The Pathophsiology Of Heart Failure

Question 1

Define heart failure

Answer 1

A clinical syndrome arising fromthe inability of the heart to maintain cardiac output to meet the demands of body

Question 2

What is the most common cause of heart failure ?

Answer 2

Ischaemic heart disease ( also known as coronary heart disease )

Question 3

What are other common causes of heart failure apart from ischaemic heart disease ?

Answer 3

1. Second most common cause is hypertension : this is because there is an increase in total peripheral resistance which means that there is an increased afterload on ventricle.
2. Arrhythmias
3. Aortic stenosis : this increases afterload on ventricles.
4. Pericardial diseases

Question 4

What are very rare causes of heart failure ?

Answer 4

Sepsis

Severe aneaemia

Thyrotoxicosis

Question 5

How do we measure the ability of the heart to meet the demands of the body ?

Answer 5

Cardiac output = stroke volume. X heart rate

Question 6

What does ejection fraction mean ?

Answer 6

The units is : %

It is the amount of blood pumped out of a ventricle ( stroke volume ) / total amount of blood in ventricle at end diastolic volume

It is normally above 50-60%.

It is pathological when below 40%.

Question 7

What influences stroke volume ?

Answer 7

1. Increased pre-load has a positive influence of stroke volume ( increases it). This is the volume of blood in ventricle at the end of diastole.
2. An increased myocardial contractility will have a positive influence on stroke volume (increases it).
3. An increased after load , however will impede stroke volume as this is what the heart has to pump against. For example hypertension.

Question 8

Why does an increase in pre-load lead to an increase in stroke volume ?

Answer 8

According to Frank Starlings law , if we increase end diastolic volume , this increases stretch of the ventricular myocytes which means there is a greater force of contraction. This means that there is a greater volume of blood ejected.

Frank starlings law graph : end diastolic volume on x axis and cardiac output on Y axis. As x increases , y increases. But only up to a certain point due to the intrinsic property of cardiac myocytes as you can stretch them too far they won’t work.

Question 9

How does the sympathetic nervous system activation increase cardiac output ?

Answer 9

When we activate the sympathetic nervous system , we increase the contracility of the heart. Which means there is a greater cardiac output for a given left ventricular end diastolic pressure.

Question 10

Why is cardiac output reduced in heart failure ?

Answer 10

1. Stroke volume reducing due to reduced pre load ( impaired filling of the ventricle during diastole )
2. Stroke volume reducing because of reduced myocardial contractility ( muscle not able to produce same force of contraction for a given volume within ventricle )
3. Increased afterload - this is due to increase pressure against which ventricle contracting for example due to aortic stenosis , chronic severe hypertension

Question 11

Why can Reduced pre load lead to heart failure?

Answer 11

Reduced ore load is impaired filling of the ventrickle during diastole - this could be due to the size of the ventricle itself. For example , the ventricular chamber is smaller due to ventricular walls thickening so the chamber size decreases.

Another reason could be the ventricular chambers are too stiff so they do not relax enough during diastole.

REDUCED PRE LOAD IS NOT DUE TO A DECREASE IN VENOUS RETURN IN HEART FAILURE PATIENTS.

this is often termed ‘ diastolic heart failure ‘

Question 12

Why can reduced contractility lead to heart failure ?

Answer 12

This is where the ventricles cannot pump with enough force for a given end Diastolic volume.

This could be due to the muscle walls thinning / fibrosis. Could also be due to chambers enlarging due to overstretched sarcomeres. Or due to abnormal / uncoordinated myocardial contraction.

This is often termed ‘ systolic heart failure’

Question 13

What are the three methods used to classify heart failure ?

Answer 13

1. Classify according to the functional symptoms presented eg class 1 , class 11, class 111, class IV
2. Classify according to the ventricle failing - left or right ventricular heart failure
3. Classify according to the ejection fraction - eg Heart failure with reduced ejection fraction and heart failure due to preserved ejection fraction.

Question 14

How do we classify heart failure according to ejection fraction ?

