Interact CardioVasc Thorac Surg 2007;6:603-607. doi:10.1510/icvts.2007.154567
© 2007 European Association of Cardio-Thoracic Surgery
Work in progress report - Experimental |
Mitral valve implantation using off-pump closed beating intracardiac surgery: a feasibility study
Gerard M. Guiraudona,b,h,*,
Douglas L. Jonesa,c,d,
Daniel Bainbridgee and
Terry M. Petersf,g,h
a Canadian Surgical Technologies and Advanced Robotics (CSTAR), Lawson Health Research Institute, CSTAR Legacy Building, LHSC-UC, 339 Windermere Road, London, Ontario, N6A 5A5, Canada
b Department of Surgery, London, Ontario, N6A 5A5, Canada
c Department of Physiology and Pharmacology, London, Ontario, N6A 5A5, Canada
d Department of Medicine, London, Ontario, N6A 5A5, Canada
e Department of Anesthesiology, London, Ontario, N6A 5A5, Canada
f Department of Medical Biophysics, The University of Western Ontario, London, Ontario, N6A 5A5, Canada
g Department of Radiology and Nuclear Physics, The University of Western Ontario, London, Ontario, N6A 5A5, Canada
h Imaging Research Laboratories, Robarts Research Institute, London, Ontario, N6A 5A5, Canada
Received 22 February 2007;
received in revised form 23 May 2007;
accepted 24 May 2007
 Supported in part by the Canadian Institutes for Health Research, Canadian Foundation for Innovation and the Ontario Research Development Challenge Fund, and a grant from the Department of Surgery at UWO. No conflict of interest with industry.
*Corresponding author. Tel.: +1 519-685-8500 (ext 32645)/+1 519-643-8610; fax: +1 519-663-2930.
E-mail address: gguiraud{at}uwo.ca (G.M. Guiraudon).
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Abstract
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We have developed the Universal Cardiac Introducer® (UCI) with the aim of modernizing the off-pump, closed, beating, intracardiac approach. This paper reports our ongoing experience with positioning of a prosthetic MV, under image-guidance, substituting for direct vision. The UCI is comprised of two detachable parts: an attachment-cuff and an airlock-introductory chamber for bulky tools. A prosthetic MV was introduced into the left atrium in 12 pigs via the UCI (LA appendage). Transesophageal and 4D epicardial ultrasound were used for guidance. Limitations of ultrasound imaging prompted the development of a multimodality virtual reality (VR) system introduced in the last three animals. There were no complications associated with cardiac access, while achieving proper valve positioning. TEE contributed to navigating, while 4D epicardial ultrasound was adequate for positioning the prosthesis into the MV orifice. VR provided a 3D context for real-time US imaging with precise navigation and positioning using augmented reality representation of the valve. We demonstrated the feasibility of positioning MV prostheses via the UCI. These results suggest the tremendous potential of virtual reality in making access safe and effective for many intracardiac targets, with the ultimate goal of a safe, versatile, clinical application.
Key Words: Experimental surgery; Mitral valve surgery; Off-pump surgery; Image-guidance; Virtual reality guidance; New technologies
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1. Introduction
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Current cardiac surgery uses either open-heart techniques, which are associated with significant morbidity and mortality [1], or a closed, beating heart, epicardial approach, with or without cardio-pulmonary bypass [2].
Since 2003, our group has revived and modernized off-pump, closed, beating, intracardiac surgery [3] using a new device for access and image guidance for substitution for direct vision [4–7]. This approach could be an alternative to open heart surgery and catheter-based intracardiac interventions [8–10].
1.1. The Universal Cardiac Introducer
Our goal was to develop a device providing safe intracardiac access. The Universal Cardiac Introducer® (UCI) [11, 12] was developed for access to any cardiac chamber. The UCI is composed of two components: an attachment-cuff (cuff), and an introductory-airlock chamber with 1–4 sleeves for introduction of tools and devices.
The cuff controls the port access, and has a secure attachment to the heart chamber. It is made of a soft, collapsible material that is easily and quickly occluded by a vascular clamp. The cuff has a safe connection with the introductory-airlock chamber.
The introductory-airlock chamber is impervious to prevent bleeding and air embolism. The sleeves fit snugly to the holders or handles to avoid blood leakage and air suction. The airlock chamber acts as a bubble trap, with its upper sleeves well above the heart port access, allowing venting of air before opening the UCI to the cardiac chamber. The design also allows for the introduction tools or devices in a retrograde fashion, to accommodate larger tools or devices through the heart port access, while having the handles as narrow as possible. The connecting system between the cuff and the airlock chamber should be tight, resilient, and easy to release (Fig. 1).
