Cardiac drugs : decrease afterload & alter contractility

Question 1

Indications for cardiac drugs that decrease afterload

Answer 1

• mitral valve regurgitation
• cardiomyopathy

Question 2

How can afterload be decreased directly?

Answer 2

arterial dilator

Question 3

How can afterload be decreased indirectly?

Answer 3

decrease ventricular volume

Question 4

What is Hydralazine

Answer 4

• arterial vasodilator
• manage mitral valve regurgitation

Question 5

What is usually administered concurrently with Hydralazine?

Answer 5

negative chronotropic drug due to reflex tachycardia

Question 6

Common adverse effect of Hydralazine

Answer 6

hypotension

Question 7

How does Phosphodiesterase inhibitor decrease afterload?

Answer 7

indirectly increase effects of nitric oxide by inhibiting breakdown of cGMP

Question 8

What vessel does phosphodiesterase inhibitor affect?

Answer 8

pulmonary arteries in dogs

Question 9

What is mechanism of action for Amlodipine?

Answer 9

Ca2+ channel block vasodilator
- decrease intracellular Ca2+
- decrease smooth muscle contraction
- minimal cardiac effect due to low affinity

Question 10

Indication for Amlodipine

Answer 10

cats with systemic hypertension
dogs with hypertension & refractory congestive heart failure

Question 11

How does prazosin decrease afterload?

Answer 11

• selective alpha 1 receptor blocker
• relaxes smooth muscle in both arteries & veins

Question 12

How does beta blocker decrease afterload?

Answer 12

• decrease sympathetic tone
• decrease cardiac contractility
• decrease renin release from kidneys

Question 13

What are positive inotropic drugs used for?

Answer 13

increase cardiac contractility
treat cardiomyopathy

Question 14

General characteristics of Pimobendan

Answer 14

• inodilator

Question 15

Mechanism of action of pimobendan to increase contractility

Answer 15

1. inhibition of phosphodiesterase 3 & increase intracellular cAMP
   - increase contractility & improve muscle relaxation
2. Ca2+ sensitizer
   - minimize increase of O2 demand
3. arteriole dilation
   - lower vascular resistance
   - inhibition of phosphodiesterase 3 & 5
   - increase cAMP & cGMP in peripheral blood vessels
4. neurohumoral balance
   - redcuce sympathetic imbalance

Question 16

Indication of Pimobendan

Answer 16

cardiomyopathy & mitral valve regurgitation

Question 17

Adverse effects of pimobendan

Answer 17

decreased appetite, lethargy, diarrhea, dyspnea

Question 18

Mechanism of action of Digoxin

Answer 18

1. inhibition of Na/K ATPase
   - increase intracellular Na
   - trigger Na/Ca exchange
   - increase Ca release from SR
2. increase vagal tone
   - decrease HR

Question 19

Adverse effects of Digoxin

Answer 19

GI: anorexia, vomiting, diarrhea
Cardiac: tachyarrhythmia/ bradyarrhythmia, AV block

Question 20

Electrolyte interaction of Digoxin

Answer 20

• hyperkalemia: reduce effectiveness
• hypokalemia: facilitate mechanism ( potentially cause toxicosis
• hypercalcemia can cause toxicosis (Ca2+ influx into myocardial cells)

Question 21

Drug interactions of Digoxin

Answer 21

• Quinidine : displace digoxin from tissue binding sites
• Furosemide: decrease clearance
• spironolactone: increase K; less effective

Question 22

Treatment for Digoxin toxicity

Answer 22

• decrease/ stop digoxin
• administer antiarrhythmics
• administer K+
• anti-digoxin antibody

Question 23

Mechanism of action of Dobutamine

Answer 23

Stimulation of beta 1 receptor
- increase heart contractility
- increase release ca2+ from the intracellular storage
- does not increase HR

Question 24

Why can’t Dobutamine be used for long-term management of cardiomyopathy?

Answer 24

down-regulation of beta1 receptor over time

Question 25

How are dobutamine administered?

Answer 25

CRI due to short half life

Question 26

Adverse effect of dobutamine

Answer 26

- tachycardia & ventricular arrhythmia with high dose - can cause seizure at low infusion rates in cats

Question 27

Drug reaction of Dobutamine

Answer 27

incompatible with alkaline fluid & bicarbonate

Question 28

What are Dopamine used for?

Answer 28

- correct hypotension when there is no response to fluid volume replacement - short-term management of congestive heart failure

Question 29

What does Dopamine bind at low dose?

Answer 29

dopamine receptor ( vasodilation)

Question 30

What does dopamine bind at medium dose?

Answer 30

beta 1 receptor ( cardiac stimulation)

Question 31

What does dopamine bind at high dose?

Answer 31

alpha receptor (vasoconstriction)

Question 32

Adverse effects of Dopamine

Answer 32

excessive vasoconstriction in the kidn eys

Question 33

What are the indications for negative inotropic drugs?

Answer 33

hypertrophic cardiomyopathy