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Chitwood WR Jr, Nifong LW. Minimally Invasive and Robotic Valve Surgery.
In: Cohn LH, Edmunds LH Jr, eds. Cardiac Surgery in the Adult. New York: McGraw-Hill, 2003:10751092.

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Chapter 44

Minimally Invasive and Robotic Valve Surgery

W. Randolph Chitwood, Jr./ L. Wiley Nifong

EVOLUTION OF MINIMALLY INVASIVE VALVE SURGERY
????Level 1: Direct-Vision
????Level 2: Video-Assisted
????Level 3: Video-Directed and Robot-Assisted
????Level 4: Telemanipulation and Robotic
INCISIONS FOR MINIMALLY INVASIVE VALVE SURGERY
????Aortic Valve
????Mitral Valve and Tricuspid Valve
PERFUSION TECHNOLOGY
????Arterial Access
????Venous Drainage
????Myocardial Preservation
????Aortic Occlusion
????Cardiac Air Removal
ROBOTIC TECHNOLOGY
CURRENT STATUS
????Minimally Invasive Aortic Valve Surgery
????Minimally Invasive Mitral Valve Surgery
????Robotic Mitral Valve Surgery
CONCLUSIONS
REFERENCES

?? INTRODUCTION
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Surgeons and their patients have become energized by the benefits and possibilities of minimally invasive heart valve surgery (MIHVS). Until 1995, cardiac surgery lagged far behind other specialties in the development of minimal access methods. Then, Cohn and Cosgrove, along with several European colleagues, first modified cardiopulmonary bypass techniques and reduced incision sizes to enable safe, effective minimally invasive valve surgery.13 Concurrently, Port-Access methods, using endoaortic balloon occluders, were developed and rapidly became popular.4,5 Despite early enthusiasm for MIHVS, most surgeons were skeptical and many were very critical of cardiac surgery done through small incisions, owing to possibilities of unsafe operations and/or inferior results.69 Despite this circumspect reticence, significant advances occurred in a short time and encouraging clinical series began to emerge. Concurrent advances in cardiopulmonary perfusion, intracardiac visualization, instrumentation, and robotic telemanipulation hastened a technologic shift toward efficient, safe MIHVS. Today, both replacing and repairing cardiac valves through small incisions have become standard practice for many surgeons, and patients are becoming more aware of the increasing availability.


?? EVOLUTION OF MINIMALLY INVASIVE VALVE SURGERY
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To perform the ideal cardiac valve operation (Table 44-1) surgeons need to operate in restricted spaces through tiny incisions, which requires assisted vision and advanced instrumentation. Although this goal has not been achieved widely, MIHVS has continued to evolve toward video-assisted or video-directed operations. Moreover, new robotic methods now offer near endoscopic possibilities for mitral valve surgeons. Both video-assisted and direct-vision limited-access valve surgery are now within the reach of most cardiac surgeons.


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TABLE 44-1 Ideal cardiac valve operation

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Minimally invasive cardiac surgery has not enjoyed a standard nomenclature. The terms minimally invasive or limited-access cardiac surgery have referred to the size of the incision, the avoidance of a sternotomy, use of a partial sternotomy, or abstention from cardiopulmonary bypass. However, the development of MIHVS may be considered analogous to an Everest ascent, embarking from a conventional or "base camp" operation and advancing progressively toward less invasiveness through experience and acclimatization. A nomenclature that parallels this "mountaineering" analogy is shown in Table 44-2. In this scheme, levels of technical complexity are mastered starting with small incision, direct vision approaches (level 1), then moving toward more complex video-assisted procedures (level 2 or 3), and finally to robotic valve operations (level 4). With the constant evolution of new technology and surgical expertise, many established surgeons already have attained serial "comfort zones" along this MIHVS trek.


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TABLE 44-2 Minimally invasive cardiac surgery

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Level 1: Direct-Vision

Early MIHVS was based solely on modifications of previous incisions, and nearly all operations were done under direct vision. In 1996 the first truly minimally invasive aortic valve operations were reported.13,1012 At that time surgeons found that minimal-access incisions also provided adequate exposure of the mitral valve.10,11,13,14 Using either ministernal or parasternal incisions, Cosgrove, Cohn, Gundry, and Arom each showed encouraging results with low surgical mortality (1%3%) and morbidity for valve surgery.1,2,10,15 In Cosgrove's first 50 minimally invasive aortic operations, perfusion and cardioplegia times approximated conventional operations, and his operative mortality was only 2%. Over half the patients were discharged by the fifth postoperative day.2 In early 1997, Cohn presented 41 minimally invasive aortic operations and first defined the economic benefits of these operations.1

