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J Thorac Cardiovasc Surg 2005;130:1348-1357
© 2005 The American Association for Thoracic Surgery
Evolving Technology |
a Department of Cardiac Surgery and Cardiology, Children's Hospital and Harvard Medical School, Boston, Mass
b Department of Aerospace and Mechanical Engineering, Boston University, Boston, Mass
c Division of Engineering and Applied Sciences, Harvard University, Cambridge, Mass
Read at the Eighty-fifth Annual Meeting of The American Association for Thoracic Surgery, San Francisco, Calif, April 10-13, 2005.
Received for publication March 28, 2005; revisions received June 20, 2005; accepted for publication June 28, 2005. * Address for reprints: Pedro J. del Nido, MD, Department of Cardiac Surgery, Children's Hospital-Boston, 300 Longwood Ave, Boston, MA 02115 (Email: pedro.delnido{at}tch.harvard.edu).
| Abstract |
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METHODS: The operations were conducted under the sole guidance of a modified real-time 3-dimensional echocardiography guidance system with a x4 matrix transducer (Sonos 7500, Philips Medical Systems, Andover, Mass). Eighteen swine were anesthetized, and after median sternotomy, the echo probe was applied directly to the surface of the right atrium. To create an atrial septal defect, balloon atrial septostomy and atrial septal defect enlargement were performed. Subsequently, 3 different techniques of atrial septal defect closure were attempted: group I, direct suture closure; group II, closure of the atrial septal defect using the Amplatzer device (AGA Medical Corp, Golden Valley, Minn); and group III, patch closure of the atrial septal defect (n = 6 each).
RESULTS: Real-time 3-dimensional echocardiography guidance provided sufficient spatial resolution and a satisfactory frame rate to provide a "virtual surgeon's view" of the relevant anatomy during the entire procedure. All atrial septal defects were enlarged, and the mean final size was 8.5 ± 1.8 mm. Atrial septal defect closure was successfully accomplished with all the 3 surgical techniques examined. In groups I and III, the needles (1-3 sutures) and staples (6-12 staples) penetrated the tissue and patch material consistently, whereas in group III, the Amplatzer atrial septal defect device was easily deployed. There was no incident device/staple embolization or air introduction. Neither intraoperative 2-dimensional color Doppler echocardiography nor postmortem macro-evaluation revealed any residual shunts.
CONCLUSIONS: Beating heart atrial septal defect closure under real-time 3-dimensional echocardiographic guidance is feasible and, unlike catheter-based devices, applicable for any type of secundum atrial septal defect.
| Introduction |
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Despite allowing direct visualization of intracardiac structures, cardiopulmonary bypass (CPB) has a number of adverse effects, including generation of microemboli and an inflammatory response associated with increased cytokine production and complement activation, which together can result in neurologic dysfunction in adults and neurodevelopmental dysfunction in children.
1,2
Furthermore, the long-term effects of CPB still remain unclear, and its deleterious effects may be more pronounced in infants than in patients of older age. Recently, investigators have attempted beating heart intracardiac surgery without CPB;
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however, the imaging systems used were deemed suboptimal for satisfactory visualization of the intracardiac structures.
Over the last 4 decades, echocardiography has evolved from single-beam imaging to sophisticated 3-dimensional (3D) techniques that enable study of the cardiac structures and functions, and the hemodynamics in great detail.
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Recently, real-time 3-dimensional echocardiography (RT3DE) was developed, which serves as a new modality for clinicians and surgeons for visualizing the heart noninvasively without electrocardiographic or respiratory gating. A new probe was developed that creates a fully sampled 2-dimensional (2D) array and allows 3D imaging with instantaneous on-line volume-rendered reconstruction, direct manipulation of thresholding, and planes cut on the ultrasound unit. This new 3D probe has great potential for expanded applications, not only for medical diagnosis but also for image-guided surgical intervention. We previously demonstrated that RT3DE provided adequate anatomic detail for surgical-task performance in an in vitro model.
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In this study, we assessed the feasibility of 3 techniques for beating atrial septal defect (ASD) closure without CPB in a swine model.
| Materials and Methods |
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Surgical Devices
A semiautomatic suturing device developed by us for off-pump intracardiac surgery was used as previously described (Figure 1, A).
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In brief, a needle with a conical point is threaded with 4-0 silk thread. The base of the needle is affixed in a niche on the tip of the proximal jaw of the semiautomatic suture device by pulling the thread down with 1 hand. The jaws close after the needle is passed through the tissue to be fixed. When the jaw is slowly opened again, the tip of the needle is automatically grasped by the distal jaw, which has a resilient slit. When the device is gently moved off the tissue, it is ensured that the thread has penetrated the tissue appropriately. After the device is pulled out of the cardiac cavity with the needle, the same action is repeated for the opposing edge of tissue. The device is 5 mm in diameter. A commercially available knot pusher (Olympus Co, Tokyo, Japan) was used for suture ligation in minimally invasive cardiac surgery. A suture cutting device consisting of a shaft, cutting edge, and handle was used to cut the sutures (Figure 1, B).
