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Ann Thorac Surg 2002;73:830-836
© 2002 The Society of Thoracic Surgeons
a Division of Cardiovascular Surgery, Mayo Clinic, Rochester, Minnesota, USA
b St. Jude Medical Cardiovascular Group, Inc, Minneapolis, Minnesota, USA
c Pathology Associated International, Frederick, Maryland, USA
Accepted for publication November 15, 2001.
* Address reprint requests to Dr Schaff, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA
e-mail: schaff{at}mayo.edu
Presented at the Thirty-seventh Annual Meeting of The Society of Thoracic Surgeons, New Orleans, LA, Jan 2931, 2001.
| Abstract |
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Methods. In 12 dogs, coronary saphenous vein grafts were made to the left anterior descending coronary artery and to the circumflex coronary artery; one anastomosis was completed with the St. Jude Medical stainless steel connector device, and the other with conventional suturing. A 30-day coronary angiogram was performed in surviving animals, and, after sacrifice, anastomoses were measured, examined grossly, and submitted for histologic study.
Results. All 12 animals survived the procedure, and 9 survived to sacrifice at 30 days. Comparing the connector grafts and sutured grafts, no significant differences were found between vessel diameters, intraoperative graft flows, graft patency, and histology. The average loading time for the connector was 8.5 minutes (range 4 to 16 minutes). Mean time for the 12 connector anastomoses was 3 minutes (range 2 to 5 minutes) compared with 8.4 minutes for suture (range 4 to 13 minutes).
Conclusions. The side-to-side stainless steel connector anastomotic device produces a secure anastomosis with minimal variability; compared with suture methods, it is expeditious and has comparable 30-day histology and angiographic results. It promises to be an important addition to the surgical armamentarium for the treatment of coronary artery disease.
| Introduction |
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Recently, St. Jude Medical Cardiovascular Group, Inc (Minneapolis, MN) has developed metallic connectors and delivery systems for aortosaphenous and saphenous vein-to-coronary anastomoses that appear to be equivalent to those created by suture and can be performed in far less time and with minimal training. Thus, this connector system may be ideally suited for less invasive coronary artery bypass grafting. Unlike clips or staples that have been used for vascular anastomoses [2, 3], the new connector system can be used with atherosclerotic arteries because penetration or eversion of the calcified walls is unnecessary.
The purpose of this study was to compare the new method of mechanically created side-to-side saphenous vein-to-coronary artery anastomosis with the conventional suturing technique in terms of time required to construct the anastomosis, reliability, failure rate, leak rate, intraoperative flow rates, 30-day patency, and histopathology.
| Material and methods |
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All animals underwent induction of anesthesia with sodium thiopental (15 mg/kg to effect). After orotracheal intubation, the animals were ventilated mechanically and anesthesia maintained with halothane (1% to 1.5%). The electrocardiogram and blood pressure through a femoral arterial line were monitored continuously throughout the procedure. Cefazolin (1 g IV) was given during induction of anesthesia and continued postoperatively every 8 hours for the first 24 hours. Initial muscle relaxation was obtained with only one injection of pancuronium bromide (0.05 to 0.1 mg/kg).
Animals were placed in a supine position, and we harvested both saphenous veins under sterile conditions. The proximal and distal outer diameters (OD) of the veins were measured. To facilitate loading of the device, veins with a minimum OD of 4 mm were chosen as grafts. After the animal was repositioned, a left fifth intercostal space thoracotomy was made, heparin was administered (300 U/kg), and the right femoral artery was cannulated for extracorporeal perfusion. Next, the pericardium was incised, and a venous return cannula was inserted through the right atrial appendage.
During normothermic cardiopulmonary bypass, fibrillatory arrest was induced to obtain a still field. The middle third of the left anterior descending coronary artery (LAD) and proximal portion of the left circumflex coronary artery (LCX) were dissected, and ODs of the vessels were measured. In each animal, one sutured and one connector SVG-to-coronary artery anastomoses were performed. Because this specific connector design requires a coronary artery inner diameter (ID) of 2.5 mm or greater, arteries with an OD of 3 mm or greater (estimated ID of 2.5 mm or more) were chosen for a connector anastomosis.
Proximal and distal 4-0 Prolene (Ethicon, Somerville, NJ) snares were used to control bleeding through the coronary artery during construction of anastomoses. Sutured distal anastomoses were made with running 7-0 Prolene. Hearts were cardioverted after finishing the distal anastomoses, and with partial cardiopulmonary bypass, the upper descending aorta was partially occluded with a side-biting clamp, and the aorto-SVG anastomoses were performed with running 6-0 Prolene.
