Myocardium Flashcards
What is the myocardium?
constitutes bulk of heart mass; externally lined by pericardium & internally by endocardium
How is myocardium similar to & different from skeletal muscle?
Myocardium has striations (sarcomeres) like skeletal muscle.
Unlike skeletal muscle, myocardial fibres are branched & join each other through intercalated disks.
What are abundant in myocardium & important for energy?
contain abundant mitochondria & myoglobin
What is the cell mb of cardiomyocytes called?
Sarcolemma
What is the cytoplasm of cardiomyocytes called?
sarcoplasm
What does the sarcoplasm contain?
Myofilaments which form bands (A, I, Z bands)
Each sarcomere goes from…
… 1 Z line to another
What is the myocardium’s capacity to regenerate?
unlike skeletal muscle, myocardium has practically no capacity to replace lost myofibers & therefore normal repair is impossible
What are cardiomyocytes particularly susceptible to? what else can cause injury?
Particularly susceptible to hypoxia & free radicals. Injury can also be caused by viruses, bacteria, cardiotoxins, or parasites
Degeneration & necrosis in cardiomyocytes?
microscopically, degeneration & necrosis are similar to that in skeletal muscle. myofibres undergoing degeneration swell, become hypereosinophilic, lose striations (dissolution of sarcoplasm & myofibrils), nuclear condensation, & eventually become fragmented
What is myocardial calcification/mineralization?
Calcium plays important role in normal physiology of heart. in many degenerative diseases this mineral cannot be removed from & becomes sequestered in sarcoplasm & organelles of myocardial cells.
How do excessive calcium deposits appear microscopically?
As dark-blue granules in sarcoplasm
Following necrosis, what happens to affected myocardial fibers?
They undergo cardiomyolysis & shortly after, macrophages & some neutrophils start cleaning up this myofiber debris
B/c cardiac muscle has practically no capacity to repair by regeneration, what happens?
Instead, necrotic tissue is replaces by CT (fibroblasts & collagen) which eventually results in cardiac fibrosis (scar)
Gross appearance of myocardial degeneration & necrosis?
pale discolouration of myocardium, wht scarring
What is ischemic myocardial necrosis?
Heart attack: plaque builds up in a place like the coronary artery, blood clot blocks artery blood flow.
Epidemiology of ischemic myocardial necrosis?
- v common in humans
- v rare in animals
Give 7 examples of causes of toxic myocardial necrosis
- Cardiac glycoside containing plants: Oleander
- other toxic plants: Phalaris, Lantana camara, Karwinskia humboldtiana (coyotillo), Cassia occidentalis, Vicia villosa (hairy vetch), Eupatorium rugosum (wht snakeroot), cottonseed meal (containing gossypol), avacado leaves (Persea americana)
- acute selenium toxicosis: ingestion of selenium-accumulating plants ex: locoweed (Astragalus & Oxytropis), Western Aster (Symphyotrichum ascendens)
- cantharidin due to ingestion of blister beetles (Epicauta spp)
- Doxorubicin (Adriamycin)
- Ionophores (Monensin, lasalocid, salinomycin)
- sodium fluoroacetate (compound 1080)
8 important facts of wht muscle disease
- mjr economic loss worldwide
- often manifests itself as sudden death
- affects farm animals, not Ca or Fe
- occurs mostly in rapidly growing animals
- for unknown reasons, sometimes WMD affects only skeletal muscle, or cardiac muscle, & sometimes both
- affects fetuses & causes abortion
- exacerbated by exercise or stress
- responds well to treatment, but only @ early stages of disease
Pathogenesis of wht muscle disease
- Cardiac & skeletal muscle cells utilize oxygen for normal physiology & as result oxygen radicals (free radicals) are normally & constantly generated in any healthy animal
- free radicals are highly toxic for cells but free-radical scavengers, ex: vit E & Selenium - containing enzyme glutathione peroxidase, neutralize these radicals & prevent cell injury
- deficiencies in Vit E & Se translate into reduced availability of free radical scavengers
- when free radicals overwhelm scavengers, excessive free radicals accumulate & cause peroxidation of cell mbs leading to cell degeneration
- degenerated cells are unable to pump out calcium & calcium accumulates in cells leading to mineralization
Gross lesions of wht muscle disease?
myocardial necrosis & calcification, wht discolouration of ventricular wall & septum, wht discolouration of skeletal musculature
Where in the heart does WMD affect?
for unknown reasons, WMD affects RV in lambs & LV in calves
What do you send when submitting tissues for histopathology for wht muscle disease?
send myocardium from both sides of heart
Appearance of wht muscle disease under microscope?
mineralized cardiomyocytes, and dark (blk) cells with von-kossa stain for calcium
What do Sw get instead of wht muscle disease?
