EXAM #2: CV PHARM 1

Question 1

What is the definition of excitability?

Answer 1

Ability of a cell to respond to an electrical stimulus

Question 2

What is the definition of automaticity?

Answer 2

Ability for a cell or group of cells to initiate an action potential

Question 3

What is the definition of conductivity?

Answer 3

Ability of a cell or region of cells to receive and transmit an action potential

Question 4

What is the definition of dromotropism?

Answer 4

Ability to alter the rate of conduction

Question 5

What is the definition of refractoriness?

Answer 5

Inability of a cell to receive and transmit an action potential

E.g. during portions of the action potential

Question 6

What phases of the cardiac action potential does the QRS complex correspond with?

Answer 6

Phase 0,2, and 3

Question 7

What phases of the cardiac action potential does the p-wave correspond with?

Answer 7

Phase 0 of the atrial

Question 8

What is the rule regarding electrical and mechanical activity of the heart?

Answer 8

Electrical activity ALWAYS comes before mechanical

Question 9

What phase of the cardiac action potential does the T-wave correspond with?

Answer 9

Repolarization

Question 10

Draw and label the phases of the cardiac action potential.

Answer 10

N/A

Question 11

What ion channel mediates phase 0 if the cardiac action potential?

Answer 11

• Na+

Question 12

What is the difference between fast and slow Na+ current?

Answer 12

Fast= initial current for depolarization

Slow= maintained throughout action potential

Question 13

What ion channels mediate phase 2 of the cardiac action potential?

Answer 13

1) Ca++ channels (L-type) inward

2) K+ outward

Question 14

What maintains the plateau of phase 2?

Answer 14

Balance of Ca++ in an K+ out

Question 15

What ion channels mediate phase 3 of the cardiac action potential?

Answer 15

K+ efflux

Question 16

What happens to the cardiac action potential with K+ channel blockers?

Answer 16

AP is prolonged b/c of less efflux for phase 3

Question 17

What ion channel is responsible for phase 4 of the cardiac action potential?

Answer 17

Funny current

Question 18

What locations of the heart normally have phase 4 depolarization?

Answer 18

SA and AV node

Question 19

What are the three phases of the cardiac Na+ channel?

Answer 19

1) Resting
- Activation gate closed
- Inactivation gate open

2) Activated
- Both gates open

3) Inactivated
- Inactivation gate closed

Question 20

What is the effect of increased late Na+ current?

Answer 20

Prolonged cardiac action potential

Question 21

When is a prolonged Late Na+ current seen?

Answer 21

Ischemia
Heart Failure
Arrhythmia
Peripheral arterial disease

Question 22

Outline the pathophysiology associated with enhanced Late Na+ current.

Answer 22

1) Increased Na+ influx leads to elevated intracellular Na+
2) Elevated intracellular Na+ activates the Na+-Ca++ exchanged
- Exchange of Na+ (out)
- Ca++ into the cell
3) This causes increased intracellular Ca++
4) Ca++ overload develops

Question 23

What are the consequences cellular Ca++ overlaod?

Answer 23

1) Electrical instability–>after-depolarizations/ arrhythmia
2) Mechanical dysfunction–>abnormal contraction and relaxation

Question 24

Draw the SA node action potential.

Answer 24

N/A

Question 25

What causes phase 0 in the SA node AP? How does this compare to the ventricular tissue?

Answer 25

• Ca++ current in SA node

- Na+ in ventricular myoctye

Question 26

What phases are missing from the SA node AP?

Answer 26

No phase 1 and 2

Question 27

What do Na+ channel blockers effect more, nodal or ventricular tissue? Why?

Answer 27

Ventricular/ myocyte b/c these tissues have a fast inward Na+ current that causes depolarization

Question 28

What is the ERP/ADP ratio? Why is this important?

Answer 28

This is the ratio of the “effective refractory period” to the “Total action potential duration”

The LOWER the ratio, the EASIER it is for depolarization by aberrant impulses i.e. the longer the APD is with a shorter ERP–>arrhythmia*

Question 29

Draw the cardiac action potential and the effective/ relative refractory periods.

Answer 29

N/A

Question 30

What are the two major categories of mechanisms of arrhythmogenesis?

Answer 30

1) Disorders of impulse formation

2) Disorder of impulse conduction

Question 31

List the disorders of impulse formation.

Answer 31

• No change in pacemaker site e.g. sinus tachy or bradycarida
• Ectopic foci
• Early and delayed after-depolarizations

Question 32

List the disorders of impulse conduction.

Answer 32

• AV Block
• Ventricular re-entry
• AV re-entry

Question 33

How is atrial tachycardia manifested on ECG?

Answer 33

Change in shape and rate of p-waves

Question 34

What is an early after-depolarization?

Answer 34

Depolarization in the relative refractory period, during a prolonged plateau phase

Question 35

What is a common consequence of an early-after depolarization?

Answer 35

Torsades De Pointes

Question 36

What is a delayed after-depolarization?

Answer 36

• Occurs in high intracellular Ca++ concentrations
• Normal upstroke followed by abnormal depolarization that leads to a secondary uptroke
• Abnormal rhythm results

Question 37

What is the difference between a 1st, 2nd, and 3rd degree AV block?

Answer 37

1st= prolonged PR interval 
2nd= not all p-waves followed by QRS 
3rd= no P/QRS relationship i.e. AV dissociation

Question 38

What is AV Nodal Reentrant Tachycardia?

Answer 38

• Patient has 2x conduction paths/velocities in the AV node*****
• Ectopic ATRIAL PREMATURE BEAT finds fast pathway in refractory period (via normal SA nodal pathway)
• Slow pathway depolarized and enters fast pathway b/c it is fast enough to repolarized enough for stimulation
• Circular motion begins

Note that this does not have to occur just in the AV node.

Question 39

What are the manifestations of re-entry?

Answer 39

• A-flutter
• AVNRT
• Accessory SVT
• Ventricular re-entry