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Fig. 1. Sequential synoptical views of the Universal Cardiac Introducer® (UCI), its attachment and left atrial access for mitral valve (MV) prosthesis introduction. (a) A schematic representation of the UCI. The mitral valve with its holder is within the introductory chamber inserted through one of the sleeves. One sleeve will admit the clip applier and the other the left atrial pressure line. (b) A diagram of the thoracic cavity during positioning of the UCI and its contents as well as the TEE probe in the esophagus. LV: left ventricle. (c) Photograph of the attachment-cuff which has been sewn over the cardiac port access opening in the left atrial appendage that has been occluded with the Satinski clamp. (d) Photograph of the UCI with the valve holder and the tracking system. The sensor is buried at the tip of the holder and taped in place. (e) Photograph of the UCI with the MV prosthesis inside before being attached to the cuff. (f) Photograph of the airlock-introductory chamber being connected to the cuff. (g) Photograph of the UCI after completion of the attachment with the MV holder and additional sleeves occluded with snares. The prosthetic MV and its holder are inside the left atrium and being navigated towards the native MV orifice. (h) Photograph of post mortem examination showing the prosthetic MV snugly inside the native MV orifice. Two attachment clips are in place.
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The lack of direct vision of the intracardiac target was substituted with ultrasound (US) imaging alone [12]. Later, tracked US imaging was integrated with tracked instruments in a virtual reality (VR) environment (Atamai Viewer).
Implantation of an unmodified mitral valve (MV) prosthesis was selected to document that the UCI can accommodate bulky devices. The study focused on the introduction and positioning (implantation) of the prosthetic MV, to test the introducer and image-guidance system.
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2. Methods
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2.1. Animal experiments
2.1.1. Surgical protocol
The protocol was approved by the Animal Care and Use Committee of the University of Western Ontario and followed the Guidelines of the Canadian Council on Animal Care. A total of twelve pigs were used.
2.1.2. Surgical preparation
Animals were tranquilized with Telazol and Rompun before transportation to the laboratory. After intubation, they were ventilated mechanically and anesthesia was maintained with nitrous oxide and Isoflurane. Surface EKG, arterial pressure, end tidal carbon dioxide and pulse oximetry were monitored continuously throughout the procedure. The heart was exposed via a left anterior thoracotomy. The pericardium was opened and the left atrial appendage was exposed.
2.1.3. The Universal Cardiac Introducer®
The UCIs were custom-made with vascular graft material. A UCI with four sleeves was selected and preclotted. The left atrial appendage was excluded using a large Satinski vascular clamp. The LAA was opened with a straight incision. Trabeculations were divided when necessary for unobstructed access. The cuff was attached to the appendage using 4/0 Prolene running suture.
Then, the MV prosthesis and its holder were introduced in a retrograde fashion into the airlock chamber. The connecting orifice of the airlock chamber was connected to the cuff using 4/0 Prolene running suture. The pressure line was introduced into the airlock chamber and used for instilling saline to assist with de-airing; thereafter the line was connected to a transducer for monitoring left atrial pressure. The two other sleeves were occluded with small tourniquets and used later for introduction of the anchoring system, if needed. The animal was fully heparinized, and the UCI was opened into the left atrium by releasing the clamp occluding the cuff. De-airing was completed by evacuating the air bubbles by puncturing the UCI roof. The UCI was now ready for assisting in introducing the prosthesis into the left atrium, and positioning into the MV orifice.
The MV prosthesis used was a porcine heart valve (Mosaic, Medtronic Inc, Minneapolis, MN). The prostheses were used more than once, with the risk of becoming stenotic. We used a custom made valve holder, which was non-stenotic and self-releasing (Fig. 1).
2.1.4. Image guidance
Initially, ultrasound (US) was the sole image guidance. US imaging was used for the pre-implantation measurement of the native MV annulus diameter (Table 1). A transesophageal echocardiography (TEE, Paediatric omniplane, Philips Medical) was used to navigate the prosthesis into the left ventricular MV in-flow tract. Then an X4 3D probe (Philips Medical), applied directly onto the UCI, was used for positioning the prosthesis within the MV annulus and to address the following questions: (1) Was the valve axis parallel to left ventricle? (2) Was the insertion cuff in contact with the MV ring without perivalvular flow? (3) Was the prosthetic valve functioning well?
Virtual reality was developed and tested on a cardiac phantom in the imaging laboratory [13, 14] (Fig. 2).
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Fig. 2. Photograph of the computer screen during Virtual Reality using the phantom. The image is taken from the Atamai® viewer that can integrate different image modalities and augmented reality. The screen shows the CT scan of the phantom, with the chamber wall, the partition, and the Cryogel membrane with a hole simulating the mitral valve. The structures are displayed in various shades of gray or color for easy interpretation. The 2D probe that was used for the phantom study is represented with its field of view. The cuff of the valve with its holder is displayed. The pointer that was used to track the phantom 3D position is also displayed in its 3D position.
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3. Results
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Twelve pigs had MV prostheses positioned into their native MV orifices without complications. In seven animals, the valve was positioned only; in the remaining five, positioning of a clip applier was attempted. The implantation was discontinued in one pig because the prosthesis had become too stenotic after multiple uses.