Answer 14

1. Heart failure with reduced ejection fraction( HFrEF) - this is a systolic dysfunction where there is a problem with contractility. This could due to the ventricles enlarging due to sarcomeres over stretching , could be due to arrhythmias, could be due to thinning of the ventricular walls. The ejection fraction in this case would be below 40%
2. Heart failure with preserved ejection fraction ( HFpEF) : this is a diastolic dysfunction. There is a problem with the filling of the ventricles. This is caused by a reduction in pre load often caused by a decrease in the size of ventricles. The ejection fraction would be the same.

Question 15

How can the heart be failing if the ejection fraction is maintained in ‘HFpEF’ ?

Answer 15

The ventrickle ejects less volume in a heartbeat as less volume of blood to begin with.
Fraction of what is available to eject is still more than 50%.

Hence ejection fraction is preserved.

Question 16

What is the most common type of heart failure ( according to the ejection fraction classification ) ?

Answer 16

HFrEF

Question 17

How to measure ejection fraction ?

Answer 17

Echocardiogram

Question 18

How to classify heart failures based on the ventricles involved ?

Answer 18

1. Left ventricle ( most commonly involved). This leads to subsequent involvement of the right ventricle.
2. Right ventricle ( this can occur isolation or secondary to chronic lung diseases). The MOST common cause for right ventricular heart failure is left ventricular heart failure.
3. Biventricular ( congestive ) heart failure

Question 19

How does frank-starlings curve in heart failure look like in someone with HFrEF ?

Answer 19

In a normal healthy heart , increased left ventricular filling leads to a big increase in cardiac output.

Increased left ventricular filling in failing heart leads to a very little increase in cardiac output. Eventually it leads to worsening of cardiac output.

Question 20

What are the compensatory mechanisms involved with heart failure?

Answer 20

Due to the decreased cardiac output , there will be w decrease in blood pressure. Two mechanisms are involved to try and increase blood pressure :

1) baroreceptor in the carotid sinus detect that less blood is being ejected out of the heart , so this would stimulate the sympathetic nervous system which would work to increase heart rate and increase peripheral resistance. This increases afterload of the heart which increase cardiac work ( BAD )
2) Actuvation of the renin-angiotensin aldosterone pathway due to decreased renal perfusion. This would lead to aldosterone being released from adrenal cortex. Stimulation of ADH. Vasoconstriction. And enhanced sympathetic activity. This in turn increases pre load because there is a larger circulating volume due to Na+ and water retention. And increases afterload to the increase in blood pressure.

Question 21

Outline the process by which tissue fluid is formed in normal , healthy beings

Answer 21

At the arterial end , there is a very high hydrostatic pressure compared to the oncotic pressure.

This pressure difference forces fluid out of the capillaries into the interstitial space.

As the fluid moves out of the capillaries , there is a decrease in hydrostatic pressure across the vessel.

So towards the venule end , hydrostatic pressure drops below the oncotic pressure. This means that fluid then moves back into the vessel due to oncotic pressure being greater than hydrostatic pressure.

Question 22

Outline the formation of tissue oedema

Answer 22

If there is failing right or left ventricles , this leads to higher pressures in venous circulation ( blood just pools out into Veins that they entered in).

This leads to an increase in hydrostatic pressure at venule end of the capillary bed. This means that there will be less favourable gradient between hydrostatic and oncotic pressures at venule for fluid returning to the capillaries. So more fluid accumulates in the interstitium , more moves out and less moves back in,

Question 23

What are symptoms associated with left ventricular heart failure ?

Answer 23

Fatigue / lethargy
Breathlessness ( exertions)
Orthopnoea ( shortness of breath when laying down)
Paroxysmal nocturnal dyspnoea ( wake up in the night gasping for breath)
Basal pulmonary crackles
Cardiomegaly - displaced Apex beat indicating enlarged LV

Question 24

What are symptoms associated with right ventricular heart failure ?

Answer 24

Fatigue
Breathlessness
Peripheral oedema
Raised jugular venous pressure so it is palpable in the neck
Tender , smooth enlarged liver ( liver congestion )