Treatment of Cardiac Arrhythmias Flashcards
what are the basic mechanisms of arrhythmogenesis?
altered automaticity
triggered activity
re-entry
what arrhythmias are associated with altered automaticity?
slow atrial, junctional, and ventricular escape rhythms
idioventricular rhythms
some atrial tachycardias
what is triggered activity associated with?
sympathetic stimulation
drugs
bradycardia
what are the criteria for a re-entrant circuit?
unidirectional conduction block
multiple conduction pathways
critical slowing of propagation to allow impulse conduction to previously refractory area
when should you treat an arrhythmia?
clinical signs
sustained ectopy
short coupling interval
multifocal complexes
natural history with known risk of sudden death
what is the vaughan-williams classification based on?
electrophysiologic mechanisms of action
what are some class Ia drugs?
procainamide
quinidine
disopyramide
what are some class Ib drugs?
lidocaine
mexiletine
tocainide
what is quinidine used for?
conversion of atrial fibrillation in horses
how can quinidine increase the heart rate?
vagolytic effect
what is procainamide used for?
ventricular and supraventricular arrhythmias
what are some side effects of quinidine?
proarrhythmia, torsade de pointes
horses: colic, hypersensitivity, urticaria, sweating
tachycardia
GI signs, skin rash, hypotension, cardiovascular collapse
what tissue do class Ib drugs work on?
diseased/ischemic myocardium
what is lidocaine used for?
first line emergency drug for ventricular tachycardia
some supraventricular arrhythmias may also respond
what are the side effects of class Ib drugs?
vomiting, seizures, ataxia, CNS depression especially in cats/horses
increased defibrillation threshold
suppression of escape rhythms
what type of drugs are the class II antiarrhythmic drugs?
beta blockers
what are the class II drugs?
atenolol
carvediliol
metoprolol
bisoprolol
esmolol
propanolol
when are class II drugs useful?
ventricular or supraventricular arrhythmias
cardiomyopathy
subaortic stenosis
pulmonic stenosis
left ventricular outflow tract obstruction
hyperthyroidism
intoxication with certain compounds
what are the side effects of class II antiarrhythmic drugs?
negative chronotropism
negative inotropism
hypotension
bronchospasm
hypoglycemia
what type of drugs are the class III antiarrhythmics?
K channel blockers
what are the class III antiarrhythmics?
sotalol
amiodarone
what are the effects of class III antiarrhythmics?
prolong action potential duration
beta-blockade
depress AV nodal conduction
increase atrial refractory period
increase fibrillation threshold
in what is sotalol especially effective?
boxer cardiomyopathy
what is sotalol used for?
ventricular and supraventricular arrhythmias
what is the most common side effect of amiodarone?
hepatopathy
what are the side effects of class IV antiarrhythmics?
excessive negative chronotropism
negative inotropism
excessive vasodilation
what are the main effects of digoxin?
potent inhibitor of Na/K ATPase pump
parasympathomimetic
improved baroreceptor function
what are the main clinical uses of digitalis glycosides?
treat supraventricular tachyarrythmias
+/- treat congestive heart failure
what are the side effects of digitalis?
lethargy, anorexia, vomiting, diarrhea, malaise
arrhythmias associated with digitalis toxicity
increased with concurrent hypokalemia, azotemia
what are the consequences of cardiac arrhythmias?
reduced cardiac output
syncope
weakness
decompensation of CHF
death
what is the decision to treat an arrhythmia based on?
hemodynamic compromise
natural history of arrhythmia, breed
potential for further electrical instability and sudden death
potential for tachycardiomyopathy or CHF
risk benefit analysis
what is sinus arrhythmia?
cyclic/rhythmic variation in P-P intervals
can be respiratory origin
when should you treat sinus bradycardia?
is hemodynamic status is not okay
what do you treat in sinus tachycardia?
underlying cause: shock, hypovolemia, fever
what are the two types of supraventricular premature depolarizations?
atrial premature depolarization: from atria
junctional premature depolarization: from AV junctional tissue
what is supraventricular tachycardia?
runs or paroxysms of ectopic complexes from atria or AV junctional tissue
more than 3 in number
what is the preferred drug for emergent therapy of rapid supraventricular tachycardia?
IV diltiazem
what is the most likely underlying cause of supraventricular tachycardia in a lab or boxer puppy?
orthodromic atrioventricular reciprocating tachycardia
what is the hallmark of atrial fibrillation?
irregularly irregular R-R intervals
what drugs can be used to slow AV conduction?
amiodarone
beta blocker
calcium channel blocker
digoxin
what are the treatment options for atrial fibrillation with no significant heart disease?
goal often conversion to sinus rhythm
quinidine
diltiazem, sotalol, class I
other drugs
cardioversion: ECG synchronized
what are some options if lidocaine does not work for ventricular tachycardia?
procainamide
esmolol
sotalol
amiodarone
synchronized cardioversion
does accelerated idioventricular rhythm usually require treatment?
not usually
what is sick sinus syndrome?
periods of sinus arrest often followed by paroxysm of supraventricular tachycardia
syndrome often characterized by bradycardia and tachycardia
who is predisposed to sick sinus syndrome?
older female schnauzers, westies, pugs
what are the general options for sick sinus syndrome treatment?
atropine response test
medical management
cardiac pacing
what is atrial standstill?
atrial activity is totally absent
what are some causes of atrial standstill?
atrial muscular dystrophy
hyperkalemia
hypothermia
terminal event
what do the class Ia drugs do?
prolong action potential and effective refractory period
what do the class Ib drugs do?
short action potential duration and effective refractory period
what do the class Ic drugs do?
marked depression in phase 0 upstroke
no change in action potential or effective refractory period
does procainamide significantly depress ventricular function?
no
what are some side effects of procainamide?
sympatholytic: hypotension
proarrhythmia, AV block
GI upset
coat color changes
what is mexiletine used for?
ventricular arrhythmias
often in combination with class II and III
when are class II antiarrhythmics useful with cardiomyopathy?
if CHF absent/well controlled
what is amiodarone used for?
ventricular and supraventricular arrhythmias
what are the side effects of amiodarone?
hepatopathy
thyroid dysfunction
pulmonary fibrosis
blood dyscrasias
neuropathy
angioedema, collapse, hypotension
do the dihydropyridines or non-dihydropyridines of the class IV antiarrhythmics have nodal effects?
non-dihydropyridines
is sick sinus syndrome usually life-threatening?
not unless under anesthesia
what are some options for bradycardias?
sympathomimetics
vagolytics
temporary transvenous pacing lead
transthoracic pacing
permanent pacemaker
in what percentage of dogs do complications from pacemakers occur?
20%
which cats with third degree AV block need treatment?
those with symptomatic third degree AV block: transdiaphragmatic epicardiac pacemaker
