EKG - Axis Determination / Fascicular Blocks

AXIS

direction of depolarization through the heart

VECTOR

general direction of movement of depolarization

MEAN QRS VECTOR

Fixed end-point of the Vector at the AV NODE

Average of all vectors of the ventricles into one

What direction does the Mean QRS vector normally point

Left and downward due to larger depolarization of LV

What plane is used to plot a QRS vector

Frontal palnt

What is a normal axis

Between 0 and 90 degrees (LLQ)

Axis Deviation

Any anatomic displacement of the heart also displaces the Mean QRS Vector

Tall skinny patients tend to have an axis deviation to the

Right

Obese patients tend to have axis deviation to the

Left

LV Hypertrophy will cause an axis deviation to the

Left

Myocardial infarction will cause an axis deviation

The opposite side of the hear from the infarct

What can be obtained from measuring Mean QRS Vector

The POSITION of the Heart

Indication of any HYPERTROPHY (POINTS TOWARD)

Information regarding INFARCTION (POINTS AWAY)

What leads are used to assess mean QRS vector

I

aVF

How do lead I and aVF determine axis deviation

Lead I = Determines left or right

• QRS (+) = Mean QRS is to left

• QRS (-) = Mean QRS is to right

Lead avF = Determines superior / inferior

• QRS (+) = Mean QRS points down

• QRS (-) = Mean QRS points up

How does left axis deviation appear on EKG

Lead I → Positive QRS

aVF → Negative QRS

How does right axis deviation appear on EKG

Lead I → Negative QRS

aVF → Positive QRS

How does extreme right axis deviation appear on EKG

Lead I → Negative QRS

aVF → Negative QRS

What lead sits at 0 degress for axis

Lead I

What lead sits at 90 degress for axis

avF

What lead sits at 60 degress for axis

II

What lead sits at 120 degress for axis

III

What lead sits at -150 degress for axis

aVR

What lead sits at -30degress for axis

aVL

Axis

Right Aix Deviation

Axis

Left Axis Deviation

“Fascicular Block” / “Hemi-Block”

a conduction BLOCK

Cuases of Right Axis Deviation

Possible Left Posterior Hemiblock

Normal in small children and thin adults

Severe RV Hypertrophy

PE

Advanced pulmonary lung disease

Causes of Left Axis Deviation

Left Anterior Hemiblock

AMI

Axis

Left Axis Deviation