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Evaluation of a Novel Cryoablation System: In vitro Testing of Heat Capacity and Freezing Temperatures

Weimar, Timo MD; Lee, Anson M. MD; Ray, Shuddhadeb MD; Schuessler, Richard B. PhD; Damiano, Ralph J. Jr MD

Innovations: Technology & Techniques in Cardiothoracic & Vascular Surgery: November/December 2012 - Volume 7 - Issue 6 - p 403–409
doi: 10.1097/IMI.0b013e3182853e74
Original Articles

Objective: Cryoablation has been used to ablate cardiac tissue for decades and has been shown to be able to replace incisions in the surgical treatment of atrial fibrillation. This in vitro study evaluates the performance of a novel cryoprobe and compares it with existing commercially available devices.

Methods: A new malleable 10-cm aluminum cryoprobe was compared with a rigid 3.5-cm copper linear probe using in vitro testing to evaluate performances under different thermal loads and with different tissue thicknesses. Radial dimensions of ice formation were measured in each water bath by a high-precision laser 2 minutes after the onset of cooling. Probe-surface temperatures were recorded by thermocouples. Tissue temperature was measured at depths of 4 mm and 5 mm from the probe-tissue interface. Time to reach a tissue temperature of −20°C was recorded.

Results: Ice formation increased significantly with lower water-bath temperatures (P < 0.001). Width and depth of ice formation were significantly less for the rigid linear probe (P < 0.012 and P < 0.001, respectively). There was no difference between the probes in the maximal negative temperature reached under different thermal loads or at different tissue depths. The malleable probe achieved significantly lower temperatures at the proximal compared with the distal end (−61.7°C vs −55.0°C, respectively; P < 0.001). A tissue temperature of −20°C was reached earlier at 4 mm than at 5 mm (P < 0.001) and was achieved significantly faster with the 3011 Maze Linear probe (P < 0.021).

Conclusions: The new malleable probe achieved rapid freezing to clinically relevant levels in up to 5-mm–thick tissue. Both probes maintained their performance under a wide range of thermal loads.

From the Division of Cardiothoracic Surgery, Department of Surgery, Washington University School of Medicine, Barnes-Jewish Hospital, St Louis, MO USA.

Accepted for publication December 8, 2012.

Supported, in part, by the National Heart, Lung and Blood Institute at the National Institutes of Health (grants RO1 HL032257, RO1 HL085113, and T32 HL07776).

Disclosures: Richard B. Schuessler, MD, receives research support from AtriCure, Inc, Cincinnati, OH USA. Ralph J. Damiano, MD, is a consultant for AtriCure, Inc, Cincinnati, OH USA, and Medtronic, Inc, Minneapolis, MN USA, and has received research grants from AtriCure, Inc. Timo Weimar, MD; Anson M. Lee, MD; and Shuddhadeb Ray, MD declare no conflict of interest.

Address correspondence and reprint requests to Ralph J. Damiano, Jr, MD, Division of Cardiothoracic Surgery, Washington University School of Medicine, Barnes-Jewish Hospital, Suite 3108 Queeny Tower, 1 Barnes-Jewish Hospital Plaza, St Louis, MO 63110 USA. E-mail: damianor@wustl.edu.

Copyright © 2012 by the International Society for Minimally Invasive Cardiothoracic Surgery. Unauthorized reproduction of this article is prohibited.