Lecture 19 Flashcards
What is heart failure?
Inability of the heart to meet the demands of the body (deliver a blood volume that allows body tissues to function as required)
-clinical syndrome (collection of signs and symptoms) of reduced cardiac output, tissue hypoperfusion, increased pulmonary pressures, tissue congestion
What enables the heart to work as an effective pump?
- one way valves
- chamber size (big enough to allow filling of blood)
- functioning muscle (adequate muscle, coordinated contraction)
Anything interfering with these can cause impairment of cardiac function
What is the most common cause of heart failure?
Ischaemic heart diseases (coronary arteries)
MI is also common leading to fibrosis: stiffening
Common causes of heart failure?
- hypertension (increased afterload on ventricles: hypertrophy/risk factor for atherosclerosis)
- arrhythmias
- aortic stenosis (increased afterload on ventricles)
- cardiomyopathies (disease of heart muscle: dilation/hypertrophic)
- pericardial disease
- valvular/structural diseases (acquired/congenital)
Rarely can occur in grossly elevated demand on cardiac output (sepsis, severe anaemia, thyrotoxicosis:excess of TH)
Equation to work out CO:
CO= SV x HR
SV: how much you eject by ventricle in single beat
-only a fraction of the blood that was sat in the ventricle during diastole is ejected leaving the end diastolic volume (EDV)
-EJECTION FRACTION
CO: volume expelled per ventricle per min
What influences SV?
Increase SV
- pre-load increased (volume in ventricle at end of diastole:stretch on ventricle just before contraction)
- myocardial contractility
Decrease SV
-increased after-load (TPR)
What is Frank-Starling’s law?
Increased EDV = greater CO
(Intrinsic property of cardiac myocytes: greater they are stretched, the greater the force of contraction, up to a certain point)
What nervous system increases contractility of the heart?
Activation of sympathetic nervous system
- increased sympathetic activity, greater the contractility= greater CO
- this means frank-stirlings curve is shifted up and to the left
Why is the CO reduced in heart failure?
SV is reduced
- reduced preload (due to impaired filing of ventricle- not due to little blood returning to the ventricle)
- reduced myocardial contractility
- increased after-load
What are the two broad reasons why the heart can fail?
Filling problem (diastolic) -Ventricular capacity for blood is reduced: ventricle walls too stiff/not relaxing enough/ventricle walls thickened: hypertrophy (EDV/preload reduced)
Contractility (ejection) problem
-heart can’t pump with enough force (no change in size of ventricle), muscle wall is thin/fibrosis, chambers enlarged/overstretched, abnormal/uncoordinated contraction)
What is the difference between systolic/diastolic heart failure?
Systolic heart failure
-weakened heart muscle: contractility/ejection problem
Diastolic heart failure
-filling problem
How do you classify heart failure?
HFrEF (heart failure with reduced ejection fraction)
- systolic dysfunction
- contractility problem
HFpEF (heart failure with preserved ejection fraction)
- diastolic dysfunction
- filling problem (still as a percentage eject most of blood from ventricle but you are working with a smaller volume of blood)
What is the most common type of heart failure?
HFrEF
What is a normal ejection fraction?
> 50% (usually 60-70%)
Abnormal is <40%
How do you work out ejection fraction?
Measured on an echocardiogram
Amount of blood pumped out of the ventricle/total amount of blood in the ventricle
SV/EDV
How do you classify heart failure according to ventricles involved?
LV: most commonly involved, with subsequent involvement from right ventricle
Biventricular/congestive: both ventricles
RV: can occur in isolation secondary to chronic lung diseases (most common cuase it LV heart failure)
How does increased ventricular filling effect CO in a failing heart?
- increased ventricular filing in a failing heart= minimal gains, little increase in CO
- worsens CO
How does neuro-hormone activation affect the heart?
- helpful in heathy heart
- unhelpful in unhealthy heart as it increases cardiac work
What negative feedback does decreased CO evoke?
Low BP
- baroreceptors detect in carotid sinus
- increased sympathetic drive (increasing HR and TRP)
- increasing afterload
- increasing cardiac work
- activation of RAAS pathway
- vasoconstriction and enhanced sympathetic activity (increasing afterload)
- stimulates ADH and increase circulating volume due to Na+ and a water retention via aldosterone (increases pre-load)
- increasing cardiac work
Not good for failing heart but good for healthy heart
Signs and symptoms of heart failure:
- fatigue/lethargy
- breathlessness
- increased interstitial fluid (oedema in pulmonary tissues/maybe peripheral tissues)
How does tissue fluid form?
Due to high arterial pressure: hydrostatic forces greater than oncotic forces= net movement of fluid into interstitium
-venule end hydrostatic pressure falls so fluid is pulled back into vessel a oncotic pressure is now higher
Oncotic pressure remains same as proteins stay in vessel
Why does oedema occur in heart failure?
Increased capillary hydrostatic pressures at venule end leads to less fluid being drawn back into venule end
-due to failing left/right ventricle
Specific symptoms involved in left/right ventricular heart failure:
LVHF: (blood returning back to lungs, so backlog there)
- fatigue/lethargy
- breathlessness (exertional)
- orthopnoea (breathlessness when lying down)
- paroxysmal nocturnal dyspnoea (waking in night gasping for breath)
- basal pulmonary crackles: pulmonary oedema
- cardiomegaly (displaced apex- indicating enlarged LV)
RVHF: (blood returning back from rest of body)
- fatigue/lethargy
- breathlessness
- peripheral oedema (pitting)
- raised jugular venous pressure
- tender/smooth enlarged liver(liver congestion)
What happens to Frank-Starling’s law in heart failure?
- increased LV filling in failing heart leads the very little increase in CO: shallow gradient (normally it increases CO)
- eventually leads to CO worsening: curve dips
- increased EDV resulting in falling CO and pulmonary congestion
What is pressure in the right internal jugular vein used as a reflection of?
Pressure in the right side of the heart
