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Ann Thorac Surg 2000;70:2029-2033
© 2000 The Society of Thoracic Surgeons

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Original article: cardiovascular

Endoscopic computer-enhanced beating heart coronary artery bypass grafting

^a Department of Cardiothoracic Surgery, Stanford University Medical Center, Stanford, California, USA
^b Section of Cardiothoracic Surgery, Veterans Administration Palo Alto Health Care System (HCS), Palo Alto, California, USA

Accepted for publication June 14, 2000.

Address reprint requests to Dr Falk, Department of Cardiothoracic Surgery, Stanford University Medical Center, 300 Pasteur Dr, Stanford, CA 94305
e-mail: vfalk{at}stanford.edu

	Abstract

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Background. Telemanipulation systems have enabled coronary revascularization on the arrested heart. The purpose of this study was to develop a technique for computer-enhanced endoscopic coronary artery bypass grafting on the beating heart.

Methods. The operation was performed using the daVinci telemanipulation system. Through three ports, the left internal thoracic artery was harvested in 10 mongrel dogs (30 to 35 kg) using single right-lung ventilation and CO₂ insufflation. Through a fourth port an articulating stabilizer, manipulated from a second surgical console, was inserted to stabilize the heart. The left anterior descending artery was snared using silicone elastomer slings anchored in the stabilizer cleats and the graft to coronary artery anastomosis was performed.

Results. In 7of 10 dogs, total endoscopic beating heart bypass grafting, cardiac stabilization, arteriotomy, and arterial anastomosis were performed using computer-enhanced technology. Endoscopic stabilization and temporary left anterior descending artery occlusion were well tolerated. All grafts were patent although minor strictures were found in 2. In 3 dogs, the procedure could not be completed (1 ventricular arrhythmia, 1 left atrial laceration, and 1 right ventricular outflow tract compression).

Conclusions. Endoscopic beating heart coronary artery bypass grafting is possible in a canine model using a computer-enhanced instrumentation system and articulating stabilization.

	Introduction

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
The introduction of telemanipulation systems has enabled the development of endoscopic coronary artery bypass grafting on the arrested heart [1, 2]. Although it has been possible to perform coronary revascularization with the left internal thoracic artery (LITA) to left anterior descending artery (LAD) using only three trocars or thoracoscopic ports as access, a peripherally based cardiopulmonary bypass system and cardioplegic arrest (ie, port-access technique) were still required. Recently, Falk and coworkers [3] presented a preliminary report of endoscopic coronary artery bypass grafting on the beating heart in the canine model. However, a number of problems became evident during laboratory evaluation of a total endoscopic approach to beating heart coronary revascularization. Because the angles of the pads, or "feet," of the endoscopic stabilizer were fixed once it was unfolded, the placement and orientation of insertion became critical; it was clear that planar placement parallel to the vessel was not always possible using this device. Another important issue for endoscopic coronary operation is control and occlusion of the target vessel. Although used in minimally invasive direct coronary artery bypass grafting and off-pump coronary artery bypass grafting, vessel snares or loops are not easily placed in an endoscopic setting. Temporary coronary shunts are equally difficult to use because bleeding during shunt insertion can become uncontrollable with catastrophic consequences. Finally, issues with exposure and retraction during the anastomosis in endoscopic coronary artery bypass grafting on the arrested heart become magnified in the setting of endoscopic beating heart operation.

Thus, this study was intended to address the limitations of endoscopic beating heart coronary revascularization and to develop a system that will eventually permit an endoscopic approach to coronary artery bypass grafting in humans.

	Material and methods

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Ten mongrel dogs (30 to 35 kg) were used. Atropine (0.05 mg/kg intramuscularly) was used for premedication. For induction, ketamine (10 mg/kg intravenous [IV]) and diazepam (0.5 mg/kg IV) were given. Selective intubation of the right lung was performed. Amiodarone was infused to prevent arrhythmias. Inhalational anesthesia was maintained with Isoflurane 1.5% to 2.5%. An arterial line was placed in the right femoral artery and a central venous line was placed in the right jugular vein. The animals were placed in the right lateral decubitus position. Monitoring included electrocardiogram, arterial blood pressure, central venous pressure, and oxygen saturation. Intermittent positive pressure ventilation was used. Ringer’s lactate solution was given at a maintenance dose of 10 to 20 mL/kg per hour. Volume boluses were given as needed.

