1 - Antiarrhythmics Flashcards
What are cardiac arrhythmias caused by?
- Disease
- Cardiac injury
- Drugs
What are arrhythmias a result from?
- Abnormal impulse formation
- Abnormal impulse conduction
- Combination of both
What are the different types of arrhythmias?
- Premature contractions - PVC’s or PACS
- Tachycardia
- Flutters - atrial flutter (300 bpm), re-entry
- Fibrillations - uncoordinated contractions
- Bradycardia - normal but slower
- Heart block:
- Complete - His purkinje system cut in half, atria & ventricles work independently
- Partial - some more than others
What do antiarrhythmic medications do?
- Depress parts of the heart that are beating abnormally
What are the pharmacological effects of antiarrhythmic medications?
- Change of slope of depolarization
- Raise threshold for depolarization
- Alter conduction velocity in different parts of the heart
Where do most antiarrhythmic medications work (in which phase)?
At the effective refractory phase
What is the absolute (effective) refractory phase?
- Phases 0,1,2 and most of 3 (to about -50mV)
What is the relative refractory period?
- Middle of phase 3 to beginning of phase 4
What term is synonymous with absolute (effective) refractory period?
Depolarization
What are the 3 areas of the heart that have pacemaker activity?
- SA node
- AV node
- Purkinje fibers
What drives automaticity?
Spontaneous opening and closing of K+ channels
What is important in determining how easily and how frequently cells can depolarize?
Threshold and resting membrane potentials
How does the effective refractory period (ERP) relate between packemaker area cells and mycocardial cells?
ERP in pacemaker areas is longer than myocardial cells
Different arrhythmias require that the ERP be _________ or _________?
Lengthened of Shortened
When are drugs used to induce an arrhythmia?
- Ventricular arrhythmias due to AV node block
- Temporary heart block until pacemaker insertion
- Epinephrine
- Isoproterenol - beta 1 and beta 2 agonist
- Hypokalemic diuretics
What are the contraindications for antiarrhythmics?
- Complete AV heart block
- Congestive heart failure
- Hypotension
- Known hypersensitivity to the drug
What does the Class IA Antiarrhythmic drug’s mechanism of action?
- Na+ channel blocker (medium)
- Blocks conduction
- Prolongs duration of AP
What does the Class IB Antiarrhythmic drug’s mechanism of action?
- Na+ channel blocker (fast)
- Blocks conduction
- Decreases ERP
- Shortens the AP
What does the Class IC Antiarrhythmic drug’s mechanism of action?
- Na+ channel blocker (slow)
- Blocks conduction
- Little effect on ERP
- Slows conduction without affecting AP
What does the Class II Antiarrhythmic drug’s mechanism of action?
- Beta Blocker
- Decreases SA node automaticity
- Reduces sympathetic activity
What does the Class III Antiarrhythmic drug’s mechanism of action?
- K+ channel blocker
- Prolongs the AP
- Prolongs phase 3 repolarization
What does the Class IV Antiarrhythmic drug’s mechanism of action?
- Ca+ channel blocker
- Slows conduction velocity at AV node
- Decreases firing rate of SA and AV nodes
What are the 3 drugs classified as Class IA antiarrhythmics?
- quinidine
- procainamide (Pronestyl)
- disopyramide (Norpace)
What are some characteristics of quinidine?
- Toxic - can produce fatal arrhythmias
- Made from bark of cinchona tree –> cinchonism
- Site of action: atrial tissues
What are some characteristics of procainamide (Prnoestyl)?
- Class IA
- Derivative of the local anesthetic procaine
- Reversible lupus-like syndrome in 25% of pts
What are some characteristics of disopyramide (Norpace)?
- Class IA
- Causes peripheral vasoconstriction
- Treats ventricular arrhythmias, alternative to quinine and procainamide
What is the class IB drug of choice, used to treat ventricular arrhythmias?
Lidocaine (crossover drug)
What are other Class IB drugs that are indicated for other agents?
- Site Ventricles:
- phenytoin (Dilantin) - anticonvulsant
- Gingival hyperplasia
- mexiletine (Mexitil) - suppression of PVCs
- tocainide (Tonocard) - suppression of life-threatening ventricular arrhythmias
- phenytoin (Dilantin) - anticonvulsant
What are the characteristics of flecainide (Tambocor) and propafenone (Rythmol)?
- Class IC
- Acts on ventricles
- Approved only for use of refractory ventricular arrhythmias (life-threatening)
- Causes arrhythmias because of profound effect on Na+ channels in healthy heart tissue – Safety conern **
What class of antiarrhythmic drugs block effects of catecholamines on pacemaker cells to prolong the refractory period?
Class II
What do Class II antiarrhythmic drugs do?
- Depress automaticity
- Prolong AV conduction
- Decrease heart rate and contractility
What do Class III antiarrhythmic drugs do?
- Block K+ channels
- Prolongs AP and prolongs effective refractory period (ERP)
- Slows heart because drug reduces amount of norepinephrine released
What are some characteristics of amiodarone (Cordaron, Pacerone)?
- Class III
- Life-threatening recurrent ventricular fibrillation
- Contains iodine - blue skin
- May cause thyroid disease
- Severe toxic effects
What are some characteristics of verapamil (Calan)?
- Class IV
- Dilates coronary and peripheral arteries
What is the drug of choice for cardiac arrhythmias (PSVT)?
verapamil (Calan)
What class IV antiarrhythmic medication is also called a cardiac glycoside?
Digoxin - used for treatment of congestive heart failure
What does Digoxin do?
- Inhibits Na/K ATPase pump
- Increases intracellular Na/Ca exchange
- Increases intracellular Ca leading to increased contractility
What is used to treat bradyarrhythmias?
- atropine (anticholinergic) - elevates sinus rate, accompany MI
- isoproteronol (Isuprel) - beta agonist (beta1 and beta2), AV nodal block
What is used to treat ectopic pacemakers?
- Postassium
- Magnesium ion
What are the toxic reactions to antiarrhythmics?
- Hypersensitivity
- Hypotension, shock
- Paradoxical arrhythmias
- GI disorders
- Cinchonism - quinidine
