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J Thorac Cardiovasc Surg 2003;125:742-743
© 2003 The American Association for Thoracic Surgery
Letters to the Editor |
Division of Cardiovascular Surgery, University of Freiburg, D-79106 Freiburg, Germany
Reply to the Editor:
We thank Boudjemline and Bonhoeffer for their valuable comments on our study.
1 As we know from our initial experimental work 1,2 started in 1996 using an infrarenal appproach, it is very difficult to position a valved stent directly into the aortic annulus without previously removing the native porcine leaflets. Native leaflets are very flexible and large enough to occlude their coronary ostia while the valved stent or a single stent is being deployed in pigs. As Andersen and colleagues 3 demonstrated in 1992, the implantation of a valved stent into the annular position is impossible in a porcine model because of the restriction of coronary blood flow. Therefore, in a series of 14 animals we evaluated the aortic valved stent in the descending aorta and in the subcoronary and supracoronary positions. 1 Eleven of them were successfully implanted (descending, n = 6; supracoronary, n = 3; subcoronary, n = 2) and demonstrated low transvalvular gradients with good angiographic and echocardiographic results.
Boudjemline and Bonhoeffer's approach is very appealing, as it accurately implants the valved stent transannular without occluding the coronary ostia by any of the new commissures of the valved stent or native ovine leaflets. In a series of 12 lambs, they successfully transluminally implanted an optimally functioning valved stent in 4 animals of the descending aorta group and in 1 animal of the orthotopic group via a carotid approach. 4 Whether such a method is also implementable in porcine aortic annuli due to its deployment strategy is still unknown, because different species may have different distances between their coronary arteries and leaflets. Furthermore, a 2-step deployment strategy 4 is more demanding from the infrarenal approach that we used 1,2 than from a carotid approach. 4 Changes in hemodynamic parameters and in the coronary blood flow after supracoronary valved stent implantation should be considered in future studies. This has not been carried out by previous studies either, unfortunately. 3,4 Because we performed only short-term studies, the long-term durability of this kind of aortic valved stent remains unclear. 1
Percutaneous implantation is one of several advancements toward ideal percutaneous aortic valve replacement, that is, in human beings with a calcified stenotic aortic valve. 1 The development of various techniques for implementing this replacement should also be considered. 1,2 Percutaneous aortic valve ablation techniques 2 for aortic stenosis, a stable scaffold enabling those intra-aortic procedures, filters avoiding systemic embolization, and circulatory support during percutaneous aortic valve ablation and implantation using femoro-femoral bypass and left ventricular venting should be developed.
Deployment lasted about 2 minutes in our short-term study. At any rate, a longer operating time (>3 minutes) in the ascending aorta is necessary for percutaneous aortic valve ablation and implantation, and one would expect resulting hemodynamic instability. More complex procedures on the native aortic valve using ablation techniques 2 should be performed with circulatory support. 1 Such approaches would open the door to new perfusion and microsurgical techniques. After aortic valve ablation, one has no bothersome calcified leaflets to deal with between the stent and coronary arteries, therefore reducing paravalvular leaks and valved stent migration.
References
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