antiarrhythmic agents Flashcards
what drugs are class I agents
- quinidine (1A)
- procainamide (1A)
- lidocaine (1B)
what drugs are class II agents
- propranolol
- atenolol
- esmolol
beta blockers
what drug is a class III agent
sotalol
K channel inhibitors, extend ERP
what drug is a class IV agent
diltiazem
inhibits SA node
calcium channel blocker, decreases HR and contractility
what are determining factors of the rate of pacemaker cells
- duration of AP (longer AP = slower BP)
- duration of diastolic interval
- max diastolic potential (takes longer to reach threshold –> bradycardia)
- slope of phase 4 depolarization
- threshold potential
what is the goal of therapy for arrhythmias
- reduce ectopic pacemaker activity
- modify conduction or refractoriness to disable reentry
the SA node _____ APs
the AV node _____ APs
generates
conducts
what type of sodium channels are blocked by class 1A
open or activated sodium channels
what class 1 antiarrhythmic agent lengthens the duration of the action potential, increasing ERP, what agent shortens it
1A - lengthens
1B - shortens, decreasing time of ERP
what antiarrythmic agent can block both activated and inactivated sodium channel but has no effect on the duration of APs
1C
what class of antiarrhytmics reduces adrenergic activity on the heart by suppressing sympathetic effects
Class II, beta blockers
what class of antiarrhytmics are potassium channel blockers
Class III
what class of antiarrhytmics are calcium channel blockers
class IV
what is happening during phase 0 in cardiac cell AP
Ca channels slowly start to open, Na enters cell
what is happening during phase 1 in cardiac cell AP
K+ efflux
what is happening during phase 3 in cardiac cell AP
rapid repolarization as Ca channels gradually inactivate and K+ starts exciting cell
what is happening during phase 2 in cardiac cell AP
plateu of prolonged depolarization as K exits and Ca enters
what is the MOA of Quinidine
- binds to open & activated Na channels
- blocks K+ channels (prolongs depolarization)
- muscarinic receptor blockade (increases HR and AV conduction)
- blocks alpha receptors (hypotension)
BA of Quinidine
variable due to first pass effect
metabolism of Quinidine
80% liver
20 kidney
what is the half life of Quinidine
6 hrs in dogs, 8 hrs in horses
usually not used in cats
what is Quinidine useful in treating
- supraventricular & ventricular arrythmias
- re-entrant arrythmias (like atrial fibrillation)
contraindications of Quinidine
patients w/
* myasthenia gravis
* AV block
* digitalis toxicity or on digoxin
adverse effects of Quinidine in dogs
anorexia, V+, negative inotropism (decreased contractility)
adverse effects of Quinidine in horses
coloc, ataxia, swelling of nasal mucosa, urticaria, laminitis (rare)
adverse effects of Quinidine (non-breed specific)
D+, hypotension, widened QRS complex, prolonged QT interval, AV block, ventricular tachycardia
what are the differences b/w Quinidine and Procainamide
Procainamide….
* less prominant of a muscarinic and alpha receptor blocker
* more effective in treating ventricular arrhythmias
* has fewer drug interactions than quinidine
* is not as effective in horses
what drug is used in the txt of arrhythmias of ventricular origin
Lidocaine
no vetmed product, all ELDU
how does Lidocaine work
- Binds to inactivated Na+ channels fast binding dissociates fast
- Decreases action potential duration & shortens ERP due to blocking slow Na ‘window’ currents
how is lidocaine administered
IV ONLY
where is lidocaine metabolized
90-95% in liver
lidocaine toxicity
- Primarily CNS signs in dogs → muscle twitching, convulsions
- Hypotension → if IV bolus given too rapidly
- Cats → more susceptible to toxicity
lidocaine effects
- No significant effects on QRS, QT intervals
- Decreases duration of APD and ERP
- Causes less hypotension than procainamide
- No depressant action on myocardial contractility
- No vagal blocking
- Not effective for supraventricular arrhythmias
B1 selective blocking agent indicated for the treatment of supraventricular tachyarrhythmias, systemic hypertension and hypertrophic cardiomyopathy
Atenolol
is propranolol or aetenolol longer acting
atenolol
B1 specific blocking agent used in acute management of supraventricular tachycardia
and decreases HR in severe ventricular tachycardia in dogs/cats
Esmolol
what is propranolol used in the treatment of
- hypertrophic cardiomyopathy in ferrets
- hypertension
- thyrotoxicosis
- ventricular tachycardia in horses
all extra label
class III drug that is also a non-selective beta andrenergic blocker
sotalol
what is sotalol traditionally used for
arrhythmogenic cardiomyopathy in boxers
what type of arrhythmias are class IV drugs (Ca channel blockers) effective in treating
supraventricular tachyarrhythmias
what drug produced vasodilation but not reflex tachycardia
Diltiazem
what conditions is Diltiazem used to treat
- atrial fibrilation (can be used in combination w/ quinidine in horses)
- supraventricular tachycardia
- hypertrophic cardiomyopathy in cats and ferrets
- hypertension
adverse effects of Diltiazem
- bradycardia in dogs
- V+ in cats
- GI or CNS disturbances
- increases liver enzymes
- negative inotropic effect
the blocking of _____ receptors by Quinidine results in an increased HR and AV node conduction
muscarinic
because Quinidine blocks ___ receptors, it has the potential to cause reflex tachycardia
Alpha, which causes hypotension
most common route of administration for Quinidine
oral, safe & rapid onset
- bioavailability is variable due to the first pass effect
what animals is quinidine used in
dogs and horses
what drug causes vasodilation w/out reflex tachycardia
Diltiazem
what drug causes bradycardia in dogs & V+ in cats
Diltiazem
what drug is only useful in treating arrhythmias of ventricular origin
lidocaine
what drug has CNS toxicity in dogs
lidocaine
what drug is used to see if long lasting beta blockers could be an effective treatment
Esmolol
ultrashort acting
what drug can treat hypertrophic cardiomyopathy in both dogs and cats
Diltiazem
what sodium channel blocker does NOT cause a decrease in contractility; therefore causing less hypotension than procainamide
Lidocaine
what kind of arrhythmias are class IV Ca+ channel blockers effective at treating
- they interupt atrial arrhythmias that rely on AV node re-entry
- also useful in supraventricular tachycardia
