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Ann Thorac Surg 1999;68:1542-1546
© 1999 The Society of Thoracic Surgeons
a Department of Cardiac Surgery, University Hospital Munich-Grosshadern, Munich, Germany
b Institute for Surgical Research, University Hospital Munich-Grosshadern, Munich, Germany
Address reprint requests to Dr Boehm, Department of Cardiac Surgery, University Hospital Munich-Grosshadern, Marchioninistr 15, D 81366 Munich, Germany
e-mail: boehm{at}hch.med.uni-muenchen.de
Presented at Evolving Techniques and Technologies in Minimally Invasive Cardiac Surgery, San Antonio, TX, Jan 22–23, 1999.
Abstract
Background. To achieve an endoscopic coronary bypass anastomoses we performed a study with endoscopic robotic instrumentation and camera guidance using three-dimensional (3-D) visualization.
Methods. The surgical robotic system ZEUS (Computer Motion Inc, Goleta, CA) consists of three interactive robotic arms and a control unit allowing the surgeon to move the instrument arms in a scaled down mode. The third arm (AESOP, Computer Motion Inc, Goleta, CA) positions the endoscope via voice control. The study had three phases. Phase I: In a phantom model, end-to-side anastomoses between vein grafts and the left anterior descending coronary artery (LAD) of 109 pig hearts were performed. Phase II: In 6 dogs (FBI, 20–25 kg) the left internal mammary artery (LIMA) was harvested endoscopically. During Port-Access (Heartport Inc, Redwood City, CA) cardiopulmonary bypass (CPB), LIMA and LAD were then anastomosed endoscopically with the help of telemetric ZEUS instruments (Computer Motion Inc). Phase III: A total of seven patients were operated on with help of the ZEUS system (Computer Motion Inc). After endoscopic LIMA harvesting and CPB using the Port-Access (Heartport Inc) system, the bypass graft (LIMA to LAD) was anastomosed endoscopically through three thoracic ports in 2 patients. Another 3 patients were operated on off-pump with regional stabilization and 2 patients with sternotomy and routine CPB.
Results. The practice with the phantom model and the subsequent animal experiments allowed the surgeons to gain sufficient experience for the clinical setting. In the clinical cases, times for anastomoses ranged from 20 to 42 minutes. Median internal mammary artery flow rate was 74 mL per minute (range 36–110 mL per minute). One patient in the off-pump group was converted to CPB and routine anastomosis. All patients had an uneventful angiographic control and postoperative course.
Conclusions. Using telemetic technology, a completely endoscopic anastomosis of LIMA to LAD is possible on the arrested heart, as well as on the beating heart.
The ultimate goal of minimally invasive direct coronary artery bypass grafting is to perform the anastomosis entirely endoscopically. Significant technological advances over the last decade enabled the development of minimally invasive endoscopic operative techniques in a variety of disciplines. These procedures are ultimately aimed at reducing patient morbidity, length of hospital stay, and overall costs.
However, efforts to decrease the surgical incision in comparison to the now well-established minimally invasive direct coronary artery bypass grafting operation [1–3] are limited by several factors: (1) current endoscopic instrumentation does not permit a safe, easy and precise anastomosis; (2) instrument handling is awkward, time consuming, and affects the surgeon’s ergonomics unfavorably; (3) current two-dimensional (2-D) visualization is insufficient for performing a precise anastomosis; and (4) the anatomy of the chest wall and the limited space in relation to the location of the coronary arteries does not facilitate endoscopic manipulation [4].
In the meantime, telemanipulation, derived from space and military technology, is used to provide surgeons with the tools to perform totally endoscopic coronary anastomoses by allowing several degrees of freedom of motion. The combination of robotics and 3-D visualization creates the necessary platform to overcome the above-mentioned limitations [4, 5]. The surgeon can operate in an ergonomically favorable position, using telemanipulated instruments, obviating any natural tremor and increasing dexterity and precision. Combined with 3-D vision, the system creates depth perception and increases speed and safety.