The Stanford group performed the first minimally invasive mitral valve replacements, using intra-aortic balloon occlusion (Port-Access) and cardioplegia in early 1996.1417 Subsequently, surgeons at the University of Leipzig reported 24 mitral valve repairs done through a minithoracotomy using Port-Access techniques.5 This group later reported a high incidence of retrograde aortic dissections and neurologic complications, which seemed to be related to new catheter technology and limited surgeon experience.18 By early 1997, Colvin and Galloway had performed 27 direct-vision, Port-Access mitral repairs or replacements with a single death. They experienced no aortic dissections, and 63% of patients had mitral valve repairs with no reoperations for leakage.19 By December of 1998, Cosgrove had done 250 minimally invasive mitral valve operations using either a ministernotomy or parasternal incision with no mortality.3 The successes of these early MIHVS procedures became the springboard to the current direct-vision techniques described herein.

Level 2: Video-Assisted

Avant-garde endoscopic surgical techniques in the 1980s became routine general, urologic, orthopedic, and gynecologic operations in the 1990s. This was related primarily to successes with extirpative endoscopic operations. In contrast, fine anastomotic and complex reparative procedures are the centerpieces of cardiac surgery. Because of difficulty in acquiring the fine video dexterity needed for these operations, cardiac surgeons have been the last to explore the benefits of operative video assistance.

As mentioned, most Port-Access, sternal modification, and parasternal mitral valve operations have been done using direct vision. In early 1996, Carpentier performed the first video-assisted mitral valve repair through a minithoracotomy using hypothermic ventricular fibrillation.20 Shortly thereafter, we completed the first video-assisted mitral valve surgery through a minithoracotomy, using a new percutaneous transthoracic aortic clamp and retrograde cardioplegia.21,22 This clamping and visualization technique was simple and cost-effective, and has remained the mainstay of isolated mitral valve operations at our center.

In 1997 Mohr reported 51 minimally invasive mitral operations, done using Port-Access cardioplegia techniques, a 4-cm incision, and for the first time three-dimensional videoscopy.23 In this series three-dimensional (3-D) assistance aided mitral replacements; however, these surgeons found that less complex reconstructions were significantly more difficult than sternotomy-based operations. At about the same time Loulmet and Carpentier deployed an intracardiac "mini-camera" for lighting and subvalvular visualization; however, they concluded that two-dimensional visualization was inadequate for detailed repairs.24 Concurrently, our group reported 31 successful mitral operations done using two-dimensional video assistance.25 Complex repairs were possible and these included quadrangular resections, sliding valvuloplasties, chordal transfers, and synthetic chordal replacements. Our initial results were encouraging.

Level 3: Video-Directed and Robot-Assisted

In 1997 Mohr first used the Aesop 3000 voice-activated camera robot in minimally invasive videoscopic mitral valve surgery.23 Six months later we began using the Aesop 3000 to perform both video-assisted and video-directed minimally invasive mitral valve repairs.26 We have continued to use this device during most isolated mitral valve surgery. This instrument provides the surgeon with camera-site voice activation, precluding the translation errors that are inherent with verbal transmission to an assistant. Camera motion has been shown to be much smoother and more predictable, and requires less lens cleaning than during manual direction. Currently, if necessary, we are able to do over 90% of a mitral repair under video direction with the Aesop 3000. Mohr termed this method "solo mitral surgery" and reported 8 patients undergoing successful mitral repairs using this robotic technique.23 Since these early procedures, over 1500 videoscopic and robot-assisted mitral valve repairs have been done worldwide with excellent results.

Level 4: Telemanipulation and Robotic

In June of 1998 Carpentier and Mohr did the first true robotic mitral valve operations using the da Vinci surgical system.27,28 In May of 2000 the East Carolina University group performed the first da Vinci mitral repair in the United States.29 This system provides both tele- and micromanipulation of tissues in small spaces. The surgeon operates from a console through micro wrist instruments that are mounted on robotic arms inserted through the chest wall. These devices emulate human X-Y-Z axis wrist activity throughout seven full degrees of manipulative excursion. These motions occur through two joints that each affect pitch, yaw, and rotation. Additionally, arm insertion and rotation, as well as variable grip strength, give additive freedom to the operating "wrist." Mohr and Chitwood have the largest experiences in this area and independently have determined this device effective for performing complex mitral valve repairs.28,30 Using the Zeus system, Grossi et al performed a partial mitral valve repair but had limited ergonomic freedom.31 Lange et al in Munich were the first to perform a totally endoscopic mitral valve repair using only 1-cm ports and da Vinci.32


?? INCISIONS FOR MINIMALLY INVASIVE VALVE SURGERY
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The type and size of the musculoskeletal incision remain central to MIHVS discussions. A myriad of modified small sternal, parasternal, and thoracotomy incisions have been used for cardiac valve access. To date, most minimal-access cardiac surgery has been done under direct vision (level 1), requiring larger incisions than needed for videoscopic operations (levels 24).

