Principles of therapy Flashcards
What are the 4 key steps involved in treating heart dz and failure?
- correct ID of underlying dz process
- staging of the severity of dz (deciding whether tx is required and what the aims of the tx are?)
- applying evidence-based medicine
- if no evidence-based, make informed and rational decision based on types of signs and types of therapy that would be most effective
What are the evidence based drugs used to treat MVD in dogs?
Pimobendan (strong evidence)
ACE inhibitors
Spironolactone
What are the evidence based drugs used to treat dilated cardiomyopathy?
Pimobendan
ACE inhibitors
What are the evidence based drugs used to treat HCM in cats?
Clopidogrel (anti-thrombotic, strong evidence)
Pimobendan?
ACE inhibitors?
What are the 5 different ways heart failure can be characterised by?
increased preload (force that blood returns to heart)
increased afterload
impaired inotropy (contraction force)
impaired lusitropy (ability to relax)
abnormalities of rate/rhythm
What can we use as information about heart failure when chosing drugs?
the 5 different causes/characteristics are targets to be modified:
- preload
- afterload
- inotropy
- lusitropy
- cardiac rate and rhythm
What can we target to modify preload?
venous tone
fluid volume (diuretics)
What can we target to modify the cardiac function?
Systolic
Diastolic
What can we target to modify afterload?
Arterial tone (vasodilators)
How do diuretics affect heart failure?
reduces venous filling
= stops the increased venous pressure also causing fluid to leak into tissues
reduces circulating fluid volume and relieves signs of congestion
How do venodilators affect heart failure?
dilate the veins = stops increased venous pressure also causing fluid to leak into tissues
How do arteriodilators affect heart failure?
dilate arteries = allows for normal filling and proper perfusion
reduces work by heart to eject blood
How do inotropic drugs affect heart failure?
enhance the cardiac contraction allowing for more blood to be pumped out
How do lusitropic drugs affect heart failure?
enhance cardiac filling allowing for more blood to be pumped out
What are the classes of diuretics and examples used for heart dz?
loop diuretics: furosemide, torasemide
thiazides: chlorothiazide, hydrochlorothiazide
potassium sparing: spironolactone, amiloride
How do we use diuretics for heart dz?
usually start diuresis with a single agent. most common: furosemide
adminiaster at higher doses and IV where animal in most severe heart failure
What are the options when a patient becomes refractory to furosemide
increase the dose
increase the frequency
introduce second diuretic (sequetial blockade: spironolactone)
swap to trasemide
What are the risks of diuresis?
Hypovolaemia (excessive diresis)
Hypotension (reduced CO)
Electrolyte disturbances (potassium, magnesium, sodium)
Stimulation of RAAS
What are the types of venodilatation and examples for heart dz?
Venodilators: glyceryl trinitrate
Balanced vasodilators (act on arteries and veins): ACE I, pimobendan, nitroprusside
What is afterload?
the peak ventricular wall tension during systole
primarily determined by the resistance to ejection from the ventricle
What causes increased afterload?
increased systemic vascular resistance
obstruction of outflow tract associated with high resistance to ejection (AS or PS)
What can reduce afterload if there are no fixed obstructions?
arteriodilators
What are the benefits of afterload reduction?
Reduced resistance to outflow resulting in increased SV, increased CO, decreased mitral regurgitation
Reduced systolic wall tension reduces cardiac work whcih decreases myocardial oxygen demand and improved oxygenation of myocardium
What are the risks of afterload reduction?
Hypotension (chronic)
Reduction in systemic venous resistance may result in decreased BP if cardiac output doesn’t increase
Decreased BP may compromise perfusion of essential vascular beds
What are the tx agents categories with examples for afterload reduction?
Balanced vasodilators: ACE inhibitors, pimobendan, etc.
Calcium channel blockers: amlodipine
Arteriodilators: Hydralazine
What are the problems with pure inotropes?
Increased myocardial work (could be associated with increased rate of myocardial deterioration)
Increased myocardial oxygen demand (exacerbate ischaemia/hypoxia, may lead to rhythm disturbances)
How is digoxin different with other inotropes?
causes reduced HR
decreased sympathetic tone
What is the effect of digoxin on survival?
None, same as placebo
but does make ptx feel better aka better quality of life
What type of drug is pimobendan?
its an inodilator
acts to increase cardiac contractility and vasodilates
associated with approved outcome in dogs
increases affinity of troponin for calcium
What evidence supports the use of pimobendan and when?
good evidence of efficacy in degenerative mitral valve dz and dilated cardiomyopathy BEFORE the onset of heart failure
animals took longer to go into heart failure when on pimobendan
When is digoxin indicated as an inotrope?
heart failure associated with systolic failure of myocardium
supraventricular rhythm disturbance: A.Fib.
When is a dobutamine infusion indicated as an inotrop?
where short term support is required as emergency measure
How do we choose and prioritise drugs vs the problems causing heart failure?
is heart failure wet or dry? (too much fluid?)
- preload reduction
- diuretics/venodilators
is it cold or warm? (is there poor peripheral perfusion?)
- inotropes, afterload reduction, anti-arrhythmics
What are the aims of therapy in heart dz?
restore adequate peripheral perfusion
control rate and frequency of abnormal rhythm
restore sinus rhythm when possible/necessary
prevent sudden death
Which antidysrhythmic medications are given for ventricular arrhythmias?
lignocaine
procainamide
beta-blockers
etc.
Which antidysrhythmic medications are given for supraventricular arrhythmias?
digoxin
calcium channel blockers
beta-blockers
Which antidysrhythmic medications are given for bradyarrhythmias?
atropine
propantheline bromide
xanthines
pacing
When diagnosing AFib, how do we decide to treat?
tx when evidence of underlying dz and significant atrial enlargement
if animal in heart failure try digoxin then if rate still high with adequate digoxin levels add dilitiazem
if not in heart failyre try beta-blockers
