Lecture 4 - Myocardium

PATHOLOGY OF THE CARDIOVASCULAR SYSTEM

Shannon Martinson, 2018 VPM 2220 – Systemic Pathology II

http://people.upei.ca/smartinson/

Lecture 4 - Myocardium

• The myocardium has striations (sarcomeres)

• Myocardial fibres are branched and join each other

through the intercalated disks

• The cardiomyocytes contain abundant mitochondria

and myoglobin

MYOCARDIUM

Normal structure

Sarcomere

Z Z

Myofilaments

Nucleus

Sarcolemma Sarcoplasm

Unlike skeletal muscle, the myocardium has little/no capacity to replace lost myofibers, therefore normal repair is impossible

MYOCARDIUM

Normal structure

• Cardiomyocytes are susceptible to damage from hypoxia, free radicals, viruses, bacteria, toxins, etc • Microscopically, degeneration and necrosis are similar to that in skeletal muscle

Normal Myocardium: Striation and myofilaments have an

orderly arrangement in the sarcoplasm

Myocardial degeneration: Loss of striations, hypereosinophilia,

swelling, dissolution of sarcoplasm and myofibrils, and nuclear condensation.

MYOCARDIUM – NECROSIS

Degeneration and Necrosis

• Cardiomyocytes are susceptible to damage from hypoxia, free radicals, viruses, bacteria, toxins, etc • Microscopically, degeneration and necrosis are similar to that in skeletal muscle

Normal Myocardium: Striation and myofilaments are orderly

arranged in sarcoplasm

Myocardial degeneration: Loss of striations, hypereosinophilia,

swelling, dissolution of sarcoplasm and myofibrils, and nuclear condensation.


Degeneration and Necrosis

• Calcium plays an important role in normal cardiac physiology • In many degenerative diseases this mineral is sequestered in the sarcoplasm / organelles of

the cardiomyocytes • Causes myocardial calcification or mineralization

Ca++

Ca++


Cell Necrosis and Calcification

Ca++

Ca++


Cell Necrosis and Calcification Excessive calcium deposits appear microscopically as a dark-blue granules in the sarcoplasm

Gross: Pale white foci in the myocardium


Myocardial Necrosis and Repair • Necrosis elicits a leukocytic

response • Macrophages and neutrophils

infiltrate and start phagocytizing necrotic debris

Images: Dr. C. Legge


Myocardial Necrosis and Repair • Cardiac muscle has almost no

capacity to repair • Necrotic tissue is replaced by

connective tissue (fibroblasts) • Results in myocardial fibrosis

(scarring)

Gross: Pale white foci in the myocardium


Ischemic Myocardial Necrosis

• Myocardial infarcts • Very common in

humans: • Atherosclerosis

→Heart attack • Rare in animals

Cardiomyocyte necrosis can be : • Ischemic • Toxic • Nutritional • Neurogenic


Toxic Myocardial Necrosis

Myocardial degeneration and necrosis in left ventricle • Monensin toxicity in a horse

Examples of cardiotoxins: • Ionophores • Antineoplastic meds

• Cyclophosphamide • Doxorubicin

• Doxycycline • Toxic plants

• Gossypol • White snakeroot • Nerium oleander • Cassia occidentalis

• Cantharidin (blister beetle)

Noah’s arkive

• Affects farm animals

• Often manifests as sudden death

• Occurs mostly in rapidly growing animals

• Exacerbated by exercise or stress

• Can affect fetuses and cause abortion

• For unknown reasons, sometime WMD affects only skeletal muscle, or cardiac muscle, and sometimes both

• Responds well to treatment, but only at the early stages of the disease


Nutritional Myopathy White Muscle Disease


Nutritional Myopathy White Muscle Disease

Selenium and Vitamin E deficiency

Decreased scavenging of free radicals

Peroxidation of cell membranes

Cardiac and skeletal muscle necrosis and mineralization

Free radicals are produced during normal cardiac metabolism

Pathogenesis

White Muscle Disease


Nutritional Myopathy

• 2 day old calf – failure to thrive since birth • Sudden collapse – brought to AVC • Irregular heart rhythm • Marked ↑CK and AST • Marked hyperkalemia, hypochloremia, hyponatremia




