Histopathology

The hallmark histopathological feature of feline ARVC/D is partial or almost entire replacement of the RV free wall by prevalent fatty (25% of cases) or fibrofatty (75% of cases) tissue [8]. The fibro-fatty pattern consists of focal or diffuse RV myocardial atrophy associated with adipose tissue and replace-

Table 8.1 • Comparison of clinical and pathologic findings of canines and felines with ARVC/D [8,15]

Canine ARVC/D (n=23)

Feline ARVC/D (n=12)

No. or Mean±SD

%

Comments

No. or Mean±SD %

Comments

Demographics

Age (years)

9.1±2.3

7.3±S.2

Gender

Male

12

S2

7

60

Female

11

4S

S

40

Body weight (kg)

30±5.4

4.S±1.S

Clinical features

Syncope

12

S2

Common

1

S

Rare

Ventricular arrhythmias,

1g

S3

g

7S

LBBB pattern

Right-sided heart failure

3

13

Uncommon

S

67

Common

Familial

10

43

Yes

NA

NA

Suspected

Sudden death

g

3g

Common

0

0

Uncommon

Pathologic features

Morphologic Pattern

Fatty form

S

3S

3

2S

Fibro-fatty form

1S

6S

g

7S

Myocarditis

RV myocarditis

14

61

10

S3

LV myocarditis

16

70

S

67

LA or RA

4

17

g

7S

Apoptosis

g

3g

g

7S

Myxomatous valve degeneration

7

32

Fatty tissue (mean % area)

Antero-lateral RV

46.7±19.7

NA

Posterior RV

29.2±1S.9

Infundibular RV

45.2±12.2

ARVC/D, arrhythmogenic right ventricular cardiomyopathy/dysplasia; LBBB, left bundle branch block; LV, left ventricle; NA,data

not available;RV, right ventricle

  1. 8.1 • Hearts from two cats with ARVC/D and congestive heart failure. There is severe right atrial and right ventricular dilatation, and thinned, translucent right ventricular walls associated with marked trabecular flattening; the septo-parietal bands appear prominent. ECG showed ventricular tachycardia (left bundle branch block morphology)
  2. 8.1 • Hearts from two cats with ARVC/D and congestive heart failure. There is severe right atrial and right ventricular dilatation, and thinned, translucent right ventricular walls associated with marked trabecular flattening; the septo-parietal bands appear prominent. ECG showed ventricular tachycardia (left bundle branch block morphology)
Fig. 8.2 • Whole heart histological section from a cat with ARVC/D and ventricular ectopy.There is anterior and apical RV free wall thinning and aneurysm. Heidenhain trichrome stain. From [8] with permission

ment-type fibrosis (Figs. 8.2, 8.3). The fatty pattern within the RV wall and trabeculae is characterized by multifocal or diffuse areas of adipose cell infiltration with only mild patchy fibrosis. Islands of myocytes are often surrounded by fat or fibrofatty tissue. In both forms, residual surviving myocytes

Fig. 8.3 • Higher magnification (x45) of the apical aneurysm from Fig. 8.2.There is severe transmural fibrofatty replacement with organized mural thrombosis and thickened epi-cardium. Heidenhain trichrome stain. From [8] with permission

are usually scattered within the areas of fibrosis or fat, and fibro-fatty replacement usually extends from the epicardium toward the endocardium. Focal or multifocal RV myocarditis is most prevalent in ARVC/D cats with the fibro-fatty pattern. It consists mostly of T lymphocytes associated with my-ocyte cell death and mild-to-severe fibrous tissue deposition. Similar findings may be also present in left and right atrial walls, as well as LV free wall and ventricular septum. Fatty infiltration is occasionally present in the LV free wall but not in the ventricular septum. Abnormal intramural small vessels, with thickened walls (due primarily to medial hypertrophy), are uncommon. Apoptotic myocytes have been identified by TUNEL histochemical investigation in 75% of affected cats.

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