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The shaft of this device consists of an inner and outer tube, and the outer diameter of the outer tube is 2.5 mm. The inner shaft has the cutting edge, which is used to insert and cut the thread. The handle is connected to the end of the shaft and is used to turn the inner tube. The thread is cut by placing it between the inner and the outer cutting edge.
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We also used the Amplatzer ASD device (AGA Medical Corp, Golden Valley, Minn) for the ASD closure (Figure 1, C). In brief, this device is made of a Nitinol wire mesh, and the wires are shaped to form double discs with a short connecting waist. Dacron is sewn inside the discs with a polyester thread to increase its closing ability. A female screw is welded to the center of the right disc for attachment to the delivery cable. Because the device can be easily rotated at the time of deployment, a simple delivery sheath is used for the deployment. For patch closure of the ASD, an original-design patch-opener device, consisting of a self-expanding ring of nitinol and a grip, was used (Figure 1, D).
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A 0.1-mm polytetrafluoroethylene patch (Gore-Tex, W. L. Gore & Associates, Inc, Flagstaff, Ariz) was appropriately trimmed, and then sutured along the ring with 6-0 Prolene (Ethicon Inc, Somerville, NJ). This device is delivered through a long sheath (5 mm in diameter), and the nitinol ring with the patch is advanced through the end of the sheath and allowed to expand.
ASD Closure
All animals received humane care in compliance with the "Principles of Laboratory Animal Care," prepared by the National Society for Medical Research, and the "Guide for the Care and Use of Laboratory Animals," prepared by the Institute of Laboratory Animal Resources and published by the National Institutes of Health (NIH publication no. 86-23, revised in 1985).
Twenty-one swine weighing 73.7 ± 5.8 kg were used. Anesthesia was induced in the animals by intramuscular injection of tiletamine/zolazepam (7 mg/kg) and xylazine (4 mg/kg), and after the animals were intubated with a cuffed endotracheal tube, anesthesia was maintained with 2% isoflurane. Each animal was ventilated at a peak inspiratory pressure of 20 cm H2O, an inspired oxygen fraction of 0.21, and a respiratory rate of 10 to 20 breaths/min, with a pressure-control type ventilator (Healthdyne model 105; Healthdyne Technologies, Marietta, Ga). The electrocardiogram was continuously monitored throughout the procedure. A median sternotomy was performed; the right atrium was suspended upward with a few stay sutures, and the echocardiographic transducer was directly applied to its surface. Figure 2
shows the schema of the operation. Our previous water-tank experiment demonstrated that the best images were obtained with the ultrasonic transducer at distances of 4 to 6 cm from the target.
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Therefore, where necessary, a stand-off was placed between the transducer and the right atrium to optimize the image and range of the field. A purse-string suture of 3-0 polypropylene was placed around the right atrial appendage, and in the group undergoing patch closure of the ASD, another additional purse-string suture for insertion of the patch was placed below the superior vena cava in the right atrium.
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After ASD closure was accomplished, the residual atrial shunt was graded by 2D epicardial echocardiography, as previously described
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: (1) none, no defect as visualized by 2D echo and no color Doppler disturbance on the right atrial side; (2) trivial, no defect by 2D echo and minimal color disturbance on the right atrial side (<1 mm width at origin of the color Doppler jet); (3) small, no defect by 2D echo and 1 to 2 mm width at the origin of the color Doppler jet; (4) moderate, defect visualized on 2D echo and more than 2 mm width at the origin of the color jet; or (5) large, defect visualized by 2D echo and large and/or multiple color jets. Off-pump ASD closure was considered to have been successfully accomplished when the residual atrial shunt was graded as none or trivial, all the sutures were tightly knotted, and no significant air bubbles were introduced into the cardiac cavity, as observed by echocardiography, during the procedure.
| Results |
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| Discussion |
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CPB has been widely recognized to have a number of deleterious effects, resulting in blood coagulation abnormalities, changes in erythrocyte and plasma proteins, and a nonspecific inflammatory response. Gas and particulate emboli, and various vasoactive and otherwise biologically active substances are also produced as a result of contact between blood and foreign surfaces during CPB, which can cause pulmonary, myocardial, and neurologic dysfunction.
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ASD closure in a beating heart without CPB has been performed by some surgeons and researchers. Warinsirikul and associates
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reported their clinical experience of 74 patients, in whom they successfully accomplished closure of ASD without CPB, thereby avoiding the adverse effects of CPB. They used a sandwich patch made of Teflon material, which was passed into the right atrium through a purse-string suture and fixed with an endoscopic stapler. However, all the maneuvers were guided solely by the surgeon's index finger passed into the right atrium. Sogawa and associates
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reported closure of the foramen ovale without CPB using an intracardiac endoscope in a canine experiment. A glass tube with a round bottom 11 mm in diameter fixed with an endocardioscope was pushed against the luminal surface of the right atrium to visualize the foramen ovale at the center of the endocardioscope. A stapler 5.3 mm in diameter was used in this study; however, they found it impossible to conduct the stapling under endoscopic monitoring because of blood rushing into the space between the luminal surface and the glass tube as soon as the staple entered the atrial septum, necessitating blind stapling.
