JPC Systemic Pathology

CARDIOVASCULAR SYSTEM

February 2025

C-M09

 

Signalment (JPC# 2370157): A 1-year-old spayed female domestic shorthair cat

 

History: This cat died unexpectedly 6 days after routine ovariohysterectomy. 

 

Histopathologic description: Heart: Diffusely expanding the endocardium of the left ventricle up to five times normal (50µm) and infiltrating and separating subjacent myofibers is abundant eosinophilic beaded to fibrillar material (fibrin), hemorrhage, and clear space (edema), admixed with moderate numbers of fibroblasts, neutrophils, lymphocytes, plasma cells, macrophages, and eosinophilic cellular and karyorrhectic debris (necrosis). Multifocally, inflammatory cells infiltrate the underlying myocardium, expand the interstitium, and separate, surround, and replace cardiomyocytes that are occasionally either swollen and vacuolated (degenerate), or shrunken with hypereosinophilic sarcoplasm, loss of cross striations, and pyknotic nuclei (necrotic).

Morphologic diagnosis: Heart, left ventricle: Endocarditis, fibrinous, subacute, diffuse, moderate, with edema, hemorrhage, and multifocal subendocardial myocarditis, domestic shorthair cat, feline.

 

Etiologic diagnosis: Idiopathic endocarditis

 

CAUSE: Unknown

 

CONDITION: Endomyocarditis (EMC)

 

General dISCUSSION:

PATHOGENESIS:

• Unknown; often occurs within 3 months of stressful events
• EMC may progress to LVEF if the cat survives
• Predilection for male, neutered cats
• Thromboemboli are a common sequela

TYPICAL Gross findings:

• Enlarged heart, dilated left atria
• Left ventricular subendocardial hemorrhage
• White to gray fibrinous material adherent to the left ventricular endocardium, especially papillary muscles and left ventricular outflow tract
• Sometimes aortic thromboembolism

TYPICAL LIGHT Microscopic findings:

• Acute: Severe infiltration of neutrophils, lymphocytes, plasma cells, and macrophages in the myocardium and endocardium
• Older lesions have marked fibroplasia and/or granulation tissue
• Typically limited to the left heart; most severe in the dorsal septal wall (basal intraventricular septum)
• Concurrent interstitial pneumonia with hyaline membranes lining alveolar space is a common comorbidity in affected cats

Differential diagnosis: 

For cardiac disease in cats:

• Left ventricular endocardial fibrosis (LVEF) or restrictive cardiomyopathy (RCM): Older cats; endocardial thickening with mural thrombosis
• Dilated (congestive) cardiomyopathy: Bilateral enlargement of all heart chambers associated with dietary taurine deficiency in cats; carnitine deficiency in dogs
• Hypertrophic cardiomyopathy (C-M10)
  • Marked hypertrophy of the ventricles, especially the left ventricle
  • Cardiomyocyte hypertrophy and disarray of sarcomeres
  • Hereditary in Persian cats
• Hyperthyroidism (E-N03)
  • Concentric, usually bilateral, ventricular hypertrophy
  • Enlarged thyroid glands 
• Endocardial fibroelastosis (C-M03): Young Burmese, Siamese
  • Differentiate from EMC by lack of inflammation
• Aortic stenosis, hypertension
• Systemic reactive angioendotheliomatosis (C-M12): Intraluminal proliferation of spindle cells within vessels; often involves the heart with resultant myocardial dysfunction

Comparative pathology: 

• EMC is unique to cats among animals, though humans have a similar classification system for restrictive cardiomyopathy which has been adapted
• Ulcerative endocarditis: Distinct ulcerative lesion in the left atrium of dogs, associated with acute renal insufficiency

 

Valvular endocarditis:

• Bovine: Trueperella pyogenes
• Pigs: Streptococcus sp. and Erysipelothrix rhusiopathiae
• Horses: Strongylus vulgaris larval migration, S. zooepidemicus, and Actinobacillus equuli
• Dogs and Cats: Streptococcus sp. and E. coli

 

Cardiomyopathies:

• Dogs - Most commonly recognized cardiomyopathy is the dilated (congestive) form in giant and large-breed dogs; HCM is much less common than the dilated form
• Cattle - Cardiomyopathies have been described in certain breeds (Japanese black cattle, Australian polled Herefords, and Holstein-Friesian); inheritance is autosomal recessive
• Pigs - Dilated and hypertrophic cardiomyopathies have been described 
• Hamsters - An inherited cardiomyopathy exists in certain strains of Syrian hamsters causing atrial thrombosis
• Mice – Frequently get atrial thrombosis; left auricle is most commonly affected; precipitated by multisystemic amyloidosis, also common in BALB/C; left heart failure due to atrial thrombosis is the most common cause of noninfectious dyspnea in mice
• Guinea pigs – Cardiac glycogenosis (rhabdomyomatosis) – considered an incidental finding; seen grossly as pale streaks in the heart most commonly in the left ventricle – composed of numerous vacuolated myofibers; the vacuoles contain glycogen

References:

1. Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Wiley Blackwell; 2016: 99, 241-242.
2. Gal A, Castillo-Alcala F. Cardiovascular system and lymphatic vessels. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:697.
3. Kimura Y, et al. Pathological features and pathogenesis of the endomyocardial form of restrictive cardiomyopathy in cats. J Comp Pathol. 2016;155(2-3):190-198. 
4. Robinson WF, Robinson WF. Cardiovascular system. In: Maxie MG, ed. Jubb, Kennedy and Palmer’s Pathology of Domestic Animals. Vol 3. 6th ed. St. Louis, MO: Elsevier; 2016: 46-47.

 

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