Mulberry heart disease
What is mulberry heart disease in Sw from?
Vit E & Selenium deficiency
Gross signs of mulberry heart disease?
hemorrhage (petechia) & necrosis in myocardium, fibrin deposits attached to epicardium
Histo signs of mulberry heart disease?
hemorrhage & myocardial necrosis
What is neurogenic myocardial necrosis?
aka Brain-heart syndrome: trauma in brain or spinal cord sometimes can induce lesions in heart b/c of overstimulation of parasympathetic NS which will stimulate lrg release of catecholamines.
Signs of neurogenic myocardial necrosis?
Multifocal subendocardial areas of pale discolouration corresponding to myocardial necrosis & fibrosis, will also produce necrosis & vasoconstriction in coronary arteries, these individuals may also have edema, tachycardia, etc.
Myocarditis rarely occurs alone, it’s typically part of …
systemic disease (viral, bact, fungal, parasite)
according to exudate, myocarditis is classified as:
- suppurative (neutrophils)
- lymphocytic
- eosinophilic
- hemorrhagic
- granulomatous
This disease causes hemorrhagic enteritis in dogs, but can also cause myocarditis in young puppies?
Canine Parvo
Presentation of canine parvovirus myocarditis?
pale discolouration of myocardium, fiber disarray of myofibres, & intranuclear inclusion bodies
In the past, Histophilus somni was most commonly associated w/?
Infectious Thrombotic Meningoencephalitis (ITME), pneumonia, arthritis, & repro probs
In recent years, Histophilius somni has emerged as an important cause of ?
Bo myocarditis, particularly in feedlots
how does Histophilus somni myocarditis manifest in animals?
in some as acute death while in others it progresses to chronic form w/ progressive heart failure
How does Histophilus somni myocarditis present?
Locally extensive areas of infarction (secondary to vasculitis & thrombosis), & suppurative myocarditis which may progress to abscess formation. lesions primarily involve papillary muscles & L ventricular free wall
How does Staphylococcus aureus myocarditis in lambs & kids present?
bact colonies & neutrophils present, multifocal suppurative myocarditis affecting outer L & R ventricles,
Truperella (Arcanobacterium) pyrogenes does what?
Can cause infection & inflammation in many organs including lungs, liver, joints, etc. In some cases blood dissemination leads to heart abscesses or endocarditis.
Gross appearance of heart in Cow from Trueperella pyogenes?
large abscesses in myocardium, adjacent myocardium appears fibrotic
Parasitic myocarditis?
Ex: cysticercosis:
typical cysticerci: fluid filled cysts containing wht larvae
3 examples of cysticercosis parasites?
- Taenia saginata - cysticercus bovis
- Taenia ovis - C. ovis
- Taenia solium - C. cellulosae
Which cysticercosis parasite’s final host is humans?
Taenia saginata
5 examples of protozoa causing parasitic myocarditis?
- Sarcocystis spp
- Toxoplasma gondii
- Neospora caninum
- Leishmania spp
- Trypanosoma cruzi
example of nematode causing parasitic myocarditis?
Trichinella spiralis
What is Chagas disease?
