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Ann Thorac Surg 2000;69:1989
© 2000 The Society of Thoracic Surgeons
a Department of Cardiothoracic Surgery, Shaare Zedek Medical Center, PO Box 3235, 91031 Jerusalem, Israel
e-mail: cts.szmc.org.il
To the Editor
We found interest in the article by Gross and associates comparing the Prima stentless xenograft (Baxter Health Care Corporation, Edwards CVS Division, Irvine CA) to homografts [1]. They found a higher mean resting gradient in the Prima valves (13 vs 6 mm Hg). The authors attribute this finding to stiffer cusps due to glutaraldehyde preservation, rigidity of the Dacron sewing ring, and inward folding of the Dacron cuff beneath the coronary ostia.
We wish to suggest another mechanism, the preservation of the noncoronary sinus. In common practice, the noncoronary sinus is preserved during implantation of valves such as the Prima, which are supplied as a full root, scalloping only the left and right sinuses. In contrast, when homografts are implanted using freehand technique, all three sinuses are scalloped. Assuming this difference in insertion technique was applied in Gross’s group (a point that was not clear in their description of the surgical technique), the nonresected prosthetic aortic wall may explain the higher gradients in the xenografts due to the added bulk in the aortic root. We compared hemodynamics at rest and during exercise of the Toronto Stentless Porcine Valve (TSPV; St Jude Medical, Minneapolis MN) and normal native aortic valves, and found a mean gradient of only 6 mm Hg across the Toronto valves. This resting mean gradient did not increase at exercise [2]. Others [3] have found lower mean gradients across the Toronto valve, irrespective of valve size. Like the Prima, the TSPV is a porcine valve, glutaraldehyde preserved, and reinforced with Dacron. Unlike the Prima, the TSPV is fully scalloped. This design difference may explain the difference in gradients.
Another question that is yet unanswered is whether preservation of the noncoronary sinus causes uneven distribution of forces on the valve, possibly compromising durability.
Finally, the advantage of stentless valves must be realized in improved patient survival. It seems obvious that lower gradients are better, but where is the cutoff? David and associates have shown in a retrospective study that stentless xenografts afford better survival than stented bioprostheses, probably due to better preservation of the left ventricle [4]. Whether this is dependant on gradient, or at what gradient this advantage is lost, is still unclear. Although it is still early to tell, stentless xenografts may indeed be a favorable substitute for homografts.
References
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