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J Thorac Cardiovasc Surg 2001;121:859-870
© 2001 The American Association for Thoracic Surgery
Evolving Technology |
From the University of California, San Francisco, Calif, the Medical College of Virginia, Richmond, Va, and the Armed Forces Institute of Pathology, Washington, DC.
Received for publication May 4, 2000. Revisions requested Aug 15, 2000; revisions received Nov 3, 2000. Accepted for publication Nov 9, 2000. Address for reprints: Arthur C. Hill, MD, Department of Surgery, University of California at San Francisco, San Francisco General Hospital, 1001 Potrero Ave, Box 0807, San Francisco, CA 94143-0807.
| Abstract |
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| Introduction |
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A new device, the nitinol U-Clip device (Coalescent Surgical, Inc, Sunnyvale, Calif), has been designed to facilitate coronary anastomosis by reducing the complexity and difficulty of the anastomotic process. The device consists of a self-closing nitinol wire releasably attached to a flexible member and needle(Fig 1). The nitinol wire, once detached from the flexible member, functions to approximate and hold tissue together similar to interrupted suture. The superelastic property of the nitinol wire is used to allow precise delivery and positioning of the device and produce strong and atraumatic tissue approximation. Conventional sutured anastomosis, for optimal performance, requires an assistant for suture management (suture tensioning and positioning) and requires knot tying. The nitinol U-Clip device facilitates microvascular anastomosis by eliminating suture management and knot tying; it is especially useful for endoscopic and robotic methods of CABG.
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| Materials and methods |
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Experimental protocol
The study was divided into 2 experimental subprotocols: (1) anastomosis of the right internal thoracic artery (RITA) graft to a coronary artery on the beating heart (OPCAB) with the use of the nitinol U-Clip anastomosis device and (2) carotid arteriotomy closure comparing the nitinol U-Clip repair to polypropylene suture repair.
Animals
The experiments were performed after approval of the local ethics committee and in accordance with the "Guide for the Care and Use of Laboratory Animals," as revised by the National Institutes of Health in 1985.
5 Thirteen consecutive Holstein calves (age 2 to 4 months; weight 63-118 kg) were used. All animals received 650 mg of aspirin daily from 3 days before the operation until they were put to death. Postoperative care was delivered in an intensive care unit, and all animals were housed in a barn or pasture until being put to death.
Coronary anastomosis
The calves underwent general anesthesia and were placed in the right lateral decubitus position. After sterile preparation, a left lateral thoracotomy incision was made in the fifth intercostal space. The RITA was mobilized throughout its intrathoracic length. Intravenous heparin (10,000 U) was administered. RITA flow was measured by means of a Doppler ultrasound 3-mm flow probe (Transonics Systems, Inc, Ithaca, NY) before and after anastomosis. RITA internal diameter, wall thickness, and pedicle length were measured with calipers. A target vessel was selected (left anterior descending, obtuse marginal, or diagonal branch, depending on anatomic presentation and artery size), and its internal diameter was measured. Motion reduction at the anastomotic site was accomplished by means of a stabilizer. Preischemic conditioning was used before coronary artery occlusion. The coronary artery was occluded with flexible tapes (Retract-O-Tape; Quest Medical, Inc, Allen, Tex) during the anastomosis. The anastomoses were performed with nitinol U-Clip devices. All anastomoses were accomplished with a uniform technique intended to optimize precision of clip placement, allow maximal intraluminal visualization, and avoid anastomotic narrowing. Clips were placed by grasping the attached curved suture needle with standard needle drivers and sequentially piercing each vessel wall at the desired location in identical fashion as conventional suture. Once the tissue was approximated, the needle and flexible member were pulled through the vessel walls until the vessel walls were seated within the open clip in the desired apposition. Once accurately placed, a needle holder was used to compress a 1-mm long segment of the device at the junction of the flexible member and the nitinol clip (the release mechanism), thereby producing simultaneous detachment of the needle/flexible member from the clip and automatic closure of the clip from a U-shaped configuration to a closed loop configuration. On completion of all anastomoses, the grafted coronary artery was occluded just proximal to the anastomosis with a ligature.
Carotid arteriotomy repair
The left carotid artery was exposed through an incision along the anterior aspect of the sternocleidomastoid muscle. Two carotid arteriotomies, 2.5 cm each, were placed and separated from each other by 3 cm of normal arterial tissue. The carotid artery was occluded during arteriotomy and repair. One carotid arteriotomy was repaired with interrupted nitinol U-Clip devices and the other with continuous 6-0 polypropylene suture.
Angiographic analysis
All coronary anastomoses were studied by angiography immediately after the operation. Subsequent coronary angiographic studies were performed at the following intervals: 7 days (n = 3), 8 weeks (n = 8), and 26 weeks (n = 2). Coronary angiographic patency was quantified on the basis of the FitzGibbon criteria
6 for anastomotic patency. At the same intervals used for performing the coronary angiograms, left carotid angiography was also performed on all animals to assess the left carotid arteriotomy repair sites. An experienced radiologist independently evaluated all angiograms at the completion of the study.
