Exam 3- Intro to 12 Lead EKG

Question 1

Define depolarization

Answer 1

Contraction occurs when a positive charge spreads from sinus node through myocardium

Question 2

Define repolarization

Answer 2

When electrical conduction ends and sinus node and myocardium regain a resting negative charge

Question 3

Describe the flow of electrical current through the heart as it is represented on the 12 lead EKG

Answer 3

Electrical activity in 3 orthogonal directions

Cardiac axis created by interaction of leads with each other

Question 4

Define the 3 orthogonal directions of electrical activity

Answer 4

Right to Left
Superior to Inferior
Anterior to Posterior

Question 5

Explain the cardiac axis created by interaction of leads with each other

Answer 5

Mean direction of action potentials traveling through ventricles during ventricular activation (depolarization)
V1, V2, V3: predominantly negative because electricity is moving away from these leads
V3 & V4: biphasic
V5 & V6: should be completely positive because electricity is moving toward these leads

Question 6

Define the P wave represented on the 12 lead EKG

Answer 6

Atrial depolarization

Question 7

Define the QRS complex represented on the 12 lead EKG

Answer 7

Ventricular depolarization

Question 8

Explain the waves of the QRS complex and define normals and capital/lowercase

Answer 8

Normal 80-120 ms (0.08-0.12 s)
3 small boxes or less (boxes on the pokokokaper)
Q wave = 1st downward deflection
R wave = 1st upward deflection
S wave = 1st negative deflection after an R wave
CAPS = > or = 2 small boxes
Lowercase = less than 2 small boxes

Question 9

Define the ST segment represented on the 12 lead EKG

Answer 9

Total ventricular repolarization time (return to steady state)

Question 10

Define the location of the ST segment and describe pathologic definition and findings

Answer 10

Flat line between the QRS and T wave
Pathologic = deviation of 1-2 mm above or below baseline
Isoelectric baseline must be defined not as + or - (just in the middle)
Concave ST = bad
J-point = OK

Question 11

Define the T wave represented on the 12 lead EKG

Answer 11

Rapid phase of ventricular systole (recovery)

Question 12

Explain what happens to the myocytes during the T wave and explain what inversion of T wave and peaked T wave mean

Answer 12

Myocytes regain negative charge (repolarization)
Inversion = ischemia
Peaked appearance = hyperkalemia

Question 13

Define the length/time of 1 small box on the 12 lead EKG

Answer 13

40 ms (0.04 s)

Question 14

Define the length/time of 1 large box and its equivalence to smaller boxes on the 12 lead EKG

Answer 14

200 ms (0.2 s) = 5 smaller boxes

Question 15

Define the PR interval represented on the 12 lead EKG

Answer 15

Beginning of the P wave to the start of QRS complex

Question 16

Define PR interval normals and abnormals including their causes

Answer 16

Normal: 120-200 ms (0.12-0.2 s)
0.2 s = 1st degree AVB
Depression below baseline = pericarditis- usually very subtle

Question 17

Define the QT interval represented on the 12 lead EKG

Answer 17

Entirety of ventricular systole

Question 18

Explain QTc

Answer 18

Corrected QT (QTc) accounts for HR - anytime HR varies from 60, you have to correct

Question 19

Describe how unipolar leads are obtained

Answer 19

Draw an intersecting line through each of the angles created by Einthoven’s triangle = new vectors through which to view electrical activity

Question 20

Define and describe the 3 unipolar leads

Answer 20

aVR, aVL, aVF (only positive pole)
aVR: Augmented voltage RA- combination of leads I and II
aVL: Augmented voltage LA- combination of leads I and III
aVF: Augmented voltage foot- combination of leads II and III

Question 21

Describe how the 3 bipolar leads operate (don’t need to define leads here)

Answer 21

Positive and negative pole

Record electrical voltages in 1 position relative to another

Question 22

Define and describe the 3 bipolar leads

Answer 22

Comprise Einthoven’s triangle
Lead I: electrical difference between LA (+) and RA (-)
Lead II: electrical difference between LL (+) and RA (-)
Lead III: electrical difference between LL (+) and LA (-)

Question 23

Compare and contrast the unipolar and bipolar leads

Answer 23

Unipolar leads record voltages at 1 location relative to 0 rather than relative to another lead (like in bipolar)
For unipolar, leads are “augmented” over the actual voltage from each extremity

Question 24

Define and describe Einthoven’s triangle

Answer 24

3 sides of an equilateral triangle with the heart in the middle (leads I-III)
An imaginary formation of three limb leads in a triangle
Produces zero potential when the voltages are summed

Question 25

Define and describe Einthoven’s equation

Answer 25

Magnitude of deflection of lead II = sum of deflections of leads I & III
Lead II = sum of electromotive forces in heart
Einthoven’s equation: I + III = II (Leads I and III cancel each other out)

Question 26

Describe the relationship of the unipolar and bipolar leads in their creation of the cardiac axis

Answer 26

Inferior Heart = leads 2, 3, and aVF
Lateral heart= leads 1, aVL, V5, V6
Anterior = V3 and V4
Septal & anterior = V1 and V2

Question 27

Explain prolongation of the QRS complex and variation causes

Answer 27

Prolongation = delay in conduction through 1 or both bundle branches
Variations- scar tissue, conduction delays, normal variant

Question 28

Explain HR affect on QT interval, and QT interval normals

Answer 28

Increase in HR = shorter QT
Decrease in HR = longer QT
QT should be less than 1/2 R-R interval (less than 500 ms)
Less than 440 ms