Principles of Cardiovascular Therapy

Question 1

What characteristics of heart failure can be modified by drugs?

Answer 1

1. Increased preload
2. Increased afterload
3. Impaired intotropy
4. Impaired lustitropy
5. Impaired chronotropy

Question 2

How do diuretics work and what are the main classes of diuretics used for heart disease patients?

Answer 2

How they work:
Inhibit re-uptake of sodium and hence water in the nephron which allows blood volume in venous circulation to drop, reduces amt of blood in venous reservoir so no fluids leak out into body cavities, pulmonary parenchyma and other tissues

Classes most used:
Loop diuretics - most effective
Thiazides - not v effective
Potassium sparing diuretics

Question 3

What is the most commonly used loop diuretic in heart failure patients?

Answer 3

Furosemide primarily

Spironolactone (K sparing) is refractory

Question 4

What drug can you switch to if your heart patient becomes refractory to furosemide? Which class does it belong to?

Answer 4

Torasemide - Loop diuretic

Question 5

What is the initial dose rate for furosemide in heart patients?

Answer 5

2-3mg/kg BID-TID orally

Higher IV is in heart failure

Question 6

What risks are associated with giving diuretics?

Answer 6

Hypovolaemia
Hypotension
Electrolyte disturbances
Stimulation of RAAS

Question 7

Give 2 examples of drugs in each diuretic classes..

Answer 7

1. Loop
   Furosemide
   Torasemide
2. Thiazides
   Chlorothiazide
   Hydrochlorothiazide
3. Potassium sparing
   Spironolactone
   Amiloride

Question 8

How does spironolactone work?

Answer 8

Aldosterone anatagonist

- Blocks aldosterone receptors in the kidney

Question 9

Why is it important to monitor the effects of diuretics in heart hearts?

Answer 9

Can get initial profound diuresis and sodium loss

This loss stimulates all reabsorption mechanisms in the body so within a few days the patient has reach new equilibrium

This equilibrium is now set at a lower Na concentration than initial because while the drug has been given a net loss of sodium has occured

Question 10

How do venodilators work?

Answer 10

They increase the capacity of veins to store blood by relaxing their vascular smooth muscles

Question 11

In what kind of heart failure are venodilators contraindicated for and why?

Answer 11

There are contraindicated in forward failure (inadequate output at normal filling pressure) because the reduce filling pressure and could therefore be detrimental to patients

Question 12

Which drugs can be used to decrease preload? Do there improve CO and perfusion to tissue?

Answer 12

Diuretics and venodilators

• Furosemide
• Spironolactone
• Pimobendan
• ACEi
• Glyceryl trinitrate

These only drop preload, don’t improve CO or perfusion to tissues

Question 13

Give examples or venodilators and balanced venodilators…

Answer 13

Venodilators:
Glycerol trinitrate

Balanced venodilators - dilate both veins and arteries
ACE inhibitors
Pimobendan
Nitroprusside

Question 14

What are the main uses of ACE inhibitors? How do they work?

Answer 14

ACE inhibitors prevent conversion of Angiotensin I –> Angiotensin 2 and thereby prevent the following from happening:
Vasoconstriction
Increased sympathetic tone
Release of aldosterone from kidneys
Increased re-absorption of sodium from kidneys
Release of ADH from pituitary

Mainly used to treat:
Hypertension
Congestive heart failure

Question 15

How do arteriodilators work?

Answer 15

Relax smooth muscle in arteries to reduce afterload which decreases systemic vascular resistance

Question 16

What is afterload and what is it determined by?

Answer 16

It is the peak in ventricular wall tension during systole

Primarily determined by SVR

Question 17

What are the benefits of afterload reduction?

What are the risks of afterload reduction?

Answer 17

Benefits:
Increased SV and CO
Decreased mitral regurg
Decreased myocardial o2 demand
Improved oxygenation of myocardium

Risks:
Hypotension if excessive which would compromise perfusion of essential vascular beds

Question 18

Give some examples of arteriodilators…

Answer 18

Hydralazine

Balanced:
ACEi
Pimobendan

Question 19

What drugs would you give to cats with high blood pressure?

Answer 19

Amliodipine - arteriodilator

Question 20

How do inotropes works? Do they alter preload or afterload?

Answer 20

The alter the force of myocardial contraction
+ve - Increased force
-ve - Decreased force

They have an indirect effect on reducing preload

Question 21

What are the risks of +ve inotropes?

Answer 21

Increased myocardial work

Increased o2 demands of myocardium

Question 22

Give some examples of positive inotropes and what you would use them for…

Answer 22

Digoxin - positive inotrope and anti-arrhythmogenic
Reduces heart rate and sympathetic tone and tends to be used more for its anti-arrhytmogenic properties rather than its effect on myocardial contraction

Pimonbendan - positive inotrope and vasodilator
Regulates interaction between troponin and calcium - sensitized and increases their binding efficiency
Good for DMVD and DCM before onset of heart failure

Question 23

What classes of drugs would you use for patients with congestive heart failure?

Answer 23

Diuretics and venodilators

wet => dry patient

Question 24

How would you treat a patient with forward failure?

Answer 24

Inotropes, vasodilators and anti-arrhythmic drugs.

cold => warm patient

Question 25

What drugs would you use to treat ventricular arrhythmias in small animals?

Answer 25

Lignocaine, procarinamide, beta blockers

Question 26

What drugs could you use to treat supraventricular tachycardia in small animals?

Answer 26

Digoxin, calcium channel blockers, beta blocker

Question 27

What drugs could you used to treat bradyarrhythmias?

Answer 27

Atropine, propantheline bromide, xanthines

Question 28

Explain the process of treating an AF patient in small animals…

Answer 28

1. Look for underlying disease
2. Evidence of underyling disease and significant atrial enlargement
   a. In heart failure - Digoxin first, add diltiazem if not working
   b. Betablocker if not in heart failure