Pathology of the Cardiovascular System 3

Question 1

DISEASES OF THE ENDOCARDIUM

Answer 1

(Wall of the heart)

1. INFLAMMATION- MURAL ENDOCARDITIS- necrotising endocarditis
2. DEGENERATION- calcification, fibrosis.

Question 2

NECROTISING ENDOCARDITIS

Answer 2

Associated with uraemia of acute or chronic renal failure.
Degeneration and necrosis of the LEFT ATRIAL endocardium (not particularly understood why)
Yellow-white plaques on atrial wall, may see associated ulceration and calcification
-Signs seen due to presumed toxic damage to small blood vessels and necrosis of the overlying cells.
-May be release of ammonia and pro-inflammatory cytokines.

Question 3

INHERITED ARRHYTHMIAS AND CONDUCTION DISORDERS

Answer 3

In humans and animals, inherited arrhythmias and cardiac conduction system disease occur in very young patients.
Can be congenital heart disease, or occur in a structurally normal heart.
Mutations responsible for the majority of inherited arrhythmias occur in genes encoding for CYTOSKELETAL PROTEINS, SARCOMERIC PROTEINS, ION CHANNELS.

Question 4

ARRHYTHMIA

Answer 4

Variation in rhythm

Question 5

CONDUCTION DISORDER

Answer 5

Abnormality in the conduction system of the heart.

Question 6

PRIMARY ARRHYTHMIAS/CONDUCTION DISORDERS

Answer 6

NO MORPHOLOGICAL ABNORMALITIES.

May be normal in some species/breeds- often disappear with increased activity (horses)

Question 7

SECONDARY ARRHYTHMIAS/CONDUCTION DISORDERS

Answer 7

Seen secondary to underlying disease.

eg. Atrial fibrillation in cardiomyopathy.
eg. Ventricular tachycardia in ventricular hypertrophy.
eg. Heart block following myocardial damage.

Question 8

INHERITED

Answer 8

Transmitted through genetic line, but may not be seen at birth. Can manifest when the animal is older.
Hereditary. Transmitted from parent to offspring.

Question 9

CONGENITAL

Answer 9

Present at birth, may not be inherited.

Congenital anomaly or defect.

Question 10

INHERITED ARRHYTHMIAS IN DOGS

Answer 10

-Arrhythmogenic Right Ventricular Cardiomyopathy- Boxers. Generally only seen in adult/older dogs.
Signs include ventricular premature contractions (VPCs) or ventricular tachycardia (VT)

• Dilated Cardiomyopathy in the Doberman. Increased VPCs or VT are evidence of occult disease.
• Inherited Ventricular Arrhythmias in German Shepherd Dogs- Sudden death syndrome at approximately 4-20 months. Check heart/lung/brain- true sudden death may not have obvious developed pathology.

Question 11

SICK SINUS SYNDROME

Answer 11

aka. BRADYCARDIA-TACHYCARDIA SYNDROME.
A group of conduction disorders involving the sino-atrial node.
May or may not involve the atrio-ventricular node and bundle of His/branches.

Potentially life threatening- Periods of ventricular standstill cause syncope.
-Paroxysms of supraventricular tahcycardia cause syncope.

Usually idiopathic (spontaneous), but may have ischaemia of SA node. 
Possibly inherited in some breeds- miniature Schnauzer (especially bitches)

Question 12

HEART BLOCKS

Answer 12

FIRST DEGREE- DELAY of impulse through AV node.
SECOND DEGREE- Intermittent FAILURE of conduction through AV node, with dropped beats.
Normal in the horse.
First degree can progress to second degree.
THIRD DEGREE- Complete failure of conduction (complete block)

Heart blocks are associated with areas of myocardial scarring in the horse and dog.

Question 13

FAMILIAL

Answer 13

Present in some families and not others, or occurs more in family members than would be expected by chance.
Usually but not always inherited.

Question 14

ACQUIRED

Answer 14

Originating after birth- not caused by hereditary or developmental factors, but instead by a reaction to environmental influences outside of the organism.

Question 15

HEART AND GREAT VESSEL DEVELOPMENT

Answer 15

3 basic development stages.

1. Looping
2. Septation
3. Separation of common truncus arteriosus in to aorta and pulmonary artery

Question 16

STRUCTURES OF FOETAL CIRCULATION

Answer 16

FORAMEN OVALE- opening between left and right atria.
Allows blood to flow from RIGHT to LEFT- right-left shunt bypasses lungs.

DUCTUS ARTERIOSUS- connects pulmonary artery and aorta.

DUCTUS VENOSUS- Portal and umbilical veins are connected to the vena cava (liver)

Pressure changes at birth should force the foramen ovale shut immediately, allowing blood to reach the lungs for oxygenation.

Question 17

CONGENITAL DEFECTS- 3 MAIN CATEGORIES

Answer 17

1. FAILURE OF CLOSURE OF FOETAL STRUCTURES
2. SEPTAL DEFECTS
3. GREAT VESSEL DEFECTS (defects of outflow tracts- aortic or pulmonary valves- dysplasia, stenosis or malposition/fusion)

Question 18

PATENT FORAMEN OVALE

Answer 18

Failure of closure of opening between atria.

Right to left shunt allows deoxygenated (right atrium) and oxygenated (left atrium) blood to mix.

Question 19

PATENT DUCTUS ARTERIOSUS

Answer 19

(PDA)
Pulmonary artery (deoxygenated) and aorta (oxygenated) remain connected.
Oxygenated blood is shunted from left to right VENTRICLE.
This causes pulmonary hypertension -> thickened right ventricle.

Question 20

PORTOCAVAL SHUNTS

Answer 20

CONGENITAL anomalies.
Normal flow from portal vein is diverted to systemic circulation, bypassing the liver.
Normal hepatic detoxification of portal flow is incomplete.
Build up of toxins, especially ammonia, causes HEPATIC ENCEPHALOPATHY.

