Lecture 4

Question 1

Phase 0 is __________ and deals with the electrolyte _____

Answer 1

rapid depolarization
Na

Action potential is initiated by an increase in Na conductance through ion-specific fast channels

Question 2

Phase 1 is ______________

Answer 2

early rapid repolarization

Na permeability is rapidly inactivated over 1-2ms
The cell starts to repolarize

Question 3

Phase 2 is ______

Answer 3

Plateau

Repolarization is delayed by an increase in conductance of Ca through slow channels

Question 4

Phase 3 is ________ and deals with the electrolyte ____

Answer 4

rapid repolarization
K

Complete repolarization due to inactivation of Ca conductance and an increase in K permeability

Question 5

Phase 4 is ___________, this phase is the _______________

Answer 5

Spontaneous depolarization
absolute refractory stage

Slow depolarization characteristic of all pacemaker cells.
Results from a complex interaction between inward and outward currents of Ca and K during diastole

Question 6

Slow channels are _______ mediated

Answer 6

Calcium

Question 7

Fast channels are ______ mediated

Answer 7

Sodium

Question 8

Mechanism of arrhythmias include:

Answer 8

impulse generation (automaticity)
re-entry

Question 9

Cells that undergo spontaneous phase 4 depolarization are automatic and _______________________.

Answer 9

capable of impulse generation

Question 10

In ventricular cells, Ca accounts for the _______ phase, whereas in SA node cells, Ca accounts for the ____________ phase

Answer 10

plateau phase (phase 2)

initial depolarization (phase 0)

Question 11

Factors that reduce automaticity at the higher pacemaker sites will ________ favor the movement of the pacemaker to lower sites.

Answer 11

passively

vagal influences

• digitalis drugs
• parasympathomimetic drugs
• halothane

Question 12

__________ result from enhanced automaticity at a site outside the SA node (Ectopic Pacemaker)

• sympathomimetic influences
• hypercarbia
• hypoxia
• dig toxicity

Answer 12

Ectopic foci

Question 13

Re-entry forms new pathways/tracts that bypass pacemakers (such as ____________) For re-entry to occur:

Answer 13

Wolf Parkinson White

unidirectional block of impulses conduction (area of injury)
slow conduction via an alternative pathway
impulse finds the unidirectional block repolarized and able to conduct the impulse retrograde
impulse reactivates the alternate pathway and repeats the process

Question 14

Re-entry can occur at these sites:

Answer 14

SA Node: SA node re-entry
Atrium: Atrial tachycardia or flutter
AV node: AV nodal re-entry and tachycardias mediated by accessory pathways
Ventricle: VT

Question 15

Na channels work on the _________

Answer 15

Atria and Ventricles (Muscle)

Question 16

Ca channels work on the ________

Answer 16

SA node and AV node (nodes)

Question 17

Class I antiarrythmics work by _________

examples include:

Answer 17

inhibit fast Na channels
IA: quinidine, procainamide
IB: Lidocaine, mexilitine
IC: Flecainide, Propafenone

Question 18

Class II antiarrythmics work by _______

examples include:

Answer 18

Decrease rate of depolarization

Beta blockers

Question 19

Class III antiarrythmics work by ___________

Examples include:

Answer 19

Inhibiting potassium ion channels

Amiodarone, Sotalol, Ibutilide, Dofetilide, Bretylium

Question 20

Class IV antiarrythmics work by ____________

Examples include:

Answer 20

Inhibit slow calcium channels

Diltiazem, Verapamil

Question 21

__________ slow conduction and prolong the QRS complexes in the atria and ventricles

Answer 21

Na channel blockers (Type I)

Question 22

_________ slow the atrial rate (SA node effect) and slow the conduction through the AV node (prolonging the PR interval)

Answer 22

Ca channel blockers (Type IV)

Question 23

______ interrupts reentry by slowing the conduction or increasing the refractory period.
Prolongs the QT interval and induces triggered activity in the ventricle causing polymorphic VT (torsades de pointes)

Answer 23

K Channel Blockade (Type III)

Question 24

Effects on the action potential:
Type 1a
Type 1b
Type 1c
Type II
Type III
Type IV

Answer 24

Type 1a: slows phase 0, prolongs 3
Type 1b: Slows 0, shortens 3
Type 1c: Very slow 0, no 3 effects
Type II: Reduces slope of 4
Type III: Prolongs 3
Type IV: Reduces slope of 4

Question 25

Class _____ blocks fast Na channel with or without K channel blockade

Answer 25

I

Question 26

Class I__ has the most significant effect on K.

Answer 26

IA

Question 27

Class I___ has the highest risk of arrythmias

Answer 27

IC

Question 28

Unclassified antirhythmic mediations include

Answer 28

adenosine and digoxin

Question 29

Classification of Procainamide is _____. It is a ____ and ____ channel blocker. Depresses automaticity by decreasing the slope of phase ____ depolarization, increases refractoriness. Prevent reentry by converting unidirectional to bidirectional block.

Answer 29

IA
Na and K
4

Question 30

Indications of procainamide:

Answer 30

SVT, A-Fib, PVCs, and VT