Haemodynamic disorders

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Functions of the cardiovascular system:

maintain normal systemic arterial blood pressure

ensure adequate supply to metabolising tissues (brain, heart etc)

maintain normal venous and capillary pressures (usually first function to be sacrificed in chronic heart failure)

Stroke volume influenced by:

contractility (systolic function)

preload (venous return: Frank-Starling)

afterload (systemic vascular resistance)

ventricular compliance (diastolic function

heart rate

heart rhythm

valvular function

Neuro-endocrine response to decreased cardiac output:

Tachycardia and increased contractility

Arteriolar constriction (regional)

Sodium and water retention

close down circulation to hands and feet

main areas that are important = brain, heart +kidneys

increased preload

increased cardiac output

myocardial hypertrophy (eccentric/concentric)

*angiotensin II produced at the tissue level plays an important role in the pathophysiology of heart failure

*lengthening and widening of cardiac myocytes as a result of cardiac overload

Volume overload = eccentric hypertrophy

valvular insufficiencies

myocardial failure

congenital left to right shunts

chronic severe anaemia)

Pressure overload = concentric hypertrophy

aortic/pulmonary stenosis

dynamic outflow obstruction

hypertension (systemic and pulmonary)

Impedance to cardiac inflow:

pericardial disease

congenital mitral and tricuspid valve stenosis

intracardiac mass lesions

Sustained expression of Angiotensin II and aldosterone:

myocardial hypertrophy

myocardial, vascular and renal fibrosis

sympathetic stimulation

sodium retention

endothelial cell dysfunction

inflammatory response

Heart Failure:

- a clinical syndrome caused by heart disease that results in systolic and/or diastolic cardiac dysfunction severe enough to overwhelm the compensatory mechanisms of the CV system

Signs:

congestion/oedema

decreased peripheral perfusion

venous congestion and oedema (backward - congestive - failure)

reduced cardiac output (forward failure)

- Both may be acute or chronic (left or right sided)

- failure of one side of the circulation may progress to failure of both

- chronic congestive failure is most common in animals

- acute decompensation may occur (due to arrhythmia or chordal rupture)

Signs of left ventricle failure:

exertional weakness, pallor, syncope

weight loss/stunting

azotaemia (pre renal), oliguria

pulmonary oedema, cough, pulmonary crackles

pleural effusion

Signs of right ventricular failure:

exertional weakness, pallor, syncope

systemic venous congestion

hepatic (and/or splenic) congestion

diarrhoea, weight loss, malabsorption

effusions (pleural, ascitic, pericardial)

subcutaneous oedema (rare in small animals)

Causes of oedema:

raised capillary pressure

reduced plasma oncotic pressure

altered capillary permeability

lymphatic insufficiency

*Starling's forces influence fluid transit across capillary walls

Classification of myocardial diseases:

Primary/idiopathic cardiomyopathy:

- cause unknown (many genetic)

- diagnosis of exclusion

Secondary/specific myocardial disease:

- known external cause

metabolic

endocrine

nutritional

infiltrative

inflammatory

fibrosis: muscular dystrophy

Toxic (alcohol)

Others e.g. CNS disease, electric shock

Cardiogenic shock = decreased cardiac output and evidence of tissue hypoxia in the presence of adequate intravascular volume

Cardiogenic shock may occur secondary to:

systolic failure

diastolic failure

valvular disease

arrhythmias

*heart worm can physically obstruct flow into heart and out of heart

*pericardial effusion prevents cardiac filling, resulting in decreased cardiac output