Pathopysiology Of Heart Failure Flashcards
What is heart failure?
What is heart failure*?
“inability of the heart to meet the demands of the body”
Not a condition but Heart failure is a clinical syndrome arising from inability of the heart to
maintain cardiac output to meet demands of body
i.e. deliver a blood volume (carrying oxygen/glucose etc) that allows body tissues to function as required
“clinical syndrome of reduced cardiac output, tissue hypoperfusion, increased pulmonary pressures and tissue congestion” (2016 ESC Guidelines)
What enables the heart to wrok as a pump?
Input, output, one way valves, ventricular chamber size adequate, muscle functioning
What is the most common cause of heart failure?
• Most common cause of HF is IHD (coronary heart disease)
– myocardial dysfunction e.g. through fibrosis (scarring), remodelling of muscle
What are other causes of hart failure
Hypertension (increased afterload on ventricle & accelerates atherosclerosis [inc. in coronary arteries])
Cardiomyopathies (e.g. hypertrophic/dilated)
Aortic stenosis (increased afterload on ventricle)
Arrhythmias
Other valvular or myocardial structural diseases (acquired or congenital) Pericardial diseases
• Rarely, can occur if a grossly elevated demand on cardiac output - heart cant keep up - often acute e.g. sepsis,
severe anaemia, thyrotoxicosis [high output heart failure]
How do we measure the ability of the heart to meet demands of the body?
CO = SV x HR
CO = vol delivered per min (expelled per ventricle per min) SV = volume ejected by a ventricle in a single beat
What influences stroke volume?
What influences stroke volume? i.e. the volume of blood a ventricle can eject in a single beat?
Pre-load (volume in ventricle at end of diastole =EDV)..the stretch on the ventricle just before contraction
After-load Total peripheral resistance
Myocardial Contractility
What is frank-starlings law
More ventricular distension during diastole = Greater volume ejected (SV) during systole
Intrinsic property of cardiac myocytes…the greater they are stretched the greater their force of contraction…up to a certain point… - there is a point where catin-myosin overlap is optimal, then at a point the myocytes are stretched too much there is very little overlap so contraction is very poor
See slide for graph
What can increase the contractility o the heart?
Contractility of the heart can increase with increased sympathetic activity (curve shifted upwards and to the left)
Greater CO for a given LVEDP (more volume is forced out)
See slide for graph
Why is CO reduced in heart failure?
Why is cardiac output reduced in heart failure?
CO = SV X HR
• Stroke volume can be reduced due to
– Reduced pre load (reduced EDV)
• Impaired filling of ventricle during diastole – Reduced myocardial contractility
• Heart muscle no longer able to produce same force of contraction for – Increased afterload
• Increased pressure against which the ventricle is contracting against
a given volume at the end of diastole (EDV)
e.g. secondary to aortic stenosis, chronic severe hypertension
What are the 2 main reasons the heart can “fail”
1) A filling problem (diastole) - “space” available in ventricle receive blood is reduced… EDV (preload) therefore reduced
• Ventricular chambers too stiff/not relaxing enough
• Ventricular walls thickened (hypertrophied)
2) A contractility (ejection) problem
(systole) - “space” available in ventricle not an issue but poor ventricular contraction so unable to empty it as well
• Can’t pump with enough force (for a given EDV)
• E.g. muscle walls thin/fibrosed, chambers enlarged
(overstretched sarcomeres), abnormal or uncoordinated myocardial contraction
What is systolic and diastolic heart failure
Systolic - Ejection problem (LV capacity to fill is larger…but not able to empty it as well)
Diastolic - Filling problem (concentric remodelling of ventricle/ stiff)
How is heart failure classified
Heart Failure with reduced Ejection Fraction (HFrEF)
– [systolic dysfunction]
– More common
Heart Failure with preserved Ejection Fraction (HFpEF)
– [diastolic dysfunction]
– Nearly 50% patients
What is ejection fraction
Measured on echo EF%= amount of blood pumped out os ventricle/total amount of blood in ventricle Ejection fraction: • Normal ≥50% • Reduced <40%
How does a filling problem affect ejection fraction?
If “filling problem”..
- Ventricle ejects less volume (hence stroke volume reduced) as less volume to begin with
- But fraction of what is available to eject is still >50%
- Hence “Ejection Fraction” is ‘preserved’
What are types of heart failure
- Emptying (systolic) vs filling (diastolic) dysfunction
- Reduced vs preserved ejection fraction (HFrEF vs HFpEF)
- Involve the left or right ventricular
- Most commonly involves the left ventricle
- But with subsequent involvement of the right ventricle
- Involvement of both ventricles- biventricular (congestive) heart failure • Right ventricular heart failure can occur isolation, secondary to chronic lung diseases (cor pulmonale)
- Much less common than left ventricular heart failure
- Note that the most common cause for RV heart failure is LV heart failure
Describe franks starlings curve in heart failure
See slide Increased LV filling in the failing heart leads to a very little increase in CO…eventually it leads to worsening CO
Markedly increased LVEDP [in attempts to increase SV] result in pulmonary congestion
What mechanisms are triggered by a drop in CO?
Damaged ventricular tissue -> Reduction in efficiency of -> ventricular contraction -> Reduced stroke volume -> Reduced cardiac output -> Neuro-hormonal activation
The compensatory mechanisms, however, ultimately lead to an increased cardiac demand and a further reduction in stroke volume (further deterioration in cardiac output and the condition)
Describe the effects of decreased Co
See slide
What are teh clinical signs and symptoms o heart failure?
Clinical Signs and Symptoms • Presenting symptoms will often include – Fatigue/ lethargy, – Breathlessness – +/- leg swelling • Many signs (and symptoms) arise as a result of increased interstitial fluid (oedema) – Pulmonary tissues – Peripheral tissues (dependent areas i.e. lower limbs)
Describe th formation of tissue oedema
Formation of Tissue Oedema Increased capillary hydrostatic pressures leads to less fluid being drawn back intravascularly at venule end
Gradient between Hydrostatic and Oncotic pressures less favourable for fluid returning to capillary
If failing right or left ventricle higher pressures in venous circulation -> increased hydrostatic pressure at venule end of capillary beds
What is oedema
-
What are presenting symptoms of LV heart failure?
Fatigue, lethargy, breathlessness (exertions), Orthopnoea (made worse by lying flat), paroxysmal nocturnal dyspnoesa, basal pulmonary crackles, cardiomegaly (displaced apex beat-indicating enlarged LV)
What are the presenting symptoms of RV heart failure?
Fatigue/lethargy, breathlessness, peripheral oedema (pitting), raised jugular venous pressure, tender, smooth enlarged liver
What ones the raised JVP indicate?
Measurement of the pressure in the right internal jugular vein can be used as a direct reflection of pressures in the right side of the heart
