Heart block and mesothelioma of the atrioventricular node

Histological evidence for cell proliferation activity in cystic tumor (endodermal heterotopia) of the atrioventricular node

Cystic tumor (endodermal heterotopia) of the atrioventricular (AV) node in a 95-year-old female is described. Electrocardiograms showed complete AV blockage with a narrow QRS morphology resulting from the long-standing first degree of AV blockage since age 61. A cardiac pacemaker was implanted at age 83. The patient died of pneumonia at age 95. Autopsy demonstrated a normal heart weight (320 g), normal coronary artery and normal myocardium. Histological examination of the conduction system revealed a marked fibrotic sinoatrial (SA) node and a cystic lesion in the lower right atrium, including the approaches to the AV node. The bundle of His and its branches were completely intact. Cellular nests and cystically dilated tubules were scattered within a loose tissue stroma, which measured 18 x 12 x 5 mm. There were several mitotic figures among the tubules, as well as nuclear fragments similar to apoptotic bodies and exfoliation of the tumor cells. Immunohistochemical studies demonstrated a positive reaction for epithelial membrane antigen, carcinoembryonic antigen, CA19-9, cytokeratin and secretory component in the tubular cells, and a negative reaction for thrombomodulin. Endocrine cells among the tubules were positive only for calcitonin and serotonin. Ultrastructurally, sparse microvilli and desmosome-like structures between the tumor cells were observed. These findings support that this lesion originates from the endoderm. Moreover, it is likely that progression in the degree of AV block may be explained by the cell proliferation activity of the tumor.

Mesothelioma of the AV node

A 21-month-old boy died suddenly six months after presenting with heart murmur and second-degree atrioventricular (AV) block. Autopsy revealed a mesothelioma completely replacing the AV node and extending into the central fibrous body. The bundle of His and bundle branches were not involved. Mesothelioma of the AV node is a rare cause of supra-His (AV) block, arrhythmias, and sudden death.

Congenital polycystic tumor of the atrioventricular node: possible familial occurrence and critical review of reported cases with special emphasis on histogenesis

Congenital polycystic tumor of the atrioventricular node is a rare tumor of disputed histogenesis. It constant location in the atrioventricular node separates it from other cardiac cysts and tumors of indisputable endodermal origin. New studies of the embryogenesis of conduction tissues provide a reasonable explanation for the site of the lesion. Morphologic and histochemical features of the tumor fail to conclusively favor either a mesothelial or an endodermal genesis. A recently studied case provides some new morphologic observations (complex desmosomes, granule-containing epithelial cells) and suggests the possibility of of familial occurrence.

Atrioventricular block in childhood caused by mesothelioma

The case of a girl who was first seen at 3.5 years of age with longstanding asymptomatic heart block is reported. Electrophysiological study disclosed a block proximal to the His bundle. She grew up normally until the age of 11.5 years, when a syncopal attack occurred. Before a pacemaker could be inserted, she suffered a second fatal attack. Necropsy revealed a tumor of the atrioventricular node diagnosed as mesothelioma. Our findings are compared to the 38 cases already described in the literature.

De subitaneis mortibus. XXVI. Fatal electrical instabiltiy of the heart associated with benign congenital polycystic tumor of the atrioventricular node

Benign congenital polycystic tumors of the atrioventricular (A-V) node are an unusual but not very rare cause of heart block. Two such cases are presented and discussed in conjunction with the reported experience of other. The tumor is always within and only very near the A-V node, seldom involves more than the proximal end of the His bundle, and has not been reported to occur in the sinus node. Although sudden death has been reported in conjunction with these tumors, a surprising number of other patients have lived to old age and died of causes unrelated to the A-V nodal tumor. As a corollary it is important to consider a diagnosis of A-V nodal tumor in any patient of any age who presents with otherwise unexplained heart block or syncope. From accumulated experience it appears that such patients do not tolerate electronic pacing safely and some possible explanations for this are discussed. Escape rhythm in all reported cases has been characterized by QRS complexes which are narrow and a ventricular rate which is from half to two-thirds of the sinus rate. Reasons why an A-V junctional rhythm which is 66% of sinus rate may be especially stable are discussed.

Ultrastructure of the mesothelioma of the atrioventricular node

In order to determine the histogenesis of tumors of the atrioventricular node, so-called conduction tumors, two such tumors were serially blocked for electron microscopy. Ultrastructurally these tumors were composed of nests of cells arranged in small channels and tubules set in a connective tissue stroma. The cells lining the tubules were flattened or low cuboidal and had abundant microvilli over the lumen surface. The cells were joined by specialized junctions along their lateral adjacent borders, especially at the luminal surfaces, and intercellular spaces delineated by specialized junctions were frequent. Microvilli, intercellular spaces bounded by tight junctions, and complex intercellular junctions are features of mesothelial cells, and especially of benign mesothelioma of the genital tract. These results strongly suggest that the cardiac conduction tumor is derived from mesothelial cells and is in fact a mesothelioma of the atrioventricular node.