EKG - Determining the Axis Flashcards
Mean Electrical Axis and defining the direction of the axis
● 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.
the normal ventricular axis (the direction of the mean vector) lies between _____
0 and +90 degrees
To determine the cardiac axis, we look at the QRS complex in ______
Lead I and Lead aVF
There are four types of Axis Directions:
○ Normal Axis
○ Right Axis Deviation (RAD)
○ Left Axis Deviation (LAD)
○ Indeterminate Axis (sometimes
called Extreme Right or Extreme
Left Axis Deviation)
Right Axis Deviation (RAD)
● Right Axis Deviation is an axis between +90 and +180 degrees.
Right Axis Deviation is commonly caused by:
○ 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.)
If the QRS complex is more _____ in Lead I, then the axis
must be headed away from Lead I to some extent.
negative
If the QRS complex is more _____ in Lead aVF, then the axis must be headed towards aVF to some extent.
positive
Left Axis Deviation (LAD)
LAD is an axis between -30 and -90 degrees according to specialists.
○ 0 to -90 degrees for our purposes
Left Axis Deviation is commonly caused by:
○ Left Ventricular Hypertrophy (LVH)
○ Left Bundle Branch Block (LBBB)
○ Something else (like abdominal obesity, pregnancy, etc.)
If the QRS complex is more positive in Lead I and s more negative in Lead aVF, then the axis
must be headed towards ______
towards Lead I to some extent and away from aVF (LAD)
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 _____
LAD.
Indeterminate Axis (Extreme Axis)
Indeterminate Axis (Extreme Axis) is an axis deviation
between -90 degrees and -180 degrees.
Indeterminate Axis Deviation is commonly caused by:
○ Myocardial Infarction
○ Ventricular Rhythm (VT or VF)
○ Leads placed incorrectly
If the QRS is negative 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 right (-90 to -180 degrees). This is Indeterminate Axis
If the QRS is biphasic/isoelectric in Lead I, then that means _____
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).
Precisely Defining the Axis
● 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
