Heart Failure

Question 1

Define heart failure

Answer 1

Failure to provide a sufficent CO for the body’s physiological needs

Question 2

What are the 3 main underlying causes of Heart Failure?

Answer 2

1) High resistance to CO (afterload) - aortic stenosis/arterial hypertension
2) Heart valves not closing properly
3) Heart muscle damage (cardiomyopathy/MI)

Question 3

What are the principles of treating HF?

Answer 3

Remove the underlying condition (replace valves)
Relieve aggregation condition (eg anaemia)
Relieve CVP to reduce oedema
Increase CO (+ve inotropes, to decrease skeletal muscle fatigue).
Decrease resistance to CO (vasodilation) to decrease skeletal and cardiac muscle fatigue.

Question 4

How are positive inotropes used to treat heart failure and what 3 classes can be used?

Answer 4

Increase intracellular Ca++, bind to troponin C and increase contractile force.

1) Cardioglycosides - eg digitalis
Inhibit Na/K pump, increase intracellular Na+, indirectly inhibit Na/Ca+ pump therefore increase intracellular Ca++.

2) B1 sympathomimetics - eg iv dobuatmine or dopamine (emergency)
- active B1 receptor, activate adcyc, increase cAMP levels. cAMP inhibitions the inhibition of the slow inward Ca current (Isi) therefore increase Ca++ intra-cellularly.

3) PDE inhibitors eg milrinone
- inhibit metabolism of cAMP
- increase cAMP…inhibits the inhibition of Isi…increase Ca++.

Therefore increase CONTRACTILE FORCE.

Question 5

Explain the drugs which decrease CVP.

Answer 5

1) Venodilators - glyceride trinitrate (GTN)
- dilate central veins to decrease CVP but can also cause oedema and decrease LVEDP and therefore decrease CO - so only use with positive inotropes.
2) Diuretics - furosemide (decrease BV) and spironolactone = aldosterone antag…decrease mortality (unclear mechanism).

Question 6

Explain drugs that decrease afterload

Answer 6

Arteriolar dilators - hydralazine - direct (receptor independant) arteriolar dilation…increase cGMP and decrease Ca++ = reduce muscle faitgue

Question 7

Explain drugs that decrease afterload and preload.

Answer 7

(decrease oedema and muscle fatigue)
Prazosin - alpha 1 antag; blocks vaso/venoconstriction effects of NA/Adr
1)Captopril - ACE inhibitor…less Ang II…less veno/vasoconstriction AND decrease BV (Diuretic action)

Question 8

Explain the action of ANG II receptor blockers.

Answer 8

Losartan
effective like ACE inhibitors but safer
BUT ACE induced bradykinin = troublesome

Question 9

Explain the action of Beta blockers

Answer 9

Have a parodoxical effect - carvedilol. metoprolol

• symptoms initially worsen, long term symptoms lessen
• risk of death decreases
• inhibit the adverse remodelling in the heart