19. Pathophysiology Of Heart Failure Flashcards
What is heart failure?
Inability of heart to meet the demands (deliver a blood volume that allows body tissues to function as required) of the body
What is the most common cause of heart failure?
Ischaemic heart disease (coronary heart disease)
What are some other causes of heart failure?
Hypertension Arrhythmias Aortic stenosis Other valvular or myocardial structural diseases Cardiomyopathies Pericardial diseases
What is fraction ejected?
Stroke volume/end diastolic volume
What influences stroke volume?
Pre-load - volume in ventricle at end of diastole
Myocardial contractility
After-load - total peripheral resistance
What is Frank-Starling’s Law?
More ventricular distension during diastole = greater volume ejected (SV) during systole
How can contractility of the heart change?
Contractility of the heart can increase with sympathetic activity
Why is cardiac output reduced in heart failure?
Stroke volume can be reduced due to reduced pre load, reduced myocardial contractility or increased afterload
What is a filling problem (diastolic) with the heart?
Ventricular volume/capacity for blood is reduced due to:
- ventricular chambers too stiff/not relaxing enough
- ventricular walls thickened
What is a contractility (ejection) problem (systolic) with the heart?
Can’t pump with enough force due to:
- muscle walls thin/fibrosed
- chamber enlarged
- abnormal or uncoordinated myocardial contraction
What is HFrEF?
Heart failure with reduced ejection fraction
Systolic dysfunction
Contractility problem
Most common type
What is HFpEF?
Heart failure with preserved ejection fraction
Diastolic dysfunction
Filling problem
What is the normal ejection fraction?
> 50%, typically >60%
How can a heart be failing if EF is maintained?
Ventricle ejects less volume in a heartbeat as less volume to begin with
Fraction of what is available to eject is still >50%
Hence ejection fraction is maintained
Which ventricle is usually involved in heart failure? What is involvement of both ventricles called?
Usually left ventricle, but with subsequent involvement of the right ventricle
Involvement of both ventricles is biventricular (congestive) heart failure
Describe Frank-Starling’ curve in heart failure
Increased LV filling in failing heart leads to a very little increase in CO
Eventually it leads to worsening CO
Markedly increased LVEDP result in falling CO and development of pulmonary congestion
What does the drop in cardiac output trigger to try and correct the falling CO?
Damaged ventricular tissue Reduction in efficiency of ventricular contraction Reduced stroke volume Reduced cardiac output Neurohormonal activation
How is cardiac work increased when cardiac output is decreased?
Blood pressure decreases leading to 2 pathways:
- Baroreceptors sense, increased sympathetic drive (inc. heart rate, inc. peripheral resistance)
- Activation of renin-angiotensin-aldosterone pathway, increases circulating volume due to Na+ and water retention, stimulates ADH, vasoconstriction, enhances sympathetic pathway
What are the clinical signs and symptoms of heart failure?
Symptoms: fatigue/lethargy, breathlessness, leg swelling
Many signs and symptoms due to increased interstitial fluid (oedema) in:
- pulmonary tissues
- peripheral tissues
How is tissue fluid formed?
Gradient between hydrostatic and oncotic pressure governs movement of fluid out of or back into capillaries
Higher hydrostatic in arterial end, higher oncotic pressure at venule end
How does tissue oedema form?
Increased capillary hydrostatic pressures leads to less fluid being drawn back intravascularly at venule end
Why is raised jugular venous pressure important?
Measurement of the pressure in the right internal jugular vein can be used as a direct reflection of pressures in the right side of heart
