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Ann Thorac Surg 2000;70:835-838
© 2000 The Society of Thoracic Surgeons

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Original articles: cardiovascular

Robotic-assisted instruments enhance minimally invasive mitral valve surgery

^a Division of Cardiothoracic Surgery, Department of Surgery, New York University School of Medicine, New York, New York, USA

Address reprint requests to Dr Grossi, Department of Surgery, New York University Medical Center, 530 First Ave, Suite 9V, New York, New York 10016
e-mail: grossi{at}cv.med.nyu.edu

Presented at the Thirty-sixth Annual Meeting of The Society of Thoracic Surgeons, Fort Lauderdale, FL, Jan 31–Feb 2, 2000.

	Abstract

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Background. The potential for totally endoscopic mitral valve surgery has been advanced by the development of minimally invasive techniques. Recently surgical robots have offered instrument access through small ports, obviating the need for a significant thoracotomy. This study tested the hypothesis that a microsurgical robot with 5 degrees of freedom is capable of performing an endoscopic mitral valve replacement (MVR).

Methods. Dogs (n = 6) were placed on peripheral cardiopulmonary bypass; aortic occlusion was achieved with endoaortic clamping and transesophageal echocardiographic control. A small left seventh interspace "service entrance" incision was used to insert sutures, retractor blade, and valve prosthesis. Robotically controlled instruments included a thoracoscope and 5-mm needle holders. MVR was performed using an interrupted suture technique.

Results. Excellent visualization was achieved with the thoracoscope. Instrument setup required 25.8 minutes (range 12 to 37); valve replacement required 69.3 ± 5.39 minutes (range 48 to 78). MVR was accomplished with normal prosthetic valve function and without misplaced sutures or inadvertent injuries.

Conclusions. This study demonstrates the feasibility of adjunctive use of robotic instrumentation for minimally invasive MVR. Clinical trials are indicated.

	Introduction

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
The ability to perform open-heart surgery through small incisions has recently been enhanced by the availability of perfusion cannulas and equipment optimized for nonsternotomy cardiopulmonary bypass. With removal of perfusion tubing from the thoracic incision, the surgeon can perform the operation through smaller thoracic incisions. The mitral valve can be approached through a small anterior thoracotomy with cardiopulmonary bypass, endoaortic occlusion, and antegrade or retrograde cardioplegia [1–3]. To facilitate this technique special long instruments have been developed which allow the surgeon to work through this "operative tunnel" without obstructing the view of the valve. The use of a thoracoscope has been advocated as an adjunct to improve nonobstructed visualization [4, 5]. A similar approach for minimally invasive coronary artery bypass grafting (CABG) has recently been facilitated by the use of robotically assisted devices [6–8].

Recent advances in surgical robotics have tailored this technology to the challenging task of performing minimally invasive open-heart surgery. Robotic technology was first introduced in the form of voice control of the endoscope [9]. Subsequently, a robotic telemanipulator with seven degrees of freedom (DOF) (Intuitive Surgical Inc, Mountain View, CA) has been used for mitral valve repair [10]. Although capable of performing the task, this system requires port instruments 11 mm in diameter to obtain the seven DOF within the body cavity and the system’s size limits access to the patient by the surgical assistant.

In this study, we tested the hypothesis that a surgical robotic manipulator with only five DOF, allowing for smaller instrumentation (3.9 mm diameter), would be able to provide the dexterity necessary to assist the surgeon in an endoscopic approach to mitral valve replacement.

	Material and methods

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Six adult mongrel canines (mean weight: 31.6 ± 3.38 kg) were placed under general anesthesia. All animals were treated in compliance with the "Principles of Laboratory Animal Care" formulated 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 (National Institutes of Health publication No. 85-23.1985). Cardiopulmonary bypass (CPB) was instituted by femoral cutdown using an aortic cannula (16F, Bard Inc) and a long femoral venous cannula (17F DLP, Medtronic, Inc, St. Paul, MN ). Transesophageal echocardiographic (TEE) (Hewlett Packard Omniplane I) guidance was used to position and verify placement of the endoclamp (EndoCPB System, Heartport, Redwood City, CA) which was inserted through an internal carotid artery cut-down. Myocardial protection was achieved with antegrade blood cardioplegia through the endoclamp after its balloon inflation in the ascending aorta.

The dogs were placed in a right lateral decubitus position, and one 10-mm and two 5-mm trocars were inserted. The first port (10 mm) was placed for the 0° 2-D scope (Karl Storz, GmbH, Tuttiingen, Germany) in the left fourth intercostal space at the midclavicular line. The next two ports (5 mm each) were placed in the fourth and sixth intercostal spaces at the anterior axillary line. These ports were used for the placement of the right and left robotic instruments respectively. A "service entrance" incision (3 cm) was created in the left seventh intercostal space for insertion of sutures, an atrial retractor blade, and a valve prosthesis.

The Zeus Robotic System (Computer Motion Inc, Goleta, CA) was used to control the two surgical instruments and endoscope. This system consists of three robotic arms directly attached to the operating room table. These arms are placed in such a manner as to allow the operating staff access to the patient (Fig 1). The medial, endoscopic arm is used for voice-controlled manipulation of the thoracoscope; the two lateral arms are used to grasp and manipulate various surgical instruments. The needle-holding instruments used in this study were 3.9 mm in diameter with a nonarticulating tip length of 9 mm. The two robotic arms are controlled by a console (Fig 2) where the magnified view of the operative field is displayed to the surgeon on a video screen [8]. The movements of the robotic instruments are controlled by handles which are similar to those of the surgical instruments. These movements are scaled and any natural tremor of the surgeon is filtered to enhance dexterity. This system allows motion with five DOF within the chest cavity: vertical, horizontal, in and out, rotational, and grasping [8].

