

Anterior Descending and Diagonal artery

Question 3

Name the main coronary artery that supplies this artery.

Answer

Left Main Coronary artery

Lesson #5: Quick Check 4 323

Question 1

Name the lateral view leads.

Answer

I, aVL, V5 & V6

Question 2

Name the arteries that supply the lateral wall.

Answer

Circumflex and Obtuse Marginal

Question 3

Name the main coronary artery that supplies this artery.

Answer

Left Main Coronary artery

Lesson #6: Indicative vs Reciprocal

Views of the heart

Views seen on a 12-Lead EKG that look directly at a surface of the heart are referred to as “indicative leads” i.e. the views provided on a standard (left side of the chest) ECG like II, III, aVF – inferior etc.

If additional views are required to view the right ventricle or posterior of the heart directly, the chest leads would actually have to be physically moved to either the right side or posterior wall of the chest.

This is not always practical or prudent in the emergency setting…so, many providers initially rely upon indirect (reciprocal) views.

Continued

Views of the heart that or indirect are often referred to as “mirror-image” or “reverse” or “reciprocal” views.

In this instance morphologic changes that we would typically expect to see would be the reverse or opposite change. Meaning, what we would expect to see elevated would be depressed and changes reflected in depression would be elevated.

What is up would be down and down would be up!

Lesson #7: Ischemia, Injury Infarction

Part 1

Think of the process of ischemia, injury and infarction as a worsening continuum.

If immediate, aggressive and effective care is not provided, ischemia will worsen (or progress) to injury and ultimately infarction (tissue death)

Ischemia, injury and infarction each impact the cardiac complex in unique ways.

Part 2

12-Lead Analysis requires we follow these steps of analysis.

ST segment for presence of deviation
T wave morphology changes
Q wave morphology changes

Part 3

The changes I have been referring to must occur in anatomically contiguous leads. This refers to 2 or more leads “looking” at (viewing) the same part of the heart or numerically consecutive chest leads

Examples Include:

II, III, aVF (2 of the 3 leads must show changes. It does not have to be all three)
I, aVL can show changes and not effect V5 and V6 to still be clinically significant
Numerically consecutive chest leads

We always recall that V1 is next to V2, but do not forget that V2 is also contiguous with (next to) V3…if V2 & V3 are showing changes, this is clinically significant too. See the next slide for an illustration.

Lesson #8: Numerically Consecutive Contiguous Leads

Illustration

12lead ecg image chest leads

Lesson #9: Ischemia

Introduction

Ischemia causes a delay in repolarization and causes specific changes to either or both the ST segment and T wave.

Ischemia is evidenced when ST segment depression of 1 mm or more or T wave inversion is seen in two or more anatomically contiguous leads

ST Segment Depression

T Wave Inversion

Lesson #10: Injury

Introduction

Ischemia delayed for even a few minutes can progress (worsen) to myocardial injury.

Injury is evidenced when ST segment elevation of 1 mm or more is seen in two or more anatomically contiguous leads

EKG

Injury Examples.
Note: ST Elevation in both examples

Lesson #11: Infarction

Introduction

A normal (physiologic) “Q” wave measures less than 0.04 second

Depth measures less than 1/3 height of R wave

EKG

An abnormal (pathologic) “Q” wave measures 0.04 (small box) second or greater in duration, and/or the depth measures greater than or equal to 1/3 height of R wave

Once an MI is completed, the ST segment will return to the baseline and the T wave will return to its normal orientation, but “Q” waves are often the one remaining change to a cardiac complex as evidence that tissue necrosis or tissue death (infarction) has occurred.

Lesson #12: Quick Check 5 323

Question

What is the term used that refers to direct changes seen on a 12-Lead ECG?

Answer

Indicative changes

Question

What is the term used that refers to reverse or indirect changes seen on a 12-Lead ECG because the ECG is looking at that surface of the heart indirectly?