Cardio-Antiarrhythmics

Question 1

what is the result of depolarizaiton in terms of AP?

Answer 1

Depolarization opens ion-specific channels which creates an Action Potential

Question 2

what are the 3 phases of the Action potential?

Answer 2

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

Question 3

what is the excitation-contraction coupling:

Answer 3

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

Question 4

what is Arrhythima?

Answer 4

electrical alterations -> abnormalities in heart rhytm. this may not affect the CO.

Question 5

what is altered initiation?

Answer 5

SA node, altered rate, altered site

Question 6

what is altered conduction?

Answer 6

heart block (bradyarrhythmias) 
reentry conduction (tacharrhythmias)

Question 7

what is ventricular fibrillation?

Answer 7

its irrgular rapid contraction of ventricles -> cannot pump blood properly. if not treated immediately it could be fatal.

Question 8

how do defibrillators work?

Answer 8

they stop fibrillation by temporarily stopping all electrical activity to allow normal rhythm to resume.

Question 9

where are 4 classes of antiarrhythimic agents.

Answer 9

class 1: Na+ channel blockers
class 2: beta-blockers
Class 3: Prolonged action potential/K+ channel blaocks
class 4: Ca2+ channel bloackers

Question 10

what do Na+ channel blockers do?

Answer 10

reduce recovery of Na+ channels, therefore reduce conduction and excitation

Question 11

what do K+ channel blockers?

Answer 11

prolong the Action Potential therefore refractory period.

Question 12

describe the Na+ channel blocker 1A- Quinidine:

Answer 12

prototypical drug in this class, now less frequency used due to side-effects.

Question 13

describe the Na+ channel blocker 1B- Lidocaine

Answer 13

most commonly used IV anti-aahythmic

Question 14

describe the Na+ channel blocker 1C

Answer 14

also affect K+ channels- only used for severe ventricular arrhythmias

Question 15

describe the class 2 beta bloackers.

Answer 15

propranolol, metropriolol
inhibits SNS effects & slows HR
most useful antiarrhythmics currently available

Question 16

describe the class 3 K+ channel blockers

Answer 16

prolong action potential duration

also affect beta receptors & Na+ & Ca2+ channels

Question 17

describe the class 4

Answer 17

Ca2+ channel blockers verapamil

decreases cardiac contractility.