The animals were weaned off bypass, and, once normal hemodynamics were obtained, flows through the grafts were measured using a Doppler flow probe (Small Animal Blood Flow Meter T-206, Transonic Systems, Inc, Ithaca, NY), before and after ligating the native coronary arteries proximal to the graft anastomosis. Protamine sulfate (1 mg for each 100 U of heparin) was then given, and meticulous hemostasis was achieved. The pericardium was approximated, and a small drainage tube was placed in the left pleural space. The wound was closed in layers, and, after the animal recovered from anesthesia, the chest tube was removed.
Postoperative care
Cefazolin (1 g IV) was administered every 8 hours for the first 24 hours postoperatively. Buprenorphine hydrochloride (0.005 mg/kg intramuscularly) was used for pain control. Aspirin (325 mg orally) and dipyridamole (20 mg orally) were given once a day until the day of sacrifice.
Conclusion of survival period
After 30 days, all the animals underwent general anesthesia, as during the surgical procedure, and a graft angiogram was obtained with standard techniques. With the animal heparinized (10,000 U IV) and still under deep general anesthesia, an overdose injection of pentobarbital followed by 40 mEq of potassium chloride was given. After euthanasia, the heart, bypass grafts, and thoracic aorta were excised en bloc and pressure-perfused at physiologic pressures with 10% neutral-buffered formalin for a minimum of 2 hours. The specimens were then sent for gross and microscopic evaluation. Sections from the proximal and distal anastomoses, vein grafts, and coronary arteries immediately distal to the anastomoses were examined.
The connectors were processed through and embedded in methylmethacrylate (MMA), cut using a diamond band saw (EXAKT System), and ground and surface stained with hematoxylin and eosin. The remainder of tissues were embedded in paraffin and stained with hematoxylin and eosin, Massons trichrome, and Verhoeffs elastic stains. The entire myocardium was examined grossly for the presence of infarction. Numerical data were analyzed using the Students t test (SAS Institute, Inc, Cary, NC).
| Results |
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Three animals died before sacrifice; animal 3 was found dead 4 hours postoperatively, and examination of the heart showed that grafts were patent with no evidence of myocardial infarction. Animal 8 died on postoperative day 10 due to intrathoracic bleeding. Animal 10 died on postoperative day 8, and autopsy showed a small, tan, nonocclusive thrombus in the lumen of the distal graft-LAD connector anastomosis. Histologically, we found a poorly organized thrombus that partially filled the lumen of the graft. A large subacute infarct was present just distal to the patent LCX sewn graft anastomosis with a much larger acute infarct distal to the subacute one.
All the 30-day surviving animals had patent grafts at angiography before sacrifice (Fig 4). All the distal anastomoses were photographed after opening the opposite coronary wall longitudinally; on gross examination, healing of anastomoses created by the connecting device was similar to that of sutured anastomoses (Fig 5). The dimensions of the anastomoses after pressure fixation with formalin were a mean of 2.3 x 2.2 mm for the connector and 3.8 x 2.6 mm for the sutured ones. The sutured anastomoses were larger than those created with the connector (7.8 mm2 versus 4.08 mm2, p = 0.0008).
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| Comment |
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Anatomic characteristics of canine coronary arteries are predictable, and the large canine model is suitable for device testing to gather data relating to potential application in humans. The actual design of the stainless steel anastomosis connector requires a coronary artery ID of 2.5 mm or more for optimal performance, but these devices can be scaled up or down to accommodate vessels of different diameters or anatomic positions. We anticipate that this technique will be applicable to coronary arteries with diameters of 1.5 mm. There were no significant differences in the ODs of the saphenous veins used as conduits or in the ODs of the coronary arteries grafted with a connector or sutured graft. Although circular device anastomoses were smaller than elliptical anastomoses created with suture, blood flows through the SVG before and after ligation of the native coronary arteries proximal to the anastomoses were equivalent for connector and sutured grafts.
Pathologic examination 30 days postoperatively showed no compromise of the lumens of the anastomoses by neointimal growth, and there was no evidence of inflammatory or foreign body reaction to the stainless steel connectors. We recognize that longer-term studies are necessary, and preliminary analysis of such an investigation at the University of Minnesota shows little reaction to the connecting device of animals sacrificed 3 months postoperatively.
Postoperative angiography demonstrated widely patent anastomoses with smoothly tapered grafts; there was no evidence of encroachment of thrombus from the blind end of the ligated vein graft (Fig 4). The side-to-side technique has several advantages including uniform size of the distal vein opening that facilitates device loading and avoidance of trauma to the lumen of the body of the vein. Also, this technique can be applied to in situ internal thoracic artery grafts.
An important issue with vascular connectors is the time required to load the device. With this connector, an experienced operator can load the device in 5 minutes or less, and because the connection is made as the heart is exposed, device preparation does not add to the duration of the operation. We anticipate that loading time will be reduced further with newer prototypes. Again, all endoluminal graft manipulation occurs through the distal end of the graft, a portion that will be ligated, thus minimizing risk of intimal injury.
