General Characteristics

To identify specific features of cardiomyocytes in right ventricular tissue obtained from hearts of children and adults with ARVC/D, EMB samples were compared with those from patients with dilated car-diomyopathy (DCM). Donor hearts at cardiac transplantation served as normal control [19].

Adult cardiomyocytes in a normal heart are covered by a ~50-nm thick surface coat, also termed gly-cocalyx, which forms a continuous layer on the cell membrane. The cardiomyocyte membrane shows specialized regions including the transverse tubular system, termed T- tubules, and the ID. Cells are characterized by a well-developed regular sarcomeric apparatus, oval mitochondria distributed between contractile fibrils, single glycogen particles, and a regular sarcoplasmic reticulum network. Oval nuclei are located in the cell center. Single Golgi apparatus, consisting of flattened cisterns, rough endoplasmic retic-ulum and single lipofuscin granules are localized in the perinuclear space.

In ARVC/D, there was no impairment of cell membrane continuity or dilatation of sarcoplasmic reticulum cisterns. The T-tubules were normal and there was a variable amount of lipofuscin granules. The nuclei were often highly convoluted and contained dense aggregates of chromatin below the nuclear membrane. In single cardiomyocytes not exhibiting myolytic features, dilated T-tubules and numerous profiles of Golgi apparatus and vacuoles were present (Fig. 6.1a) Abundant glycogen and variously sized lipid droplets were seen in many myocytes. Irregular organization of contractile filaments and widening of Z bands were observed in ARVC/D hearts, similar to that seen in DCM hearts. A characteristic feature of ARVC/D was thickening of the glycocalyx covering the cell membrane in some normal cardiomyocytes (Fig. 6.1b) and a pale structure of ID junctions. Giant lipid droplets were present in some cardiomyocytes (Fig. 6.1c). Such features were not found in DCM. The general characteristics of ARVC/D cardiomyocytes in comparison with DCM and donor transplanted hearts (controls) are presented in Table 6.1.

  1. 6.1 • Electron microscopic images of human ARVC/D cardiomyocytes. a Perinuclear region with injured mitochondria (M), numerous Golgi (G), lipid droplets (L),dilated T-tubules (T) and highly convoluted nuclear (N) membrane. Bar = 600 nm. b Widened Z-bands (Z), normal mitochondria (M) and T-tubules (arrowhead), thick glycocalyx (arrow) that covers cell membrane. Bar = 600 nm. c Cardiomyocyte from ARVC/D heart with giant lipid droplets (L) and numerous mitochondria (M) and disarrangement of contractile fibrils. Bar = 2 ^m
  2. 6.1 • Electron microscopic images of human ARVC/D cardiomyocytes. a Perinuclear region with injured mitochondria (M), numerous Golgi (G), lipid droplets (L),dilated T-tubules (T) and highly convoluted nuclear (N) membrane. Bar = 600 nm. b Widened Z-bands (Z), normal mitochondria (M) and T-tubules (arrowhead), thick glycocalyx (arrow) that covers cell membrane. Bar = 600 nm. c Cardiomyocyte from ARVC/D heart with giant lipid droplets (L) and numerous mitochondria (M) and disarrangement of contractile fibrils. Bar = 2 ^m

Table 6.1 • General ultrastructural findings

Cell structure

Characteristic

ARVC/D; (21 pts); (%)

DCM; (10 pts); (%)

Controls; (10 pts); (%)

Cell membrane

Continuous

100

100

100

Glycocalyx

Thickening

57

0

0

Nucleus

Highly convoluted

100

35%

5

Oval in single cells

28,5

0

Numerous

T- tubules

Dilated

76,2

80

0

Sarcoplasmic reticulum

Normal

100

100

100

Mitochondria

Polymorphic

28,5

33,3

10

Irregular cristae

23,8

13,3

0

Increased number

80,8

100

37,4

Sarcomers

Normal

90

33,3

100

Contraction bands

100

30

6,5

Lipofuscin

Various number

100

80

30

Glycogen

Abundant in some cells

100

60

30

Lipid droplets

Various size in single cells

85,7

60

20

Giant

14

0

0

Vacuoles

Various size

76,2

30

0

Golgi

Numerous

33,3

Single

Single

ID junctions

Pale

80,8

0

0

ARVC/D,arrhythmogenic right ventricular cardiomyopathy; DCM,dilated cardiomyopathy; Pfs=patients

ARVC/D,arrhythmogenic right ventricular cardiomyopathy; DCM,dilated cardiomyopathy; Pfs=patients

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