ImportantCar

Question 1

cardiac output

Answer 1

the quantity of blood pumped into the systemic circulation by the ventricle each minute
- dependent upon the heart rate and stroke volume

Question 2

Stroke volume

Answer 2

the amount of blood ejected by the left ventricle with each heart beat or contraction

Question 3

Preload

Answer 3

time for the heart to fill with blood + enough volume of blood entering the right side of the heart; necessary for adequate stroke volume

Question 4

Afterload

Answer 4

describes the force needed to push blood out of the ventricles or arterial pressure against which the ventricle must pump

Question 5

what factors influence cardiac output?

Answer 5

high blood pressure and/or constriction of the vasculature

Question 6

in response to hypotension the sympathetic nervous system releases ?

Answer 6

Renin-Angiotensin-Aldosterone system + norepinephrine to increase heart rate and cause vasoconstriction of small arteries as a short term solution to raise blood pressure

Question 7

What does the Renin-Angiotensin-Aldosterone system do in response to hypotension?

Answer 7

activated when the kidney detects hypotension and the juxtaglomerular cells release renin and angiotensinogen

Question 8

How are Angiotensinogen and ACE related/work together?

Answer 8

Angiotensinogen converts angiotensin1 to angiotensin2 which is a potent vasoconstrictor, and supports blood pressure. The enzyme that enables conversion of angiotensin1 to angiotensin2 is called angiotensin converting enzyme also known as “ACE”

Question 9

How does the RAA system influence blood pressure?

Answer 9

causes the release of the mineralcorticoid hormone aldosterone from the adrenal gland –> the kidney conserves sodium and water –> blood pressure maintenance

Question 10

Clinical signs of advanced heart disease are caused by?

Answer 10

response to decreased cardiac function, low cardiac output and poor venous return, thus the body tissues no longer receive sufficient blood and oxygenation

Question 11

RAA cascade as a short term vs long term solution

Answer 11

short term - good solution to low blood pressure and cardiac output
long term - increase in sodium and water retention as well as vasoconstriction eventually makes it more difficult for the heart to work against the systemic pressure and weakens the heart muscle

Question 12

What are important treatments of CHF /focus of cardiac drug therapy

Answer 12

inhibinting the RAA system and/or vasodialation by other mechanisms of action, diuresis to remove excess fluid, and strengthenign the force of heart muscle contration

Question 13

What are the (important) sympathetic adrenergic receptors involved with cardiac function?

Answer 13

Alpha-1 (peripheral vessel constriction, increase BP)
Beta-1 (increase HR, force of constriction and blood glucose)
Beta-2 (bronchodilation)

Question 14

compare the functions of the different sympathetic adrenergic receptors involoved with cardiac function

Answer 14

Alpha-1 (peripheral vessel constriction, increase BP)
Beta-1 (increase HR, force of constriction and blood glucose)
Beta-2 (bronchodilation)

Question 15

What compensatory mechanisms will the heart take on to decrease workload on the heart and increase cardac output in response to a failing heart?

Answer 15

the heart will enlarge in an attempt to pump out more blood (dilated cariomyopathy and hypertrophic cardiomyopathy)

Question 16

compare dilated cardiomyopathy and hypertrophic cardiomyopathy

Answer 16

DC- heart chamber dilation
HC- thickened myocardium

Question 17

Postitive Inotropes

Answer 17

• Drugs that increase the heart’s stroke volume by increased force of heart muscle contraction
• are used if the heart muscle is too weak to adequately pump
• Drugs in this category include the cardiac glycosides, and sympathomimetic drugs which mimic the action of adrenergic sympatheticstimulation.

Question 18

What am I?
- cardiac glycoside
- derivative of purple foxglove plant (Digitalis purpurea)
- treat CHF and arrhytmias (atrial fibrillation and supraventricular tachycardia)
- narrow margin of safety
- interact with many other drugs
- must be dosed based on lean body mass and monitored through periodic blood testing (due to adverse effects and toxicity)
- fallen out of favor with the development of less toxic drugs

Answer 18

digoxin (Cardoxin) and Digitoxin (Crystodigin)

Question 19

What am I?
- sympathomimetic
- directly stimulates the heart
- used in cases of shock, severe allergic reactions and cardiac asystole emergencies
- affects both alpha and beta adrenergic receptors –> increased heart rate and contractility, increased blood pressure, increased blood glucose, bronchodilation, constriction of peripheral vessels and antagonizes the effects of histamine
- immediate onset when administered intracardiac, IV or intratracheal in emergency situations

Answer 19

Epinephrine (Adrenalin)

Question 20

What is a contraindication of Epinephrine?

Answer 20

use cautiously due to caridac side effect of causing arrhythmias (ventricular fibrillation and hypertension)

Question 21

Why would Epi be added to a local anesthetic?

Answer 21

The solution (Epi) is available in various strengths and is an ingredient found in local anesthetics such as lidocaine for its ability to constrict local vessels allowing the lidocaine to remain in the area.

Question 22

Pay attention! Theres a cardiovascular emergency, why should you pause before administering Epi (solutions)?

Answer 22

Lidocaine is also used to correct ventricular arrhythmias such as PVCs and ventricular tachycardia, therefore DO NOT USE lidocaine intended for local anesthesia in these cases since it contains epinephrine as it will cause tachycardia and worsen arrythmias!!