View larger version (23K): [in this window] [in a new window]   Fig 1. Overhead diagram of robotic arm placement for mitral surgery in canine. In the above diagram, A = AESOP endoscopic arm controller, L & R = the left and right robotic instrument arms respectively.

View larger version (119K): [in this window] [in a new window]   Fig 2. The Zeus Robotic System surgeon’s console.

Upon completion of the valve replacement, the atriotomy was closed, the heart deaired and the endoclamp released. The animals were weaned from CPB after rewarming was completed. Transesophageal echocardiography (TEE) was used to evaluate prosthetic valve function. Postmortem gross anatomical examination was performed to evaluate the suture placement and to explore for unrecognized intracardiac injury.

	Results

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Excellent visualization of the mitral valve in all of the animals was achieved with the 0° thoracoscope. Table 1 contains the mean operative times. Instrument setup, including trocar placement, required a mean ± SD of 25.8 ± 11.2 minutes. Mean valve replacement required 69.3 ± 5.4 minutes with a mean cardiopulmonary bypass time of 144.3 ± 39.1 minutes. The times for each individual experiment are also depicted graphically in Figure 3. Individual suture placement was readily performable for all positions around the annulus. In situations where the dominant hand’s instrument approached the annulus at a perpendicular angle, suture placement was facilitated by using the nondominant hand’s instrument. Because the instruments and endoscope were positioned in a nearly equilateral triangle, the nondominant hand’s instrument would therefore approach the point on the annulus from a more obtuse angle.

View larger version (36K): [in this window] [in a new window]   Fig 3. Individual experimental times for each of the six cases performed. (Setup = setup time including the trocar placements; VRT = valve replacement times; CPB = cardiopulmonary bypass time.)

	Comment

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
There is a growing interest in minimally invasive cardiac surgery (MICS) on the part of both the patient and the surgeon. Despite early criticisms, MICS has become the preferred method of mitral valve repair and replacement in many institutions throughout the world with excellent results [5, 11–13]. This approach has been made possible with advancements in both closed chest cardiopulmonary bypass techniques and "beating heart surgery" [1–3, 14]. However, these techniques require the use of long instruments to allow the surgeon to perform the procedure through a "tunnel" in the anterior chest wall. Despite the excellent results reported by the experts, limited mobility through the operative ports can affect the dexterity of the surgeon and add to the complexity of the procedure [15].

Microsurgical robotic-assisted surgical systems now have been introduced into the realm of open-heart surgery. Initially, with the addition of a robotic-assisted voice-controlled thoracoscope, Falk and colleagues were able to perform eight "solo" minimally invasive mitral valve operations [9]. This robotic assistance gave the operator complete control of the operative field of vision, obviating the need for a second assistant. Recently, the same group reported their experience with a different surgical robotic telemanipulation system [10]. In the latter study, the daVinci Surgical Robot (Intuitive Surgical, Inc, Mountain View, CA) was used to perform ten mitral valve repairs. The Intuitive System used articulating instruments, which allowed for seven degrees of freedom (vertical, horizontal, in and out, rotational, grasping, pitch, and yaw). However, larger and bulkier instruments were required (11 mm vs 3.9 mm diameter) [7, 8] and overall system size made assistant access to the patient more difficult.

Through the use of the Zeus Robotic System we were able to successfully replace the mitral valves. At first, the most difficult aspect of the procedure was the proper positioning of the trocars within the canine chest cavity. This accounted for the longer instrument setup times required initially: 25.8 minutes (range 12 to 37 minutes). Ultimately, the ports were placed in locations similar to those used by Loulmet and coworkers in their clinical endoscopic CABG study [7]. Overall, the valves were replaced within a mean time of 69.3 minutes (range 48 to 79 minutes) which is comparable to standard Port-Access mitral valve replacement (PA-MVR) [13]. Although initial surgical times were prolonged, this trial demonstrated benefits to the surgeon from this robotic technology. In addition to providing excellent, unobstructed viewing of the mitral valve, ergonomic access for instrument control benefited the surgeon. Not only was instrument manipulation moved into a "comfort zone," but also movement scaling and tremor filtering allowed for a more accurate procedure as previously commented upon [8].

An assistant used the "service entrance" for suture loading, atrial retractor placement, and insertion of the prosthesis. It became apparent that close coordination between the robotic surgeon "inside the chest" and the surgical assistant was necessary to prevent crossing or misplacement of sutures in the prosthesis. We facilitated this coordination by providing video displays of the surgeon and assistant to each other.

In conclusion, we have demonstrated the feasibility of using robotic instrumentation with five DOF as an adjunct to minimally invasive mitral valve surgery. The success in this canine feasibility study suggests that clinical trials are indicated.

	Acknowledgments

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Supported in part by the Foundation for Research in Cardiac Surgery and Cardiovascular Biology.

	Footnotes

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
This article has been selected for the open discussion forum on the STS Web site: http://www.sts.org/section/atsdiscussion/

	References

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 

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