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Atria assist device to restore transport function of fibrillating atrium

^a Cardiovascular Surgery Department, CHUV, Lausanne, Switzerland
^b Department of Internal Medicine, Friburg Hospital, Friburg, Switzerland
^c Center for Technology Transfer, University of Yverdon-les-Bains, Switzerland

Received 6 September 2007; received in revised form 16 September 2007; accepted 18 September 2007.

^_* Corresponding author. Address: Service de Chirurgie Cardiovasculaire, Centre Hospitalier Universitaire Vaudois, Rue du Bugnon 46, 1011 Lausanne, CH, Switzerland. Tel.: +41 21 3142280; fax: +41 21 3142278. (Email: Piergiorgio.Tozzi{at}chuv.ch).

Objective: The Maze procedure can restore sinus rhythm in patients suffering from chronic atrial fibrillation but often fails to restore the mechanical function of the atrium, the so-called atrial kick and requires long-term anticoagulation most of the time. A micro motorless pump (Atripump) based on artificial muscle technology positioned on the external surface of the atrium could compress the heart chamber, restoring atrium transport function. A bench model reproducing the mechanical function of human atrium and human environment has been developed to assess the circulatory support that such a pump can provide. Methods: Atripump (Nanopowers SA, Switzerland) is a dome-shape, silicone-coated nitinol actuator to be sutured on the external surface of the atrium. A pacemaker-like control unit drives the actuator and manages the external compression of the atrium. The bench model consists of an open circuit made of rubber bladder, 60 cc in volume, connected to a vertically positioned and scaled tube that is filled at different levels reproducing changes in cardiac pre-load and after-load. The pump was placed on the outer surface of the bladder and both were immersed in water having a constant temperature of 37 °C. Pressure, volume and temperature at the interface dome–bladder were recorded. Results: Pump ran 24 h for three consecutive months. During the experiment, no technical failure occurred and the pressure and volume values were repeatable during the experience. Nitinol fatigue was assessed measuring the wire's electric resistance that remained 400 ± 10 /m. Contraction rate was 1 Hz with power supply of 12 V, 400 m and heating time of 300 ms. Pre-load ranged from 11 to 15 mmHg. When inserted in the bath at 37 ± 0.5 °C, maximal temperature between silicone membrane and rubber bladder was 39 °C. Maximal volume pumped was 492 ml/min. Conclusions: This artificial muscle pump can reproduce the mechanical effect of a normal human atrium. It is compact, reliable and follows the Starling law. The surface temperature is in the physiologic range and it could represent a new tool to restore the atrial kick in persistent atrial fibrillation.

Key Words: Artificial muscle • Cardiac assist device • Atrial fibrillation