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What is an arrhythmia?
an abnormality in the rate, regularity, or site of origin of the cardiac impulse or a disruption in impulse conduction such that the normal sequence of atrial and ventricular activation is changed
What are arrhythmias associated with?
the imbalance of the parasympathetic and sympathetic branches of the ANS; changes in serum electrolyte concentrations (K+ and Ca++); hypoxemia; acidosis; changes in concentration of carbon dioxide; excessive stretch of cardiac tissue; mechanical trauma; myocardial disease states (CHF and viral myocarditis); numerous drugs; ischemia and infarction of the heart muscle
What do Class III drugs produce?
a prominent prolongation of the action potential, thereby extending the refractory period
What is the common mechanism of action of Class I drugs?
blockade of fast sodium channels in the myocardial cell membrane
What do Class IA agents do?
depress conductino in normal and abnormal cardiac tissue and prolongs repolarization
What are the Class IB agents?
lidocaine and its derivatives (tocainide and mexiletine) along with phenytoin
How do Class IV drugs act?
by inhibiting the function of the slow L-type calcium channels on cardiac cell membranes
What is the obvious drug of choice when severe sinus bradycardia or sinus arrest is presented secondary to vagal discharge and accumulation of acetylcholine?
The capability of quinidine to directly prolong the refractory period of atrial fibers is thought to account for what?
its ability to convert atrial fibrillation to sinus rhythm
Quinidine has generally been less successful in treatment of what in small dogs?
Procainamide is more effective in controlling what?
ventricular arrhythmias rather than atrial arrhythmias
In general, phenytoin is considered to be effective in controlling what?
digitalis-induced arrhythmias of all types and is useful in treating ventricular arrhythmias
Lidocaine is a local anesthetic drug that has been found to exert what effect?
Which species is particularly susceptible to adverse effects of lidocaine and therefore need to be dosed carefully?
What is mexiletine indicated for treatment of?
chronic treatment of ventricular tachyarrhythmias in dogs
What is the mechanism of action for propranolol?
it slows the rate of spontaneous discharge of the SA and ectopic pacemakers and slows both antegrade and retrograde conduction through anomalous pathways of the heart
What is atenolol used for in dogs and in combination with what?
slow the heart rate in patients with atrial fibrillation combined with digoxin
What is atenolol used for?
slow heart rate with atrial fibrillation, treat supraventricular tachycardia and ventricular tachyarrhythmias and is used in attempts to prevent sudden death in dogs with severe subaortic stenosis
Which Class II antiarrhythmic agent is ultrashort-acting and used commonly for intravenous administration?
Beta-blocking agents should be administered with caution in patients with what?
reduced cardiac reserve
What should be monitored during treatment with amiodarone and why?
thyroid function because amiodarone inhibits T3 and T4 secretion from canine thyroid glands
The drug dose of sotalol must be decreased in which animals?
animals that have compromised renal function
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