Cardiac failure Lecture 7

Question 1

What are the causes of heart failure?

Answer 1

Impaired contractility (2/3)

• Myocardial Infarction
• Chronic Volume overload

Increased afterload (1/3)

-Uncontrolled hypertension - pressure overload

Systolic dysfunction leads to left heart failure which generally leads to right heart failure (backward failure)

Starlings relainship - If the ejection is less than 50% indicative of heart failure- dilated ventricle, increased EDV, depressed contractility

Failing hearts have depressed curves

-Patients with greatly enlarged EDV get pulmonary oedema

Question 2

What are the signs and symptoms of congestive heart failure?

Answer 2

Coughing

Tiredness

Shortness of breath

Pulmonary oedema

Heart pumping becomes weaker

Pleural effusion

Ascites

Oedema in ankles and legs

Question 3

What is the new York heart association classification of heart failure and its significance?

Answer 3

1. No limitation of physical activity
2. Slight limitation of activity. Dyspnoea and fatigue with moderate physical activity
3. Marked limitation of activity. Dyspnoea with minimal activity
4. Severe limitation of activity. Symptoms are present even at rest

At class 1&2 SV can still be normalised at rest by an increase in EDV Class 34 the starlings relationship is approaching horizontal

Question 4

What is the importance of the baroreceptor reflex in heart failure?

Answer 4

• Decreased CO -> decreased ABP
• Reduction in baroreceptor activity initiating reflex
• This causes increased sympathetic activity to heart and blood and decreased vagal activity to heart
• Increased symp. causes constriction in venous (raised EDV) and arterial (raised TPR) vessels
• Increased ADH and RAAS for water and Na+ reabsorption. Also increase in renin-angiotensin system to retain Na+. Aldosterone also does this to increase water and Na+

Decompensation- worsens primary condition- more volume overload.

> More overfilling of heart and veins - increased pre-load

• > Increased afterload
• > Blunting of endothelium-dependent dilatation

Needs vasodilators, diuretics, beta1 blockers Sensitivity of baroreceptors decreases and so ABP goes uncorrected

Question 5

What is ANP and BNP?

Answer 5

Atrial natriuretic peptide (ANP) Released in response to increased atrial stretch and ventricular volume overload

BNP is only produced in heart failure

Act on the NPR-A receptor to cause vasodilation

Also result in increase diuresis and naturesis to decrease blood volume- counteracts Angiotensin 2 and its effects on aldosterone and ADH secretion

Question 6

What are the adverse outcomes from decompensation?

Answer 6

1. Increased sympathetic to heart

• Increased myocardial metabolic demand results in ventricular hypertrophy and arrythmogenesis
• Downregulation of beta1 receptors, upregulation of Gi proteins (Decreases NAd sensitivity)

2. Loss of vagal effects

-Causes heart rate variability

3. Increased AngII (angiotensin II)

• Increased cytokine production - activates macrophages
• Increased ROS generation
• These both lead to fibrosis and re-modelling of heart -> stiffening (impairs diastole filling)

4. Chronic raised sympathetic activity to heart and vasculature

5. Baroreceptor reflex sensitivity is blunted

6. Increased ADH despite volume overload

-Can lead to hyponatraemia - causes CNS oedema

7. Peripheral chemoreceptor activity is raised

-Due to reduced delivery of O2 to carotid bodies

8. Exercise intolerance as exercise reflex is exaggerated

-Causes further sympathetic activation and dyspneoa

9. Endothelial dysfunction

Question 7

What are the underlying mechanisms underlying exercise intolerance?

Answer 7

During exercise in heart failure

• Smaller increase in CO, contractility and HR (reduced O2 delivery)
• Lungs are congested via stiffness and oedema, further contributing to reduced oxygenation
• Exercising muscles get smaller increase in blood flow due to blunted endothelium-dependent dilation (due to oxidative stress)
• This causes accumulation of metabolites which exaggerates metaboreceptor stimulation -> greater exercise reflex
• This reflex causes reduction in kidney blood flow, increased ANG release
• The lungs increase respiration by reflex, increasing blood flow - “stealing” blood from limb muscles to use it in respiratory muscles
• This causes +ve feedback effects and downward spiral leading to death

Question 8

Explain exercise intolerance in CHF patients

Answer 8

Lungs- increase vascular resistance, lung stiffness, oedema, decrease O2 diffusion

Heart and blood- smaller CO, smaller systemic O2 delivery

Skeletal muscle- smaller increase in blood flow, less O2 supply, increase metabolite accumulation, exaggerated music!me reflex

Exercise rehabilitation helpos to prevent downward spiral