Pathophysiology Flashcards
Cardiac dz affects what % of dogs in vet hospital population?
11%
What is the definition of heart failure
complex syndrome initiated by an inability of the heart to maintain a normal cardiac output at normal filling pressures
How does heart failure occur? (5)
- pump failure
- volume overload
- pressure overload
- arrhythmias
- diastolic heart failure
What do all heart diseases share?
the capacity to cause real or percieved underfilling of the arterial circulation -> initiates a cascade of events resulting in heart failure
What is pump failure?
when failure of systolic function of the myocardium results in inadequate stroke volume and fall in cardiac output
What are the primary diseases resulting in systolic/pump failure?
dilated cardiomyopathy (flappy heart)
coronary vascular disease (narrowing/blockage of coronary arteries)
What is volume overload?
when necessity for a cardiac chamber to chronically increase output can result in overwork and eventually failure of the heart
What are primary diseases resulting in volume overload?
valvular insufficiencies (mitral, aortic)(don’t close properly = backflow)
shunting diseases (VSD, PDA)
chronic anaemia
What is the problem with mitral insufficiency?
LV tries to pump out total stroke volume
which is the forward stroke volume + additional regurgitant stroke volume
Overworking to pump out excessive amounts of blood
What is pressure overload?
when there is a chronic increase of pressure against which a ventricle has to pump blood can eventually result in failure of myocardium
What are primary diseases resulting in pressure overload?
hypertension (systemic or pulmonary)
narrowing of outflow tract (pulmonary stenosis, aortic stenosis)
What are arrhythmias?
Abnormalities of cardiac rhythm that affect both cardiac filling and heart rate and can compromise output
What are the consequences of arrhythmias?
low HR results in drop of CO
very high HR = diastole is too short to allow adequate filling = fall of SV and CO
disorganised electrical activity
What is diastolic failure?
when inability of the heart to relax normally can compromise filling and result in fall of CO
What are primary diseases resulting in diastolic failure?
hypertrophic cardiomyopathy
dilated cardiomyopathy (myocardial fibrosis)
pericardial effusion (fluid around heart)
When there is an increase in blood volume what comes into play?
RAAS: angiotensin II, aldosterone
ADH
Renal autoregulation of flow (decreased renal flow = increased sodium retention)
When there is a decrease in blood volume, what comes into play?
Natriuretic peptides
Renal autoregulation of flow (increased renal flow = decreased sodium retention)
What are the short term effects of heart failure?
drop in CO = drop in arterial BP = arterial underfilling
sensed by baroreceptors
decrease parasympathetic activity + increase sympathetic activity
trying to restore BP with increased HR, contractility and vasc. resistance
What are the neural regulation of decreased CO?
Norepinephrine causes
increased HR
increased cardiac contraction
improved cardiac relaxation
stimulation of renin release and RAAS
What are the endocrine system in HF (medium term)?
RAAS
ADH
Natriuretic peptides of vascular tone (Nitric oxide, prostaglandins, endothelin)
What stimulates the release of renin?
renal sympathetic nerve stimulation
reduced pressure in afferent arteriole
reduced sodium in distal tubules
What are the advantages of RAAS in HF?
increased circulating fluid volume, increased preload, increased CO
increased systemic vascular resistance improved BP
What are the disadvantages of RAAS in HF?
long term stimulation = excessive fluid retention
excessive resistance to ventricular emptying
direct and indirect deleterious effects on myocardium
What do we know about survival vs RAAS?
canine heart failure patients with pharmacological antagonism of RAAS have better long term survival
What is the effect of enalapril on mortality in severe CHF?
lower probability of death
What is the difference in HR in animals developing HF VS not?
with CHF all have increased HR over time
How does ADH have an effect in HF?
only in severe HF
increases vascular resistance to protect BP, ultimately deleterious
increases fluid retention (but without sodium)
What is a consequence of ADH in HF
hyponatraemia
retention of free water w/o sodium
How do natriuretic peptides have an effect in HF?
counter regulatory hormones that are released in response to increased ventricular and atrial pressures
increased levels associated with HF = biomarker
What is hypertrophy in HF?
long term alteration in pressure or volume loading of the ventricle that results in a structural adaptation of the ventricle
What mediates hypertrophy in HF?
adrenergic stimuli
angiotensin II
aldosterone
intracellular calcium
What are the 2 different hypertrophy patterns and their causes?
Concentric: thick walls, small chamber (pressure overload)
Eccentric: large chamber (volume overload)
What are the consequences of hypertrophy in HF?
initially adaptive and allows patient to compensate
then increases myocardial oxygen demand and can result in fibrosis + hypoxia of myocardium
excessive hypertrophy is detrimental
What characterizes HF in the short term?
alteration in autonomic tone: increased sympathetic + decreased parasympathetic
What characterizes HF in the medium term?
stimulation of endocrine systems
What characterizes HF in the long term?
hypertrophy
What are the clinical signs of HF?
tachycardia (increased sympathetic)
poor peripheral perfusion (vasoconstriction)
fluid retention (RAAS, ADH)
What is the clinical signs of left sided heart failure?
evelation in filling pressures in L side of heart
retained fluid within pulmonary circulation
What is the clinical signs of right sided heart failure?
elevation in filling pressures in the R side of heart
retained fluid found within systemic veins
What is the normal function of vasculature?
distribute cellular metabolic substrates around body
remove cellular metabolic waste products
maintain fluid homeostasis
primary homeostasis
What are the signs of vascular disease?
Underperfusion (vascular obstruction)
increased vascular permeability (oedema or haemorrhage)
abnormal flow
abnormal pressures
What are the types of disturbance in starling equilibrium?
increased hydrostatic pressures (CHF or venous occlusion)
increased vascular permeability (vasculitis)
decreased oncotic pressure (hypoproteinaemia)
decreased lymphatic drainage (lymphoedema)
What are the types of vascular diseases?
Obstructive (thrombosis and embolism)
Degenerative
Inflammatory (vasculitis)
Malformations (congenital or acquired)
What needs to be present for thromboembolism to form?
one or more:
disturbance of flow
disturbance of endothelial integrity
disturbance of haemostasis
What are the causes of thromboembolism?
Cardiac dz
cushing’s dz
parasitic dz
protein losing nephropathies
neoplasia
autoimmune haemolytic anaemia
