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Ann Thorac Surg 1997;64:1096-1098
© 1997 The Society of Thoracic Surgeons

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Original Article: Cardiovascular

In Vivo Morphology of Woven, Collagen-Sealed Dacron Prostheses in the Thoracic Aorta

Division of Thoracic and Cardiovascular Surgery, Surgical Center, and Division of Diagnostic Radiology I, Radiological Center, Hannover Medical School, Hannover, Germany

Accepted for publication April 18, 1997.

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Background. Long-term changes in knitted Dacron grafts inserted into the infrarenal aorta have been addressed by a number of studies indicating their potential for postoperative dilatation. In contrast, the behavior of woven, collagen-presealed, double-velour Dacron grafts used to replace the thoracic aorta is not known.

Methods. Forty-five patients were examined at a mean of 32.4 ± 14.8 months after insertion of woven, collagen-coated, Dacron double-velour prostheses (Meadox woven with Hemashield, Meadox, Oakland, NJ) in the thoracic position under highly standardized conditions using spiral computed tomography.

Results. Compared with a manufactured diameter of 26 mm, all grafts showed an increase of 1 to 5 mm (mean, 3.0 ± 1.2 mm [11.6% ± 4.4%]; p < 0.0001) with greater enlargement of the ascending than of the descending aortic portions (p = not significant). A further statistically significant progressive dilatation failed to occur. Degenerative changes, including false aneurysm formation, could be excluded.

Conclusions. Woven, collagen-coated Dacron prostheses are considered a safe replacement material for the thoracic aorta.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Dacron double-velour prostheses have been used for many years as replacement material for the abdominal and thoracic aorta. However, during long-term follow-up, several investigators have observed that they dilate and also that some structural changes occur in the perianastomotic region [1–10]. In all these studies, knitted Dacron prostheses were used as the replacement material in the abdominal aorta. Since the end of the 1980s, woven, collagen-coated prostheses have become popular for aortic replacement because of their greater structural stability as compared with knitted Dacron prostheses. In a relatively small and heterogeneous patient population, Alimi and associates [11] showed that the structural stability of woven prostheses is significantly greater than that of the knitted variate. The coating of prosthetic grafts in the thoracic aorta is important because they are exposed to a high intravascular pressure and also because they do not benefit significantly from perivascular fibrous tissue. We studied whether woven, collagen-coated vascular grafts in the thoracic aorta undergo a time-dependent change in their stability, that is, whether they progressively dilate and whether the graft configuration changes as a result of localized degeneration of the fabric.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
We have been inserting collagen-coated, Dacron double-velour prostheses (Meadox woven with Hemashield; Meadox, Oakland, NJ) in patients at our institution since 1989. To minimize the possibility of a systematic error, the patients we selected for this study had had implanted a graft with a manufactured diameter of 26 mm. We also only studied prostheses inserted in the ascending and descending aorta, because the prosthetic tube courses practically vertically in these regions. In this way, errors of measurement caused by distortion in an oblique section of the graft could be minimized. During postoperative follow-up, spiral, contrast-enhanced computed tomograms of the thorax were obtained and analyzed by two independent experienced investigators. The short diameter of the aorta was measured at defined levels. The spiral, contrast-enhanced computed tomogram allowed for optimal assessment of the inner diameter of the graft, thereby excluding errors in measurement related to inclusion of the graft with the native aortic wall or to a possible perigraft reaction.

A total of 62 spiral, contrast-enhanced computed tomograms from 45 patients who had been operated on between 1989 and 1994 and received a vascular graft of the type described in the ascending or descending portion of the aorta were studied. Six patients, who had undergone consecutive replacements of the ascending and descending aorta, were counted twice as separate patients. The mean age of the patients was 55.0 ± 12.4 years. These were 28 male and 17 female patients. The mean follow-up in all patients was 32.4 ± 14.8 months.

The ascending aorta was replaced in 32 patients (mean age, 54.3 ± 13.0 years; mean follow-up, 33.0 ± 15.6 months), and a descending aortic graft was implanted in 13 (mean age, 56.7 ± 11.2 years; mean follow-up, 30.8 ± 13.4 months).

To evaluate the long-term fate of the grafts, the patients with ascending aortic prostheses were divided into five groups according to their yearly follow-up intervals. There were no significant differences among the groups in terms of the mean age and the underlying conditions.

Two to four scans had been obtained postoperatively in 12 patients. These patients were entered in only one control investigation using the last study. In addition, an intraindividual comparison of the diameters of these 12 aortic prostheses was done.

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
All follow-up investigations showed the presence of well-healed grafts with no localized aneurysmic dilatation. A small aneurysm at the distal anastomosis was seen in only 1 patient, who had undergone replacement of the ascending aorta (Fig 1). Intraluminal thrombus or obvious perigraft reaction could not be identified. All patients were clinically asymptomatic at the time of their investigations.

View larger version (116K): [in this window] [in a new window]   Fig 1. . Three-dimensional reconstruction of spiral, contrast-enhanced computed tomogram showing a small anastomotic aneurysm that formed after ascending aortic replacement.