Downing and colleagues
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demonstrated beating-heart mitral valve suturing under 2D echocardiographic guidance. However, with 2D imaging guidance alone, it may not be possible to perform complex surgical interventions because spatial relationships cannot be assessed instantaneously. Also, obtaining favorable images in which both the target tissue and the surgical device can be monitored simultaneously is time-consuming, making it impractical to use this modality for real-time guidance. Other investigators have reported that despite the lower temporal and spatial resolution compared with conventional 2D images, operating under 3D echo guidance was superior to 2D for navigation.
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Our colleagues previously demonstrated that the completion time for simple surgical maneuvers was significantly decreased with 3D echo guidance compared with 2D echo guidance (50% [P = .046] vs 77% [P = .009]), with improved navigational accuracy (46%, P = .040)
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comparable to endoscope-guided performance. We therefore consider that RT3DE allows a "surgeon's view" to be obtained in real time, enabling the surgeon to perform surgical interventions in the same manner as during endoscopic surgery.
Since the first successful attempt at per-catheter ASD closure by King and Mills in 1974,
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a variety of devices have been launched for transcatheter closure of ASDs. However, these devices are still associated with occasional complications. Poor patient selection (eg, those with very large defects), poor device selection (low ratio of device to defect), operator-related failure resulting from inadequate experience, and tearing of the interatrial septum especially at the lower rim of the ASD owing to catheter and device manipulation have been reported to result in acute failure of these devices.
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Furthermore, chronic/late failure has been reported owing to unbuttoning and fracture of the framework of the device,
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and thromboembolic episodes as a result of poor endothelialization of these devices, necessitating long-term use of anticoagulants or even surgical removal of the device.
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Berdat and colleagues
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reported from their clinical experience that surgery was required after transcatheter closure of an ASD or a patent foramen ovale in 8% of their patients. Therefore, if surgery could be accomplished through a smaller incision compared with that for conventional open surgery, and CPB is avoided, it may become an acceptable alternate approach to device closure.
There are some limitations of our study method. One is the difficulty of visualization of metallic surgical devices by echocardiography. Metallic devices frequently cause significant acoustic interference because of shadowing, side-lobe artifacts, and inconsistent tool appearance. Currently, the authors (J.A.S, P.E.D) are involved in developing a new surface coating for devices to make them compatible with ultrasound beams. Also, overlaying of the virtual configuration of the surgical device on the echo images by mounting a magnetic tracker system on the device may be another solution to aid in instrument navigation inside the heart. Second, the spatial resolution of RT3DE still needs to be optimized to advance its application from simulation into a clinical setting. Finally, the transducer is too large to be applied directly to the heart through a small incision because the operating field is restricted. To minimize the incision size for RT3DE-guided beating heart surgery, further technologic development advancements of the RT3DE system are mandatory.
| Conclusion |
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| Discussion |
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With regard to instrumentation, we relied on a computer motion robotic system, but no specifically designed devices were available for us. Thus again, this is major progress with regard to the devices that were available for this study and that have been developed in this context.
I have 3 questions.
Dr Suematsu, can you tell us something about handling of blood loss that must have occurred with the purse string suture access?
Dr Suematsu. Thank you, Dr von Segesser. In this study, we used a conventional purse string suture for device entry under median sternotomy because this was the first step of our beating heart project. Fortunately, we did not encounter critical blood loss in this series. However, we are currently developing a 2-valved intracardiac port to prevent possible blood loss and air entry.
Dr von Segesser. Can you give us some indications with regard to the time required for completion of your 3 different procedure techniques?
Dr Suematsu. Although that depends on the ASD size, actual time to complete the procedure is less than 10 minutes for ASD direct suture closure and 1 minute for device closure, and 10 to 15 minutes for patch closure. We believe this is acceptable.
Dr von Segesser. Do you have any recommendations for capturing moving targets on the 3D echo, such as aortic valve leaflets?
Dr Suematsu. Unfortunately, we don't have any experience with the aortic valve. Another target is actually the mitral valve repair under real-time 3D echo guidance. In our preliminary study of beating heart mitral valve surgery through an apical ventricular approach, we could easily grasp the leaflet by endoscopic forceps because time resolution is very high. However, image quality of the mitral valve is critical for that purpose. The frequency range of the current 3D echo probe is 2 to 4 MHz and quite low to visualize the leaflet in this setting. Therefore, a high-frequency real-time 3D echo probe is needed to go forward with this project.
Dr von Segesser. Thank you very much for your excellent work.
| Footnotes |
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| References |
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