Cardiac Exam Lecture 4 (EKG)

Question 1

What does the EKG measure?

Answer 1

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

Question 2

What do the upward and downward reflections of an EKG recording mean?

Answer 2

Up and down deflections result in vector moving towards or away from an electrode

Question 3

What does the EKG tell us about contractile activity or strength?

Answer 3

NOTHING, the EKG tells us nothing about contractile activity or strength

Question 4

Explain the twelve leads of an EKG

Answer 4

3 Bipolar Limb Leads: I, II, III

3 unipolar limb leads: aVF, aVR, and aVL

6 unipolar/pericardial leads: V1-V6

Question 5

In most people with normal cardiac function, which lead has the largest QRS complex?

Answer 5

Lead II, which is why it is used as emergency standard

Question 6

Where does the normal frontal plane vector of the heart point?

Answer 6

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

Question 7

Think about the diagram where the APs are shown above the EKG so you can see when things depolarize

Answer 7

Question 8

Draw the EKG that shows the activation of different cardiac tissues within the EKG

Answer 8

Question 9

Explain the rule of 300 and how you calculate HR on an EKG

Answer 9

For the Rule of 300: you count how many big boxes are between each R spike.

300/# of boxes btwn QRS complex

Question 10

How fast is a normal QRS segment?

Answer 10

100 ms

that is 0.10 seconds

(for reference the blink of an eye is 0.30 s or 300 ms)

Question 11

Draw Eintoven’s Triangle

Answer 11

Question 12

Explain the placement of the positive and negative electrodes for the following leads:

Lead I

Lead II

Lead III

Answer 12

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

Question 13

Draw the snowflake diagram

Answer 13

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

Question 14

Explain what the following vectors lead to on the EKG:

Atrial Depolarization Vector

Septal Depolarization vector

Ventricular Depolarization Vector

Ventricular Repolarization

Answer 14

Atrial Depolarization: P wave

Septal Depolarization: Q wave (downwards)

Ventricular Depolarization: R wave

Ventricular Repolarization: T wave