View larger version (20K): [in this window] [in a new window]   Fig 2. . Frequency distribution of graft dilatation. ( d = change in diameter.)

The postoperative interval (ie, the time during which the prosthesis was in place) was not found to have an influence on the measured prosthetic diameters (Table 1). Although the mean enlargement of the graft in group 5, with a postoperative follow-up of 60 months, was greater (4.0 mm) than that in the other groups, the difference was not significant. Importantly, no linearity in prosthetic dilatation was observed during follow-up. Table 2 summarizes the amount of the dilatation of the grafts as a function of the preoperative diagnosis. The differences revealed by this comparison appear to be very small and again are not statistically significant. The prosthetic diameter in the 12 patients who had two or more CT scans obtained during follow-up remained stable during the entire postoperative period (Table 3).

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment References

The diagnostic methods used to assess prosthetic dilatation are of prime importance. Spiral, contrast-enhanced computed tomography appears to be the best method for reliably measuring the diameters of the thoracic aorta, whereas transthoracic and esophageal sonography allow only a limited assessment of the aorta. Conventional computed tomography suffices for studying the aorta in general but is not exact enough for the postoperative evaluation of prosthetic diameters, whereas spiral, contrast-enhanced computed tomography is able to assess the entire prosthesis, thereby enabling exact measurement of its diameter. Only in this way can the artifacts resulting from the prosthetic inclusion or other changes around the graft be distinguished from the true aortic diameter. Even considering the controlled conditions of the investigations used in our study, there could have been an error of approximately ±1 mm, corresponding to ±3.8%. The thickness of the aortic segment studied, pulsation artifacts, the measuring scales of the computed tomograph, and the inadvertent measurement of an oblique aortic section of vessels not actually coursing vertically are factors that could have caused errors in measurement.

The follow-up period during which the woven, collagen–sealed grafts were assessed, amounting to a maximum of 66 months, admittedly is relatively short, considering that the life expectancy of most patients with thoracic aortic replacement is greater than 10 years. Nunn and colleagues [7], who studied knitted aortic bifurcational prostheses, were able to show a remarkable dilatation after a mean follow-up of 175 months. The minimal initial dilatation of woven grafts, as compared with that of the knitted variety, demonstrated by Alimi and associates [11] and the lack of progressive dilatation during follow-up in our study support the hope that woven, collagen-coated, Dacron double-velour prostheses are a more reliably stable replacement material for the aorta.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Address reprint requests to Dr Franke, Klinik für Thorax-, Herz-, und Gefäßchirurgie, Medizinische Hochschule Hannover, D-30623 Hannover, Germany.

	References

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 

1. Nunn DB, Freeman MH, Hudgins PC. Postoperative alterations in size of Dacron aortic grafts: an ultrasonic evaluation. Ann Surg 1979;189:741–5.[Medline]
2. Kim GE, Imparato AM, Nathan I, et al. Dilatation of synthetic grafts and junctional aneurysms. Arch Surg 1979;114:1296–1303.[Medline]
3. Clagett GP, Salander JM, Eddleman WL, et al. Dilatation of knitted Dacron aortic prostheses and anastomotic false aneurysms: etiologic considerations. Surgery 1983;93:9–16.[Medline]
4. Tuchmann A, Wagner O. Anastomotic aneurysms as a late complication of reconstructive vascular surgery of the lower extremity. Langenbecks Arch Chir 1984;362:89–95.[Medline]
5. Lundquist B, Almgren B, Berwald S, et al. Deterioration and dilatation of Dacron prosthetic grafts. Acta Chir Scand 1985;29(suppl):81–5.
6. Van Den Akker PJ, Brand R, van Schilfgaarde R, et al. False aneurysms after prosthetic reconstructions for aorto-iliac obstructive disease. Ann Surg 1989;210:658–66.[Medline]
7. Nunn DB, Carter MM, Donohue MT, Hudgins PC. Postoperative dilatation of knitted Dacron aortic bifurcation graft. J Vasc Surg 1990;12:291–7.[Medline]
8. Blumenberg RM, Gelfand HG, Barton EA, et al. Clinical significance of aortic graft dilatation. J Vasc Surg 1991;14:175–80.[Medline]
9. Den Hoed PT, Veen HF. The late complications of aorto-ilio-femoral Dacron prostheses: dilatation and anastomotic aneurysm formation. Eur J Vasc Surg 1992;6:282–7.[Medline]
10. Tardito E, Biondo B, Caputo V, et al. Anastomotic dysjunction in long-term patent vascular synthetic grafts in Dacron. J Cardiovasc Surg (Torino) 1993;34:369–80.[Medline]
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12. Mikati A, Marache P, Watel A, et al. End-to-side aortoprosthetic anastomoses: long-term computed tomography assessment. Ann Vasc Surg 1990;4:584–91.[Medline]
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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Michael J. Jurmann Thorsten Wahlers Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Franke, U. Articles by Borst, H.-G. Search for Related Content PubMed PubMed Citation Articles by Franke, U. Articles by Borst, H.-G.