Week 1

Question 1

2 Types of Action Potentials in the heart

Answer 1

• Slow action potentials in pacemaker (nodal)cells

- Fast action potentials in myocytes

Question 2

Where is your normal pacemaker?

Answer 2

SA node in the atrium–>AV node–>bundle of His–>Purkinje fibers–>ventricles

Question 3

How do you measure an action potential?

Answer 3

Do this by looking at an ECG

Question 4

ECG

• P wave
• QRS complex
• T wave

Answer 4

• P wave is representing SA and atrial depolarization
• QRS complex with ventricular depolarization
• T wave represents repolarization of ventricles

Question 5

Why don’t you see atrial depolarization on ECG?

Answer 5

It’s buried in QRS; it’s a smaller muscle group compared to that of the ventricles

Question 6

Types of leads

• Bi-polar; specifically
• Unipolar

Answer 6

• negative and positive; with current flowing from negative to positive; I, II and III
• one lead that is positive and is going to positive

Question 7

How is the current flow of heart (vector) in relation to lead polarity?

• same direction
• going against the natural current
• perpendicular to current

Answer 7

• same direction (parallel), you get upward deflection (top pic)
• get a downward deflection
• you get a solid straight line

Question 8

Bipolar lead directions

• Lead I
• Lead II
• Lead III

Answer 8

• Lead I: R arm (-) to L arm (+)
• Lead II: R arm (-) to L leg (+)
• Lead III: L arm (-) to L leg (+)

Question 9

Augmented leads

• aVR
• aVL
• aVF

Answer 9

• aVR is positive at the right arm; will be downward deflection
• aVL is positive at left arm; depends on where the heart sits
• aVF positive towards bottom at foot; will be upward deflection

Question 10

V1-V6

Answer 10

• V1: located 2 cm to right of sternum at intercostal space 4.
• V2 2 cm to left of the sternum at 4th intercostal space.
• V4 is mid clavicular at 5th intercostal space.
• V3 between V2 and V4 along 5th rib.
• V6 is mid axillary along the 5th intercostal space with
• V5 being in between V4 and V6.

Question 11

PR interval

• what is it?
• what does it represent?

Answer 11

• from beginning of P to R

- shows conduction of atria

Question 12

PR segment

Answer 12

• from end of P wave to beginning of R

Question 13

QRS interval

• what is it?
• what does it represent?

Answer 13

• From beginning of Q to end of S

- ventricular contraction

Question 14

QT interval

Answer 14

• beginning of Q to end of T

Question 15

ST segment

Answer 15

• S to beginning of T

Question 16

Boxes and EKG

• 1 small box
• 1 large box
• 1 sec?
• 1 min

Answer 16

• 0.04 sec
• 5 small boxes, .20 seconds
• 5 large boxes
• 1500 small boxes of 300 big boxes.

Question 17

Using angles to detect heart disease

• where does heart sit
• leads to look at to detect shift in heart axis, and their normal
• LAD
• RAD

Answer 17

• between -30 and +90
• Lead I and AVF, normal is positive (upward) on EKG
• If lead 1 is positive but aVF is negative direction, it’s LAD
• If lead 1 is negative and aVF is positive it’s a RAD