Pathophysiology Of CV Disease Flashcards
What is the difference between heart disease and heart failure?
A patient can have heart disease without showing outward signs (only seen with diagnostics)
Once they start to show inadequacy of CO or congestion - Heart failure.
What are the two broad types of heart failure?
Forward failure
Backward/congestive failure
What is forward failure?
Inadequacy of delivery into the arterial circulation
Seen as an acute drop in CO
What is backward/congestive failure?
Because of a chronic inadequacy of delivery of blood into the arterial circulation, fluid is retained which leads to congestion within the venous circulation.
How can forward and backward failure be broadly seen in patients?
Forward failure
—inadequate output at normal pressures
— inadequate output at abnormal pressures
Backwards failure
— Adequate output at abnormal pressures
— Inadequate output at abnormal pressures
What are five possible reasons for heart failure to occur?
Pump failure Volume overload Pressure overload Arrhythmias Diastolic heart failure
How are changes in pressure in the arterial circulation perceived?
Baroreceptors
What is usually the first step in the development of heart failure?]
How long does it take?
Baroreceptors sense underfilling of arterial circulation
Variable - Can take months/years or shorter
What is meant by the term ‘pump failure’?
Failure of systolic function of the myocardium.
Results in inadequate stroke volume and fall in CO
What condition can cause heart failure as a result of pump failure?
DCM
Failure of the myocardium leads to dilation of the heart and inadequacy of delivery into the arterial circulation
What is volume overload?
Heart chronically overworked because it is having to pump a greater volume of blood than normal.
What conditions can result in volume overload?
Valvular insufficiencies (mitral, aortic)
Shunting diseases e.g. VSD, PDA
Chronic anaemia (e.g. due to nutritional deficiencies)
What is mitral insufficiency?
Degeneration of the mitral valve which leads to the introduction of an insufficiency within the circulation
How does mitral insufficiency result in volume overload?
Total stroke volume=forward stroke volume+ regurgitation stroke volume
Systole causes blood to go to the aorta (normal) AND back into the atrium
This increases total stroke volume
What is pressure overload?
Diseases which chronically increase the pressure against which the ventricle has to pump.
What conditions can cause pressure overload?
Hypertension - systemic or pulmonary
Narrowing of the outflow tract - pulmonic or aortic stenosis
— can have congenital narrowing
How can arrhythmias result in syncope?
Sudden drop in HR = sudden drop in CO
How can arrhythmias compromise CO?
Low heart rates result in a drop in CO
Very high heart rates = diastole too short to allow adequate filling therefore SV and CO fall.
What is diastolic failure?
Inability of the heart to relax normally
— also something compressing heart and not allowing it to fill properly
Compromises filling and decreases CO
What conditions can cause diastolic failure?
HCM
DCM - myocardial fibrosis
Pericardial effusion
Which species is more likely to get HCM?
Cats
How can HCM lead to diastolic failure?
Hypertrophy leads to a very stiff myocardium which is difficult to fill.
What is the general progression of responses which are initiated by a drop in CO?
Autonomic response
Endocrine response
Hypertrophic response
What mechanisms increase blood volume?
RAAS - angiotensin II, aldosterone
ADH
Renal autoregulation of flow
How does Angiotensin II increase blood volume?
Increases:
— sympathetic activity
— Tubular Sodium reabsorption and K+ excretion
— aldosterone secretion from adrenal cortex
— Arteriolar vasoconstriction to increase BP
— ADH secretion from posterior pituitary
How does Aldosterone increase blood volume?
Increases tubular sodium (and chloride) reabsorption and potassium excretion
Therefore water is retained
How can renal auto regulation of flow increase blood volume?
Decreased renal flow increases sodium retention
What mechanisms decrease blood volume?
Natriuretic peptides
Renal autoregulation of flow
What are natriuretic peptides?
Peptides which induce natriuresis - the excretion of sodium from the kidneys
How can renal autoregulation of flow decrease blood volume?
Increased renal flow decreases sodium retention
What is the theme in cardiac disease?
Disease
Adaptation
Maladaptive response
Heart failure
What effects does sympathetic stimulation have on the heart/circulating volume?
