Cardiac axis

Question 1

What is cardiac axis?

Answer 1

A representation of the overall direction of electrical activity in the heart.

Question 2

What factors can influence the axis?

Answer 2

The size of myocardium, the death of myocardium, a mechanical shift (physical movement of the heart) and conduction defect (such as LBBB).

Question 3

Why do we measure cardiac axis?

Answer 3

If the axis has deviated, it can indicate underlying pathology. It can also be useful in measuring the progression of chronic conditions (such as heart failure) and can help steer the provisional diagnosis for the patient.

Question 4

Name 3 causes of left axis deviation.

Answer 4

Left ventricular hypertrophy, conduction defects (such as LBBB), inferior wall MI, congenital cardiac defect, hyperkalaemia, mechanical shifts or paced rhythm.

Question 5

Name 3 causes of right axis deviation.

Answer 5

Limb lead reversal, right ventricular hypertrophy, RBBB, lateral wall MI, congenital cardiac defect, dextrocardia, pneumothorax, mechanical shifts or conditions leading to right ventricular strain.

Question 6

What position on the Hexaxial Reference System does each variation of QRS axis lie upon?

Answer 6

Normal QRS axis = -30 - +90
Left axis deviation = -90 - -30
Right axis deviation = +90 - 180
Extreme axis deviation = -90 - 180

Question 7

If Lead 1 and aVF are positive, what is the axis?

Answer 7

Normal axis.

Question 8

If Lead 1 is positive and Lead aVF is negative, what is the axis?

Answer 8

Left axis deviation.

Question 9

If lead 1 is negative and Lead aVF is positive, what is the axis?

Answer 9

Right axis deviation.

Question 10

If Lead 1 and aVF are negative, what is the axis?

Answer 10

Extreme axis deviation.