EXAM #1: REVIEW OF ECG

Question 1

Where is the Cl- concentration high?

Answer 1

Extracellular

Question 2

Is the cardiac cell negatively charged or positively charged intracellularly?

Answer 2

Negative

Question 3

What are the five phases of the cardiac action potential?

Answer 3

0=  Rapid upstroke/ depolarization 
1=  Early repolarization
2= Plateau 
3= Rapid repolarization
4= Resting membrane potential

Question 4

Describe the ion flux in phase 0 of the cardiac action potential.

Answer 4

• Rapid influx of Na+
• FAST Na+ channels

“Rapid depolarization”

Question 5

Describe the ion flux in phase 1 of the cardiac action potential.

Answer 5

• Na+ channels close
• Voltage-gated K+ channels OPEN and K+ moves OUT

“Early repoarlization”

Question 6

Describe the ion flux in phase 2 of the cardiac action potential.

Answer 6

• Slow Ca++ channels open

- Opposing movement of Ca++ IN and K+ out= PLATEAU

Question 7

Why is the plateau phase of the action potential important?

Answer 7

This phase corresponds to systole; the pause allows contraction to occur

Question 8

Describe the ion flux in phase 3 of the cardiac action potential.

Answer 8

• Ca++ channels close
• K+ channels are still OPEN
• K+ OUT

“Rapid repolarization”

Question 9

Describe the ion flux in phase 4 of the cardiac action potential.

Answer 9

• Na+/K+ ATPase
• Only K+ channels are open and a SMALL amount of K+ fluxes

“Resting membrane potential”

Question 10

How many phases are there in the nodal action potential? What are they?

Answer 10

Three phases: 0, 3, and 4

Question 11

What phases are missing from the nodal action potential?

Answer 11

1 and 2

Question 12

How does the resting membrane of the nodal action potential differ from the cardiac myocyte action potential?

Answer 12

Cardiac myocyte= -90mV

Nodal= -60 mV

Question 13

Describe the ion flux in phase 0 of the nodal action potential.

Answer 13

• Upon reaching threshold, Slow Ca++ channels open

- Ca++ INFLUX

Question 14

Describe the ion flux in phase 3 of the nodal action potential.

Answer 14

• After depolarization, K+ channels open

- K+ EFFLUX

Question 15

Describe the ion flux in phase 4 of the nodal action potential.

Answer 15

• Funny channels open (HCN)
• K+ efflux progressively declines
• Ca++ influx occurs, leading to slow depolarization

Question 16

Outline the normal sequence of depolarization in the heart.

Answer 16

1) SA node
2) Atrial syncitium/ internodal tracts
3) AV node
4) Bundle of His
5) Purkinjie fibers
6) Ventricles

Question 17

What sequence of depolarization occurs in the ventricles?

Answer 17

1) Interventricular septum
2) Apex of the heart
3) Ventricular free walls

Question 18

What are the two branches of the left bundle branch?

Answer 18

Left aterosuperior fasicle

Left posteroinferior fasicle

Question 19

What is the conduction velocity of the cardiac depolarization in the SA node?

Answer 19

Less than 0.01 m/sec

Question 20

What is the conduction velocity of the cardiac depolarization in the atrial myocardium?

Answer 20

1.0- 1.2 m/sec

Question 21

What is the conduction velocity of the cardiac depolarization in the AV node?

Answer 21

0.02-0.05 m/sec

Question 22

What is the conduction velocity of the cardiac depolarization in the Bundle of His?

Answer 22

1.2- 2.0 m/sec

Question 23

What is the conduction velocity of the cardiac depolarization in the bundle branches?

Answer 23

2.0- 4.0 m/sec

Question 24

What is the conduction velocity of the cardiac depolarization in the Purkinje fibers?

Answer 24

2.0-4.0 m/sec

Question 25

What is the conduction velocity of the cardiac depolarization in the ventricular myocardium?

Answer 25

0.3 -1.0 m/sec

Question 26

Where is the conduction velocity the fastest in the heart?

Answer 26

Prukinje fibers

Question 27

Where is the conduction velocity the slowest in the heart?

Answer 27

AV node

Question 28

What does the p-wave of the ECG represent?

Answer 28

Atrial myocyte depolarization

Question 29

What does the PR Interval represent?

Answer 29

Time it takes for the stimulus to spread through the atria and pass through the AV junction

Question 30

What is the normal PR interval?

Answer 30

0.12- 0.2 seconds i.e. 3-5 small boxes Note that 1mm = 0.04 sec

Question 31

What does the QRS complex correspond to?

Answer 31

Ventricular myocyte depolarization

Question 32

What does the T-wave represent?

Answer 32

Ventricular repolarization

Question 33

What does the ST segment represent?

Answer 33

Ventricular myocyte plateau

Question 34

What does 10mm or 2x large boxes represent vertically on ECG paper?

Answer 34

1 mV

Question 35

What does 7 large boxes between R-waves represent in terms of rate?

Answer 35

43 bpm

Question 36

Draw the hexaxial diagram.

Answer 36

p. 36, 5-2

Question 37

What does the QT interval correspond to?

Answer 37

Entire ventricular action potential

Question 38

How can you specifically determine the mean QRS axis?

Answer 38

1) Take biphasic lead 2) 90 degrees from that OR 1) Average of 2x tallest QRS complexes

Question 39

What is the quick way to determine the mean QRS axis?

Answer 39

Looks at leads I, II, and III

Question 40

What does an upward I, II, and III indicate?

Answer 40

Normal axis (between -30 and 100)

Question 41

What does an upward I, mid II, and downward III indicate?

Answer 41

"Physiologic left-axis deviation"

Question 42

What does upward I and downward II and III indicate?

Answer 42

LAD

Question 43

What does down I and upward III indicate?

Answer 43

RAD (100+)

Question 44

What does downward I and upward II and III indicate?

Answer 44

Extreme axis deviation

Question 45

What are the general steps to interpreting and ECG?

Answer 45

1) Rate 2) Rhythm 3) Axis 4) Conduction 5) Infarction