Acute Heart Failure Flashcards
What is heart failure?
Inability to provide adequate CO to support the needs of the tissues (or can do so at the expense of a raised filling pressure)
What is acute heart failure?
Cardiogenic shock
What type of heart failure evolves over months, years and decades?
Chronic heart failure
How is aortic pressure kept constant, even if the system is failing around it ?
By the activity of the baroreceptors in the aortic arch
At what pressure is aortic pressure kept constant?
100mmHg
What happens to CO in right HF?
- Impaired pumping causes the output of both ventricles to be reduced so that the CO falls to 6L/min (from 8)
- The left and right circulations are in series so that fall in the right CO must cause a fall in the left CO
What impacts on the progression of the disease?
How the baroreceptor reflex achieves constant aortic pressure
How does RHF affect blood pressure?
- Systemic venous pressure rises bc RV EDP is increased i.e. the RH backs up
- However, circulatory reflexes tend to maintain mean pulmonary artery pressure, LV EDP and aortic pressure at virtually normal levels
How does LHF affect CO?
- Impairing pumping causes the output of both ventricles to be reduced so that CO falls
How does LHF affect BP?
- Pulmonary venous pressure rises bc LV EDP is increased i.e. the LH backs up
- However circulatory reflexes tend to maintain mean aortic pressure at virtually normal levels
- The elevated pulmonary venous pressure is transmitted through the lungs bc they are low resistance, causing a slight rise in pulmonary artery pressure to 40mmHg
- Pressures elevated on both sides of the pulmonary circulation
What type of heart failure occurs in most patients?
Congestive heart failure
What causes congestive heart failure?
Heart failure is principally due to failure of LV which in turn affects the performance of the RV
What are the effects of congestive heart failure?
When moderately severe, HF is accompanied by:
- Fall in CO
- Significant elevation of pulmonary venous pressure to 16mmHg bc left EDP is increased (i.e. the LH backs up)
- Modest elevation fo mean pulmonary artery to 40mmHg (bc lungs back up)
- Systemic venous pressures (bc RV also backs up)
What are the 3 primary causes of heart failure?
1) Pressure overload
2) Volume overload
3) Contractile dysfunction
How does pressure overload lead to HF?
Hypertension, aortic stenosis
How does volume overload lead to HF?
Aortic or mitral valve regurgitation, causing the volume to be higher than normal
What are causes of contractile dysfunction leading to heart failure?
1) Ischaemic heart disease
2) Myocardial disease
3) Pregnancy (pregnancy-induced HF)
4) Congenital cardiomyopathies (protein, heart muscle is compromised)
What is LaPlace’s Law?
- For a fixed wall stress (i.e. muscular effort) a small ventricle can generate higher pressures than a large ventricle
- For the same pressure, a smaller radius can tolerate a higher pressure
How does LaPlace’s Law apply to heart failure?
- In a heart, wall stress is the force needed from the muscle
- So when the heart gets bigger, to maintain the same BP, it must either increase the amount of work done in the fibres in the wall of the heart or increase wall thickness
How does the heart contract?
The fibres in the walls generate tension or ‘wall stress’
What happens to the heart wall in the early stages of heart failure?
The disease is in its compensated phase → it maintains pressures (and output) by increasing wall thickness
Why is increasing the wall thickness of the heart a problem?
It exacerbates the underlying problem with the compromised ventricular muscle → eventually the heart dilates i.e. the lumen gets bigger without an associated increase in wall thickness
How does heart dilation lead to decompensated heart failure?
If the lumen gets bigger (R increases) without an increase in width, then the pressure must drop otherwise the myofibrils will have to work even harder to maintain wall stress → this will push the heart into the viscous spiral of the decompensated phase of failure
Why does compensated heart failure eventually fail?
- In compensated heart failure, wall stress is normalised by concentric hypertrophy
- However, as this muscle is not normal heart muscle, it will fail
- This leads to an increase in radius (heart dilation) and wall stress
What happens during severe aortic stenosis or hypertension?
- The acute effect is an increase in wall stress
- The heart responds by thickening its wall so that, during the compensated phase, wall stress is normalised by concentric hypertrophy
- However, when dilation develops, radius increases and wall stress rises
- This has a number of deleterious consequences
What conditions lead to volume overload?
Aortic/mitral valve regurgitation
What occurs in volume overload?
- Initially leads to ventricular dilation → increased radius
- Some hypertrophy can then normalise wall stress (but not normal muscle)
- However, when failure sets in, the degree of dilation exceeds the degree of hypertrophy and wall stress increases
What are two types of contractile dysfunction?
1) Hypertrophic cardiomyopathy
2) Dilated cardiomyopathy
What happens in the two stages of hypertrophic cardiomyopathy?
1) Compensated concentric hypertrophy leads to a normal relation between wall thickness and wall stress
2) The development of dilation leads to myocardial failure (inadequate hypertrophy, failing)