Our studies did not answer important questions concerning the thrombogenicity of device anastomoses. Antiplatelet drugs were used in this study, but the small number of animals prevents any meaningful conclusions regarding thrombus formation or the best methods for its prevention. Certainly, advances in antithrombotic management of coronary stents might be applicable to this connector, but further animal studies will be necessary.
The side-to-side stainless steel connector anastomosis device produces a reliable anastomosis, with minimal variability; the connector can be deployed rapidly, and hemostasis is excellent. In this preliminary study, gross and microscopic pathology 30 days postoperatively demonstrated similar healing of device-constructed and sutured anastomoses. This or similar technologies may become an important addition to the surgical armamentarium for the treatment of coronary artery disease and may be particularly useful in off-pump and minimally invasive approaches.
| Acknowledgments |
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| Footnotes |
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| Discussion |
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As we have seen, this device allows the manufacture of extremely reproducible and morphologically excellent anastomoses. As a complement to the presentation of Dr Schaff and before asking him some questions, we are pleased to present to the audience a very short video of the worldwide first experience with a saphenous vein to coronary artery anastomosis, which was performed at the University of Bern, Switzerland, in November 2000.
For this initial experience, we decided to include only patients undergoing cardiopulmonary bypass who would receive at least one saphenous vein graft. In general, all other anastomoses were realized using arterial conduits. Here you see the right coronary artery. The diameter is 3 mm. The next step is to pierce the artery with the blade, and then to dilate the hole. Now you can see the preloaded vein on the device. The device is introduced into the coronary artery. The balloon is expanded. Now that the balloon is deflated, the catheter is removed. Here you can see the testing of the anastomosis with the proximal inflow; it is patent and dry. Here is the final view of the anastomosis. We have included the angios, which show patent connector anastomosis to the right coronary artery, and to the obtuse marginal in another patient. Thank you very much.
Of 14 patients who we had evaluated in-depth for such a procedure, 8 received one distal anastomosis using the St. Jude distal connector device. The main exclusion criterion was the size of the recipient vessel, which was smaller than an inner diameter of 2.5 mm, thus excluding 6 patients. All connectors could be deployed without difficulties and there was no leakage in any of the patients. However, the learning curve for the loading of the vein on the device was significantly longer and more difficult than for the aortic connector device for proximal anastomosis, but this problem has already been solved in the next generation of the device.
Angiography was performed in every patient immediately at the end of the operation. All anastomoses were patent, but in 1 patient the deployment of the device had led to an obstruction of retrograde flow into the proximal portion of the native coronary artery. The device was removed without difficulty and a conventional handsewn anastomosis was performed without complications.
This leads me to three questions that I would like to ask of Dr Schaff.
The first one is on the evaluation of the quality of the coronary artery wall of the segment designed to receive such an anastomosis. We have been afraid to consider even major-sized vessels if significant atherosclerotic changes are evident, especially in the posterior part of the vessel wall, because atherosclerosis may adversely affect the quality of the anastomosis. Would you please comment on this point?
The second question is related to the material chosen for such devices. Because there has been a lot of experience with coronary stents and developments are still forthcoming (now with stent coating, for instance, or brachytherapy), do you think that stainless steel is the optimal material to be used in this particular field?
And the third question is more philosophical. It is related to the future of these devices. Do you see any potential combination of this technique, which is actually applied under direct vision with video-assisted procedure or even with robotic assistance? On the same subject, could you please comment on your view of teaching these new methods to our residents?
Again, I congratulate you for the nice presentation.
DR SCHAFF: Thank you, and congratulations to you and your group for the successful clinical use of this device. As you know, there is a great difference between the vessels of an experimental animal and those of a patient with atherosclerotic coronary artery disease, and the next challenge in development is application of connecting devices to vessels with variable wall thickness. I am optimistic that this technical problem can be overcome.
The second issue relates to the material used to construct the device, which is stainless steel. As you know, cardiologists have used a variety of devices for stents, and considerable progress has been made in reducing thrombogenicity of the surfaces. These same technologies can be used for connecting devices.
And finally, to address your important points about ultimate application of the method and teaching the technique to residents, it is clear that this and other connecting devices should facilitate video-assisted coronary artery surgery and, possibly, robotic coronary revascularization. It is too early to develop tools for teaching the method to residents, but from my experience this should not be difficult.
DR DAVID ADAMS (Boston, MA): Can you tell us about your antiplatelet strategy given the thrombotic risk both early and late and how you see that impacting on clinical studies?
DR SCHAFF: You ask an important question regarding risk of thrombosis, and I should clarify that we did use antiplatelet therapy with aspirin and Persantine in these animals. Also, I want to emphasize that this study was not designed to examine thrombogenicity in any detailed fashion, but this is of critical importance in establishing the safety of anastomotic devices.
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