In the past decade, minimally invasive surgical techniques have become prevalent in the field of cardiac surgery, including minimally invasive direct coronary artery bypass (MIDCAB), off-pump coronary artery bypass (OPCAB), and minimal access atrial septal defect (ASD) closure and mitral and aortic valve surgery. In addition to the development of new technologies such as visualisation systems, specially designed retractors, stabilisers, and alternative methods of vascular cannulation and cardiopulmonary bypass, surgeons have become capable of performing simple cardiac procedures through much smaller incisions than with conventional approaches. However, the limited incision size has imposed a corresponding increase in the technical difficulty of the procedure accompanied by a potential for a reduced safety margin due to incomplete cardiac exposure.
Recently, robotically assisted surgical systems have been introduced to increase the precision of endoscopic surgery and facilitate minimally invasive cardiac surgery. These computer-guided systems can control both surgical instruments and endoscopic cameras. Robotic instrumentation provides access to the heart and offers the surgeon the ability to operate precisely in limited spaces, overcoming the lack of precision that results from the additive effects of instrument length and operator tremor by filtering high-frequency motion. Dexterity is further enhanced through computer motion-scaling, which allows the surgeon to make large, easy-to-perform macroscopic movements at the console and have these movements scaled down by the computer to microscopic movements of the instrument tip inside the patient. Endoscopic magnification also improves the accuracy of surgical maneuvers by providing enhanced visualisation.
In 1998, Carpentier and colleagues reported the first cardiac surgeries (several kinds of mitral valve repairs) to be performed in adults using a prototype of the current da Vinci system (Intuitive Surgical, Sunnyvale, CA).1These operations were performed through small thoracotomy incisions. Subsequently, endoscopic robotic coronary operations were described the following year2, 3, soon after, a totally endoscopic, robotically assisted cardiac surgery procedure for the repair of atrial septal defects was reported.4
All the robotically assisted cardiac surgery procedures performed to date have either been extra-cardiac procedures or procedures that were performed inside an arrested heart. In the past, beating-heart procedures were attempted, but these approaches fell into disfavor after cardiopulmonary bypass (CPB) became available, which allowed direct visualisation of the intra-cardiac structures. Nevertheless, CPB is widely recognised as having a number of adverse effects, including the generation of microemboli and an inflammatory response associated with increased cytokine production and complement activation, which together can result in neurological dysfunction in adults and neurodevelopmental dysfunction in children.
Several investigators have recently attempted a variety of beating heart approaches for the repair of intra-cardiac pathologies, including atrial septal defects, ventricular septal defects, and mitral valve regurgitation, but the results were all suboptimal and not applicable in clinical situation.
On the other hand, the recently introduced real-time three-dimensional echocardiography (RT3DE) system with a 2D matrix array of piezoelectric crystals (Philips Medical Systems) provides clinicians and surgeons with a new perspective for visualising the heart non-invasively. When RT3DE is used for image-guided surgical tasks, some complex tasks required for intra-cardiac repair can be performed using echo guidance alone.5 This system has sufficient spatial resolution and frame rate to give the surgeon a “virtual surgeon’s view” of the relevant anatomy. Currently, we have adapted RT3DE with specialised instrumentation to facilitate beating-heart repair of Atrial Septal Defect ASD and mitral valve plasty in animal experiments (Figure 1).6, 7In our preliminary experiment, we also examined the feasibility of robotic assisted RT3DE guided beating-heart repair of ASD. Compared to 2-dimensional echo guidance, completion times of performing clipping improved by 70% (p<.0001), and deviation of clipping by the robotic system was significantly smaller (2DE: 3.5±2.2 mm, 3DE: 0.2±0.3 mm, p=.0002) in RT3DE guided tasks. In water bath experiment of ASD closure, RT3DE provided satisfactory images and sufficient anatomical detail for suturing (Figure 2). All surgical tasks were successfully performed with accuracy. We therefore expect that the combination of new intra-cardiac imaging technology and tool-tracking systems with the dexterity and stability of robotic instruments will enable safe and reliable off-pump intra-cardiac repair, including ASD closure and the repair of mitral valve insufficiency.