Question 23

Compare/contrast Dopamine and Dobutamine

Answer 23

Both :Dopamine and dobutamine are sympathomimetics used in critical care settings to increase cardiac output and have the effects of increasing heart rate, heart contractility and blood pressure.
- Due to their shortduration of action these drugs are given as a constant rate of infusion.
Dopamine is able to increase organ perfusion, especially blood flow to the kidney but is more likely to have tachycardia as a side effect.
Dobutamine is less likely to cause tachycardia as a side effect but does not have as much ability to increase blood flow to the viscera and kidney.

Question 24

Vasodilator

Answer 24

drugs used in cardiac therapy to bring about the vasodilation of arteries and/or veins to allow for improved cardiac output

Question 25

What are the two groups of vasodilators?

Answer 25

There are two groups of vasodilators that work by relaxing the smooth muscle of blood vessels or by inhibiting angiotensin converting enzyme, also known as ACE inhibitors.

Question 26

What is one side effect all vasodilators share?

Answer 26

All vasodilators have the side effect of producing hypotension and are contraindicated in patients with existing hypotension and/or hypovolemia, and dehydration.

Question 27

What am I?
- a venodilator that typically comes as an ointment or adhesive patch applied to the inner aspect of the pinna, axillary or inguinal regions.
- Clients should be warned to wear gloves when applying either the ointment or the patch
- an E-collar may be necessary to avoid licking or chewing of patches and ointments.

Answer 27

Nitroglycerin (Nitrol)

Question 28

What am I?
- an arterial dilator that reduces afterload in treatment of CHF
- Improves Cardiac Output
- Side Effects: Hypotension, GI signs

Answer 28

Hydralazine (Apresoline®)

Question 29

What am I?
- a “combined”vasodilator which means that it works by causing vasodilation of both the arteries and veins.
- Used to treat CHF, dilated cardiomyopathy, hypertension/pulmonary hypertension
- Side Effects: Hypotension, GI Signs

Answer 29

prazosin (Minipress®)

Question 30

What do enalapril (Enacard®) and captopril (Capoten®) have in common?

Answer 30

• ACE inhibitors
• are combined vasodilators that work on the arterial and venous vessels by blocking the angiotensin converting enzyme preventing the formation of the potent angiotensin II vasoconstrictor.
• These drugs also act as diuretics by stopping the release of aldosterone, thereby reducing sodium and water retention.

Question 31

What are the preferred drugs of choice in early heart disease?

Answer 31

• ACE inhibitors
• are an effective treatment for cardiac disease involving either the right or left ventricles.
• These drugs improve cardiac output with no change in heart rate and conserve potassium so can be used safely in conjunction with other diuretics commonly used for CHF such as furosemide (Lasix®).

Question 32

What am I?
- The newest FDA approved drug for management of mild to severe CHF
- This drug is an “inodilator” that works both as a balanced vasodilator (arterial and venous) and positive inotrope to strengthens the force of heart contraction.
- has become a popular drug of choice for CHF because it begins to act within one hour of dosing, has a duration of action up to 12 hours and is available in chewable tablets. (fast acting, 12hr duration, easy po admin)
- Since it is has positive inotropic activity, it may cause arrhythmias as a side effect, which is not the case with ACE inhibitors such as enalapril.
- can safely be used in conjunction with ACE inhibitors and with diuretics such as furosemide (Lasix®) in cases of more severe heart disease.

Answer 32

pimobendan (Vetmedin®).

Question 33

Antiarrhythmic (use and categorization)

Answer 33

• used for the treatment of various arrhythmias in animals
• categorized as Class I –IV according to their mechanism of action.
  [Class III drugs (potassium channel blockers) are not as commonly used in veterinary medicine and will not be discussed]

Question 34

what is the function of Class 1 antiarrhythmic agents?

Answer 34

stabilize cell myocardial cell membranes by inhibiting sodium influx and prevent cell depolarization.

Question 35

What is the drug of choice from the class 1 antiarrhythmic agents?

Answer 35

The drug of importance in this category is lidocaine.

Question 36

What am I?
- similar in action to lidocaine
- available orally to treat arrhythmias (PVC’s and ventricular tachycardia)

Answer 36

Tocainide (Tonocard®)

Question 37

How do Quinidine and procaninamide differ from lidocaine?

Answer 37

they are also used to treat some atrial arrythmias
- have less adverse effect of GI upset - > better tolerated in horses (cannot vomit)

Question 38

Beta-Blockers

Answer 38

AKA - Class II antiarrhythmic agents
- they work by blocking Beta-1 and Beta-2 adrenergic receptors –> decreased blood pressure and control of tachyarrhythmias by decreasing the heart rate and cardiac conduction.

Question 39

Class IV antiarrhythmic drugs (function and members)

Answer 39

• work by blocking calcium channelsin smooth muscle.
• Members of this group are all human products and include diltiazem (Cardizem®), verapamil (Isoptin®) and amlodipine (Norvasc®).
• Of particular importance is amlodipine since it is now the drug of choice for systemic hypertension due to kidney disease, hyperthyroidism, and cardiomyopathy in cats, and due to its long half-life only requires once daily dosing.