M. F. Purser, G. Buckner, D. Cormier, North Carolina State University, Raleigh, NC; R. Cook, University of British Columbia, Vancouver, BC, Canada
A prototype annuloplasty band with a shape memory alloy stiffener has been developed to facilitate minimally invasive mitral valve reconstruction. In its activated (austenitic) phase, this prototype band provides the same mechanical properties as commercial semi-rigid bands. In its pre-activated (martensitic) phase, this band is flexible enough to be introduced through an 8 mm trocar and easily manipulated within the heart. The stiffener is constructed of 0.508 mm diameter NiTi wire, and is shape set in a furnace during fabrication to the appropriate size and optimal geometry. During deployment, the band is cooled below its Ms temperature (24 deg C) in a saline bath prior to surgery, making it compliant and easy to manipulate. After suturing, the stiffener is heated above its Af temperature (41 deg C, slightly above normal body temperature) using an electrical activation device which has been developed to allow in vivo activation of the band by the surgeon. This enables the NiTi to assume its optimal geometry and stiffness characteristics indefinitely. Extensive material testing and hemodynamic evaluations on explanted pig hearts confirm that the prototype band has characteristics equivalent to commercially available semi-rigid bands.
Summary: A prototype annuloplasty band with a shape memory alloy stiffener has been developed to facilitate minimally invasive mitral valve reconstruction. In its pre-activated (martensitic) phase, this band is flexible enough to be introduced through an 8 mm trocar and easily manipulated within the heart. An electrical activation device which has been developed will allow in vivo activation of the band by the surgeon. This enables the band to assume its optimal geometry and stiffness characteristics indefinitely.
