title: Midterm results of transapical aortic valve replacement via real-time magnetic resonance imaging guidance.
abstract: OBJECTIVE
  Percutaneous valve replacements are presently being evaluated in clinical trials. As delivery of the valve is catheter based, the safety and efficacy of these procedures may be influenced by the imaging used. To assist the surgeon and improve the success of the operation, we have performed transapical aortic valve replacements using real-time magnetic resonance imaging guidance.
  
  
  METHODS
  Twenty-eight swine underwent aortic valve replacement by real-time magnetic resonance imaging on the beating heart. Stentless bioprostheses mounted on balloon-expandable stents were used. Magnetic resonance imaging (1.5 T) was used to identify the critical anatomic landmarks. In addition to anatomic confirmation of adequate placement of the prosthesis, functional assessment of the valve and left ventricle and perfusion were also obtained with magnetic resonance imaging. A series of short-term feasibility experiments were conducted (n = 18) in which the animals were humanely killed after valve placement and assessment by magnetic resonance imaging. Ten additional animals were allowed to survive and had follow-up magnetic resonance imaging scans and confirmatory echocardiography at 1, 3, and 6 months postoperatively.
  
  
  RESULTS
  Real-time magnetic resonance imaging provided superior visualization of the landmarks needed. The time to implantation after apical access was 74 +/- 18 seconds. Perfusion scanning demonstrated adequate coronary flow and functional imaging documented preservation of ventricular contractility in all animals after successful deployment. Phase contrast imaging revealed minimal intravalvular or paravalvular leaks. Longer term results demonstrated stability of the implants with preservation of myocardial perfusion and function over time.
  
  
  CONCLUSIONS
  Real-time magnetic resonance imaging provides excellent visualization for intraoperative guidance of aortic valve replacement on the beating heart. Additionally, it allows assessment of tissue perfusion and organ function that is not obtainable by conventional imaging alone.
authors.affiliation: National Heart, Lung, and Blood Institute, National Institutes of Health: the Cardiothoracic Surgery Research Program, Bethesda, MD 20892, USA. khorvath@nih.gov
authors.forename: Keith A
authors.initials: KA
authors.lastname: Horvath
authors.forename: Dumitru
authors.initials: D
authors.lastname: Mazilu
authors.forename: Michael
authors.initials: M
authors.lastname: Guttman
authors.forename: Arthur
authors.initials: A
authors.lastname: Zetts
authors.forename: Timothy
authors.initials: T
authors.lastname: Hunt
authors.forename: Ming
authors.initials: M
authors.lastname: Li
mesh_terms: D000818:Animals; D001021:Aortic Valve / Q000601:surgery*; D001705:Bioprosthesis; D002404:Catheterization; D006350:Heart Valve Prosthesis; D019918:Heart Valve Prosthesis Implantation / Q000379:methods*; D008279:Magnetic Resonance Imaging; D019028:Magnetic Resonance Imaging, Cine; D025321:Surgery, Computer-Assisted / Q000379:methods*; D013552:Swine; D016896:Treatment Outcome