• 2 day old calf – failure to thrive since birth • Sudden collapse – brought to AVC • Irregular heart rhythm • Marked ↑CK and AST • Marked hyperkalemia, hypochloremia, hyponatremia

Myocardial Degeneration and Calcification

• Often affects the LV in calves




• Often affects the right ventricle in lambs

• Submit samples from the LV and RV for histology




Von-Kossa stain for Calcium

Pheochromocytoma in a dog

• Brain trauma can cause myocardial necrosis • Possibly due to release of catecholamines

• Catecholamine release from a pheochromocytoma causes the same lesions

Brain Heart Syndrome


Neurogenic myocardial necrosis

Myocarditis rarely occurs alone, it is typically part of a systemic disease

MYOCARDIUM

Myocarditis

Suppurative Lymphocytic

Eosinophilic Hemorrhagic

Granulomatous

• Canine parvovirus causes enteritis

• Can also cause myocarditis in newborn pups

MYOCARDIUM

Myocarditis Parvoviral myocarditis

Pathology of Domestic Animals, Elsevier, 2016 Pathologic Basis of Veterinary Disease. Elsevier 2012

Canine Parvovirus (CPV-2)

• Histophilus somni may cause

• Thrombotic Meningo-Encephalitis (TME)

• Bronchopneumonia

• Myocarditis – feedlots especially

• Arthritis

• Reproductive problems

MYOCARDIUM

Myocarditis Histophilosis

Histophilus somni

MYOCARDIUM

Myocarditis Histophilosis • Causes vasculitis with infarction of the myocardium • Often involves the papillary muscles • Can also cause multifocal abscesses Histophilus somni

Can cause acute death

or chronic progressive

heart failure.

• Trueperella pyogenes can cause infection and inflammation in many organs

• In some cases blood dissemination leads to heart abscesses or endocarditis

MYOCARDIUM

Myocarditis Myocardial Abscesses

Trueperella pyogenes

• Staphylococcus aureus often causes systemic infections in lambs and kids

• One of the lesions is myocarditis which progresses from acute to chronic to

organized myocardial abscesses

MYOCARDIUM

Myocarditis Tick pyemia Staphylococcus aureus

FMVZ-UNAM

Indirect cycle

Cysticercus Taenia

Gross appearance of cysticerci: • Fluid filled cysts

containing white larvae

MYOCARDIUM

Myocarditis Cysticercosis Taenia spp

Cardiomyopathy refers to a myocardial abnormality that results in changes in cardiac wall thickness, causes electrical disturbances and often results in sudden unexpected death

• Genetic or idiopathic (suspected genetic) in origin • Mutations in genes coding for contractile proteins,

cytoskeletal proteins, mitochondrial enzymes • In animals, most are idiopathic

MYOCARDIUM - CARDIOMYOPATHY

Courtesy of Amanda Kelly

Mostly affect dogs and cats

Four main forms of Cardiomyopathy 1. Hypertrophic

Cardiomyopathy (HCM) 2. Dilated Cardiomyopathy

(DCM) 3. Restrictive Cardiomyopathy

(RCM) 4. Arrhythmogenic Right

Ventricular Cardiomyopathy (ARVC)

• So called “Secondary cardiomyopathies” • Non-genetic in origin

• Hyperthyroidism in cats • Concentric ventricular hypertrophy

• Taurine deficiency in cats • Eccentric biventricular hypertrophy

• Must also rule out anomalies such as congenital shunts, valvular disease and hypertension


Cardiomyopathy refers to a myocardial abnormality that results in changes in cardiac wall thickness, causes electrical disturbances and often results in sudden unexpected death

• Most common form of feline cardiomyopathy • Clinical signs include: lethargy, discomfort / hiding,

dyspnea, tachypnea, acute paralysis of the hindlimbs; or no overt signs but detection of murmur

