Myocardial Disease

Question 1

What physiological changes can occur to the myocardium?

Answer 1

• Atrophy due to decreased workload
• Concentric hypertophy - increased myofibre width due to addition of sarcomeres in parallel. Get pressure overload which leads to valvular stenosis and systemic hypertension
• Eccentric hypertrophy - increased myofibre length due to addition of sarcomeres in series. Get volume overload which can be caused by valvular insufficiencies and septal defects

Question 2

Describe degeneration of the myocardium

Answer 2

• Can be due to nutrition, toxins or ageing
• Lipofuscinosis - accumulation of lipofuscins (lipo pigments) in cells
• Fatty degeneration - accumulation of lipid vacuoles due to toxic/metabolic injury
• Vacuolar degeneration - acute cell swelling. Energy dependent pumps fail, ionic and fluid homeostasis fail
• Myocytolysis - lysis +/- necrosis due to ischaemia or infarction

Question 3

Explain changes associated with necrosis of the myocardium

Answer 3

• Due to nutrion, toxins, trauma
• Hyaline necrosis - nuclei shrink and become shiny, inflammation (macrophages mop up necrotic cells), healing via fibrosis/scarring
• Can then develop a complete heart block depending on location of necrosis

Question 4

What are the causative agents of myocarditis?

Answer 4

• Viral e.g. canine parvovirus
• Bacteria - cause suppurative myocarditis
• Parasitic e.g. dirofilariasis

Question 5

What are the consequences of necrosis/myocarditis?

Answer 5

• If very severe and generalised get sudden death
• Myocardial scarring - can result in death, chronic HF BUT can present as clinically normal
• Troponins and creatine kinase can be used as biochemical makers, can be detected from 1-3hrs to 10-14d after damage has occured

Question 6

Describe primary cardiomyopathies

Answer 6

• generally idiopathic, can be inherited/familial
• Can be hypertophic, dilated or restricted
• E.g. arrthymogenic right ventricular cardiomyopathy - fibrofatty infiltration of RV myocardium which leads to progressive myocardial failure

Question 7

Give examples of secondary cardiomyopathies

Answer 7

*any myocardial disease which is not inflammatory or inherited*

1. Feline hypertophic cardiomyopathy

• Caused by hyperthyroidism
• Marked LV hypertrophy and septal thickening
• LA enlargement
• Pulmonary hypertension and oedema, congestive heart failure and sudden death
• Histopath - disarray and hypertophy of cardiomyocytes and interstitial fibrosis

1. Restrictive CM
   * LV stiffness and lose LV diastolic function
2. Canine dilated cardiomyopathy

• Cardiac dilation and ventricle contractile dysfunction
• LHF - pulmonary oedema, progresses to CHF with dilation of all chambers
  *