Management of canine congestive heart failure (CHF)

Question 1

What is the main cause of left sided congestive HF? What sign might an animal show?

Answer 1

Pulmonary oedema

• Coughing
• Emergency situation

Question 2

What are the 3 main causes of right sided congestive HF?

Answer 2

• Ascites
• Hepatomegaly with chronic venous congestion
• Pleural effusions

Question 3

What is the first choice drug for counteracting oedema and effusions?

Answer 3

Furosemide - diuretic

Question 4

When using furosemide what needs to be considered?

Answer 4

That the aim of use is to give the lowest possible dose to control clinical signs

Question 5

When furosemide is used at home by owners what must they monitor before administration?

Answer 5

• Train owners to monitor sleeping or resting respiratory rate (number of breaths in 15 seconds x 4 for breaths/minute)

Question 6

Once RR has been monitored by owners, how will this influence the dose of furosemide?

Answer 6

• Reduce dose of furosemide provided no increase in RR (30brpm).
• Increase dose of furosemide if increased RR.

Question 7

What are the side effects of furosemide?

Answer 7

• Pre-renal azotaemia
• Hypokalaemia
• Cannot be used as long term monotherapy due to RAAS activation

Question 8

What can be used if furosemide is no longer working?

Answer 8

• optimised use of ACE inhibitors and other drugs to improve cardiac function
• consider parenteral administration if there is GIT oedema

Question 9

Which more potent ceiling loop diuretic can be used if Furosemide is no longer working?

Answer 9

Torasemide

Question 10

What are the functions of Spironolactone?

Answer 10

• Aldosterone antagonist
• Potassium sparing diuretic
• Counteracts myocardial remodelling and fibrosis

Question 11

How is a pleural effusion initially treated and why?

Answer 11

o Chest needs to be drained – can’t use diuretics as initial treatment (more for pleural oedema)
o Thoraco-centesis is indicated

Question 12

How is right sided congestive heart failure initially treated?

Answer 12

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

Question 13

What are the functions of ACE inhibitors?

Answer 13

• 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

Question 14

What are the benefits of ACE inhibitors in patients with CHF?

Answer 14

• increased quality of life and survival time

- reduction of heart wall thickness in cats

Question 15

Give examples of ACE inhibitors used in practice

Answer 15

Benazepril
Enalapril
Ramipril
Imidapril

Question 16

What are the side effects of ACE inhibitors?

Answer 16

Hypotension
Renal impairment
Hyperkalaemia
Anorexia, diarrhoea, vomiting

Question 17

How can veno-constriction be used to counteract vasoconstriction in CHF?

Answer 17

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

Question 18

Give an example of an ointment used for venodilation in pulmonary oedema

Answer 18

Topical nitroglycerine

- apply to hairless, perfused skin

Question 19

How can arterio-dilators be used to counteract vasoconstriction in CHF?

Answer 19

• 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

Question 20

Give examples of arteriodilator drugs?

Answer 20

Pimobendan (balanced vasodilator)
Amlodipine (Ca channel antagonist)
Hydralazine

Question 21

Describe the mode of action of Pimobendan

Answer 21

Ca sensitizer - Increased contractility w/o increased [Ca++]

Phosphodiesterase inhibition: Vasodilator and positive inotrope

Question 22

How is Pimobendan administered?

Answer 22

Orally - on an empty stomach as absorption is impaired by food

Question 23

How is sympathetic drive related to CHF?

Answer 23

Persistent high sympathetic drive is associated with increased mortality in dogs with CHF

Question 24

What is the main strategy in counteracting high sympathetic drive?

Answer 24

Use drugs to improve haemodynamic status so indirectly reducing sympathetic drive
- Digoxin

Question 25

What is the mode of action of Digoxin?

Answer 25

• Negative chronotrope = reduced HR
• Weak positive inotrope (contractility)
• slows conduction through the AV node

Question 26

When is Digoxin used indicated?

Answer 26

• Atrial fibrillation
• Other supraventricular tachyarrhythmias
• Rarely if ever indicated in patients with sinus rhythm with CHF

Question 27

Why is the risk of toxicity high with Digoxin use?

Answer 27

It has a narrow therapeutic index

Question 28

What are the signs of digitoxicity?

Answer 28

Excessive GIT sounds
Depression
Anorexia
Vomiting
Diarrhoea 
Cardiac arrythmias

Question 29

Which patients may be predisposed to digitoxicity?

Answer 29

• 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)

Question 30

How can digitoxicity be prevented?

Answer 30

• 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

Question 31

How can digitoxicity be treated?

Answer 31

• Stop for 3 - 5 days, start again at lower dose
• Check acid-base balance, electrolytes
• Life-threatening ventricular arrhythmias, use lidocaine or phenytoin

Question 32

What are the 4 drugs used in standard quadruple therapy of CHF in dogs?

Answer 32

• Furosemide
• ACE-I (benazepril)
• Pimobendan
• Spironolactone

Question 33

Which drug delays progression of DCM into clinical disease or death?

Answer 33

Pimobendan