Lecture 32

Question 1

Causes of arrhythmias (2)

Answer 1

direct damage to heart (chamber enlargement, cardiomyopathy)
systemic abnormalities (electrolyte or acid base abnormalities)

Question 2

clinical signs of arrhythmias(5)

Answer 2

inadequate CO->
exercise intolerance
weakness
syncopal episodes
sudden development of dysrhythmia may lead to decompensation

Question 3

Diagnosing arrhythmia

Answer 3

ECG is the key to diagnosis

Question 4

Most common arrhythmias in dogs(3)

Answer 4

supraventricular tachycardia
atrial premature complexes
atrial fibrillation

Question 5

Most common arrhythmias in cats (2)

Answer 5

SA block

ventricular premature complexes (VPC)

Question 6

Normal myocyte depolarization relies on

Pacemaker cell depolarization relies on

Answer 6

Na influx-fast

Ca influx-slow

Question 7

Na channel blockers

• type of drug
• mechanism of action
• which cells will be more affected
• use for treatment of

Answer 7

antinarrhythmics drug
bind to VO Na channels and inhibit them (pacemaker cells are not reliant on VO Na channels)
Use dependent- more active cells will be more affected
ventricular dysrhythmias

Question 8

Beta blockers

• type of drug
• mechanism of action
• what do they control
• used to treat

Answer 8

antiarrhythmic drug
inhibit sympathetic stimulation to heart- will slow SA rate and AV conduction
control dysrhythmias driven by excessive sympathetic tone
used to treat atrial tachycardias and fear related behaviors

Question 9

K channel blockers

• type of drug
• mechanism of action
• often used?

Answer 9

antiarrhythmia drug
block outward K+ channels(in charge of repolarizing cell)
not often used

Question 10

Ca Channel blockers

• Type of drug-
• mechanism of action
• Which cells are more affected
• used to treat

Answer 10

antiarrhythmia drug
block L type Ca channels (heart and VSM)->dec HR and AV conduction, dec force of contraction, and VSM relaxation
use dependence- more active cells will be more dependent
atrial tachycardia

Question 11

Digoxin
type of drug
-Mechanism of action
-used to treat
-side effect

Answer 11

used as an antiarrhythmic drug
vagal effects on pacemaker tissues- slowed AV conduction and SA rate->dec HR
dec sympathetic drive
shortened refractory period in atria and ventricles
used to treat atrial fibrillation
-BUT can cause ventricular arrhythmia because effect on NA/K ATPase

Question 12

Atrial fibrillation and supraventricular tachycardia are generally associated with (2)

Answer 12

generally associated with mitral valve failure in dogs and hypertrophic cardiomyopathy in cats

Question 13

Aim of therapy in atrial fibrillation and supraventricular tachycardia is to (2)
examples of drug types to be used for each

Answer 13

• Inc AV node refractoriness(lengthen refractory period) (digoxin, Beta blocker, Ca channel blocker)
• inc atrial refractoriness(lengthen refractory period) (na channel blocker for atrial fib in horses)

Question 14

Ventricular tachycardia is generally associated with (3)

Answer 14

associated with severe cardiac or systemic disease, refractory CHF, DCM

Question 15

Aim of therapy in ventricular tachycardia is to (2)

example of type of drug to be used

Answer 15

treat pre existing disease
dec automaticity and conduction velocity
inc ventricular muscle refractory period (Na channel blockers are drug of choice)

Question 16

Positive inotropes:
negative inotropes:
diuretics:
vasodilators:
antiarrhythmatics:

Answer 16

+: inc cardiac contractility, CO

• : dec cardiac contractility, dec preload
  diuretics: dec preload (volume overload)
  vasodilators: dec preload, afterload, or both
  antiarrhythmatics: inc CO

Question 17

If there is congestion (of heart or lungs) you would use

Answer 17

diuretics (probably frusemide maybe with K sparing)

Question 18

If you want reduction in afterload/preload to assist CO what would you use?

Answer 18

ACE inhibitors
Ca channel blockers
Beta blockers

Question 19

How would you increase contractility with CHF from DCM or mitral valve disease?

Answer 19

probably pimobendan used in conjunction with ACE inhibitor, furosemide or digoxin