9. Heart failure - causes

Question 1

What is heart failure?

Answer 1

state in which the heart fails to maintain an adequate circulation for the needs of the body despite an adequate filling pressure

Question 2

What is the difference between systolic and diastolic heart failure?

Answer 2

• systolic heart failure: ventricle can’t pump hard enough… decrease in ejection fraction to <50%… decreased CO (Frank-Starling Law)
• diastolic heart failure (HF with preserved ejection fraction): abnormal ventricle filling… decreased preload… decreased SV (but normal EF)… decreased CO

Question 3

What is the ejection fraction?

Answer 3

= SV / end-diastolic volume

Question 4

On what 4 components does CO depend on?

Answer 4

1. Heart rate ( increased HR causes decreased CO as less efficient )
2. Venous capacity / LV pre-load (amount of blood going into heart)
3. Myocardial contractility (Starling’s Law)
4. Aortic and peripheral impedence / after-load

Question 5

Which side of the heart does heart failure involve?

Answer 5

HF can be left-sided or right-sided but is most often both (biventricular) as the 2 systems work in series.

Question 6

Explain why left-sided HF often results in right-sided HF.

Answer 6

i) Left sided HF… decreased CO… increased pressure in pulmonary veins…
ii) … increased pressure in pulmonary arteries…
iii) … increased RV workload…
iv) … right sided HF

Question 7

What type of failure is usually involved in left sided HF?

Answer 7

systolic (can’t pump hard enough… decreased ejection fraction… decreased CO)

Question 8

What is the main cause for LHF?

Answer 8

Damage to the myocardium, decreasing ability of ventricle to contract.

Question 9

Name 4 conditions that can cause systolic LHF.

Answer 9

Systolic LHF from damage to myocardium by:

1. ischaemic heart disease
   
   • angina due to coronary artery atherosclerosis
   • MI and myocyte necrosis
2. hypertension
   
   • increased arterial pressure… harder to pump… LV hypertrophy… squeezes coronary arteries and increases O2 demand… weaker contraction
3. dilated cardiomyopathy
   
   • dilation of LV in attempt to increase preload and contraction strength (Frank-Starling)… works at start but eventually leads to LV wall thinning
4. toxic damage, e.g. secondary to cytotoxic chemotherapy

Question 10

Explain the causation of LHF with preserved EF.

Answer 10

i) Long standing hypertension or valvular disease (e.g. aortic stenosis, mitral regurgitation) causes concentric LV hypertrophy.
ii) So less room for filling, which causes decreased preload and SV and thus decreased CO.

Question 11

What are the main causes of RHF?

Answer 11

1. Most often caused by LHF
2. Cor pulmonale: chronic lung disease or pulmonary embolism
3. L to R shunt (ASD or VSD)
4. Valvular disease (pulmonary valve stenosis or tricuspid valve regurgitation)

Question 12

Explain why cor pulmonare occurs.

Answer 12

1. Chronic lung disease or pulmonary embolism cause chronic alveolar hypoxia… vasoconstriction to ensure perfusion matches ventilation… pulmonary hypertension.
2. Increases RV workload causing RV concentric hypertrophy.
3. Leads to ischaemia and damage to myocardium - reduced EF and systolic HF.

Question 13

Explain how R to L shunts and pulmonary/tricuspid valvular disease cause RHF.

Answer 13

1. R to L shunt and valve disease cause increased fluid volume in right side of heart.
2. Increases RV workload causing RV concentric hypertrophy.
3. Leads to ischaemia and damage to myocardium - reduced EF and systolic HF.

Question 14

Describe the NYHA functional classification of HF.

Answer 14

Class I
- no symptomatic limitation of physical activity

Class II

• slight limitation of physical activity
• ordinary physical activity results in symptoms
• no symptoms at rest

Class III

• marked limitation of physical activity
• less than ordinary physical activity results in symptoms
• no symptoms at rest

Class IV

• inability to carry out any physical activity without symptoms
• may have symptoms at rest