Principles of Cardiovascular Therapy Flashcards
What characteristics of heart failure can be modified by drugs?
- Increased preload
- Increased afterload
- Impaired intotropy
- Impaired lustitropy
- Impaired chronotropy
How do diuretics work and what are the main classes of diuretics used for heart disease patients?
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
What is the most commonly used loop diuretic in heart failure patients?
Furosemide primarily
Spironolactone (K sparing) is refractory
What drug can you switch to if your heart patient becomes refractory to furosemide? Which class does it belong to?
Torasemide - Loop diuretic
What is the initial dose rate for furosemide in heart patients?
2-3mg/kg BID-TID orally
Higher IV is in heart failure
What risks are associated with giving diuretics?
Hypovolaemia
Hypotension
Electrolyte disturbances
Stimulation of RAAS
Give 2 examples of drugs in each diuretic classes..
- Loop
Furosemide
Torasemide - Thiazides
Chlorothiazide
Hydrochlorothiazide - Potassium sparing
Spironolactone
Amiloride
How does spironolactone work?
Aldosterone anatagonist
- Blocks aldosterone receptors in the kidney
Why is it important to monitor the effects of diuretics in heart hearts?
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
How do venodilators work?
They increase the capacity of veins to store blood by relaxing their vascular smooth muscles
In what kind of heart failure are venodilators contraindicated for and why?
There are contraindicated in forward failure (inadequate output at normal filling pressure) because the reduce filling pressure and could therefore be detrimental to patients
Which drugs can be used to decrease preload? Do there improve CO and perfusion to tissue?
Diuretics and venodilators
- Furosemide
- Spironolactone
- Pimobendan
- ACEi
- Glyceryl trinitrate
These only drop preload, don’t improve CO or perfusion to tissues
Give examples or venodilators and balanced venodilators…
Venodilators:
Glycerol trinitrate
Balanced venodilators - dilate both veins and arteries
ACE inhibitors
Pimobendan
Nitroprusside
What are the main uses of ACE inhibitors? How do they work?
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
How do arteriodilators work?
Relax smooth muscle in arteries to reduce afterload which decreases systemic vascular resistance
What is afterload and what is it determined by?
It is the peak in ventricular wall tension during systole
Primarily determined by SVR
What are the benefits of afterload reduction?
What are the risks of afterload reduction?
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
Give some examples of arteriodilators…
Hydralazine
Balanced:
ACEi
Pimobendan
What drugs would you give to cats with high blood pressure?
Amliodipine - arteriodilator
How do inotropes works? Do they alter preload or afterload?
The alter the force of myocardial contraction
+ve - Increased force
-ve - Decreased force
They have an indirect effect on reducing preload
What are the risks of +ve inotropes?
Increased myocardial work
Increased o2 demands of myocardium
Give some examples of positive inotropes and what you would use them for…
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
What classes of drugs would you use for patients with congestive heart failure?
Diuretics and venodilators
wet => dry patient
How would you treat a patient with forward failure?
Inotropes, vasodilators and anti-arrhythmic drugs.
cold => warm patient
What drugs would you use to treat ventricular arrhythmias in small animals?
Lignocaine, procarinamide, beta blockers
What drugs could you use to treat supraventricular tachycardia in small animals?
Digoxin, calcium channel blockers, beta blocker
What drugs could you used to treat bradyarrhythmias?
Atropine, propantheline bromide, xanthines
Explain the process of treating an AF patient in small animals…
- Look for underlying disease
- 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