The Universal Cardiac Introducer® could be easily attached to the LAA in approximately 30 min. It proved safe and effective for introducing MV prosthesis into the left atrium, without complications. De-airing was made easy by filling in the air-lock chamber with saline, venting the air via one sleeve, and then opening the cuff that is at the bottom of the UCI, the final de-airing was done by inserting small needles through the roof of the UCI. The pre-clotted material proved tightly hemostatic and the sutures tight. There was little blood loss via the UCI. The flexibility and pliability of the UCI made manipulation easy without mechanical stress on the heart attachment. No tears were observed. The UCI is designed for easy changing of tools. In two cases, the MV prosthesis was replaced without complication. After occluding the cuff, a partial and temporary separation of the cuff from the introduction chamber, allowed removing and replacing the prosthesis, before closing the UCI as described.
The introduction of the prosthesis across the LAA ostium was performed with great care but without complication (valve sizes up to 31 mm were introduced). When too large, the prostheses were changed. The valve size calculated by TEE was used to select a prosthesis fitting snugly into the MV annulus. Prosthesis/orifice mismatch did not preclude testing the positioning of the prosthesis using image-guidance.
3.1. Image-guidance
The 2D TEE field of view displayed only a cross sectional view. However, without the 3D global anatomical context, the orientation of the valve holder, or the direction to move the valve into MV orifice could not be determined. ‘Trial and error’ method was used to place the prosthesis into the MV orifice. However, when the prosthesis was within the MV inflow track, it could be visualized by the 4D epicardial US transducer for fine positioning. The prosthesis was positioned inside the native valve, without negative effects, in a fashion accepted in clinical practice. Manipulation of the clip-applier was not intuitive, particularly as the orientation of the tip and the clips could not be visualized using US. As the unmodified tools were quite bulky, they often collided with each other, making positioning very difficult or impossible except in one case (Fig. 1).
Virtual augmented reality was introduced in the last three pigs. The VR system impacted the procedure: the magnetic field generator for the 3D tracking system needed to be placed close to the chest incision but otherwise was not obstructive. In general, equipping the various tools with tracking sensors required significant modifications of the tools, making them bulkier, and thus limiting their movement. These last experiments stressed the need for re-designing the tools to adapt to the new environment, before going further. In the test phantom, without access limitations, VR guidance allowed precise positioning of both the prosthetic device and attachment clips with an accuracy of 0.99±0.29 mm (Fig. 3).
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Fig. 3. Photograph of the results of clipping the valve on the phantom Cryogel membrane using only Virtual Reality for positioning. The most striking feature, besides the accurately positioned mitral valve and clips on the cuff, is the good radial orientation of the clips.
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4. Discussion
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Comments will focus on the limitations and future developments of this multidisciplinary project, that is more challenging and exciting than anticipated, and may require revisiting not only access and visualization but also the surgical techniques, as experience suggests.
The Universal Cardiac Introducer® implantation using graft material does not require special techniques. The UCI has been used in 47 animals, in addition to this series: for LV assist device implant, creation and closure of ASD, and surgery for atrial fibrillation, using this closed, off-pump, beating, intracardiac surgery. Closure of the UCI for chronic study is easy, using the cuff for pledgetted suture and then ligation of the LAA. The UCI was used in a chronic study for atrial fibrillation in 17 long-term animals, clinical follow up and autopsy did not document complications associated with the UCI closure or air-embolism. The UCI proved safe, versatile and effective. An approved medical grade UCI is needed to conduct a safety and effectiveness trial. Recently, we have successfully modified the cuff of the UCI for implantation over the right atrial interatrial sulcus for more conventional and user-friendly access to the left atrium. This right-sided access requires opening the left atrium under the protection of the UCI, as was done for the left ventricle. It also avoids the narrowing of the LAA neck.
4.1. Image guidance
US imaging has significant limitations for navigating, because of its only 2D display or restricted 3D view. However, US imaging has two critical advantages: (1) it is readily available in every cardiac operating room, without interfering with the procedure, and (2) it provides tracked real-time dynamic imaging that is the indispensable ‘reference’ for integrating preoperative and intraoperative other 3D modalities for virtual stereoscopic vision augmented by virtual representation of tracked tools. The combination of VR and augmented reality (AR) provided 4D visualization for navigation and the positioning of tools and devices, and made important details visible (e.g. size, orientation, position of the effective tip, etc.), which are not visible using 2D or 3D US alone. The virtual vision platform is making intracardiac access via the UCI independent of direct vision but with excellent visualization, with the additional possibility of testing while doing. The three last pigs were only used to identify the problems associated with the operative setting. Very important progress is being made. We can now envision a VR platform that will display more information than direct vision.
Mitral valve surgery was used as a major test for the UCI in introducing bulky devices. This experiment also suggested that the design of current tools is inadequate. This observation is consistent with the finding that design of tools depends on access and visualization and can only be correctly designed after the latter have been established. When adequate tools are available with support of robotics [15], we are confident that most current interventions would be duplicated and translated to clinical use.
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Abstract
1. Introduction
