CPR 21 - ECG Basics 2 - ECG Leads and Mean Electrical Axis/Vectors Flashcards
Describe the two planes through which an ECG views the heart.
Which lead numbers are the bipolar limb leads? How are they positioned and which leads are considered positive and negative?
What are the augmented limb leads? How are they positioned and which leads are considered positive and negative?
Where are each of the precordial chest leads placed?
Aside from the mass of tissue that is depolarizing/repolarizing, what would cause the amplitude of a wave to increase or decrease?
If a wave of depolarization/repolarization is moving directly towards or away from an electrode then its deflection will be maximal (for that given mass of tissue). If that wave is moving perpendicular to a lead then there will be no deflection (biphasic). Refer to image.
Draw out the circle of axis. Be sure to label the degrees and the leads associated with them. Is the circle of axis in the horizontal or vertical plane?
Vertical
Will the QRS wave have a positive or negative deflection for Lead 1? Why?
Will the QRS wave have a positive or negative deflection for lead 2? Why?
Will the QRS wave have a positive or negative deflection for lead 3? Why?
Will the QRS wave have a positive or negative deflection for lead aVR? Why?
Will the QRS wave a positive or negative deflection for lead aVL? Why?
Will the QRS wave have a positive or negative deflection for lead aVF? Why?
In what plane do the precordial chest leads view the heart?
Horizontal
In which direction does a QRS wave typically deflect for leads v1-v6?
What are the precordial chest leads used to detect?
Changes to mass of left ventricle (hypertrophy, infarcts, etc)
What is the mean electrical axis?
The average of all the instantaneous mean electrical vectors occurring sequentially during depolarization of the ventricles
What is used to calculate the mean electrical axis (MEA)? What plane is it calculated in?
Calculated in frontal plane only, using QRS deflections and amplitudes in limb leads (Leads 1, 2, 3, aVF, aVR, and aVF).
Draw out the MEA quadrants and label whether each quadrant represents a deviating or normal MEA.
What is a quick way to tell if the MEA is within the normal axis?
The QRS deflection is positive for Leads 1, 2, and aVF.
In which quadrant is this patient’s MEA? Explain.
Left axis deviation quadrant
Lead 1 is positive, lead 2 is biphasic, lead 3 is negative
How do you calculate overall QRS amplitude?
How can calculating QRS amplitude help to find the MEA angle?
How can you eyeball an MEA?
MEA will be closest to the lead with the largest QRS amplitude
MEA will be perpendicular to the lead with a biphasic QRS