Telemanipulation system and stabilizer
The daVinci telemanipulation system (Intuitive Surgical, Mountain View, CA) used in this trial has been described in detail previously [4–7]. To provide assistance, two additional manipulators and a second console, which provided a videoscopic image identical to the primary console, were used (Fig 1). The scope was inserted through the central port and manipulated at the primary console by the operating surgeon. The left and right endoscopic surgical instruments were controlled from the left and right column-mounted manipulator arms, respectively. The central column-mounted manipulator arm was controlled from the second console and used to hold the stabilizer. Additional assistance was provided by a second arm that was controlled from the second console.

View larger version (49K): [in this window] [in a new window]   Fig 1. Schematic illustration of setup for endoscopic beating heart coronary artery bypass grafting using two consoles and five manipulator arms. The surgeon at the primary console manipulates two instruments and navigates the scope, whereas the assisting surgeon directs the stabilizer and an assisting tool from a second console. A = left tool (primary surgeon), B = right tool (primary surgeon), C = stabilizer (left hand assisting surgeon), D = assisting tool (right hand assisting surgeon).

Surgical technique
The surgical approach has been described in part elsewhere [3, 4]. In brief, the entire operation was performed through left thoracoscopic ports (trocar access only). CO₂ insufflation was used to enhance exposure. The LITA was harvested and the most distal portion skeletonized. The pericardium was opened and the LAD was identified. Heparin (1,000 to 1,500 U) was administered IV, and the LITA was occluded using a vascular occluder. The distal end was clipped and prepared. In this study, the target vessel was the midportion of the LAD between the first and second collateral branch. In contrast to our earlier study [3], we did not attempt to graft the first collateral branch of the LAD. Previously, the first collateral branch appeared to be a better target given the limitations of the earlier rigid stabilizer; however, the branch vessel was generally much smaller than the LAD, making the anastomosis difficult. The stabilizer was placed through a port in the parasternal region; later in the study, a subxyphoid placement provided superior access. The epicardium was incised just proximal and distal to the target artery to facilitate passage of the silicone elastomer loop, which is mounted on a blunt needle. Vascular control was provided by crossing the silicone elastomer loops around the LAD and anchoring them under tension at the cleats of the stabilizing feet. An arteriotomy was made and extended with Potts scissors. Irrigation of the operating field was provided through a separate channel of the microforceps used in the anastomosis. Along with the integrated blower of the stabilizer, a bloodless operating field was achieved. After completion of the anastomosis, the silicone elastomer loops were relaxed and the stabilizer withdrawn. After the procedure, the animals were sacrificed and the hearts were harvested through a left lateral thoracotomy for evaluation of the anastomosis.

All animals received humane care in compliance with the "Principles of Laboratory Animal Care" formulated by the National Society of 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 85-23, revised 1985).

	Results

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
The LITA harvest was performed successfully in all animals with a mean time of 43 ± 9 minutes. Both proximal and distal LAD control was achieved in the animals. The time required for dissection of the paravascular tissue, placement of stabilizer, and anchoring the silicone elastomer loops was 16 ± 7 minutes. In 7 of the 10 animals, the procedure could be completed. The mean times required for the coronary arteriotomy and completion of the anastomosis were 4 ± 3 and 34 ± 10 minutes, respectively. Total time of LAD occlusion and total procedure time were 55 ± 13 and 251 ± 95 minutes, respectively. With parasternal placement of the stabilizer, the right instrument and the shaft of the stabilizer collided not infrequently while performing the coronary anastomosis, resulting in loss of degrees of freedom and prolonged suturing time. By placing the stabilizer in a subxyphoid position the workspace for both instrument arms was widened, thereby improving visualization and facilitating suturing. In 2 dogs, anastomotic leakage required placement of additional sutures. Both anastomoses were widely patent during postmortem inspection. At sacrifice, magnified inspection of the coronary anastomoses revealed widely patent anastomoses in 5 of 7 animals; in 2 cases, the anastomoses were slightly strictured but patent and permitted the passage of a 1.5-mm probe. The mild strictures were due to a pursestring effect of the sutures and discordant arteriotomies relative to the graft diameters. Regarding the learning curve of this endoscopic system, as the surgeon gained experience in port placement and achieving adequate retraction and exposure, the technical aspects became less challenging; nearing the end of the study, the procedures were completed in less than 3 hours.

