ECG1

Question 1

What is the SA node’s intrinsic rate?

Answer 1

60 to 100 bpm

Question 2

Define Bachman’s bundle.

Answer 2

The anterior tract that divides and extends into the LA.

Question 3

What is considered the primary pacemaker of the heart?

Answer 3

SA node

Question 4

Where is the SA node located?

Answer 4

In the superior right atrium at the entrance to the superior vena cava

Question 5

Where is the triangle of Koch located?

Answer 5

In the floor of the right atrium superior to the septal leaflet of the tricuspid valve.

Question 6

What is the only pathway to the ventricles called (in a normal person)?

Answer 6

Triangle of Koch

Question 7

What is the AV nodes intrinsic rate?

Answer 7

40 to 60 bpm

Question 8

What node is considered the secondary pacemaker?

Answer 8

The AV node.

Question 9

Why is the AV node delayed?

Answer 9

1. to allow for atrial contraction (increase preload and subsequent contraction due to Frank-Starling mechanism)
2. protects the ventricles from inappropriate high atrial rates (ie atrial fibrillation and flutter)

Question 10

Is the refractory period longer for the SA or the AV node?

Answer 10

The AV node refractory period is longer.

Question 11

Why is Ca++ important for electrical conduction in the heart?

Answer 11

Calcium is the major ion responsible for the action potential.

Question 12

What is the most proximal portion of the ventricular conduction system called?

Answer 12

Bundle of His

Question 13

What is the terminal end of the electrical conduction system called?

Answer 13

Purkinje Fibers

Question 14

What is the intrinsic rate of the Purkinje Fibers?

Answer 14

20 to 40 bpm

Question 15

Define automaticity

Answer 15

Self-excitation

(accomplished by P cells which are located in the SA node, atrial tissue, AV node, and ventricular tissue —they have different rates bc different refractory periods)

Question 16

What maintains the negative resting potential?

Answer 16

The sodium-potassium ATPase pump

Question 17

How does the ATPase pump reset the membrane to pre-depolarizing electrolyte levels?

Answer 17

It exchanges 3 Na+ ions OUT of the cell for

2 K+ ions INTO the cell

Question 18

Using the sodium-potassium ATPase pump is an active process. What does it require?

Answer 18

Magnesium and ATP(energy)

Question 19

Which phase of the action potential plot corresponds with the resting membrane potential?

Answer 19

Phase 4

Question 20

Describe phase 4 of the action potential

Answer 20

resting membrane potential (-80 to -90mV)

negativity maintained by the sodium/potassium pump

sodium out/potassium in

(corresponds with the baseline between the T and P wave)

Question 21

Where happens during phase 0 of the action potential?

Answer 21

Rapid depolarization of the cell (stimulus applied)

Sodium rushes out of the cell making it less negative

(Potassium leaks out of the cell)

Question 22

In what phase do the drugs lidocaine and procainamide work?

Answer 22

Phase 0

Question 23

Describe phase 1 of the action potential.

Answer 23

(Brief rapid initiation of repolarization)

(closure of the sodium channels)

Chloride ions enter the cell (makes it more negative)

Question 24

What effect does sympathetic innervation have on electrical conduction?

Answer 24

Increases SA nodal chronotropy, increases AV nodal dromotropy and increases myocardial iontopy

Question 25

Describe Phase 2 of the action potential.

Answer 25

"Plateau" phase Slowing of repolarization Calcium enters the cell, leading to contraction of the muscle in a sustained, slower manner

Question 26

Which class of antiarrhythmics work at phase 2 of the action potential?

Answer 26

Class IV antiarrhythmics (calcium channel blockers) Verapamil, Diltiazem

Question 27

Describe Phase 3 of the action potential.

Answer 27

Sudden acceleration in the rate of repolarization. Potassium movement into the cell causes this rapid return in intracellular negativity Sodium-potassium pump operates at this phase

Question 28

What class of antiarrhythmics work in phase 3?

Answer 28

Class III Amiodarone, sotalol (by prolonging the return to a resting potential)

Question 30

What do funny (I_f) channels do?

Question 31

Define chronotropy.

Answer 31

Effects that change the HR Positive chronotropes increase HR Negative chronotropes decrease the HR

Question 32

Define dromotropy

Answer 32

Effects the conduction speed of the AV node

Question 33

What effect does parasympathetic innervation have on electrical conduction?

Answer 33

Decreases the SA nodal chronotropy and decreases the AV nodal dromotropy