Indeed, there still are several limitations. Our RT3DE system provides adequate intraoperative images overall as an image-guided technology, but the spatial resolution of the RT3DE still needs optimisation to advance from simulation into a clinical setting. In addition, the transducer is too large to be applied directly to the heart through a small incision, since the operating field of instruments is restricted. Therefore, further technological development of the RT3DE system, such as by design of a high-frequency mini-transducer or trans-esophageal transducer, will probably be necessary to make minimal incision RT3DE-guided beating-heart surgery possible.
Other research and development
We are simultaneously investigating the potential application of an electromagnetic tool tracking and navigation system as a complementary navigation tool in beating heart intra-cardiac surgical procedures. Similar systems are currently in use for catheter tip tracking and navigation for arrhythmia ablation.8This latter system combines an electromagnetic tracking system with a catheter-based sensor that can be used to create a 3D map of the atrial chamber. We have experimentally used such a tracking tool to navigate inside a beating heart. With further development, this system could be used together with RT3DE to confirm contact with the septal wall during patch placement in ASD repairs while ensuring the avoidance of conducting tissues.
The current size of the da Vinci surgical system is the most critical limitation for its application in pediatric cardiac surgery. To date, 5mm instruments and smaller 3D endoscopes have been developed. In the near future, more technological advances are likely to extend the application of robotic surgical systems to neonates and infants.
Determination of the optimal port placement is a significant issue. Mistakes at this stage of the operation lead to delays from frequent instrument conflicts and can result in additional unnecessary incisions if the ports must be re-positioned. Using computed tomography (CT) and magnetic resonance imaging (MRI), preliminary efforts toward the development of a three-dimensional virtual cardiac surgical planning platform have been initiated for use with totally endoscopic cardiac surgery to avoid these problems. 9 We have also employed a new port placement planning platform for extra-cardiac operations in children. 10 The planned setup enables excellent exposure in addition to patient positioning, with no internal or external instrument conflicts.
The absence of tactile feedback and the inability to regulate the force applied to the tissues comprises the most endoscopic surgical techniques and instrument manipulation by the robotic system will eventually become comparable to that by the human wrist. In addition, haptic exploration of preoperative image data sets facilitate surgeon intuition during the planning of complex reconstructions. Current robotic systems were designed to complete a simple anastomotic suture line. Gulbins et al. reported that it required 30 minutes to finish a 10 suture throw in training simulators. 10 The time required for anastomosis could be reduced using novel devices for joining tissues or anchoring a surgical prosthesis, such as the Tacker spiral tack (US Surgical), the SaluteTM (Onux Medical), the Sew-RightTM and Ti-KnotTM systems (LSI Solution), or the U-ClipTM Anastamotic Device (Coalescent Surgical). Combining any of these devices with the speed and precision of robotic automation could make minimally invasive tissue fixation exponentially more efficient.
Further manipulation of the digital visual interface may also make it possible to work on the beating heart in “virtual stillness”. Lately, we have also been developing integrated motion cancelling systems, including visual stabilisation systems and motion stabilisation systems. The movement of the robotic instruments and camera would be synchronised with each heartbeat, effectively cancelling cardiac motion and increasing surgical precision.
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Reichenspurner H, Damiano RJ, Mack M, et al. Use of the voice-controlled and computer-assisted surgical system ZEUS for endoscopic coronary artery bypass grafting. J Thorac Cardiovasc Surg. 1999 Jul;118(1):11-6.
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Torracca L, Ismeno G, Alfieri O. Totally endoscopic computer-enhanced atrial septal defect closure in six patients. Ann Thorac Surg. 2001;72:1354-7.
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Suematsu Y, Takamoto S, Kaneko Y, et al. Beating atrial septal defect closure monitored by epicardial real-time three-dimensional echocardiography without cardiopulmonary bypass. Circulation 2003;107:785-90.
Suematsu Y, Marx GR, Stoll JA, et al. 3-Dimensional Echo-Guided Beating-Heart Surgery without Cardiopulmonary Bypass: Feasibility Study. J Thorac Cardiovasc Surg. 2004;128:579-87.
Smeets JL, Ben-Haim SA, Rodriguez LM, et al. New method for nonfluoroscopic endocardial mapping in humans: Accuracy assessment and first clinical results. Circulation 1998;97:2426-32.
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Gulbins H, Boehm DH, Reichenspurner H, et al. 3D-visualization improves the dry-lab coronary anastomoses using the Zeus robotic system. Heart Surg Forum. 1999;2:318-25.