The purpose of this study was to investigate the feasibility of performing clinically endoscopic coronary artery bypass grafting surgery with the enhanced technology. To achieve this goal, a three-phase approach was used, starting with the dry lab and proceeding to the animal lab and finally to the clinical study.
Material and methods
The ZEUS Robotic Surgical System (Computer Motion Inc, Goleta, CA) consisted of three interactive robotic arms fixed at the operating table, a computer controller, and an ergonomically enhanced surgeon console. One robotic arm (AESOP, Computer Motion Inc) was used to position the endoscope, while the other two robotic arms manipulated surgical instruments under the surgeon’s direct control. While seated at the console in a chair with armrests, the surgeon could view the operative site in either a 3-D head-mounted display or on a 2-D monitor display, according to the surgeon’s preference. The surgeon controlled the movements of the endoscope with simple voice commands. Movements of the surgical instruments were controlled via handles that resembled conventional surgical instruments. The movements of the instrument handles were scaled and tremor was filtered out in such a way that the surgeon was able to perform fully endoscopic and accurate microsurgery. The end-effectors were specially designed instruments, such as needle drivers or forceps, which could quickly be exchanged with scissors or special beaver blades.
Visual control was established with either 3-D (Zeiss GmbH, Oberkochen, Germany) or 2-D (Karl Storz GmbH, Tuttlingen, Germany) endoscopes or alternatively with the Vista stereo-matchbox camera (Vista Medical Technologies Inc, Westborough, MA). The 3-D image was displayed on two LCD monitors inside a special headset (Vista Medical Technologies Inc, Westborough, MA); the same image was displayed in two dimensions via a monitor above the control unit.
Phase I: dry-lab training
Porcine hearts (n = 106) were prepared by dissecting the right coronary artery for a total length of 7 cm and placing it close to the LAD in an ex vivo, on-bench model. The thoracic trainer was a reproduction of a human rib cage, covered with a 2-cm layer of neoprene, simulating soft tissues and skin and allowing various port placements. The complete trainer was fixed to a standard operating table. The porcine hearts were then placed inside the thoracic trainer in the correct anatomical orientation of a living human heart. The specialized robotic endoscopic instruments were inserted through two 5-mm ports (Autosuture/Ethicon) in the fourth and sixth intercostal space. The 2-D or 3-D endoscopes were placed through a 10-mm port in the fifth intercostal space in the anterior axillary line. Anastomosis of the free RCA segment to the LAD was performed with a running suture in an end-to-side technique using specifically manufactured 7-0 suture material (7-cm length and double-armed). Gore-Tex (W.L. Gore & Associates GmbH, Putzbrunn, Germany), Fumalen (Fumedica Medizintechnik GmbH, Herne, Germany) and Prolene (Ethicon GmbH & Co KG, Norderstedt, Germany) were evaluated. The time periods required for completion of the anastomoses were recorded and at the end of each training procedure the quality of the anastomoses was checked for patency using a coronary probe and inspected by gross pathological examination.
Phase II: animal experiments
The animal experiments were approved by the local authorities in charge; all animals received humane care in compliance with the "Guide for the Care and Use of Laboratory Animals" as published by the National Institutes of Health (NIH publication 85-23, revised 1985).
Six dogs (FBI, 20–25 kg) were included in the study. Following general anesthesia and ventilation via the right lumen of a double-lumen endotracheal tube, the left internal mammary artery (LIMA) was harvested endoscopically via a 10-mm camera port and two 5-mm instrument ports. After clipping off the distal LIMA and endoscopic clamping of the proximal LIMA, the distal end was pulled through one of the thoracoscopic ports and prepared for anastomosis.