Three animals sustained significant complications, and the procedures could not completed. In one case, the left atrium was lacerated during an unattended instrument change resulting in massive hemorrhage. This complication can be avoided by carefully tracking the instruments using the videoscope during instrument insertion and removal. In another animal, occlusion of the LAD in preparation for the arteriotomy resulted in intractable ventricular tachycardia and termination of the experiment. This arrhythmia occurred despite infusion of amiodarone. Manipulation of the LAD did not result in any arrhythmias in the other animals. In one case, too much force was generated on the right outflow tract during stabilization, resulting in right ventricular outflow obstruction that was first manifested as low end-expiratory CO₂ and later as oxygen desaturation. Unfortunately, the outflow obstruction was recognized only during the coronary anastomosis; the anastomosis was abandoned, and resuscitation was promptly initiated but was not successful. By avoiding stabilizer placement in such a proximal position, this complication can be prevented.

	Comment

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
The feasibility of endoscopic coronary artery bypass grafting has been demonstrated previously on the arrested heart in the experimental and clinical settings [8, 9]. Using a canine model, Falk and coworkers [3] described their previous experience with endoscopic coronary artery bypass grafting on the beating heart. Because of incomplete stabilization due to lack of articulation of the stabilizer, inability to reliably occlude the target coronary artery, absence of dynamic assistance, and inadequate exposure, the early procedures were cumbersome and difficult to perform.

Each problem encountered in the early experience was addressed in a systematic fashion to facilitate a total endoscopic approach to beating heart coronary revascularization. By incorporating an articulating component to the endoscopic stabilizer, we were able to provide planar stabilization of the target coronary artery independent of the point of entry. The addition of cleats to the stabilizer feet provided anchoring points for the silicone elastomer vessel loops, which provided improved control and occlusion of the target coronary arteries. These silicone elastomer loops were easily manipulated due to the six degrees of freedom of the daVinci system. The initial version of this stabilizer was electronically driven; as such, the stabilizer was much easier to position and reposition than the previous manual version that was fixed to the table. A mechanical version of the articulating stabilizer is currently being developed that can be controlled manually by the assistant at the table. Potential instrument collisions (specifically with the right instrument arm and the stabilizer arm) encountered with the previous system was largely eliminated by using a subxyphoid access for the stabilizer arm. An irrigation channel was incorporated into the end-effectors (instruments), enabling directed irrigation of the anastomotic site and enhancing exposure. The positioning of an assisting instrument, controlled from the second console, provided dynamic and tremor-free assistance that is particularly valuable during the placement of the first few sutures of the anastomosis. This additional arm simplified graft presentation and provided countertraction, thereby increasing exposure before and during the anastomosis.

Despite these improvements, only five of seven anastomoses were widely patent, whereas two were mildly strictured. The reason for the minor stenosis in two cases was a pursestring effect mainly due to discordant arteriotomies relative to the graft diameter. With continuous sutures, pursestringing can be problematic, especially in small diameter vessels as in this dog model. This problem is in part system related, because the lack of tactile feedback impairs one’s ability to judge the amount of tension applied during suture tensioning. With increased experience, visual clues may be sufficient to correctly tension and tie the sutures, thereby avoiding pursestringing. Different ways of performing endoscopic anastomoses, including an interrupted technique using nitinol clip sutures, may offer an alternative solution to this problem and are being investigated. Another limitation that was encountered infrequently during the anastomosis was what is termed as singularity. A singularity, or loss of one degree of freedom of motion, occurs when one joint has to be used at extreme angulation. Depending on the port placement, singularity may become an important factor in performing the anastomosis if the range of motion is markedly limited. Different wrist designs are being evaluated to address this problem.

Although assisting instruments were of benefit, ischemic and anastomotic times remained prolonged. The long anastomotic time is in part attributable to impaired visualization due to bleeding at the anastomotic site requiring numerous flushing maneuvers. Clearly, effective irrigation is critical to the success of endoscopic beating heart bypass grafting, and improvements in the current instrumentation are required. Additionally, the use of shunts may be considered.

