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J Thorac Cardiovasc Surg 1999;117:1233-1234
© 1999 Mosby, Inc.

LETTERS TO THE EDITOR

Myocardial pseudovascular tubes are present in the delayed rejectionof pig-to-baboon orthotopic cardiac xenografts

4101 S Wappel Dr
Columbia, MO 65203

To the Editor:

In the article by Xu and associates ¹ dealing with the rejection of pig-to-baboon orthotopic cardiac xenografts,the authors describe microvascular thromboses in a heart that has survived19 days after transplantation (see their Fig. 4). The individual thrombosesare surrounded by damaged cardiomyocytes manifesting a more or less shrunkennucleus located in the midst of a large myocytolytic vacuole or rarefied myofibrils.

Having been intrigued by the curious shapes, high number, and largediameters of the alleged microthromboses, I have found that they often containparts of cardiomyocytes in their lumina. Using Cartesian coordinates and centimetersas units for their exact localization in Fig. 4, the microthrombosis-likestructures containing cardiomyocyte nuclei are located at the following points:x = 0.6, y = 4.1; x = 1.7, y = 1.8; x = 2.5, y = 2.5; x = 6.9, y = 5.6; x= 7.3, y = 3.3. The structures containing myocytolytic vacuoles with or withoutnuclear remains are located at these points: x = 2.4, y = 2.3; x = 3.8, y= 0.3; x = 5.8, y = 0.3; x = 6, y = 2.9; x = 6.8, y = 5.3; x = 7.5, y = 3;x = 7.8, y = 2.6. Finally, the large thrombus-like structure containing rarefiedmyofibrils is present at x = 7.7, y = 3.8. Consequently, the alleged microthrombosesare not vascular structures but "myocardial pseudovascular tubes"² formed by individual hyalinized cardiomyocytes or their bundles.

Hyalinized cardiomyocytes may undergo apoptotic disintegration into"eosinophilic droplets" similar to red cells, ^3,4 creating animpression of interstitial hemorrhage. In Fig. 4, ¹ such a process is present in the form of a hook delineatedby the points x = 3.5, y = 0; x = 3, y = 6; x = 7.5, y = 6.9. Note the presenceof several "naked" cardiomyocyte nuclei close to the point x =6.5, y = 6.7. Free cardiomyocyte nuclei were described in Syrian hamster cardiomyopathy ⁵ and in the delayed rejection ofheart xenografts. ⁴ Apparently,the apoptotic disintegration of cytoplasm may precede that of the nucleus. ⁶

The purpose of this letter is not to deny the presence of genuine microthromboses,which were well documented by electron microscopy in the hyperacute and delayedrejections of cardiac xenografts and allografts, ⁷ but to increase the awareness of myocardial pseudovasculartubes in the same situations.

12/8/98219

[Response declined]

References

1. Xu H, Gundry SR, Hancock WW, MatsumiyaG, Zuppan CW, Morimoto T, et al. Prolonged discordant xenograft survival anddelayed xenograft rejection in a pig-to-baboon orthotopic cardiac xenograftmodel. J Thorac Cardiovasc Surg 1998;115:1342-9.[Abstract/Free Full Text]
   
2. Beranek JT. Are all bizarre intramyocardialartery–like structures in human cardiac allografts really coronary vessels?Histopathology 1997;30:197-8.[Abstract/Free Full Text]
   
3. Beranek JT. Apoptosis is the main mechanismof cardiomyocyte death in the hyperacute rejection of heart xeno- and allografts.Transplantation 1997;64:1632-3.[Medline]
   
4. Beranek JT. Myocardial pseudovascular tubesare present in the delayed rejection of heart xenografts. Transplantation 1997;63:486.[Medline]
   
5. Bajusz E, Baker JR, Nixon CW, HomburgerF. Spontaneous, hereditary myocardial degeneration and congestive heart failurein a strain of Syrian hamsters. Ann N Y Acad Sci 1969;156:105-29.[Medline]
   
6. Collins JA, Schandl CA, Young KK, VeselyJ, Willingham MC. Major DNA fragmentation is a late event in apoptosis. JHistochem Cytochem 1997;45:923-34.[Abstract/Free Full Text]
   
7. Forbes RDC, Guttmann RD. Histopathologyand mechanisms of rejection in xenotransplantation. In: Hardy MA, editor.Xenograft 25. Amsterdam: Elsevier Science Publishers; 1989. p. 133-47.
   

This article has been cited by other articles:

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