Meanwhile the animals were placed on cardiopulmonary bypass by femoral cannulation using the Port-Access-system (Heartport Inc). After fluoroscopically controlled inflation of the endoaortic balloon catheter (Endoclamp, Heartport Inc) and antegrade delivery of cold crystalloid cardioplegic solution (Celsior, 15 mL/kg BW), the pericardium was opened using the ZEUS-System (Computer Motion Inc), which was installed through three left lateral endoscopic ports which had already been used for LIMA harvesting. The LAD was dissected with specifically designed beaver knives, which were attached to the ZEUS-instrument driver (Computer Motion Inc). The LAD was then incised using the same devices.
After switching instruments from the knife to a needle-holder tip, the end-to-side-anastomosis (LIMA to LAD) was performed using 7/0 Gore-Tex (W.L. Gore & Associates GmbH) sutures with the ZEUS-instrument-system (Computer Motion Inc) only. The surgeon was helped by an assistant with an endoscopic forceps passed through a right parasternal thoracoscopic port. After completion of the anastomosis of the endoscopic bulldog-clamp (Heartport Inc) was removed and the bypass graft was perfused. To assess graft flow rates, the proximal portion of the LAD was ligated using a 4-0 Prolene (Ethicon GmbH and Co, KG) suture using the ZEUS-System (Computer Motion Inc). Blood flow through the LIMA graft was assessed by using ultrasonic transit-time flow measurement (Medi-Stim AS, Oslo, Norway) after the animals had been weaned from cardiopulmonary bypass. After the animals had been euthanized with a lethal dose of potassium chloride an autopsy was performed, checking the anastomosis sites for patency.
Phase III: clinical study
The study protocol was approved by the Ethics Committee of the University of Munich and, after written informed consent had been obtained, 7 patients were included for the clinical procedures.
In 5 patients, who suffered only from a proximal stenosis of the LAD, the LIMA was endoscopically harvested through three left lateral thoracic ports penetrating the fourth, fifth, and sixth intercostal space. The 10-mm camera port was inserted at the level of the anterior axillary line and the two instrument ports were inserted to the left and right of the camera port at the level of the mid-axillary line. The LIMA was dissected manually using electrocautery and endoscopic clipping of side branches under CO2-inflation limited to a maximum inflation pressure of 12 mm Hg. Before distal clipping of the LIMA, a left-parasternal-port incision was made using the fourth intercostal space, to enable one of the surgeons to assist the operator and assess the safety of instrument placement. The LIMA was then clipped distally, pulled through the port incision and prepared for the anastomosis.
In 2 of these patients the anatomical position of the LAD demanded cardiopulmonary bypass (CPB). Therefore, the right femoral artery and vein were dissected and surrounded with umbilical tapes. The specifically designed Port-Access (Heartport Inc) femoral cannulae were inserted into the femoral vessels. The venous cannula was guided into the right atrium using transesophageal echocardiographic (TEE) control. After placement of the arterial cannula, the Endoclamp (Ethicon) was introduced into the ascending aorta via the femoral artery Y-connection tube, using fluoroscopy and TEE control. The patients were then put on cardiopulmonary bypass and the hearts were emptied. Additional drainage was achieved through a previously placed endopulmonary vent catheter.
The remaining 3 patients were operated on without CPB. Following endoscopic LIMA harvesting and a minithoracotomy penetrating the fourth left intercostal space, regional wall stabilization of the LAD target area was achieved with Octopus (Medtronic GmbH, Düsseldorf, Germany) suction (n = 2) or CTS (Cardio Thoracic Systems, Cupertino, CA) (n = 1) pressure stabilization.
Two further patients required additional grafts to the distal RCA; therefore routine CPB was commenced following sternotomy and conventional LIMA harvesting.
In the endoscopic cases, the endoscopic coronary artery anastomosis was performed through the same left thoracic ports which had been used for LIMA takedown. The LAD was dissected in the target area after opening of the pericardium. In the patients with Port Access (Heartport Inc) cannulation, the endoaortic balloon was inflated until aortic occlusion was achieved and antegrade blood cardioplegia (Buckberg formulation) was administered according to the protocol for cardiac arrest. The LAD was incised through the mini-incision and the LIMA was positioned close to the LAD target area. A 7-0 Gore-Tex suture (7-cm, double-armed) (W.L. Gore & Associates GmbH) was attached to the needle-holder tip of the system and the anastomosis was performed using a running suture in end-to-side technique through the three endoscopic ports only.
