cardiovascular path 2

Question 1

Hypertrophic cardiomyopathy (HCM)
- pathophysiology
- lesion
- primary vs secondary?
- left:right ventricular free wall ratio
- lesion more common in cats

Answer 1

• diastolic failure: the heart can’t properly fill with blood during diastole, and this is the basis for heart failure.
• The lesion of HCM is hypertrophy of the ventricle (almost always the left ventricle), with a small lumen
  > resembles concentric hypertrophy
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• If we can identify a cause for pressure overload (subaortic stenosis or systemic hypertension) or some non-cardiac reason for the heart to be hypertrophied (hyperthyroidism, hypersomatotrophism), then we could call it secondary hypertrophic cardiomyopathy.
• If we can’t identify a cause, then we consider it an intrinsic disease of the heart muscle and call it primary hypertrophic cardiomyopathy
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• HCM left:right = 4:1 or more
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• The left atrium is dilated in those cats with HCM that are developing heart failure. But, left atrial dilation may not always be present.

Question 2

HCM inheritance?

Answer 2

• can be linked to mutations in proteins required for myocardial contraction (myosin, troponin, tropomyosin) in humans, and some cats
• many HCM cases have no known genetic basis

Question 3

Cats with HCM
- issues that can develop

Answer 3

• can develop congestive heart failure, or reduced cardiac output (eg with syncope), or sudden death, or death during anaesthesia.
• In some cats, turbulent flow → left atrial thrombosis → embolism to aorto-iliac bifurcation (“saddle thrombus”) → hindlimb ischemia, pain & paresis.
• On the other hand, many cats with HCM never develop heart failure

Question 4

HCM histologic lesions

Answer 4

• myocardial fibrosis
• disarray of myofibres
• replacement of myofibres by adipocytes
  > These lesions are not pathognomonic, but are quite characteristic.

Question 5

Restrictive cardiomyopathy (RCM)
- how common?
- species?
- what happens?

Answer 5

• rarer than HCM, occasional in cats
• endocardial fibrosis impairs filling of the ventricle during diastole
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• diastolic failure > heart can’t properly fill with blood during diastole
  > myocardial fibrosis or endocardial fibrosis (or both) restrict the heart from filling with blood

Question 6

Dilated cardiomyopathy (DCM)
- pathophysiology
- what happens?
- lesions / structural changes

Answer 6

• systolic failure > heart can’t properly contract during systole
• globose heart with dilation that usually affects both ventricles, and often both atria
• may have hypertrophy, even though ventricular walls are thin and flabby
• The endocardium is often diffusely thickened and white

Question 7

DCM
If we see a heart with dilation of all 4 chambers, we might think of extrinsic causes for:

Answer 7

• Failure of the myocardium to contract, such as monensin that causes myocardial necrosis, or an infection that caused myocarditis.
• Volume overload on all 4 chambers, like endocardiosis causing incompetence of the right and left AV valves.

Question 8

DCM in cats - most cases are:

Answer 8

• idiopathic
• Dietary deficiency of taurine is a classic cause of dilated cardiomyopathy in cats, but is now rare

Question 9

DCM in dogs - causes

Answer 9

• Breed associated: Doberman pinschers, giant breeds, English cockers
• taurine deficiency?? unknown

Question 10

Arrhythmogenic right ventricular cardiomyopathy
- who gets it?
- disease course / sings
- lesions, gross and histo

Answer 10

• Boxers, occasionally in other breeds and cats
• sudden death, syncope, or congestive heart failure.
• Some have dilatation of the right ventricle, but others are grossly normal
• Histologic lesions are consistently dramatic and characteristic, with replacement of myofibres in the right ventricle by adipocytes and fibrous tissue

Question 11

Cor pulmonale
- what is it?
- causes?

Answer 11

• Cor pulmonale= “heart disease secondary to lung disease”.
• Primary lung disease→ pulmonary hypertension→ right-sided heart failure with myocardial hypertrophy
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  Causes:
• chronic hypoxia of pulmonary alveoli (high altitude or widespread bronchiolar obstruction)
• interstitial lung disease
• diseases of pulmonary blood vessels

Question 12

Histophilus somni effects on heart

Answer 12

• Histophilus somni > myocarditis in feedlot cattle
  > acute onset of left heart failure
  > focal area of coagulation necrosis or abcessation that always affects the left ventricular papillary muscle, and is accompanied by pulmonary edema due to heart failure

Question 13

Clostridial myositis
- agent, effects on heart and body
- lesions

Answer 13

• blackleg, Clostridium chauvoei
• can affect either the heart or the skeletal muscle, causing sudden death
• the infected myocardium or muscle has a focal red-black dry lesion
• often mild fibrinous pericarditis

Question 14

Lymphocytic myocarditis
- how common, lesions, causes

Answer 14

• rare, no gross lesions
• There are may different cause: toxoplasmosis, canine parvovirus (in neonates, if the dam has no antibody to parvovirus), BVDV in calves, foot and mouth disease, and others—but you will need histopathology to make this diagnosis.