Positive chronotrope - increase HR Positive inotrope Positive luisitrope Vasoconstriction Stimulation of renin release and RAAS
How does the degree of sympathetic stimulation relate to survival?
Patients that survive longest have lowest concentrations of NAd.
Inverse relationship between degree of sympathetic stimulation and survival
Blocking NAd can improve survival - BETA BLOCKERS
What endocrine systems are involved in heart failure?
RAAS
ADH
Natriuretic peptides
Local regulators of vascular tone (NO, Prostaglandins, Endothelin)
What is the function of endothelin?
Vasoconstriction
What cells secrete renin?
Juxtaglomerular cells
What are the advantages of the RAAS?
Increased circulating fluid volume -> increased preload -> increased CO by starling mechanism
Increased systemic vascular resistance improves blood pressure
What are the disadvantages of the RAAS?
Long term stimulation results in excessive fluid retention
— overfilling of the venous circulation leading to signs of congestion
Excessive resistance to ventricular emptying
Direct and indirect deleterious effects on the myocardium
How do the methods employed by Aldosterone and ADH to conserve water vary?
Aldosterone - retains SODIUM then passively retains water
ADH - retains water WITHOUT retention of sodium
— Therefore sodium concentration falls
When is ADH stimulated in heart failure?
Only in severe/late stages
What is the effect of ADH secretion in heart failure?
Hyponatraemia
When are natriuretic peptides released?
How useful are they for patients and diagnostically?
When the myocardium is stretched
Effects usually overwhelmed by volume retaining systems
Increased levels associated with HF - BIOMARKER
What are the two types of hypertrophy?
Concentric
Eccentric
What type of hypertrophy is seen in Pressure overload?
Concentric e.g. Hypertension, Aortic stenosis
What type of hypertrophy is seen in volume overload?
Eccentric e.g. mitral regurgitation, shunting diseases (VSD, PDA)
How can you differentiate between concentric and eccentric hypertrophy?
Echocardiography
What are the consequences of pathological hypertrophy?
Increased myocardial oxygen demand may result in fibrosis and hypoxia of the myocardium
What is heart failure characterised by in the short, medium, and long term?
Short term - alteration in autonomic tone - increased sympathetic tone
Mid - Endocrine systems
Long - hypertrophy
What are the clinical signs of heart failure?
What are their causes?
Tachycardia - increased sympathetics
Poor peripheral perfusion - vasoconstriction
Fluid retention - RAAS and ADH
Signs of LCHF or RCHF
What is LCHF?
Diseases that result in increased filling pressures in the left side of the heart and retained fluid found in the PULMONARY CIRCULATION
- Pulmonary oedema -> breathing problems
What is RCHF?
Diseases result in elevation in filling pressures in the right side of the heart and retained fluid found in SYSTEMIC veins
- pleural effusion, ascites, peripheral oedema
What is the normal function of the vasculature ?
Distribute cellular metabolic substrates around the body (H2O, O2, glucose, triglycerides, a.a.)
Remove cellular metabolic waste products (CO2, lactate)
Maintain fluid homeostasis
— balance between intravascular, extracellular and intracellular
Primary haemostasis
What are the signs of vascular disease?
Underperfusion - vascular obstruction
- complete or partial
- Loss of function, ischaemia, necrosis
Increased vascular permeability
- oedema or haemorrhage
Abnormal flow
Abnormal pressures
Suggest what may cause increased hydrostatic pressures in vessels.
CHF
Venous occlusion
Suggest what may cause increased vascular permeability
Vasculitis
Suggest what may cause decreased oncotic pressures in vessels
Hypoproteinaemia / hypoalbuminaemia
Suggest what may cause decreased lymphatic drainage
Lymohoedema
What are the types of vascular disease?
Obstructive - thrombosis and embolism
Degenerative
Inflammatory - vasculitis
Malformations - congenital and acquired
What is meant by the term ‘thromboembolism’?
Obstruction of a BV by a clot that has become dislodged from another site in the circulation
What needs to happen for a thromboembolism to occur?
One or more of the following:
Disturbance of: Flow Endothelial integrity Haemostasis Fibrinolysis
What can cause thromboembolism?
Cardiac disease Cushing’s (hyperadrenocorticism) Parasitic disease Protein losing nephropathy Neoplasia Auto-immune haemolytic anaemia