After completion of the suture, seven knots were tied using the same instruments with a lower scaling-down mode (2.5). The endoscopic bulldog clamp or the tourniquet sutures were removed and the anastomoses were tested for hemostasis. No additional suture placement was necessary. The endoaortic balloon was then deflated and the heart was perfused. After 20 minutes reperfusion, patients were weaned from cardiopulmonary bypass without major catecholamine support. Bypass flow rates were analyzed using ultrasonic flow probes (MediStim AS, Oslo, Norway) and intraoperative angiography was performed through the Y-shaped arterial cannula by a cardiologist. Figure 1 Figure 2
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The 2 patients who required additional grafts to the distal RCA were operated on via sternotomy and routine CPB. In both patients, the distal anastomosis to the RCA was performed manually prior to the robotically assisted anastomosis of the conventionally dissected LIMA to the LAD. The Vista mini-camera was fixed with a suture at the left side of the sternal spreader and the instruments were introduced via two 5-mm ports in the third and sixth intercostal space in the midsternal line.
Total time for the surgical procedure, time on cardiopulmonary bypass, cross-clamp time, or regional ischemic time, as well as time on ventilation, time on ICU, and total hospital stay were recorded.
Results
Phase I: simulator training
Different imaging techniques for coronary anastomoses were evaluated by three surgeons using either 2-D or 3-D visualization. The median time for coronary anastomoses in 2-D was 42 minutes (range 35 to 60 minutes); in 3-D the time was 18 minutes (range 12 to 32 minutes) (p < 0.05, 2-D versus 3-D). The comparison of different suture materials revealed facilitated handling properties of Gore Tex (W.L. Gore & Associates GmbH), due to the lack of memory effect in the suture.
Phase II: animal experimental data
In all six cases, it was possible to harvest the LIMA endoscopically. The median time for LIMA harvesting in the animal experiments was 86 minutes (range 56 to 120 minutes). Median time required for Port-Access (Heartport Inc.) CPB was 95 minutes (range 82 to 200 minutes), median time for aortic occlusion was 65 minutes (range 53 to 125 minutes), and for the robotically assisted anastomoses, 42 minutes (range 35–105 minutes). All but 1 of the animals were weaned from cardiopulmonary bypass without major catecholamine support. The respective animal showed signs of impaired myocardial protection during the procedure. Despite of an acceptable LIMA-flow rate, it could not be weaned from CPB. The median LIMA graft flow rate was 38.5 mL per minute (range 22 to 45 mL per minute). At autopsy, all explanted anastomoses showed good patency with no evidence of stenosis.
Phase III: clinical cases
In the Port Access (Heartport Inc) cases, endoscopic LIMA preparation times varied between 63 minutes and 82 minutes. The setup of the ZEUS-instruments (Computer Motion Inc.), which was done in parallel to the installation of the Port-Access (Heartport Inc.) CPB, lasted between 17 and 21 minutes. Total time of CPB was 82 and 95 minutes. The aorta was occluded for 45 and 51 minutes and the times for the telemanipulated coronary anastomoses were 40 and 42 minutes. Graft flow was 110 and 36 mL per minute.
In the 3 patients operated on without CPB, the anastomosis times were 24 and 40 minutes respectively. Transit time flow measurement was 110 and 74 mL per minute. In one case, the patient had to be converted to sternotomy and routine CPB because the LAD was of small diameter and intramyocardially located.
In the clinical cases operated with sternotomy and routine CPB and additional saphenous vein grafts to the distal RCA, the times on CPB were 45 and 52 minutes; the telemetrically controlled LIMA anastomosis to the LAD required 20 and 30 minutes (Table 1). Graft flow was 88 and 47 mL per minute.