Question 15

Suppurative myocarditis cause

Answer 15

in any species, due to bacteremia.

Question 16

Myocardial Necrosis - general causes

Answer 16

nutritional, toxic, ischemic, exertional

Question 17

Myocardial Necrosis - Nutritional causes, characteristics

Answer 17

• White muscle disease
  > young ruminants, vitmain E / selenium deficiency
  > mineralization often grossly visible
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• Mulberry heart disease of pigs
  > gross lesions are multifocal or diffuse myocardial hemorrhage → fibrinous pericarditis
  > Histologic lesions are hyaline degeneration or fibrinoid necrosis of myocardial arterioles and necrosis of cardiac myofibres

Question 18

Myocardial Necrosis - toxins

Answer 18

• ionophores
• doxorubicin, gossypol, T-2 mycotoxin, sulfonamide antibiotics in feed, avocados, cobalt, Cassia spp. (senna), blister beetles, etc etc etc.

Question 20

Sequence of events following myocardial necrosis

Answer 20

1. Necrosis of myofibres
2. Infiltration of by macrophages, which remove necrotic debris
3. Regeneration is not possible, because cardiac myofibres cannot proliferate
4. Fibrosis—scarring—is a common sequel to myocardial necrosis.

Question 20

Myocardial Necrosis- excessive workload, how it can arise

Answer 20

• Overworked myofibres die!
• excessive demands on contractile fibers
• volume overload or chronic pressure overload
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• uncommonly “brain heart syndrome” (brain injury results in massive epinephrine release, causing excessive tachycardia)

Question 20

Myocardial Necrosis - ischemia

Answer 20

• can be caused by reduced myocardial perfusion (such as shock), thrombosis of coronary arteries, or by excessive cardiac hypertrophy.

Question 21

Appearance of myocardial necrosis

Answer 21

• Multifocal, diffuse, or patchy areas of pale myocardium
• may be mineralized and gritty
• can be subtle
• “breadloaf” the heart to look for lesions
  > Animals can die of myocardial necrosis or myocarditis with no grossly visible lesions, so submit samples!

Question 22

Significance of myocardial necrosis and/ or inflammation

Answer 22

• Acute heart failure due to loss of function of the myocardium
• Arrhythmias (which may be fatal) due to disruption of electrical conduction in the myocardium by necrosis or fibrosis
• Restricted filling of the heart during diastole, once the myocardium has become fibrotic and cannot expand.
• Myocardial necrosis or inflammation can lead to fibrosis. Scarring in the myocardium may be of no consequence, or may reduce myocardial contraction during systole, limit dilation of the ventricle during diastole, or lead to arrhythmia as mentioned above.

Question 23

hydropericardium
- what is it?
- causes?
- effects?

Answer 23

• Excessive clear fluid in pericardial sac; transudate
• Causes are similar to those of edema: congestive heart failure, hypoproteinemia
• Usually does not impair heart function, unless fluid accumulates very rapidly

Question 24

hemopericardium
- what is it? causes? effects?

Answer 24

• Accumulation of blood in the pericardial sac.
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  Causes:
• Rupture of a right atrial hemangiosar- coma, ruptured left atrium secondary to mitral valve disease, or rupture of the base of the aorta in horses
• Anticoagulant rodenticide toxicity
• Trauma such as rib fractures or pen- etrating injury
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  Blood accumulation may be rapid and cause cardiac tamponade, which leads to right heart failure.

Question 25

Pericarditis
- how can bacteria enter the pericardial sac?

Answer 25

• Blood-borne spread (bacteremia)
  > Often, there will be additional inflammatory lesions such as pleuritis, peritonitis, polyarthritis, meningitis
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• Penetrating injury
  > eg. hardware disease
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• Extension from an adjacent lesion
  > occasionally, myocardial abscesses rupture and induce massive pericarditis.
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• Mild fibrinous pericarditis occurs with many blackleg cases in cattle