Can be intra- or extra-hepatic.
-Intrahepatic- Persistent ductus venosus (portal/umbilical vein and vena cava)
-Extrahepatic- Portocaval shunt, Portazygos shunt.
Represents prominent dilation of various portosystemic shunts that are usually quite small vessels.

Question 21

SEPTAL (ENDOCARDIAL CUSHION) DEFECTS

Answer 21

Atrial Septal Defect

Ventricular Septal Defect

Question 22

ATRIAL SEPTAL DEFECT

Answer 22

Opening between right and left atria allows mixing of oxygenated and deoxygenated blood.
Opening is not always where the foramen ovale would be.
Signs depend on size of defect and how much blood can flow through.
Risk of pulmonary vascular damage- increased pulmonary arterial pressure (due to mixed blood in pulmonary artery- oxygenated blood from left atrium mixes with deoxygenated blood in right atrium -> RV -> pulmonary artery)
Risk of endocarditis (will also cause pulmonary vascular damage)

A large defect will cause bilateral atrial distension, as the atria are working harder to counteract the blood mixing.

Question 23

VENTRICULAR SEPTAL DEFECT

Answer 23

Seen in cattle, can be an incidental finding at PM- no clinical signs.
Blood flows from left to right (left ventricle is more muscular).

in CHRONIC/SEVERE VSD, SHUNT REVERSAL can occur.
Blood flow from left to right moves more blood to the lungs (pulmonary artery), causing pulmonary hypertension.
This allows REVERSAL of the shunt -RIGHT TO LEFT.
This only occurs in very chronic/sever/large ventricular septal defects.

Question 24

GREAT VESSEL DEFECTS

Answer 24

Congenital.
VALVULAR DEFECTS- insufficiency (regurgitation)- MITRAL or TRICUSPID DYSPLASIA

STENOSIS- outflow obstruction- AORTIC (subaortic) or PULMONIC STENOSIS (semilunar valves)

Some anomalies can produce both insufficiency and stenosis.

Question 25

ATRIOVENTRICULAR VALVE DYSPLASIA

Answer 25

Improper formation of valve. Remnants are small and dysfunctional- distorted leaflets, short chordae (restrict valve movement) Can occur in mitral (left) or tricuspid (right) valve. Sever incompetence will lead to atrial distension.

Question 26

AORTIC STENOSIS

Answer 26

Obstruction of outflow from left ventricle to aorta. Various forms: -Subaortic fibrous ridge- MOST COMMON -Subaortic stenosis- Second most common inherited heart disease in dogs. Mostly seen in large, purebreed dogs. Blood struggles to leave the heart and enter the systemic circulation. There is dramatic enlargement (hypertrophy) of the heart to try and push the blood out. Turbulent flow causes dilation of the aorta and jet lesions (fibrosis, some mineralisation)

Question 27

PULMONIC STENOSIS

Answer 27

Obstruction of outflow from right ventricle to pulmonary artery. Can be valvular, subvalvular (fibrous ridge below valve) or infundibular (not involving valve) Narrowing of valve/below valve - > Dilation of pulmonary artery above obstruction - > Thickened right ventricle

Question 28

LEFT TO RIGHT SHUNTS

Answer 28

``` Congenital abnormalities. Can be caused by: Patent ductus arteriosus Atrial septal defects Ventricular septal defects Atrioventricular canal (endocardial cushion defect) ``` Extra blood flows through the lungs, causing pulmonary hypertension and right ventricular hypertrophy.

Question 29

EISENMENGER'S SYNDROME

Answer 29

A collection of symptoms, including cyanosis (due to decreased oxygen in blood), pulmonary hypertension, erythrocytosis (due to decreased blood oxygen), caused by LEFT TO RIGHT SHUNT.

Question 30

RIGHT TO LEFT SHUNT

Answer 30

Congenital abnormalities. TETRALOGY OF FALLOT. Severity depends on extent of pulmonary stenosis. Deoxygenated blood enters systemic circulation (RV -> LV -> aorta) Causes cyanosis -'blue babies' (human). Too LITTLE blood is flowing through the lungs.

Question 31

TETRALOGY OF FALLOT

Answer 31

1. RIGHT VENTRICULAR OUTFLOW OBSTRUCTION due to pulmonary stenosis. 2. VENTRICULAR SEPTAL DEFECT allows blood to flow from left to right ventricle. 3. DEXTRAPOSED AORTA- shifted from left to right (overlies the ventricular septal defect instead of the left ventricle, so can receive blood from left and right ventricles) 4. RIGHT VENTRICULAR HYPERTROPHY- to compensate for right ventricular outflow obstruction.

Question 32

SPECIES SUSCEPTIBILITY TO CONGENITAL DEFECTS

Answer 32

DOGS- patent ductus arteriosus, pulmonic stenosis, subaortic stenosis. CATS- mitral dysplasia, atrioventricular canal CATTLE- atrial septal defect, ventricular septal defect, transposition of great vessels. HORSES- congenital defects are uncommon.

Question 33

CONGENITAL VASCULAR ANOMALIES

Answer 33

Abnormal arterial or venous connections. - Persistent right aortic arch - Portosystemic shunts (including persistent ductus venosus in the liver)

Question 34

PERSISTENT RIGHT AORTIC ARCH

Answer 34

A continuation of the ligamentum arteriousum (which normally breaks down) constricts the oesophagus. The ligamentum arteriosum connects the pulmonary artery and aorta. The oesophagus cranial to the heart is dilated. MEGAOESOPHAGUS- Regurgitation of food, especially seen in boxers and mastiffs. Control by feeding high up and giving watery food.