Aortic Valve

Initially, Cohn and Cosgrove reported both excellent valve exposure and clinical results using parasternal or trans-sternal incisions.13,33 However, these incisions largely have been abandoned because of cosmetic dissatisfaction, pain, and sternal nonunion. Currently, most minimal-access aortic and mitral valve operations are performed either through a ministernotomy or minithoracotomy (Fig. 44-1).



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FIGURE 44-1 (A) Hemisternotomy for minimally invasive mitral and aortic valve surgery. (B) Minithoracotomy for minimally invasive mitral valve surgery.

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Our group uses an upper hemisternotomy for most aortic valve operations. Following an 8- to 10-cm skin incision, the longitudinal midsternal cut is made from the notch into the 3rd to 5th interspace (ICS), deviating to the right, often without transecting the sternum. Care is taken not to injure the internal thoracic vessels. For direct aortic and right atrial venous cannulation, the sternal incision must be carried at least to the 4th ICS. When the sternal incision ends at the 3rd ICS, femoral vein cannulation is usually required because of limited atrial access. Gundry and Sardari suggested that optimal sites of either sternal division or ICS deviation are best determined echocardiographically.15,34 However, we have found that crossing into the right 4th or 5th ICS always provides excellent right atrial exposure. After pericardial edges are approximated tightly to the skin edges, a small Finochietto retractor is used to spread the sternal halves laterally. This maneuver "pulls" both the aorta and valve annulus toward the surgical field (Fig. 44-2). Generally, we cannulate the aorta near the innominate artery using a flexible guidewire-directed cannula. Early placement of commissure retraction sutures facilitates aortic valve exposure. Doty and Karagoz prefer a lower hemisternotomy to reach both aortic and mitral valves.35,36 Bennetti first reported aortic valve access through a right 2nd ICS minithoracotomy and the New York University group uses this approach routinely.37,38



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FIGURE 44-2 (A) Hemisternotomy and surgical exposure for direct-vision access during aortic valve surgery. Note that pericardial retraction sutures pull the aorta toward the operative field. (Courtesy of Dr. L.H. Cohn.) (B) Minimally invasive prosthetic aortic valve replacement via a hemisternotomy. A suction catheter is placed into the ventricle for venting. We prefer antegrade cardioplegia via frequent ostial administrations.

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Mitral Valve and Tricuspid Valve

Although many surgeons prefer the hemisternotomy approach, a right minithoracotomy yields excellent direct-vision and videoscopic mitral valve access (Figs. 44-1B and 44-3). To access the left atrium for direct vision, while maintaining a limited-access minithoracotomy, a 6- to 8-cm incision should be placed in the submammary fold along the anterior axillary line. The pectoralis and intercostal muscle fibers are divided, and the thorax is entered through the 4th ICS with minimal rib distraction and no rib cutting. The New York University group has been quite successful in combining this incision, Port-Access methods, and direct vision for both mitral and tricuspid repairs/replacements.39 A smaller 4- to 5-cm incision with minimal rib retraction can be used in video-assisted cases and is large enough for prosthesis passage (Fig. 44-4). Vanermen and Mohr perform video-assisted mitral operations routinely through 4-cm, nonretracted thoracic incisions with excellent results.4042 Minimal rib spreading, prevention of intercostal nerve injury, and intraoperative local anesthetics are the keys to minimizing postoperative discomfort. Tricuspid operations can be performed through this incision as long as bicaval cannulation with isolation is used.



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FIGURE 44-3 Right minithoracotomy and video access. The right minithoracotomy allows aortic access for the transthoracic clamp shown here as well as the video camera. With this arrangement minimal rib spreading is needed to perform mitral surgery.

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FIGURE 44-4 Small "nonretracted" minithoracotomy for video-directed mitral surgery. Using videoscopic techniques, a small nonretracted minithoracotomy provides excellent access for long instrument manipulation. Here, a soft tissue retractor mobilizes skin edges away from the incision. (Courtesy of Dr. H Vanermen.)

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The author considers the term "minimally invasive" to include the size of the actual cardiac incision. Most superior and trans-septal mitral valve approaches require a larger cardiac incision. For aortic, mitral, and tricuspid valve operations, Cosgrove uses a 4th ICS ministernotomy with direct aortic arch and right atrial cannulation.3,12,43 To access the mitral valve, he extends the atriotomy from the right atrium across the left atrial roof, continuing caudally to divide the interatrial septum (Fig. 44-5). This incision provides excellent exposure for aortic, mitral, and tricuspid valve replacements as well as repairs. Although the septal artery is divided, the incidence of atrial arrhythmias seems to parallel traditional interatrial groove atriotomies. For mitral and aortic surgery Gundry uses a similar hemisternotomy and a single right atrial cannula. He gains exposure similar to that described by opening the atrial roof, between the superior vena cava and aorta, without entering the right atrium.15 Cohn now prefers sternal modification incisions for both aortic and mitral surgery and uses a trans-septal approach for mitral exposure.44 Loulmet and Carpentier reported using a midsternal, C-shaped, partial sternotomy for exposing mitral valves through the interatrial septum.24 All of these incisions provide generous direct-vision exposure, if combined with optimal pericardial retraction.



