electrophysiology axis deviation

ElectrophysiologyAxis Deviation

EXSC 531Clinical Exercise Physiology

J. Larry Durstine, PhDProfessor and Chair

Exercise Science DepartmentSchool of Public Health

University of South Carolina

Learning Objective

• At the end of this lecture, students will be able to understand the concept of axis deviation and determine axis deviation with special considerations.

Lecture Outline

• Determine axis deviation

• Understand normal physiologic reasons for deviation.

• Understand pathologic reasons for deviation.

• Steps for determination

• Special consideration

Axis Deviation Determination

If we add up all the small vectors of ventricular depolarization (considering both direction and magnitude), we have one large“Mean QRS Vector” which represents the general direction of ventricular depolarization.


In myocardial infarction there is a necrotic (dead) area of the heart that has lost its blood and does not depolarize. The unopposed vectors from the other side Draw the Mean QRS vector away from the infarct.


Axis is the Mean QRS vector when give in degrees, and the normal axis range is 0 to +90o in the frontal plane.


In the frontal plane, there are 4 possible axis quadrants where the Mean QRS Vector may point. Visualize this large circle on the patient’s chest in the frontal plane.

Now, by looking at the QRS complex in I and AVF, you can locate the Mean QRS Vector in an Axis quadrant (in the frontal plane asit relates to the patient)

Determination of Axis Deviation

Degrees of Deviation

Axis Deviation Determination• For this method we will use only the limb and

augmented leads• Step 1 Determine quadrant

– Check leads I and AVF• Step 2 Determine the isoelectric lead

– Where the QRS has “nearly” equal positive and negative deflections

• Step 3 Move into the determined quadrant (from step 1) at a 90 degree angle

• Special consideration – If the isoelectric lead is I, what is the

quadrant?– If the isoelectric lead is AVF, what is the

quadrant?

Determine Quadrant

• Check leads I and AVF

Determine the Isoelectric Lead

Move at a Right Angle

• Move into the determined quadrant (from step 1) at a 90 degree angle

Determination

of

Axis I

IIIII F

LR

I II III R L F

1. Determine Quadrant.

2. Determine Isoelectric lead.

3. Move at right angle toward quadrant.

I

IIIII F

LR

I II III R L F

Determination

of

Axis

1. Determine Quadrant

2. Determine Isoelectric lead

3. Move at right angle toward quadrant



I

IIIII F

LR

I II III R L F

Determination

ofAxis


I

IIIII F

LR

I II III R L F

Determinationof

Axis




Lecture Outline






Lead I Lead II avR avL avFLead III

L

I

IIFIII

R

F

2. Determine Isoelectric lead3. Move at right angle toward quadrant

Lead I

Lead I

Lead AVF

Lead AVF



L

I

IIFIII

R



Lead I Lead II avR avL avFLead III

AVFAVF

Lead ILead I

G

Lecture Outline






Determination of Axis Deviation1. Mean vector2. Physiologic reasons for deviation3. Pathogenic reasons for deviation4. Steps for determination

• Determine quadrant– Check leads I and AVF

• Determine the isoelectric lead• Move into the determined quadrant at a 90 degree angle

5. Special consideration • If the isoelectric lead is I, what is the quadrant?• If the isoelectric lead is AVF, what is the quadrant?

Counting heart rates1. R to R

• Count off• Small box counting (1 and 5 contraction methods)

2. Three and six second3. Know reasons for using each

electrophysiology axis deviation

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