EKG - Determining the Axis

Question 1

Mean Electrical Axis and defining the direction of the axis

Answer 1

● We define the direction of the axis according to the degree or angle of travel
within the frontal plane. The frontal plane is created by the 6 limb leads.

Question 2

the normal ventricular axis (the direction of the mean vector) lies between _____

Answer 2

0 and +90 degrees

Question 3

To determine the cardiac axis, we look at the QRS complex in ______

Answer 3

Lead I and Lead aVF

Question 4

There are four types of Axis Directions:

Answer 4

○ Normal Axis
○ Right Axis Deviation (RAD)
○ Left Axis Deviation (LAD)
○ Indeterminate Axis (sometimes
called Extreme Right or Extreme
Left Axis Deviation)

Question 5

Right Axis Deviation (RAD)

Answer 5

● Right Axis Deviation is an axis between +90 and +180 degrees.

Question 6

Right Axis Deviation is commonly caused by:

Answer 6

○ Right Ventricular Hypertrophy (RVH)
○ Right Bundle Branch Block (RBBB)
○ Something else (like COPD with a flattened diaphragm, tall
thin person with a long torso, etc.)

Question 7

If the QRS complex is more _____ in Lead I, then the axis
must be headed away from Lead I to some extent.

Answer 7

negative

Question 8

If the QRS complex is more _____ in Lead aVF, then the axis must be headed towards aVF to some extent.

Answer 8

positive

Question 9

Left Axis Deviation (LAD)

Answer 9

LAD is an axis between -30 and -90 degrees according to specialists.
○ 0 to -90 degrees for our purposes

Question 10

Left Axis Deviation is commonly caused by:

Answer 10

○ Left Ventricular Hypertrophy (LVH)
○ Left Bundle Branch Block (LBBB)
○ Something else (like abdominal obesity, pregnancy, etc.)

Question 11

If the QRS complex is more positive in Lead I and s more negative in Lead aVF, then the axis
must be headed towards ______

Answer 11

towards Lead I to some extent and away from aVF (LAD)

Question 12

If the QRS is positive in Lead I and negative in Lead aVF, then it means the
Axis of ventricular depolarization must be headed in a direction up and to
the left (0 to -90 degrees). This means that it is _____

Answer 12

LAD.

Question 13

Indeterminate Axis (Extreme Axis)

Answer 13

Indeterminate Axis (Extreme Axis) is an axis deviation
between -90 degrees and -180 degrees.

Question 14

Indeterminate Axis Deviation is commonly caused by:

Answer 14

○ Myocardial Infarction
○ Ventricular Rhythm (VT or VF)
○ Leads placed incorrectly

Question 15

If the QRS is negative in Lead I and negative in Lead aVF, then it means _____

Answer 15

the Axis of ventricular depolarization must be headed in a direction up and to
the right (-90 to -180 degrees). This is Indeterminate Axis

Question 16

If the QRS is biphasic/isoelectric in Lead I, then that means _____

Answer 16

the axis of depolarization is not moving towards or away from the electrode, so it must
be moving either straight up or down (perpendicular to Lead I).

Question 17

Precisely Defining the Axis

Answer 17

● In order to do this, you find the limb lead in which the QRS is most biphasic
(with negative and positive deflections virtually equal in height). It may even
appear isoelectric.
○ This indicates that the Axis must be running perpendicular to that lead
● As an example, let’s say the QRS is positive in Lead I and positive in Lead
aVF. We now know that the Axis would be considered “normal,” at 30 degrees