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Doppler-guided regulation of a telemetrically operated adjustable pulmonary banding system

Nicole Sekarski, MD^*,*, Pierre Fridez, PhD, Antonio F. Corno, MD, Ludwig K. von Segesser, MD and Erik J. Meijboom, MD, PhD, FACC^*

^* Division of Pediatric Cardiology
Department of Cardiovascular Surgery of the University Hospital of Canton Vaud (CHUV), Lausanne, Switzerland
Laboratory of Hemodynamics and Cardiovascular Technology, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland

View larger version (61K): [in a new window]   Figure 1 (A) General view of the FloWatch implant. The piston has a stroke of 3 mm for tightening or loosening of the banding. The silicone membrane is flexible and extensible, protecting the piston and the inside of the case from body fluids while allowing the piston to perform its adjustment movements. The measurements of the FloWatch when clipped are 26 x 18.4 x 17 mm (length x width x height). (B) View of the implant in its two extreme positions: the adjustable surface where the pulmonary artery is confined varies with the displacement of the piston. The 3-mm piston stroke causes a variation of the adjustable surface between 72 mm2 and 38 mm2 with great precision. (C) View of the external control unit and its external antenna, which should be placed on the patient's thorax just above the implant.

View larger version (11K): [in a new window]   Figure 2 FloWatch adjustable surface in function of the FloWatch regulation range. The adjustable surface was measured using as a basis numerical pictures of the FloWatch at different positions. Error bars indicate SD (n = 6).

View larger version (26K): [in a new window]   Figure 3 Example of systolic transbanding pressure gradient as a function of FloWatch regulation range as obtained in one minipig. At implantation (week 0) the FloWatch was adjusted to get the curve. Afterward, the degree of adjustment was set to 20% (= starting working point, in white). After one week, natural growth and cardiovascular adaptation lead to the second curve (= arrival working point, in black). After full-range regulation to get the curve, the degree of regulation was again set to 20% (= working point). Two weeks later, a slower cardiovascular adaptation leads to the third curve. Then the degree of adjustment was increased to 35% (= starting working point, in white). This augmented load induces an important cardiovascular adaptation, which leads to the curve at week 5 (solid line). At week 5, the degree of regulation was diminished to 20%, which induces no more cardiovascular adaptation for the following 7 weeks.

View larger version (21K): [in a new window]   Figure 4 Systolic transbanding pressure gradient in function of FloWatch regulation range for the minipig Doppler study. Only points with at least five measurements for the same adjustment range are represented in the graph. Error bars indicate SD (5 n 7). Solid lines are a mathematical fit based on a hemodynamic model of stenosis.

View larger version (15K): [in a new window]   Figure 5 Evolution of the systolic transbanding pressure gradient range of the minipig Doppler study. White squares = situation with the FloWatch fully open (degree of regulation set to 0%, corresponding to the left end of each curve in the example on Fig. 3); white circles = maximum values tolerated by the minipig (corresponding to the right end of each curve in the example on Fig. 3); black diamonds = working points (corresponding to the gray working points of each curve in the example on Fig. 3). Error bars indicate SD (6 n 7).

View larger version (96K): [in a new window]   Figure 6 (A) Explantation of the FloWatch in one minipig after 14 months: the core of the FloWatch and the thin pacemaker-like fibrotic capsule surrounding the FloWatch. (B) Pulmonary artery (PA) of the minipig after 14 months: inside view at the location of the FloWatch.

View larger version (12K): [in a new window]   Figure 7 Evolution of the systolic transbanding pressure gradient (A) of the FloWatch regulation range (B), and of the left ventricle posterior wall thickness (C) for Patient #5 (d-transposition of the great arteries).

View larger version (14K): [in a new window]   Figure 8 Evolution of the systolic transbanding pressure gradient (A) and of the FloWatch regulation range (B) for all the patients together with exception of Patient #5 (d-transposition of the great arteries). Time is given in logarithmic scale, day 1 being the day of surgery; logarithmic scale. Error bars indicate SD (n = 7, 7, 6, 6, 7, 7, 6, 4, from left to right, respectively).