Management of Canine congestive heart failure

Question 1

What does Na+ & H2O retention lead to in left + right sided CHF?

Answer 1

*Left sided CHF = Pulmonary oedema
*Right sided CHF =
-Ascites,
-Hepatomegaly with chronic venous congestion
- Pleural effusions

Question 2

Which sided CHF is more deadly and why?

Answer 2

Left sided
Pulmonary oedema can be fatal

Question 3

What is the first choice diuretic to treat CHF?

Answer 3

Furosemide

Question 4

What dosage should you aim to give?

Answer 4

Lowest possible dose to control clinical signs

Question 5

When can you reduce dosage? When should in increase?

Answer 5

*Reduce furosemide dosage provided no increase in RR.
*Increase dose in increase respiratory rate

Question 6

What are the side effects of furosemide? What should be monitored?

Answer 6

• Pre-renal azotaemia
• Hypokalaemia
  Need to monitor renal function (urea, creatinine) & electrolytes
  (especially K+; also Na+, Cl-)

Question 7

Why shouldn’t you use furosemide on its own for a long time? What should you use with it?

Answer 7

*Monotherapy of furosemide = RAAS activation
*Use with ACE inhibitor

Question 8

What should you do if furosemide no longer works?

Answer 8

• 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)

Question 9

Why would you administer spironlactone?

Answer 9

*Anti-aldosterone effect - reduced Na+ & H2O retention + reduced cardiac remodelling

Question 10

What should you do with a right sided CHF?

Answer 10

• 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

Question 11

What is an example of ACE inhibitor?

Answer 11

Benazepril

Question 12

What are the side effects of ACE inhibitors?

Answer 12

• Hypotension
• Renal impairment
• Hyperkalaemia
• Anorexia, diarrhoea, vomiting etc.

Question 13

What is an example of angiotensin ii?

Answer 13

Telmisartan

Question 14

What does venoconstriction do?

Answer 14

*increased venous return to attempt to use Frank-Starling mechanism (elevated filling pressures)

Question 15

What does arterio-constriction do?

Answer 15

• homeostatic priority is to maintain BP. (Results in increased workload on failing heart)

Question 16

What does venodilation do?

Answer 16

Diverts blood away from cardiopulmonary circuit

Question 17

What are examples of venodilators?

Answer 17

*Furosemide IV
*topical nitroglycerine

Question 18

What does arteriodilators do?

Answer 18

*Reduce myocardial work-load
*Reduce systemic blood pressure without compromising organ perfusion
=reduced afterload, myocardial wall stress + O2 consumption
**Unloads failing heart

Question 19

What are examples of arteriodilators?

Answer 19

• Pimobendan (balanced vasodilator)
• Amlodipine
• Hydralazine
• (ACE inhibitors)

Question 20

What is pimobendan MoA + what does it do?

Answer 20

*MoA = increased contractility w/o increased Ca2+ (less arrhythimias)
*Vasodilator
*Positive inotrope

Question 21

Why is high sympathetic drive bad?

Answer 21

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

Question 22

Why would you not use B-blockers to counteract?

Answer 22

B-blockers reduce CO - patients depend on maintain CO.

Question 23

What can you use to counteract high sympathetic drive in CHF?

Answer 23

*Digoxin - enhance vagal tone
- reduce sympathetic drive
(At low doses)

Question 24

What are the qualities of digoxin?

Answer 24

• Negative chronotrope
• Weak positive inotrope
• Favourable autonomic effects

Question 25

What can you use digoxin for?

Answer 25

• Atrial fibrillation
• Other supraventricular tachyarrhythmias
• (Sinus tachycardia)
• ….with impaired systolic function

Question 26

How does digoxin enhance vagal tone + reduce sympathetic drive?

Answer 26

• Direct stimulation of vagal centres in CNS
• Sensitizes baroreceptors to changes in BP
• Enhances cardiac pacemaker responses to acetylcholine (ACh).

Question 27

What are the effects of digoxin on the nodes in the heart?

Answer 27

• slowed rate of discharge of SAN
• slows conduction through AVN
• increases refractory period in AVN

Question 28

How would you administer digoxin?

Answer 28

Slow oral

Question 29

What are the signs of digoxin toxicity?

Answer 29

• excessive borborygmi
• depression
• anorexia
• vomiting & diarrhoea
  digoxin acts on CTZ & medullary emetic centres
• Cardiac arrhythmias (any!)

Question 30

Who are the patients predisposed to digitoxicity?

Answer 30

• 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)

Question 31

How would you treat digitoxicity?

Answer 31

• Stop for 3 - 5 days, start again at lower dose
• Check acid-base balance, electrolytes

Question 32

What is the optimal treatment of CHF in dogs?

Answer 32

Quadruple therapy:
– Furosemide
– Pimobendan
– ACE-I (benazepril)
– Spironolactone
(EXPENSIVE)