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Postoperative ICU stay for all patients was between 8 hours and 2 days; total hospitalization ranged from 5 to 7 days. One patient operated with CPB developed transient postoperative delirium which ceased after 48 hours. All of the patients were discharged home in excellent condition. In the meantime, postoperative 6-week follow-up is complete in 6 cases with no evidence of wound infection, wound pain, or recurrent angina pectoris. Postoperative electrocardiograms and chest x-rays were normal. Coronary angiography was performed within 4–6 weeks postoperation, and revealed adequate anastomoses in all patients.
Comment
This report reveals experimental data and the first successful series of patients operated on using the computer-assisted and voice-controlled ZEUS system (Computer Motion Inc) for endoscopic coronary artery bypass grafting.
The advantage of the surgical systems ZEUS (Computer Motion Inc) was the easy transport and the quick setup of the complete system; it took only 19 minutes on average. The robot arms could be attached to the operating table preoperatively and passively positioned in such a way that they did not interfere with endoscopic LIMA harvesting, initiation of Port-Access (Heartport Inc) CPB, or the assistance by the second surgeon and the instrumentation by the surgical nurse. The system was relatively simple to handle, required only one technician for maintenance, and did not suffer any technical failure during the experiments or the clinical cases. A further advantage was the voice-controlled endoscopic camera positioning system allowing the surgeon to keep his hands on the instrument handles all the time while being in full control of the perceived view without the need for an assistant.
The dry-lab training was an important step in the use of the system. For each surgeon, the time required for completion of the telemanipulated anastomoses decreased with increasing training and experience. By adding realistic depth perception, 3-D visualization further shortened the required times by about 50%. It improved surgical dexterity and shortened the learning curve.
The ultimate aim of minimally invasive bypass grafting is the completely endoscopic approach. Sufficient experience in endoscopic LIMA harvesting [6], Port Access (Heartport Inc) surgery [7], and minimally invasive direct coronary artery bypass grafting surgery [1, 2, 7] are necessary requirements. In the animal trial, we were able to show that the endoscopic operation in combination with Port Access (Heartport Inc) technology is feasible and that endoscopic coronary artery anastomosis could be successfully performed using the ZEUS system (Computer Motion Inc) without any complications such as bleeding or narrowing.
The step-by-step approach was used for the clinical cases as well, by performing a sternotomy and routine CPB for the first cases and subsequently using the endoscopic approach with Port Access (Heartport Inc) cannulation. Subsequently, the feasibility of performing a telemetrically controlled anastomosis on the beating heart was assessed in a further step. For safety reasons, a mini-incision was made in the endoscopically operated patients to enable the assistant to interact with the anastomosis site immediately in the event of any complication. Times of anastomoses are still longer than they are for regular coronary artery anastomoses; however, after more experience, particularly in clinical situations, the anastomosis time will be close to the regular time, as demonstrated in the preclinical experiments. Critical issues are adequate patient selection, port positioning, and arrested versus beating heart anastomosis.
Present limitations of the system were the lack of an additional degree of freedom inside the chest cavity, which would further increase the speed and accuracy of suturing. However, the next version of the system will include an additional degree of freedom in the end effectors. A further improvement would be a force-feedback technology to enable the surgeon to sense the grasping and linear forces applied to tissues, suture, and needle. This would require measurement of the forces applied to the end effectors/instruments via piezo-resistant pressure sensors, pulsatile sensors, or vibrotactile sensors. The transfer of tactile information could be handled in several ways: acoustically, with a tactile actuator in the master handle, visually on an additional screen, or integrated into the endoscopic view.
Using endoscopic LIMA-preparation, the Port-Access (Heartport Inc) cardiopulmonary bypass system, and the voice-controlled and computer-assisted surgical system ZEUS (Computer Motion Inc), truly endoscopic coronary artery bypass surgery should be a reality in selected patients in the near future.
References
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