18 Heart Failure Flashcards
define heart failure
the inability of the heart to supply adequate blood flow and therefore oxygen delivery to peripheral tissues and organs
What is the most common cause of heart failure?
post MI
What happens to myocardium which does not receive blood flow?
hypoxia hypercapnia glycolytic and acidotic nutrient depletion risk of necrosis
How does a myocardial infarct occur?
fibro-fatty plaques may rupture, releasing substances activating platelets
thrombus forms
How is ischaemia visible on an ECG?
elevation of ST segment
How is an MI treated acutely?
PCI
What happens in a PCI?
catheter inserted into peripheral artery goes to aorta - coronary vessel punches through thrombus balloon inflated stent fitted
How quickly after the MI do you want to do a PCI?
2 hours
What is a PCI?
Percutaneous Coronary Intervention
If you do nothing to treat an MI, how much of that area will die?
70%
If you perform a PCI, how much of the area will die?
30%
Why does a PCI not reduce ischaemia to 0%?
the act of re-introducing blood flow itself is detrimental to the heart (release of ROS)
What might cause HF by pressure overload?
what is the trigger here?
HTN
aortic stenosis
pathological hypertrophy against a higher after-load
What might cause HF by contractile dysfunction?
ischaemic heart disease
congenital cardiomyopathies
what happens in ischaemic heart disease?
reduced blood flow to cardiomyocytes
don’t function as well
What happens to SV in HF?
the peak and magnitude of SV are lower
What is the effect of decreased SV on baroreceptor reflex?
decreases it
How can a decreased baroreceptor reflex increase HR?
decreased vagal and increased symp tone to SA node
How can a decreased baroreceptor reflex increase heart contractility?
increased symp activity to ventricular muscle
How does an increase in contractility increase CO?
increases SV
What happens in pathological hypertrophy?
cardiomyocytes enlarge
lose their shape
distance between capillaries and cardiomyocytes increases
how does the baroreceptor reflex interact with the adrenal gland?
what is the clinical significance of this?
a decreased reflex increases catecholamine release
the increase in serum adrenaline is measurable
What are the consequences of persistent adrenargic stimulation of the heart?
hyperphosphorylation of Ca2+ handling proteins
pathologcial hypertrophy
beta adrenoreceptor internalisation
Why is hyperphosphorylation of Ca2+ a problem?
leads to…
dysfunctional Ca2+ homeostasis
contractile dysfunction
arrhythmia
What sort of arrhythmia might we expect in HF?
delayed afterdepolarisation
DAD
What happens in DAD?
spontaneous release of SR calcium during diastole
How does calcium release cause DAD?
calcium removed by 3Na+ / Ca2+ transporter, so depolarises membrane
How can DAD be made worse?
persistent stimulation - upregulation of PKA
hyperphospharylation of ryanodine receptor, making the SR more leaky
What might be used to treat DAD?
How might they work?
beta-blockers
calcium channel blockers reduce SR Ca2+ load, making it less leaky
How does a low ABP increase renin release?
increased sympathetic activity to kidney (baroreceptor)
decreased wall tension in renal afferent arterioles
decreased Na+ delivery to macula densa
how does a reduction in cardiomyocyte function alter ABP?
decreases stroke volume
reduces ABP
How does angiotensin II increase water intake?
increases thirst drive via hypothalamus
How does angiotensin II increase water reabsorption?
ADH
Aldosterone
What effect does angiotensin II have on blood volume?
it increases it
Why is it important that we are able to increase EDV?
it helps us to maintain SV
What are the consequences of blood volume loading?
persistent loading causes them to go beyond the plateau of the Starling curve and SV can no longer be sustained
how does oedema occur in HF?
mismatch in LV and RV CO due to HF
Why do lungs not accumulate fluid in normal pulmonary circulation?
because we are constantly breathing humidified air
How does left HF cause pulmonary oedema?
increased hydrostatic pressure in pulmonary circulation
What are the effects of pulmonary oedema?
increased diffusion distance
arterial hypoxia
dyspnea
peripheral chemoreceptor activation
What can hypoxia in the lung lead to?
hypoxic pulmonary vasoconstriction
pulmonary HTN
How can you overcome pulmonary hypoxia acutely?
delivering 100% O2
How might you treat pulmonary oedema chonically?
loop diuretics
ACEi
AT1R antagonists
What is the effect of cardiac hypertrophy?
increases suceptibility to ischaemia
increases incidence of arrhythmias
increases incidence of sudden death
