Management of Canine congestive heart failure Flashcards
What does Na+ & H2O retention lead to in left + right sided CHF?
*Left sided CHF = Pulmonary oedema
*Right sided CHF =
-Ascites,
-Hepatomegaly with chronic venous congestion
- Pleural effusions
Which sided CHF is more deadly and why?
Left sided
Pulmonary oedema can be fatal
What is the first choice diuretic to treat CHF?
Furosemide
What dosage should you aim to give?
Lowest possible dose to control clinical signs
When can you reduce dosage? When should in increase?
*Reduce furosemide dosage provided no increase in RR.
*Increase dose in increase respiratory rate
What are the side effects of furosemide? What should be monitored?
- Pre-renal azotaemia
- Hypokalaemia
Need to monitor renal function (urea, creatinine) & electrolytes
(especially K+; also Na+, Cl-)
Why shouldn’t you use furosemide on its own for a long time? What should you use with it?
*Monotherapy of furosemide = RAAS activation
*Use with ACE inhibitor
What should you do if furosemide no longer works?
- If GIT oedema (R-CHF), may not be absorbing drugs: consider parenteral administration
- Tubular cell hypertrophy may result in increased Na+ retention despite furosemide, so resistance develops: Consider increasing dose or additional diuretics (= sequential
nephron blockade). - Consider substituting furosemide for a more potent ceiling loop diuretic (e.g. torasemide)
Why would you administer spironlactone?
*Anti-aldosterone effect - reduced Na+ & H2O retention + reduced cardiac remodelling
What should you do with a right sided CHF?
- Do not drain abdominal effusions unless severely compromising respiration
- Make sure R-CHF is NOT due to a pericardial effusion before starting diuretics or other cardiac drugs
What is an example of ACE inhibitor?
Benazepril
What are the side effects of ACE inhibitors?
- Hypotension
- Renal impairment
- Hyperkalaemia
- Anorexia, diarrhoea, vomiting etc.
What is an example of angiotensin ii?
Telmisartan
What does venoconstriction do?
*increased venous return to attempt to use Frank-Starling mechanism (elevated filling pressures)
What does arterio-constriction do?
- homeostatic priority is to maintain BP. (Results in increased workload on failing heart)
What does venodilation do?
Diverts blood away from cardiopulmonary circuit
What are examples of venodilators?
*Furosemide IV
*topical nitroglycerine
What does arteriodilators do?
*Reduce myocardial work-load
*Reduce systemic blood pressure without compromising organ perfusion
=reduced afterload, myocardial wall stress + O2 consumption
**Unloads failing heart
What are examples of arteriodilators?
- Pimobendan (balanced vasodilator)
- Amlodipine
- Hydralazine
- (ACE inhibitors)
What is pimobendan MoA + what does it do?
*MoA = increased contractility w/o increased Ca2+ (less arrhythimias)
*Vasodilator
*Positive inotrope
Why is high sympathetic drive bad?
- Persistent high sympathetic drive is associated with increased mortality in humans and dogs with CHF
Why would you not use B-blockers to counteract?
B-blockers reduce CO - patients depend on maintain CO.
What can you use to counteract high sympathetic drive in CHF?
*Digoxin - enhance vagal tone
- reduce sympathetic drive
(At low doses)
What are the qualities of digoxin?
- Negative chronotrope
- Weak positive inotrope
- Favourable autonomic effects
What can you use digoxin for?
- Atrial fibrillation
- Other supraventricular tachyarrhythmias
- (Sinus tachycardia)
- ….with impaired systolic function
How does digoxin enhance vagal tone + reduce sympathetic drive?
- Direct stimulation of vagal centres in CNS
- Sensitizes baroreceptors to changes in BP
- Enhances cardiac pacemaker responses to acetylcholine (ACh).
What are the effects of digoxin on the nodes in the heart?
- slowed rate of discharge of SAN
- slows conduction through AVN
- increases refractory period in AVN
How would you administer digoxin?
Slow oral
What are the signs of digoxin toxicity?
- excessive borborygmi
- depression
- anorexia
- vomiting & diarrhoea
digoxin acts on CTZ & medullary emetic centres - Cardiac arrhythmias (any!)
Who are the patients predisposed to digitoxicity?
- Thin, cachexic (reduced skeletal mm binding)
- Obese (no fat distribution)
- Ascites (over-estimate body mass)
- Hypoproteinaemia (reduced plasma protein binding)
- Hypothyroidism
- Impaired renal function
- Dobermann breed
- Hypoxia / Acidosis
- Hypokalaemia
- Alterations in [Ca++]
- Other drugs (especially Ca channel blockers)
How would you treat digitoxicity?
- Stop for 3 - 5 days, start again at lower dose
- Check acid-base balance, electrolytes
What is the optimal treatment of CHF in dogs?
Quadruple therapy:
– Furosemide
– Pimobendan
– ACE-I (benazepril)
– Spironolactone
(EXPENSIVE)
