ANTIRRYTHMIA Flashcards
(52 cards)
Give the significance of antirrythmias
1) Most common cause of death in MI
2)
Arrythmias mainly occur due to two main causes
1) Improper impulse generation (abnormal automaticity)
2) Improper impulse conduction
Action potentials in the heart can be of two types
1) Pacemaker action potentials
2) Myocardial action potentials
Give the phases of the pacemaker action potential
1) Phase 1 - Pacemaker potential
Slow positive increase in the membrane potential until it reaches threshold
2)Depolarization
3) Repolarization
Give the phases of the myocardial action potential
Phase 0 - rapid influx of sodium
Phase 1 - transient efflux of potassium
phase 2 - influx of calcium that is electrically balanced by the efflux of potassium
Phase 3 -
Phase 4
Give the classification of the Antiarrhythmic drugs
Class IA
Class IB
Class IC
Class II
Class III
Class IV
Miscellaneous
All Class one drugs block which channel (Local anaesthetics)
Sodium channel
Give examples of :
CLASS IA DRUGS
CLASS IB DRUGS
CLASS IC DRUGS
CLASS IA DRUGS
Quinidine
Disopyramide
Procainamide
CLASS IB DRUGS
Lidocaine
Mexiletine
CLASS IC DRUGS
Flecainide
Propafenone
Give the Mechanism of action of the Class IA drugs
1) Blocking the sodium channels -affect phase 0
2) Block the potassium channels - repolarization leading to delayed repolarization thus a prolonged AP
What is the effect of the class IA agents
1)Prolong the AP thus leading to Torsade de pointes
2)
Prolonged Action potential in the ecg is shown by
Prolonged QT interval - due to potassium channel blockade
Blocking the sodium channels by class IA drugs causes
Slow conduction velocity in the atria, purkinje and ventricles
Give :
1) ROA of Quinidine
2) Adverse effects of Quinidine
3) Metabolism of Quinidine
4) DDI
1) Oral
2) Cinchonism (blurred vision, tinnitus , headache , psychosis) , GIT problems , autoimmune reactions
3) CYP3A4 into active metabolites
4) i)Inhibits CYP2D6 and P glycoprotein
ii) Reduces clearance of digoxin
Both Quinidine and Disopyramide are metabolized using
CYP3A4
Give the PK of Procainamide
Procainamide may be given by IV or IM and is well absorbed orally. It is acetylated to N-acetylprocainamide (NAPA) that is eliminated in the kidney.
Give the A/E of Procainamide
Hypotension
A reversible syndrome similar to SLE
what may worsen class one drug toxicity
Hyperkalemia
Give two types of drugs that may be used to treat overdose of the class 1A drugs
1) Sodium lactate for drug induced arrhythmias
2) Pressor sympathomimetics for hypotension
Give two examples and ROA of the class 1b drugs
Lidocaine - IV or IM
Mexiletine - orally
Give two MOA of the class 1b drugs
1) Sodium channel blockade
2) Increase phase 3 repolarization thus reduced AP and reduced or unchanged QT interval
What type of tissue do the class 1b drugs affect
1) Ischemic tissue
2) Depolarized Purkinje or ventricular tissue
(Rarely have an effect on atrial tissue)
Class 1b agents usually have little effect on normal cardiac cells thus little effect on the ECG, explain?
Class IB agents usually associate and dissociate rapidly from the sodium channels thus usually affect the cells when there is rapid depolarization and repolarization
Give ROA of Lidocaine
Lidocaine may be given by IM or IV but never orally due to its very high first pass effect and the its metabolites are potentially cardiotoxic
What CYP Isoenzyme metabolizes Mexiletene
CYP2D6
