Cardiac Exam Lecture 4 (EKG) Flashcards
What does the EKG measure?
EKG records differences in voltages (wave of depolarization)
Measures direction and amplitude of VECTORS within the heart
EKG only measures electrical activity of atria and ventricles
What do the upward and downward reflections of an EKG recording mean?
Up and down deflections result in vector moving towards or away from an electrode
What does the EKG tell us about contractile activity or strength?
NOTHING, the EKG tells us nothing about contractile activity or strength
Explain the twelve leads of an EKG
3 Bipolar Limb Leads: I, II, III
3 unipolar limb leads: aVF, aVR, and aVL
6 unipolar/pericardial leads: V1-V6
In most people with normal cardiac function, which lead has the largest QRS complex?
Lead II, which is why it is used as emergency standard
Where does the normal frontal plane vector of the heart point?
The normal frontal plane vector of the heart points down and to the anatomical left because the LV is the largest chamber of the heart and therefore it generates the most electrical current
Think about the diagram where the APs are shown above the EKG so you can see when things depolarize
Draw the EKG that shows the activation of different cardiac tissues within the EKG
Explain the rule of 300 and how you calculate HR on an EKG
For the Rule of 300: you count how many big boxes are between each R spike.
300/# of boxes btwn QRS complex
How fast is a normal QRS segment?
100 ms
that is 0.10 seconds
(for reference the blink of an eye is 0.30 s or 300 ms)
Draw Eintoven’s Triangle
Explain the placement of the positive and negative electrodes for the following leads:
Lead I
Lead II
Lead III
Lead I : RA is negative electrode, Left arm is positive electrode
Lead II: RA is negative electrode, left leg is positive electrode
Lead III: LA is negatie electrode, LL is positive electrode
Draw the snowflake diagram
remember, start by putting ZERO degrees on the anatomical LA (positive end of Lead I).
As you go up from there the angles are negative
As you go down the angles are positive and just go around until you get to 180
Explain what the following vectors lead to on the EKG:
Atrial Depolarization Vector
Septal Depolarization vector
Ventricular Depolarization Vector
Ventricular Repolarization
Atrial Depolarization: P wave
Septal Depolarization: Q wave (downwards)
Ventricular Depolarization: R wave
Ventricular Repolarization: T wave