In one case, emergent resuscitation was required as a result of ventricular fibrillation. Despite the use of five robotic arms, rapid removal of the instruments and the slave manipulators was achieved in less than 30 seconds. In the clinical setting, ready access to the patient will be critical and cannot be compromised by the technology utilized. Also, to provide added safety in the clinical setting, exposure of the femoral vessels before accessing the thoracic cavity may be necessary in the event emergent cardiopulmonary bypass becomes necessary.

Total endoscopic coronary artery bypass grafting has been performed using the port-access system for closed chest cardiopulmonary bypass and cardioplegic arrest in the clinical setting [1, 2]. In these cases, an arrested heart and bloodless field greatly facilitate endoscopic suturing compared with the beating heart scenario described in this study. Although total endoscopic coronary artery bypass grafting on the arrested heart is currently the least invasive in terms of anatomic access (requiring only three trocars), the requirement for cardiopulmonary bypass can be considered to be more physiologically invasive than the beating heart approaches, such as minimally invasive direct coronary artery bypass or off-pump coronary artery bypass. Current limitations of an endoscopic beating heart coronary revascularization are numerous and include problems associated with stabilization, vascular control and occlusion, and dynamic assistance. We have attempted to address some of these issues and have presented the concept of two surgeons working remotely in an endoscopic environment using computer-enhanced instrumentation systems. Despite these improvements, the endoscopic approach to beating heart coronary artery bypass grafting remains challenging and requires further technological refinements before they can be applied clinically.

	Acknowledgments

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
We thank Frederick H. Moll, MD, for his assistance and input during this project.

	Footnotes

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Doctor Falk received a fellowship at Stanford University that is supported, in part, by Intuitive Surgical, Inc (Mountain View, CA). Doctors Fann, Grünenfelder, Daunt, and Burdon are not consultants to and have no commercial interest in Intuitive Surgical or any competitor company.

	References

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 

1. Falk V., Diegeler A., Walther T., et al. Total endoscopic coronary artery bypass grafting. Eur J Cardiothorac Surg 2000;17:38-45.[Abstract/Free Full Text]
2. Loulmet D., Carpentier A., d’Attellis N., et al. First endoscopic coronary artery bypass grafting using computer assisted instruments. J Thorac Cardiovasc Surg 1999;118:4-10.[Abstract/Free Full Text]
3. Falk V., Diegeler A., Walther T., et al. Endoscopic coronary artery bypass grafting on the beating heart using a computer enhanced telemanipulation system. Heart Surg Forum 1999;2:199-205.[Medline]
4. Falk V., Gummert J., Walther T., Hayesi M., Berry G.J., Mohr F.W. Quality of computer enhanced endoscopic coronary artery bypass graft anastomosis—comparison to conventional technique. Eur J Cardiothorac Surg 1999;13:260-266.
5. Mohr F.W., Falk V., Diegeler A., Autschbach R. Computer enhanced coronary artery bypass surgery. J Thorac Cardiovasc Surg 1999;117:1212-1213.[Free Full Text]
6. Shennib H., Bastawisy A., Mack M.J., Moll F.H. Computer-assisted telemanipulation: an enabling technology for endoscopic coronary artery bypass. Ann Thorac Surg 1998;66:1060-1063.[Abstract/Free Full Text]
7. Shennib H., Bastawisy A., McLoughlin J., Moll F. Robotic computer-assisted telemanipulation enhances coronary artery bypass. J Thorac Cardiovasc Surg 1999;117:310-313.[Abstract/Free Full Text]
8. Stephenson E.R., Sankholar S., Ducko C.T., Damiano R.J. Robotically assisted microsurgery for endoscopic coronary artery bypass grafting. Ann Thorac Surg 1998;66:1064-1067.[Abstract/Free Full Text]
9. Stephenson E.R., Sankholkar S., Ducko C.T., Damiano R.J. Successful endoscopic coronary artery bypass grafting: an acute large animal trial. J Thorac Cardiovasc Surg 1998;116:1071-1073.[Free Full Text]

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