Myocardium Flashcards
Myocardium characteristics
-intercalated disks
-striations= sarcomeres
-cardiomyocytes with lots of mitochondria and myoglobin
Repair abilities of myocardium
-no capacity to replace lost myofibers and therefore normal repair is impossible
What damages cardiomyocytes?
-hypoxia
-free radicals
-viruses
-bacteria
-cardiotoxins
-parasites
Myocardial degeneration microscopically
-loss of striations
-hypereosinophilia
-swelling
-dissolution of sarcoplasm and myofibrils
-nuclear condensation
Calcification of myocardium
-many degenerative diseases lead to sequestered calcium in the sarcoplasm and organelles of myocardial cells
-appear microscopically as dark blue granules
Clean up and repair of myocardium
-macrophages and neutrophils clean up
-no regeneration occurs, instead necrotic tissue is replaced by connective tissue= CARDIAC FIBROSIS
Myocardial Calcification
Left: myocardial fibrosis
Right: Myocardial degeneration/necrosis
Ischemic Myocardial Necrosis
HEART ATTACK
-very common in humans due to accumulation of plaques of lipids
-rare in animals; caused by vasculitis
Toxic Myocardial necrosis causes
- Toxic plants (Oleander, Karwinskia humboldtiana)
- Blister beetles (epicauta spp)
- Doxorubicin
- Ionophores
5.Sodium fluoracetate
White Muscle Disease
Nutritional Myopathy
-rapidly growing farm animals
-sudden death
-can affect skeletal, cardiac muscle or both
-exacerbated by exercise or stress
-treatable at early stages
Pathogenesis of White Muscle Disease
1.Cardiac and skeletal muscle cells use oxygen, producing free radicles
2. Free radicles removed by Vitamin E and Se Enzyme (glutathione peroxidase)
3. Deficiency in Vitamin E and Selenium
4.Results in free radicles accumulating= peroxidation of cell membranes and therefore cell degeneration
5.Degenerated cells unable to pump out Ca resulting in mineralization
White muscle disease
-Myocardial necrosis
Where is white muscle disease most commonly seen?
Lambs: Right ventricle
Calves: Left ventricle
Vitamin E/Selenium deficiency in pigs
Not white muscle disease! Get Mulberry Heart disease instead!
Appears as hemorrhage and myocardial necrosis
Mulberry Heart Disease
-Pig
-hemorrhage and necrosis
Neurogenic myocardial necrosis
-Brain-Heart syndrome
-Adrenal pheochromocytoma (tumour leading to endogenous catecholamines) or injectable (exogenous)
>resulting in sudden release of catecholamines leading to necrosis and myocardial degeneration
If you see this Adrenal gland tumour and necrosis in the heart, what could it be?
Neurogenic myocardial necrosis
-Brain-Heart syndrome
How do you classify myocarditis?
Based on exudate:
-suppurative
-lymphocytic
-eosinophilic
-hemorrhagic
-granulomatous
Canine parvovirus
-Causes myocarditis in young puppies (hemorrhagic enteritis in dogs)
Myocarditis in young puppy
-likely etiology: Canine parvovirus
Histophilus somni manifestations
-Bovine myocarditis!
>acute death or chronic progressive heart failure
-infectious thrombotic meningoencephalitis
-pneumonia
-arthritis
-reproductive issues
Myocarditis from Histophilus somni
-locally extensive areas of infarction and suppurative myocarditis which can become abscess
-common infection on papillary muscles and ventricular free wall!!
Staphylococcus aureus myocarditis in lambs and kids
-multifocal suppurative myocarditis affecting left and right ventricles
Lamb heart
Multifocal suppurative myocarditis
-left and right ventricles
Etiology: staphylococcus aureus
Cow myocardium
Myocardial abscess in cow
Etiology: Trueperella pyogenes
Trueperella pyogenes
-in cattle, can cause infection and inflammation in many organs (lungs, liver, joints) and heart (abscesses or endocarditis)
Parasitic myocarditis- Taenia
Taenia leads to cysticercus on the heart
-fluid filled cysts containing white larva
-usually incidental finding
Cysticercosis- parasitic myocarditis
Parasitic myocarditis from protozoa
-Lymphoplasmacytic myocarditis: pseudocysts with many amastigotes
Etiology: Chagas disease (vector: Kissing bug)
Primary cardiomyopathy
-myocardial abnormality resulting in changes to the cardiac wall thickness causing electrical disturbances and results in sudden unexpected death
-common in dogs and cats, sporadically in cattle, pigs or rats
-often idiopathic
-sometimes genetic predisposition
-progressive disease
What does “Cardiomyopathy is a diagnosis of exclusion” mean?
Means that cardiovascular anomalies such as congenital shunts and hypertension must be ruled out first
Types of cardiomyopathies
- Hypertrophic Cardiomyopathy (HCM)
- Dilated or congestive Cardiomyopathy (DCM)
3.Restrictive cardiomyopathy
Hypertrophic Cardiomyopathy
-most common in cats (middle aged male)
>myosin binding protein C3 mutation (Maine coon, Ragdolls)
-resembles concentric hypertrophy but no underlying cause; both ventricles but more left
-decreased ventricular filling and compliance= diastolic dysfunction
**increased heart weight as a percent of body weight
Hypertrophic cardiomyopathy
What is often linked with hypertrophic cardiomyopathy in cats?
1/3 of cats have aortic saddle thromboemboli
-less often atrial thrombi
Cat Heart
-Atrial thromboli
-increased ventricular wall thickness
=Hypertrophic Cardiomyopathy
Left: normal myocardium
Right: Hypertrophic cardiomyopathy
Dilated Cardiomyopathy
-common in dogs
-sometimes in cats, hamsters, turkeys, pigs, cows, foxes
-progressive cardiac dilation and contractile (systolic) dysfunctions
-decreased contractile force & increased end diastolic volume
Causal predispositions for dilated cardiomyopathy
- taurine deficiency in cats and foxes (but not primary anymore, would be secondary)
- Tendencies in large breed dogs (Irish wolfhound, Doberman, St. Bernard, Boxer)
- Hereditary form in Holstein cattle
Dilated Cardiomyopathy
-increased heart weight
-dilated chambers
-cardiomegaly
Dilated cardiomyopathy
-dilated ventricles
-thin walls
-attenuated papillary muscles
Arrhythmogenic right ventricular cardiomyopathy
*Variant of DCM
-boxer dogs
-an autosomal dominant trait (8bp deletion on striatin gene on chromosome 17) causing an ion channel defect
-appears as diffusely pale dilated right ventricle
Boxer dog heart
Arrhythmogenic right ventricular cardiomyopathy
-diffusely pale dilated right ventricle
*degeneration of myocytes leading to infiltration of adipose tissue
Restrictive cardiomyopathy
-common in cats
-diffuse endocardial thickening or sometimes mural thrombosis; excessive moderator bands (septomarginal trabeculae), or congenital endocardial fibroelastosis (Burmese cats)
-leads to impaired ventricular filling and diastolic dysfunction
Endocardial fibroelastosis leading to restrictive cardiomyopathy
Excessive septomarginal/moderator bands leading to restrictive cardiomyopathy