American trypanosomiasis. Caused by protozoa Trypanosoma cruzi, transmitted by Kissing bug (Triatoma spp), (they bite you, you smear their poo), causes lymphoplasmacytic myocarditis
histo of lymphoplasmacytic myocarditis in Ca w/ Chagas disease?
pseudocyst containing numerous amastigotes in cardiac myocyte
What is cardiomyopathy?
primary myocardial abnormality that results in changes in cardiac wall thickness (hypertrophy or dilation), causes electrical disturbances, & often results in sudden unexpected death
What is cardiomyopathy a diagnosis of exclusion?
b/c it means that cardiovascular anomalies ex: congenital shunts & hypertension, among others, must be ruled out first
What is characteristic of cardiomyopathy?
in humans, characterized by cardiomegaly, L mural thrombosis, & myocardial fibrosis. in animals, cardiomyopathies are less well defined
Human & animal cardiomyopathies are classified into 3 main types:
- hypertrophic cardiomyopathy (HCM)
- dilated or congestive cardiomyopathy (DCM)
- restrictive cardiomyopathy
5 facts about primary cardiomyopathies?
- Most common in Ca & Fe
- sporadically reported in Bo, Sw, Rats
- in most cases etiology is uncertain (idiopathic)
- in some instances there is genetic predisposition
- it’s typically progressive cardiac disease
What spp is hypertrophic cardiomyopathy most common in?
Most common in Cats, less common in Ca, rats, Sw
what is hypertrophic cardiomyopathy?
decreased ventricular filling & decreased compliance leads to diastolic dysfunction. it resembles concentric hypertrophy (w/ symmetric hypertrophy) but w/o underlying cause such as aortic/pulmonic stenosis, hypertension, etc.
what ventricle does hypertrophic cardiomyopathy affect?
both in majority of cases but especially notable for L ventricle
How does hypertrophic cardiomyopathy affect heart weight?
increased heart weight as percent of body weight
What kinds of cats have hypertrophic cardiomyopathy & what conditions are seen with this?
particularly in middle aged male cats, 1/3 have aortic “saddle” thromboemboli; less often have atrial thrombi; also in cats w/ myosin binding protein C3 gene mutation (Maine Coon, Ragdoll)
Histo appearance of hypertrophic cardiomyopathy?
myofibril disarray (crisscrossing) & lots of fibrosis
What spp is dilated (congestive) cardiomyopathy most common in?
Most common in Ca, also in Fe, hamsters, turkeys, Sw, Bo, foxes
what is dilated (congestive) cardiomyopathy?
Progressive cardiac dilation & contractile (systolic) dysfunctions (decreased contractile force & increased end diastolic vol)
casual predispositions to dilated (congestive) cardiomyopathy ?
- taurine deficiency in Fe & foxes (not primary cardiomyopathy)
- familial tendencies in lrg dog breeds (Irish Wolfhound, Doberman, St. Bernard, Boxer)
- hereditary form seen in Holstein cattle
Gross appearance of dilated (congestive) cardiomyopathy ?
increased heart weight, dilated chambers, cardiomegaly, thin walls, flattened papillary muscles
What is arrhythmogenic R ventricular cardiomyopathy?
A variant of dilated (congestive) cardiomyopathy; autosomal dominant trait (8-bp deletion in striatin gene located on chromosome 17) that causes ion channel defect
What sp is arrhythmogenic R ventricular cardiomyopathy seen in?
Boxer dogs
Gross appearance of arrhythmogenic R ventricular cardiomyopathy?
diffusely pale dilated R ventricle (also pale due to infiltration of adipose). LV is dark red
Histological findings of arrhythmogenic R ventricular cardiomyopathy?
R ventricular myocyte degeneration, necrosis, & loss w/ replacement by adipose or fibroadipose tissue
What is restrictive cardiomyopathy?
Impaired ventricular filling & diastolic dysfunction. Aka left ventricular endocardial fibrosis.
Which sp is restrictive cardiomyopathy most common in?
Fe
What is restrictive cardiomyopathy usually preceded by?
endomyocarditis
Gross appearance of restrictive cardiomyopathy?
diffuse endocardial thickening, sometimes mural thrombosis
What are other forms of restrictive cardiomyopathy?
- excessive moderator bands (septomarginal trabeculae)
- congenital endocardial fibroelastosis (burmese cats)
What is primary endocardial fibroelastosis?
Hereditary disease in humans & Burmese cats. no underlying cardiac disease. uncertain pathogenesis.
Histo appearance of primary endocardial fibroelastosis?
endocardium is uniformly thickened by relatively dense fibrous CT
