Ischaemia, Oedema and Heart Failure

Define haemorrhage

Escape of blood from the vascular system.

(can be overt i.e. trauma or internal ; acute/chronic)

Define diapedesis

The ability of a WBC to cross into a capillary through the wall.

Define extravasation

The movement of white blood cells from the capillaries to the tissues surrounding them

Define haematoma

A solid swelling of clotted blood within the tissues.

Define rhexis

Rupture of a vessel.

What is a cardiac tamponade?

Compression of the heart via an accumulation of fluid in the pericardium leading to diastolic filling defects.

What are petechial hemorrhages?

Small haemorrhages (1-2mm clots).

What are purpural haemorrhages?

Small-ish haemorrhages (>3mm clots).

What are ecchymoses?

Large haemorrhages (>1-2 cm clots).

How is the anatomical location of a haemorrhage named?

Haemo-[anatomical location]

List at least 3 causes of haemorrhage

• physiological

• trauma

• parasites

• bacteria

• viruses

• toxic agents

• clotting deficiencies

• neoplastic disease

• agonal (as the animal is dying)

Why do agonal haemorrhages occur?

As the heart stops, blood will pool in capillaries which may lead to haemorrhage

What are the outcomes of haemorrhage?

• Haemorrhagic (hypovolaemic) shock

• Complete recovery

• Loss of function

• Iron-deficient anaemia

How is haemoglobin degraded?

By macrophages:

How can you differentiate between haemorrhage and hyperaemia? ***

• Haemorrhage is usually localised to a particular region

• Histology would show RBCs intravascular in hyperaemic tissue; would be extravascular in haemorrhage

What is iron-deficiency anaemia usually indicative of? ***

Blood-feeding parasites.

What is oedema?

Fluid accumulates in intercellular tissue space and / or in body cavities from blood.

What is oedema a result of?

• Imbalance of forces which are responsible for transudation (with normal capillary permeability).

• increased vascular permeability associated with inflammation

• fibrinous / purulent exudates

How does non-inflammatory oedematus transudate look?

Colourless fluid (low protein content).

How can impaired venous return cause oedema?

Increases hydrostatic pressure in venous vasculature leading to NET filtration into the ECF from veins.

How can chronic protein loss lead to oedema?

Reduces plasma oncotic pressure and hence NET filtration into ECF from vasculature.

How can lymphatic obstruction lead to oedema?

Fluid in ECF is not absorbed normally and hence builds up instead of being removed.

What is a common cause of increased hydrostatic pressure in vasculature?

Heart failure.

What is a common cause of decreased plasma proteins and hence decreased plasma oncotic pressure in vasculature?

Malnutrition.

How can sodium retention cause oedema?

Due to diseased renal system leading to increased tubular Na+ reabsorption

Which diseases are characterised by oedema?

• cardiac disease - heart failure

• chronic liver disease - ↓ protein synthesis

• renal disease – protein loss

• chronic parasitism – protein loss

• protein-losing enteropathy

Define hydrothorax

Fluid in the pleural cavity.

Define hydropericardium

A build up of fluid in the cardiac cavity, the area around the heart (pericardium).

Define ascites

The accumulation of fluid in the peritoneal cavity, causing abdominal swelling.

Define anasarca

Extreme generalised oedema.

What are the main types of oedema?

Localised and generalised (at species predilection sites).

Where is it common to see oedema in a dog?

Peritoneal cavity.

Where is it common to see oedema in a cat?

Thoracic cavity

Where is it common to see oedema in a sheep?

Submandibular space or perioneum.

Where is it common to see oedema in a horse?

Limbs.

Where is it common to see oedema in a cow?

Brisket oedema (subcutaneous oedema)

Describe Bottle Jaw

• Subcutaneous, sub-mandibular oedema

• Seen in sheep, goats, cattle

• Usually caused by hypoproteinaemia

List at least 2 specialist forms of oedema

• pulmonary oedema

• oedema of the brain

• glaucoma

Give at least 2 causes of pulmonary oedema

• Left sided congestive heart failure —> passive hyperaemia.

• Irritant gases

• Inflammation

• Toxic e.g. Fog Fever

• Agonal change

What is heart failure?

• Develops slowly from gradual loss of pumping efficiency, associated with pressure or volume overload or myocardial damage

• Heart cannot pump blood at rate needed by the tissue (or can do so only from an elevated filling pressure).

How does the cardiovascular system maintain arterial pressure and perfusion?

• Increased preload of dilation —> sustaining of cardiac performance by enhancement of contractility

• Myocardial hypertrophy (± chamber dilation) —> increase of mass of contractile tissue

• Activation of neurohormonal system —> release of noradrenaline, activation of renin-angiotensin-aldosterone system, release of atrial natriuretic peptide

Why does myocardial hypertrophy occur?

In response to abnormal intra-atial/ventricular pressure increases.

What is congestive heart failure?

Build-up of venous blood in systemic and pulmonary circulation.

What are the causes of congestive heart failure? Which one causes forward heart failure? What about backwards?

• Due to reduced cardiac output and underperfusion (forward)

• Due to increased venous pressure (backward)

Give at least 2 consequences of congestive heart failure

a) oedema, tissue hypoxia

b) activation of renin-angiotensin-aldosterone system

c) chronic congestion of lungs and liver

d) fluid accumulation in peritoneal and/or thoracic cavity

What is the difference between left and right sided heart failure?

Depends on the location of the lesion (e.g. if it is the left AV valve affected only, it is left-sided heart failure).

What are the effects of left-sided heart failure on the lungs and kidney?

• consequences on lungs – pulmonary congestion and oedema

• consequences on kidneys – hypoperfusion → renin etc

What are the effects of right-sided heart failure?

(cause: pressure overload! of right ventricle)

• usually sequel of left-sided heart failure

• increased resistance within pulmonary circulation

• consequences on liver, body cavities, subcutaneous tissue

How is the heart itself effected in heart failure?

Cardiac hypertrophy:

• Concentric = due to pressure overload meaning the heart wall must thicken

• Eccentric = due to volume overload (e.g. due to leaky valves) and the actual size of the chambers increase

What are the roles of angiotensin 2 in the body?

• Constricts arteriolar walls

• Increases strength of heart beat

• Increases sodium retention in kidneys

• Increases aldosterone release to increase Na reabsorption

What is the role of ADH with respect to lowered blood pressure?

Causes increased reabsorption of water from the kidneys.

What is the effect of noradrenaline on the heart?

Increased HR, myocardial contractility

What is the function of atrial natriuretic peptide?

Counteraction of renin-angiontension-aldosterone system:

relaxation of vascular smooth muscle (decreased BP) inhibition of Na+ reabsorption in kidney, increased glomerular filtration, increased glomerular filtration, inhibition of aldosterone secretion

What is “nutmeg liver” caused by?

Right sided congestive heart failure —> passive congestion from central vein

What is the most likely outcome of chronic low-level haemorrhage e.g. blood-feeding parasite?

Iron-deficiency anaemia

Which myocardial change is induced by volume overload?

Eccentric hypertrophy

During heart failure, which hormone is secreted by the kidney which activates a homeostatic mechanism and exacerbates the heart failure?

Renin