Histologic analysis
The calves were put to death after the angiographic studies at the following intervals: 7 days (n = 3), 8 weeks (n = 8), and 26 weeks (n = 2). At sacrifice, the tissue was examined and the heart and carotid arteries were removed. These samples were perfusion-fixed at 100 mm Hg pressure with 10% buffered formalin and transferred to the Armed Forces Institute of Pathology Laboratory in Washington, DC, for preparation and analysis. Samples were split between scanning electron microscopy and light microscopy. Light microscopic samples were injected with barium gelatin before section and histologic examination. Macroscopic photographs were taken of samples designated for scanning electron microscopic analysis. Quantitative measures of tissue healing and inflammation (neointimal thickness, intimal proliferation as percent of intimal thickness, and inflammation rating) were used as isolated observations in the coronary anastomoses and for comparison of polypropylene sutured repair versus nitinol U-Clip repair in the carotid arteriotomy repair model.
| Results |
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Pathologic findings on the carotid repairs showed similar surface irregularities between clips and sutures with full endothelialization of the endothelial surfaces. No differences could be seen on scanning electron or light microscopy between suture or clip arteriotomy closure(Figs 6, A, 6, B, and 7).
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| Discussion |
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Overall angiographic patency results before sacrifice using the scale developed by FitzGibbon (grades A, B, and O) compared very favorably with results documented in the literature, including CABG and OPCAB/MIDCAB clinical studies that have included postoperative angiography published by Tyras,
7 Berger,
8 Calafiore,
9 Gill,
10 Mack,
11 and their associates.
In animal 9185, the angiographic interpretation of the coronary anastomosis was 50% stenosis after 7 days; the histologic interpretation of the same anastomosis was no stenosis at 7 days. This discrepancy may have resulted from right internal thoracic arterycoronary flow characteristics or to limited viewing angles obtained in the use of the fluoroscopic device in the laboratory.
The principal objective of this study was to provide data to the US Food and Drug Administration regarding the relative safety of the nitinol U-Clip device before an investigational device exemption (IDE) application for clinical study; consequently, it was not specifically designed to study the difference between interrupted and continuous suture technique. However, one of the most important potential benefits of a clip that could be used to accomplish precise coronary microanastomosis is the enabling of rapid interrupted suture technique.
The question of continuous versus interrupted suture technique as applied to coronary anastomoses has received little objective study and has recently been eclipsed by the debate over the relative merits of stopped versus beating-heart methods. The relative paucity of comparative studies showing a clear advantage of an interrupted technique coupled with the historic advantages of continuous technique in terms of speed and ease of use have served to advance what is possibly an inferior practice. Problems with continuous suture technique include reduction in expansion ability in growing vessels, reduced flexibility, anastomotic narrowing, and irregularity. This technology can eliminate the disadvantages of the current sutured anastomotic technique, that is, knot tying and suture management, and may well presage a shift toward a potentially superior interrupted technique.
| Conclusions |
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| Appendix: Discussion |
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Second, you propose moving from very simple sutures, which are inexpensive, to something that would entail the use of nitinol, which is more expensive. Would that cost be easily acceptable within a cardiac surgery practice?
Third, the ultimate purpose is to do a least invasive procedure. How do you foresee that a technology like this would be incorporated in a delivery system that lends itself to lesser access?
Dr Hill. Most surgeons already possess the skill required to place this device. The placement and delivery of the device is very similar to suturing, both continuous and interrupted. There is somewhat of a learning curve in determining the site of placement of the needle holders for the release mechanism. It is very simple once the exact site is learned, and it eliminates knot tying, very difficult maneuvers in endoscopic and robotic surgery. I think the learning curve for one approaching robotics and endoscopy will be decreased.
With respect to cost, this will be more expensive than standard polypropylene suture. But again, with the push toward minimally invasive procedures, the shorter hospital stay offsets costs, and I think the costs can be offset with the increased cost of this particular device. It is estimated that this device should cost about $150 per anastomosis.
Dr Paul F. Grundeman (Utrecht, The Netherlands). I have to congratulate you, Dr Hill, for this beautiful device. I think it has great potential for endoscopic CABG.
I have 2 questions related to flow in your animal model. Mean flow was about 81 mL/min. How do you foresee that this anastomotic device will hold in a flow of about 30 mL/min in the human left internal thoracic arteryleft anterior descending bypass?
Second, do you use anticoagulant therapy during the operation, and is that continued in the recovery phase?
Dr Hill. I do not think that the decreased flow is going to produce a greater amount of thrombosis than a sutured anastomosis would. The end result should be no different from that obtained with an interrupted suture anastomosis, and I do not think the flow characteristics will be any different.
We used heparin because we occluded the coronary artery during the operation and because the hearts were beating. There was no occlusion or stenosis proximal to this site because these were healthy young calves. We continued the calves on daily aspirin after the operation, but they were not given anticoagulants per se.
Dr Antonio M. Calafiore (Chieti, Italy). I have just a technical question. What is the minimal size of the coronary artery for which this technique can be used? Can this technique be used with the bigger sutures, like 5-0, 4-0, and 2-0, for valve prostheses?
Dr Hill. The minimal size coronary artery I think is more related to the graft size than it is to device size. This device can accommodate 7-0 or 8-0 suture size. The size of the anastomosis is going to be more closely related to the size of the thoracic artery graft and avoiding mismatch with respect to small coronary sizes and large thoracic artery sizes. I do not think that this device will limit the surgeon's ability to use the smaller sizes that are currently in use. Normally surgeons do not go lower than 1 mm for coronary anastomoses. I have grafted smaller than 1-mm arteries using this device. We performed a previous study in dogs, which we presented at Utrecht, and many of those coronary arteries were less than 1 mm.
| Footnotes |
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| References |
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