Flashcards in Cardio-Antiarrhythmics Deck (17)
what is the result of depolarizaiton in terms of AP?
Depolarization opens ion-specific channels which creates an Action Potential
what are the 3 phases of the Action potential?
0) depolarization proceeds rapidly due to na+ influx through rapidly opening Na+ channels.
1-2) plateau phase due to Ca2+ influx through more slowly opening Ca2+ channels.
3) repolarization due to closure of Ca2_ channels, K+ efflux through K+ chennels.
the membrane gradient is restored by Na+/K+ ATPase
what is the excitation-contraction coupling:
1) A.P. -> ^ Ca2+
2) ^ Ca2+, binds troponin C and & uncovers myosin binding site on actin
3) actin & myosin cross-linkages form -> contraction
-relaxation = Ca2+ released from troponin & pumped back into sarcoplasmic reticulum & out of cell, actin & myosin no longer cross-linked
what is Arrhythima?
electrical alterations -> abnormalities in heart rhytm. this may not affect the CO.
what is altered initiation?
SA node, altered rate, altered site
what is altered conduction?
heart block (bradyarrhythmias)
reentry conduction (tacharrhythmias)
what is ventricular fibrillation?
its irrgular rapid contraction of ventricles -> cannot pump blood properly. if not treated immediately it could be fatal.
how do defibrillators work?
they stop fibrillation by temporarily stopping all electrical activity to allow normal rhythm to resume.
where are 4 classes of antiarrhythimic agents.
class 1: Na+ channel blockers
class 2: beta-blockers
Class 3: Prolonged action potential/K+ channel blaocks
class 4: Ca2+ channel bloackers
what do Na+ channel blockers do?
reduce recovery of Na+ channels, therefore reduce conduction and excitation
what do K+ channel blockers?
prolong the Action Potential therefore refractory period.
describe the Na+ channel blocker 1A- Quinidine:
prototypical drug in this class, now less frequency used due to side-effects.
describe the Na+ channel blocker 1B- Lidocaine
most commonly used IV anti-aahythmic
describe the Na+ channel blocker 1C
also affect K+ channels- only used for severe ventricular arrhythmias
describe the class 2 beta bloackers.
inhibits SNS effects & slows HR
most useful antiarrhythmics currently available
describe the class 3 K+ channel blockers
prolong action potential duration
also affect beta receptors & Na+ & Ca2+ channels