Cardiac glycosides and inodilators

Question 1

Maybe know what the general cardiac ECG looks like

Answer 1

P wave: contracting auricles
QRS: sudden depolarization
T wave: potential starts to recover; see hyperpolarization

Question 2

What species would be likely to see dilated cardiomyopathy?

Answer 2

Doberman

Question 3

What species would be likely to see endocardiosis/

Answer 3

Cavalier king charles

Question 4

What are the different classes of CHF?

Answer 4

Class I: only strenuous exercise limited
Class 2: Fatigue, shortness of breath, coughing on exercise
Class 3: Comfortable at rest but exercise is minimal
Class 4: No capacity for exercise, symptoms at rest

Question 5

What would be used to treat CHF at classes 2-4?

Answer 5

Digoxin
Pimobendan
Ace inhibitors

Question 6

What is the mechanism of action for cardiac glycosides?

Answer 6

Inhibits Na/K ATPase, which leads to a rise in intracellular Na

Na-Ca exchange system is slowed = increase in sarcoplasmic Ca

Rise in the release of Ca to interact with contractile proteins

Increase in force of contraction and CO; decrease HR

Question 7

What is the overall effect of cardiac glycosides?

Answer 7

Increase the force of contraction and CO of the heart

decrease the HR

Question 8

What is a positive inotropic action?

Answer 8

Increased force and velocity of contraction; can be seen in a normal and failing heart

Question 9

What is a negative chronotropic effect?

Answer 9

slowing of the heart rate

Question 10

What is the mechanism of a negative chronotropic effect?

Answer 10

Stimulation of the Vagus nerve and improved baroreceptor sensitivity countering sympathetics

Question 11

What is a negative dromotropic effect?

Answer 11

Slowing of conduction at the AV node

Question 12

What are some side effects of the cardiac glycosdie Digoxin?

Answer 12

Auricular arrhythmia/tachycardia
AV block
Ventricular arrhythmia

Question 13

What are some symptoms seen with Digoxin toxicity?

Answer 13

Disturbances in the heart rhythm = extrasystole and coupled beats (pulsus bigemini)
GI disturbances like anorexia, vomiting, diarrhea

Question 14

How would you treat Digoxin toxicity?

Answer 14

Withdraw Digoxin
Treat ventricular arrhythmias with lidocaine or propranolol
Give IV fluids to maximize renal clearance

Question 15

What would Pimobendan be classified as?

Answer 15

Inodilator

Question 16

What is the mechanism of action for Pimobendan?

Answer 16

Ca sensitizer and phosphodiesterase 3 inhibitor

Question 17

So what does Pimobendan do?

Answer 17

Increases the binding of calcium to Troponin C
PDE 3 inhibitor prevents cAMP breakdown and increases pKA action = increases voltage-gated Ca currents and keeps Ca channels open longer

Question 18

How does the body respond to Pimobendan or cardiac glycoside treatment?

Answer 18

Increased Cardiac output/decreased heart rate
Decreased venous pressure
Decrease in heart size
Increased water loss and reduced body weight

Question 19

What are two clinical conditions in vet med that you would use cardiac glycosides?

Answer 19

Endocardiosis

Dilated cardiomyopathy

Question 20

What is the half-life for Digoxin in dogs, cats, and horses?

Answer 20

Dogs: 23-39 hours
Cats: 25-78 hours; very variable
Horses: 13-23 hours

Question 21

How is digoxin eliminated from dogs, cats, and horses?

Answer 21

Dogs and cats: mainly renal

Question 22

What are some other positive ionotropic drugs and what do they do?

Answer 22

Dopamine: D5 receptors on heart increase cAMP

Dobutamine: Beta-1 agonist –> useful IV with acute, reversible heart failure

Amrinone: PDE 3 inhibitor; good for IV to increase cAMP which increases Ca influx