Mazilu Dumitru, Li Ming, Kocaturk Ozgur, Horvath Keith A
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J Med Device. 2012 Dec;6(4):410061-410069. doi: 10.1115/1.4007750. Epub 2012 Nov 1.
Currently, aortic valve replacement procedures require a sternotomy and use of cardiopulmonary bypass (CPB) to arrest the heart and provide a bloodless field in which to operate. A less invasive alternative to open heart surgery is transapical or transcatheter aortic valve replacement (TAVR), already emerging as a feasible treatment for patients with high surgical risk. The bioprosthetic valves are delivered via catheters using transarterial or transapical approaches and are implanted within diseased aortic valves. This paper reports the development of a new self-expanding stent for minimally invasive aortic valve replacement and its delivery device for the transapical approach under real-time magnetic resonance imaging (MRI) guidance. Made of nitinol, the new stent is designed to implant and embed a commercially available bioprosthetic aortic valve in aortic root. An MRI passive marker was affixed onto the stent and an MRI active marker to the delivery device. These capabilities were tested in ex vivo and in vivo experiments. Radial resistive force, chronic outward force, and the integrity of bioprosthesis on stent were measured through custom design dedicated test equipment. In vivo experimental evaluation was done using a porcine large animal model. Both ex vivo and in vivo experiment results indicate that the self-expanding stent provides adequate reinforcement of the bioprosthetic aortic valve and it is easier to implant the valve in the correct position. The orientation and positioning of the implanted valve is more precise and predictable with the help of the passive marker on stent and the active marker on delivery device. The new self-expanding nitinol stent was designed to exert a constant radial force and, therefore, a better fixation of the prosthesis in the aorta, which would result in better preservation of long-term heart function. The passive marker affixed on the stent and active marker embedded in the delivery devices helps to achieve precise orientation and positioning of the stent under MRI guidance. The design allows the stent to be retracted in the delivery device with a snaring catheter if necessary. Histopathology reports reveal that the stent is biocompatible and fully functional. All the stented bioprosthesis appeared to be properly seated in the aortic root.
目前，主动脉瓣置换手术需要进行胸骨切开术并使用体外循环（CPB）来使心脏停搏，以提供一个无血的手术视野。心脏直视手术的一种侵入性较小的替代方法是经心尖或经导管主动脉瓣置换术（TAVR），它已成为高手术风险患者的一种可行治疗方法。生物人工瓣膜通过导管采用经动脉或经心尖途径输送，并植入病变的主动脉瓣内。本文报道了一种用于微创主动脉瓣置换的新型自膨胀支架及其在实时磁共振成像（MRI）引导下经心尖途径的输送装置的研发情况。这种新型支架由镍钛诺制成，旨在将市售的生物人工主动脉瓣植入并嵌入主动脉根部。一个MRI无源标记物附着在支架上，一个MRI有源标记物附着在输送装置上。这些功能在体外和体内实验中进行了测试。通过定制设计的专用测试设备测量了径向阻力、慢性向外力以及支架上生物假体的完整性。体内实验评估使用了猪大型动物模型。体外和体内实验结果均表明，自膨胀支架为生物人工主动脉瓣提供了足够的加固，并且更容易将瓣膜植入正确位置。借助支架上的无源标记物和输送装置上的有源标记物，植入瓣膜的方向和定位更加精确且可预测。新型自膨胀镍钛诺支架设计用于施加恒定的径向力，因此能更好地将假体固定在主动脉中，这将有助于更好地保留长期心脏功能。附着在支架上的无源标记物和嵌入输送装置中的有源标记物有助于在MRI引导下实现支架的精确方向和定位。该设计允许在必要时使用圈套导管将支架缩回到输送装置中。组织病理学报告显示该支架具有生物相容性且功能完全正常。所有带支架的生物假体似乎都正确地安置在主动脉根部。
