L19: Pathophysiology of heart failure Flashcards
What is heart failure?
Inability of the heart to meet the demands of the body
What do we mean by ‘demands of the body’?
Deliver a blood volume that allows body tissue to function as required
What is the official definition of heart failure?
Clinical syndrome of reduced cardiac output, tissue hypoperfusion, increased pulmonary pressure and tissue congestion
What enables the heart to work as an effective pump? What happens if these change?
Valves–> unidirectional, prevent backflow
Chamber size–> sufficient room for blood
Functioning muscle–> need muscle to contract to eject the blood
Changes can potentially lead to impaired cardaic function
What are the causes (aetiology) of heart disease?
1- Most common–> ischaemic heart disease (starvation of O2)
–> Myocardial dysfunction–> scarring–> fibrosis, remodelling of muscles
2- Hypertension ↑afterload–> pump against higher pressure, more difficult, and increased risk of athersclerosis
3- Arrhythmias–> heart contracting randomly, affects filling and emptying of chambers
4- Aortic stenosis–> difficult to pump blood out of the heart
5- Other valvular dysfunction or other myocardial structural diseases
6- Cardiomyopathies –> disease of the heart–> dilated, hypertrophic, restrictive
7- Pericardial disease–> disease of the pericardium –> prevents the heart from being able to relax and fill properly
8- Grossly elevated demand on CO–> severe anaemia, thyrotoxicosis, sepsis
Why is it important to identify the cause of heart failure?
Need to treat the cause
Prevent it happening again
How is cardiac function measured?
Cardiac output is measured CO= SV x HR CO--> volume delivered per minute SV--> volume ejected by ventricle each beat HR--> number of beats per minute
What is the ejection fraction? What does it show?
Percentage of blood ejected from the heart
Amount of blood ejected from ventricle each beat (SV)/ amount of blood in the ventricle at the end of diastole (EDV)
How well the heart is functioning
What influences the stroke volume?
Pre-load–> volume in the ventricles at the end of diastole–> stretch of the ventricles
After-load–> what the heart is having to pump against –> total peripheral resistance
Myocardial contractility–> ability of the heart to contract
What happens when the pre-load is increased in a normal healthy heart?
Increase the preload, increased the force of contraction
Frank-Starlings law –> more the heart fills= harder the heart contracts
Up to a point
More ventricular distension during diastole= greater volume ejected during systole
Why does an increase in pre-load result in an increase in contraction?
Increase pre-load, increase amount of blood in the heart
Means the myocardium is stretched- intrinsic property of myocytes
Actin and myosin aren’t as overlapped so have more area to overlap during contraction
This is up to a point–> over stretched–> actin and myosin don’t overlap at all–> reduced contraction
Other than stretch what can also influence Frank-Starling law of contraction?
Sympathetic input
Alters inotrophic state of the heart
Increase sympathetic activity increased CO for a given LVEDP (more volume is forced out)
Why is the cardiac output reduced in heart failure? Why?
Stroke volume is reduced
Reduced pre-load–> impaired filling of ventricles during diastole (rarely due to decreased venous return)
Reduced myocardial contractility–> muscle not able to produce same force of contraction for given volume
Increased afterload–> increased pressure to pump against e.g. increased TPR, valvular stenosis
In simple words what causes the heart to fail?
Filling problem - diastolic
Ejecting problem - systolic
What can cause the preload to decrease?
Impaired filling or space for filling reduced
- Ventricle chambers to stiff, not relaxing enough, less blood can enter
- Ventricle walls thickened (hypertrophic)–> taken up space in the chamber