• Occasionally causes sudden death • Anesthetic death

Hypertrophic Cardiomyopathy


Gross finding: • ↑ Heart mass • Concentric hypertrophy • Symmetric or Asymmetric

• LV • IVS • +/- RV

• Left atrial dilation

• Most common form of heart disease in the cat

• Affects males more than females (2:1) • Maine Coon and Ragdoll cats

• Inherited defects in cardiac myosin binding protein gene



HCM is characterized by: • Stiff fibers • Impaired ability to accept diastolic flow from

the left atrium • Relatively normal systole until the end-stage

Gross finding: • Less common:

• Ventricular fibrosis

10-20% caudal aortic thrombi



Pathology of Domestic Animals, Elsevier, 2016

• Cats with saddle thrombi may present with pain, hind end paresis, cold hind limbs and weak or absent femoral pulses (uni or bilateral)

Gross finding: • Less common:

• Atrial thrombosis



Normal myocardium HCM: Cardiomyocyte hypertrophy and disarray

Histology

• Most common form of canine cardiomyopathy • Most common in large breed dogs

• Clinical signs include: dyspnea, depression, weight loss, syncope, murmur, arrhythmia, abdominal distension

• Occasionally - sudden death with no preceeding signs


Dilated Cardiomyopathy

Gross finding: • Increased heart mass • Biventricular and atrial dilation

(eccentric hypertrophy) • Thin flabby walls • Attenuated papillary muscles


Dilated Cardiomyopathy • Eccentric hypertrophy resembling DCM occurs in cats and farmed foxes - secondary to a dietary taurine deficiency

DCM is characterized by: • Progressive cardiac dilation • Decreased contractile force • Systolic dysfunction

Histology: • Subtle changes

• Wavy attenuation of cardiomyocytes • Degeneration and fibrosis

Restrictive Cardiomyopathy


• Primarily in cats • Often used as a functional term rather than disease

entity • Diagnosed based on echocardiography • Characterized by left ventricular stiffness and

impaired diastolic function • Ventricular thickness is typically normal • Systolic function is usually normal • One (left) or both atria are enlarged

• Murmurs and dysrhythmias are common Pathology texts often include endocardial fibroelastosis of Burmese cats and excessive

moderator bands in the RCM category

• Left congestive heart failure often occurs • Few cats survive for more than 1 year after diagnosis

Restrictive Cardiomyopathy


• Gross findings • LV fibrosis

• Endocardial • Myocardial

• Atrial enlargement • +/- Mural thrombi

Left ventricular endocardial fibrosis

• Some cases may represent end-stage HCM or infarction from HCM

• Some cases may be preceded by endomyocarditis

From: Kimura Y et al. Pathological Features and Pathogenesis of the Endomyocardial Form of Restrictive Cardiomyopathy in CatsJ CompPath 2016, Vol 155

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)


• Primarily in Boxer dogs • Striatin gene mutation

• Less often in other dog breeds and in cats

• May see • Ventricular arrhythmias • Syncope • Heart failure • Sudden death

• Gross findings • +/- Dilation of the right ventricle

• Histology: • Replacement of RV (+/- LV) cardiomyocytes by

adipose or fibroadipose tissue

From EM Oxford et al. Heart Rhythm. 2007 September ; 4(9): 1196–1205.

Excessive LV moderator bands

( = False tendons)

Congenital endocardial fibroelastosis

Other primary myocardial abnormalities


Excessive moderator bands

• CT Bands span between the IVS and LV free wall

• Minimal heart enlargement • Incidental or a rare cause of LHF

Excessive LV moderator bands

( = False tendons)

Congenital endocardial fibroelastosis


www.studyblue.com/notes/note/n/cardiomyopathy-and-heart-failure/deck/3232147

Endocardial fibroelastosis

• Hereditary disease in Burmese cats • Diffuse endocardial fibrosis • LV eccentric hypertrophy • Histology: Abnormal deposits of

collagen and elastic fibres in the endocardium

http://www.photomazza.com/?Felidae

Sincere thanks to Drs A Lopez and E Aburto, AVC, for their contribution to this material.

Date post:	06-Feb-2022
Category:	Documents
Upload:	others
View:	5 times
Download:	0 times

Lecture 4 - Myocardium

Documents