CVS 19 - Pathophysiology of Heart Failure

Question 1

What is heart failure?

Answer 1

• An inability of the heart to meet the demands of the body.

- Clinical syndrome of reduced CO, tissue hypo-perfusion, increased pulmonary pressures and tissue congestion.

Question 2

What are the 3 features of the heart that enables it to work as an effective pump that can be impaired and lead to HF?

Answer 2

1) One-way valves
2) Chamber size
3) Functioning cardiac muscle

Question 3

What is the most common cause of HF?

What are some other causes + why is the cause important?

Answer 3

• Ischaemic (coronary) heart disease
• Other causes include hypertension, aortic stenosis, arrhythmia’s, pericardial diseases, valvular/myocardial structure diseases
• Detect underlying cause to identify correct treatment option

Question 4

How do we measure cardiac output of the heart?

What 3 factors influence stroke volume?

Answer 4

• CO = SV x HR AND EF = SV/EDV

- 1) Pre-load (volume in ventricle at end of diastole/EDV) 2) After-load (TPR) + 3) Myocardial contractility

Question 5

How do Frank-Starling curves vary with different inotropic states of the heart? (influence of sympathetics)

Answer 5

• Typical FS curves increase in CO with increased EDV due to increased ventricular muscle distension (up until optimum sarcomere overlap)
• Contractility increased further with increased sympathetic activity (curve up and left), greater CO for given LVEDV.

Question 6

What are the 2 typical reasons as to why CO is reduced in HF?

Answer 6

1) Filling Problem (diastolic) - ventricular volume/capaity reduced, i.e.: ventricular wall hypertrophy or chambers stiffened = less space = lower EDV (decreasing SV + CO)
2) Contractility Problem (systolic) - poor ventricular contractility due to thin walls, enlarged chambers or abnormal myocardial contraction (decreasing SV + CO)

Question 7

What are the 2 classifications of HF according to ejection fraction?
What are they due to?

Answer 7

1) Heart failure w/reduced EF (HFrEF) -systolic/contractility problem (most common)
2) Heart failure w/preserved EF (HFpEF) - diastolic/filling problem

NB: typical EF = 50-70% (normally 60+)

Question 8

What are the classification of HF according to the ventricles involved?

Answer 8

• LV most commonly affected
• Biventricular - AKA: congestive HF
• RV HF can occur in isolation secondary to chronic lung diseases (but is quite rare) - most common cause for RV HF is LV HF.

Question 9

What is the effect of HF on the Frank-Starling curve?

Answer 9

• Increased LV EDV in failing heart leads to little increase in CO, eventually leads to worsening CO (curve dips)
• Increased LV EDP (in attempts to restore SV) results in failing CO and development of pulmonary congestion.

Question 10

Describe in full, the neuro-humoral activation mechanisms that HF triggers leading to further increased demands in CO + further reductions in SV?

Answer 10

1) Decreased BP initiates baroreflex in carotid sinus, increasing sympathetic drive (HR + TPR), therefore increasing afterload and cardiac work.
2) Decreased BP activates RAAS, Agll stimulated Na/H2) retention via aldosterone, stimulates ADH + vasoconstriction to increased preload + afterload.

Question 11

What are the clinical signs + symptoms of HF?

Answer 11

Symptoms = fatigue/lethargy, breathlessness, maybe leg swelling.

Signs = Peripheral/Pulmonary oedema due to increased interstitial fluid.

Question 12

How does HF lead to formation of tissue oedema?

Answer 12

• Usually increased pressure at arterial end of capillary, with higher hydrostatic pressure drawing water out. Oncotic>hydrostatic at venule end, water drawn back in.
• In HF, pressure rises in venous circulation, increased hydrostatic pressure at venule end of capillary beds, water not drawn back in, stays in interstitial tissues leading to oedema.

Question 13

What are the symptoms associated with LV HF and those associated with RV HF?

Answer 13

LV = fatigue, breathlessness (exertional), orthpnoea (breathlessness worse lying flat) , nocturnal dyspnoea (waking up suddenly out of breath), basal pulmonary crackles, cardiomegaly.

RV = fatigue, breathlessness, peripheral oedema (pitting/denting), raised JVP, tender enlarged liver.

Question 14

What does raised JVP indicate?

Answer 14

• Bulging neck veins indicator of raised JVP which is a direct reflection of pressures in right side of heart (indicative of RV HF).