Management of canine congestive heart failure (CHF) Flashcards
What is the main cause of left sided congestive HF? What sign might an animal show?
Pulmonary oedema
- Coughing
- Emergency situation
What are the 3 main causes of right sided congestive HF?
- Ascites
- Hepatomegaly with chronic venous congestion
- Pleural effusions
What is the first choice drug for counteracting oedema and effusions?
Furosemide - diuretic
When using furosemide what needs to be considered?
That the aim of use is to give the lowest possible dose to control clinical signs
When furosemide is used at home by owners what must they monitor before administration?
- Train owners to monitor sleeping or resting respiratory rate (number of breaths in 15 seconds x 4 for breaths/minute)
Once RR has been monitored by owners, how will this influence the dose of furosemide?
- Reduce dose of furosemide provided no increase in RR (30brpm).
- Increase dose of furosemide if increased RR.
What are the side effects of furosemide?
- Pre-renal azotaemia
- Hypokalaemia
- Cannot be used as long term monotherapy due to RAAS activation
What can be used if furosemide is no longer working?
- optimised use of ACE inhibitors and other drugs to improve cardiac function
- consider parenteral administration if there is GIT oedema
Which more potent ceiling loop diuretic can be used if Furosemide is no longer working?
Torasemide
What are the functions of Spironolactone?
- Aldosterone antagonist
- Potassium sparing diuretic
- Counteracts myocardial remodelling and fibrosis
How is a pleural effusion initially treated and why?
o Chest needs to be drained – can’t use diuretics as initial treatment (more for pleural oedema)
o Thoraco-centesis is indicated
How is right sided congestive heart failure initially treated?
o Do not drain abdominal effusions unless severely compromising respiration
o Make sure R-CHF is NOT due to a pericardial effusion before starting diuretics or other cardiac drugs
What are the functions of ACE inhibitors?
- Balanced vasodilators
- Reduce aldosterone release, so reduced Na+ & H2O retention
- Prevent Angiotensin II mediated myocardial fibrosis and remodelling
- Permissive anti-adrenergic effects
- Reduce vasopressin release
- Reduce endothelin release
- Increased levels of bradykinin & vasodilatory prostaglandins
- Prevent glomerular capillary hypertension
What are the benefits of ACE inhibitors in patients with CHF?
- increased quality of life and survival time
- reduction of heart wall thickness in cats
Give examples of ACE inhibitors used in practice
Benazepril
Enalapril
Ramipril
Imidapril
What are the side effects of ACE inhibitors?
Hypotension
Renal impairment
Hyperkalaemia
Anorexia, diarrhoea, vomiting
How can veno-constriction be used to counteract vasoconstriction in CHF?
Veno-constriction: increased venous return to attempt to use Frank-Starling mechanism (elevated filling pressures)
Increased capacitance of the circulation: Diverts blood away from cardiopulmonary circuit
Give an example of an ointment used for venodilation in pulmonary oedema
Topical nitroglycerine
- apply to hairless, perfused skin
How can arterio-dilators be used to counteract vasoconstriction in CHF?
- reduce myocardial workload
- reduce systemic blood pressure without compromising organ perfusion
- This reduces afterload, and myocardial wall stress, so reduces myocardial oxygen consumption
- Unloads the failing heart – makes it more efficient in perfusing the tissues
Give examples of arteriodilator drugs?
Pimobendan (balanced vasodilator)
Amlodipine (Ca channel antagonist)
Hydralazine
Describe the mode of action of Pimobendan
Ca sensitizer - Increased contractility w/o increased [Ca++]
Phosphodiesterase inhibition: Vasodilator and positive inotrope
How is Pimobendan administered?
Orally - on an empty stomach as absorption is impaired by food
How is sympathetic drive related to CHF?
Persistent high sympathetic drive is associated with increased mortality in dogs with CHF
What is the main strategy in counteracting high sympathetic drive?
Use drugs to improve haemodynamic status so indirectly reducing sympathetic drive
- Digoxin
What is the mode of action of Digoxin?
- Negative chronotrope = reduced HR
- Weak positive inotrope (contractility)
- slows conduction through the AV node
When is Digoxin used indicated?
- Atrial fibrillation
- Other supraventricular tachyarrhythmias
- Rarely if ever indicated in patients with sinus rhythm with CHF
Why is the risk of toxicity high with Digoxin use?
It has a narrow therapeutic index
What are the signs of digitoxicity?
Excessive GIT sounds Depression Anorexia Vomiting Diarrhoea Cardiac arrythmias
Which patients may be predisposed to digitoxicity?
- Thin, cachexic (reduced skeletal mm binding)
- Obese
- 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 can digitoxicity be prevented?
- Always start at a low dose
- Dose on body surface area
- Reduce dose if predispositions identified
- Always check a serum level after 5 – 7 days
How can digitoxicity be treated?
- Stop for 3 - 5 days, start again at lower dose
- Check acid-base balance, electrolytes
- Life-threatening ventricular arrhythmias, use lidocaine or phenytoin
What are the 4 drugs used in standard quadruple therapy of CHF in dogs?
- Furosemide
- ACE-I (benazepril)
- Pimobendan
- Spironolactone
Which drug delays progression of DCM into clinical disease or death?
Pimobendan
