Lecture 4 Flashcards
Phase 0 is __________ and deals with the electrolyte _____
rapid depolarization
Na
Action potential is initiated by an increase in Na conductance through ion-specific fast channels
Phase 1 is ______________
early rapid repolarization
Na permeability is rapidly inactivated over 1-2ms
The cell starts to repolarize
Phase 2 is ______
Plateau
Repolarization is delayed by an increase in conductance of Ca through slow channels
Phase 3 is ________ and deals with the electrolyte ____
rapid repolarization
K
Complete repolarization due to inactivation of Ca conductance and an increase in K permeability
Phase 4 is ___________, this phase is the _______________
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
Slow channels are _______ mediated
Calcium
Fast channels are ______ mediated
Sodium
Mechanism of arrhythmias include:
impulse generation (automaticity) re-entry
Cells that undergo spontaneous phase 4 depolarization are automatic and _______________________.
capable of impulse generation
In ventricular cells, Ca accounts for the _______ phase, whereas in SA node cells, Ca accounts for the ____________ phase
plateau phase (phase 2)
initial depolarization (phase 0)
Factors that reduce automaticity at the higher pacemaker sites will ________ favor the movement of the pacemaker to lower sites.
passively
vagal influences
- digitalis drugs
- parasympathomimetic drugs
- halothane
__________ result from enhanced automaticity at a site outside the SA node (Ectopic Pacemaker)
- sympathomimetic influences
- hypercarbia
- hypoxia
- dig toxicity
Ectopic foci
Re-entry forms new pathways/tracts that bypass pacemakers (such as ____________) For re-entry to occur:
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
Re-entry can occur at these sites:
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
Na channels work on the _________
Atria and Ventricles (Muscle)
Ca channels work on the ________
SA node and AV node (nodes)
Class I antiarrythmics work by _________
examples include:
inhibit fast Na channels
IA: quinidine, procainamide
IB: Lidocaine, mexilitine
IC: Flecainide, Propafenone
Class II antiarrythmics work by _______
examples include:
Decrease rate of depolarization
Beta blockers
Class III antiarrythmics work by ___________
Examples include:
Inhibiting potassium ion channels
Amiodarone, Sotalol, Ibutilide, Dofetilide, Bretylium
Class IV antiarrythmics work by ____________
Examples include:
Inhibit slow calcium channels
Diltiazem, Verapamil
__________ slow conduction and prolong the QRS complexes in the atria and ventricles
Na channel blockers (Type I)
_________ slow the atrial rate (SA node effect) and slow the conduction through the AV node (prolonging the PR interval)
Ca channel blockers (Type IV)
______ 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)
K Channel Blockade (Type III)
Effects on the action potential: Type 1a Type 1b Type 1c Type II Type III Type IV
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
