Antidysrythmic Drugs Flashcards
What is atrial fibrilation?
a chaotic rhythm of the QRS complexes
What is shown here?
an illustration of a damaged pathway
What is shown here?
Depolarization struggles to get through the muscle, but does, the P-QRS complex is just bigger
What is shown here?
re-entry
What is shown here?
Depolarization struggles to get around, but keeps going around in circles: re-entry arrhythmias
What do class I antidysrhythmic drugs do?
block voltage-sensitive Na channels
What do class II antidysrhythmic drugs do?
beta adrenoceptor antagonists (beta blockers)
What do class III antidysrhythmic drugs do?
They prolong the refractory period of the myocardium - increase the refractory period gap
What do class IV antidysrhythmic drugs do?
Calcium antagonists - impair impulse propagation in damaged areas of the myocardium and dilate coronary arteries
How do class I antidysrhythmic drugs work?
they block Na channels in the open or refractory stage (in depolarized/damaged muscle) and inhibit the refractory stage
When do class I antidysrhythmic drugs have the greatest efficacy?
when the heart is beating rapidly
What drug is a class Ib antidysrhythmic drug?
lidocaine
Class Ib antidysrhythmic drugs _______ and _______ rapidly.
associate, dissociate
What are class Ib antidysrhythmic drugs useful for?
the control of ventricular dysrhythmias after myocardial infarction
What drug is a class Ic antidysrhythmic drug?
flecainide
Class Ic associate and dissociate more ____.
slowly
Since class Ic drugs associate and dissociate more slowly what does that say about their steady state block level?
it does not vary with the stage of the cycle
What are class Ic drugs used for?
general reduction in excitation and have less effect against premature beats like class Ib
What will class Ic drugs suppress?
re-entrant rhythms
What drugs are class 1a antidysrhythmic drugs?
Procainamide and Quinidine
How do muscarinic receptors affect the heart?
they decrease heart rate and excitability
What drug is a class II antidysrhythmic drug?
propanolol - beta antagonist
What are class II antidysrhythmic drugs used to do?
reduce excitability due to sympathetic over-activity and reduce AV conduction in atrial tachycardias to slow ventricular rate
Why would you want to use propranolol in cats with thyroid hyperplasia?
because thyroid hyperplasia can cause arythmias
What is the main class III antidysrhythmic drug?
amiodarone
What is the special feature of class III antidysrhythmic effects?
they prolong the cardiac action potential and increase refractory period
What effects does Class III antidysrhythmic drugs have?
it produces ventricular and supra-ventricular antidysrhythmic effects - complex mechanism including K channel block and calcium channel block
What are the main examples of class IV antidysrhythmic drugs?
Verapamil and diltiazem
What do class IV antidysrhythmic drugs do?
they block sensitive Ca channels which inhibits transient inward current and thus suppressing premature ectopic beats and re-entrant rhythms
What do class IV antidysrhythmic drugs do to the plateau phase of the action potential?
it is shortened
What is the effect of Class IV antidysrhythmic drugs on the coronary arteries?
it dilates them
What is procainamide?
a class 1a antidysrhythmic drug
When is procainamide indicated?
in dogs for maintenance of ventricular arrhythmias or ventricular tachycardia In humans - Torsades de points
When is Procainamide contraindicated?
in dogs with conduction block
When is lidoocain used?
without epinephrine intravenously for severe acute ventricular arrhythmias of any cause
Why isn’t lidocaine given orall?
because of the efficient first pass effect through the liver
When should you reduce doses of lidocaine?
in congestive heart failure or hepatic disease
What does propranolol prevent?
reflex tachycardia
What does propranolol reduce?
blood pressure and ventricular hypertrophy in cardiomyopathy associated with hyperthyroidism
What is a possible side effect of propanolol use?
bronchial muscle spasm
What does amiodarone do?
prolongs the refractory period of cardiac action potential
What amiodarone used for?
treatment of supra-ventricular and ventricular arrhythmias
What side effects are associated with amiodarone?
pulmonary fibrosis, gastro-intestinal disturbances, corneal deposits
What is the half-life with amiodarone?
long elimination half-life
What type of drugs are Verapamil and Diltiazem?
class IV antidysrhythmic
How do Verapamil and Diltiazem work?
they inhibit slow Ca channels and dilate capillaries
What conditions are Verapamil and Diltiazem favored for?
supraventricular tachycardias
How is Verapamil favored to be given?
IV
How is Diltiazem favored to be given?
long-term oral administration