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FIGURE 44-5 (A) Hemisternotomy with an extended atrial incision. Popularized by Dr. Cosgrove, the incision begins along the ventral right atrium and extends over the dome of the left atrium and through the left atrial wall and interatrial septum. (B) Mitral valve exposure is excellent through this hemisternotomy with an extended atrial incision, and complex repairs are similar in difficulty to full sternotomy operations. (Courtesy of Dr. D.M. Cosgrove.)

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?? PERFUSION TECHNOLOGY
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By combining modified traditional perfusion methods and new technology, surgeons have been able to speed the development of MIHVS. Thin-walled arterial and venous cannulas, transthoracic aortic cannulas, endoaortic balloon occluders, modified aortic clamping devices, percutaneous coronary sinus cardioplegia catheters, and assisted venous drainage all have aided in evolution of these operations.

Arterial Access

As ministernotomy incisions lend themselves to facile antegrade aortic cannulation, most surgeons prefer central arterial cannulation. For minimally invasive aortic surgery, we cannulate the transverse aortic arch, just distal to the innominate artery through the upper incision and use either a 17F or 19F nonkinking Bio-Medicus cannula (Fig. 44-6). Port-Access surgical systems initially required retrograde femoral arterial perfusion, femoral-atrial venous drainage, and intraluminal aortic balloon occlusion (Fig. 44-7). 45 However, current specialized direct aortic cannulas can provide combined antegrade perfusion, balloon aortic occlusion, and antegrade cardioplegia.46



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FIGURE 44-6 (A) Percutaneous Carpentier dual-stage venous drainage cannula (Medtronic Inc., Minneapolis, MN). This cannula is inserted from the femoral approach using the Seldinger guidewire method. (B) Thin-walled 19F arterial perfusion cannula (Bio-Medicus; Medtronic Minneapolis, MN). A smaller 17F version is used for percutaneous internal jugular vein cannulation.

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FIGURE 44-7 Port-Access system with transfemoral artery endoaortic balloon occluder, femoral venous drainage catheter, percutaneous internal jugular retrograde coronary sinus cardioplegia catheter, and pulmonary artery vent (Cardiovations, Ethicon Inc., Norwalk, CT).

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For minimally invasive mitral surgery, we prefer retrograde femoral perfusion, employing small wire-wound Bio-Medicus arterial cannulas (17F or 19 F) inserted over a guidewire (Figs. 44-6 and 44-8). In our patients excellent flow rates with acceptable perfusion pressures have been attained with no retrograde aortic dissections. Mitral patients with peripheral atherosclerosis or small iliac vessels may require direct aortic cannulation, either placed through the incision or via a transthoracic approach. Recently, a long 21F femoral cannula has been developed for remote access antegrade perfusion through fenestrations located in the proximal catheter (Fig. 44-9).47



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FIGURE 44-8 Femoral artery cannulation for minimally invasive mitral valve surgery. Both the (17F-19 F) perfusion cannula and (23 F) venous cannula are inserted over a guidewire using the Seldinger technique after progressive coaxial dilations. Nonpenetrating oval purse-string sutures are placed in both the artery and vein for hemostasis. Echocardiographic guidance is essential for safe passage of the venous cannula to the right atrium.

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FIGURE 44-9 The Remote Access Balloon Perfusion Cannula (ESTECH Corp., Danville, CA) is inserted retrograde via the femoral artery and is unique in that antegrade arterial perfusion is established. In the same catheter a proximal balloon aortic occluder that delivers antegrade cardioplegia establishes protected cardiac arrest. Holes in the proximal catheter are the sole source of antegrade aortic perfusion, minimizing risks of retrograde aortic dissection during cardiopulmonary bypass.

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Venous Drainage

Venous access can be established in a variety of ways. At the Brigham and Women's Hospital, for aortic and mitral surgery, the right atrium is cannulated directly through the incision or separate skin incisions may be used for the isolated caval cannulation, when needed (Fig. 44-10). Cosgrove introduces a small (23F) cannula directly into the right atrium through the ministernotomy. Koernitz and Gundry insert an oval-flat or "pancake" cannula into the right atrium to minimize incision space loss.12,15



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FIGURE 44-10 For direct-vision minimally invasive mitral or aortic valve surgery, traditional cannulation methods may be modified. