Cardiac drugs : decrease afterload & alter contractility Flashcards
Indications for cardiac drugs that decrease afterload
- mitral valve regurgitation
- cardiomyopathy
How can afterload be decreased directly?
arterial dilator
How can afterload be decreased indirectly?
decrease ventricular volume
What is Hydralazine
- arterial vasodilator
- manage mitral valve regurgitation
What is usually administered concurrently with Hydralazine?
negative chronotropic drug due to reflex tachycardia
Common adverse effect of Hydralazine
hypotension
How does Phosphodiesterase inhibitor decrease afterload?
indirectly increase effects of nitric oxide by inhibiting breakdown of cGMP
What vessel does phosphodiesterase inhibitor affect?
pulmonary arteries in dogs
What is mechanism of action for Amlodipine?
Ca2+ channel block vasodilator
- decrease intracellular Ca2+
- decrease smooth muscle contraction
- minimal cardiac effect due to low affinity
Indication for Amlodipine
cats with systemic hypertension
dogs with hypertension & refractory congestive heart failure
How does prazosin decrease afterload?
- selective alpha 1 receptor blocker
- relaxes smooth muscle in both arteries & veins
How does beta blocker decrease afterload?
- decrease sympathetic tone
- decrease cardiac contractility
- decrease renin release from kidneys
What are positive inotropic drugs used for?
increase cardiac contractility
treat cardiomyopathy
General characteristics of Pimobendan
- inodilator
Mechanism of action of pimobendan to increase contractility
- inhibition of phosphodiesterase 3 & increase intracellular cAMP
- increase contractility & improve muscle relaxation - Ca2+ sensitizer
- minimize increase of O2 demand - arteriole dilation
- lower vascular resistance
- inhibition of phosphodiesterase 3 & 5
- increase cAMP & cGMP in peripheral blood vessels - neurohumoral balance
- redcuce sympathetic imbalance
Indication of Pimobendan
cardiomyopathy & mitral valve regurgitation
Adverse effects of pimobendan
decreased appetite, lethargy, diarrhea, dyspnea
Mechanism of action of Digoxin
- inhibition of Na/K ATPase
- increase intracellular Na
- trigger Na/Ca exchange
- increase Ca release from SR - increase vagal tone
- decrease HR
Adverse effects of Digoxin
GI: anorexia, vomiting, diarrhea
Cardiac: tachyarrhythmia/ bradyarrhythmia, AV block
Electrolyte interaction of Digoxin
- hyperkalemia: reduce effectiveness
- hypokalemia: facilitate mechanism ( potentially cause toxicosis
- hypercalcemia can cause toxicosis (Ca2+ influx into myocardial cells)
Drug interactions of Digoxin
- Quinidine : displace digoxin from tissue binding sites
- Furosemide: decrease clearance
- spironolactone: increase K; less effective
Treatment for Digoxin toxicity
- decrease/ stop digoxin
- administer antiarrhythmics
- administer K+
- anti-digoxin antibody
Mechanism of action of Dobutamine
Stimulation of beta 1 receptor
- increase heart contractility
- increase release ca2+ from the intracellular storage
- does not increase HR
Why can’t Dobutamine be used for long-term management of cardiomyopathy?
down-regulation of beta1 receptor over time
How are dobutamine administered?
CRI due to short half life
Adverse effect of dobutamine
- tachycardia & ventricular arrhythmia with high dose
- can cause seizure at low infusion rates in cats
Drug reaction of Dobutamine
incompatible with alkaline fluid & bicarbonate
What are Dopamine used for?
- correct hypotension when there is no response to fluid volume replacement
- short-term management of congestive heart failure
What does Dopamine bind at low dose?
dopamine receptor ( vasodilation)
What does dopamine bind at medium dose?
beta 1 receptor ( cardiac stimulation)
What does dopamine bind at high dose?
alpha receptor (vasoconstriction)
Adverse effects of Dopamine
excessive vasoconstriction in the kidn eys
What are the indications for negative inotropic drugs?
hypertrophic cardiomyopathy
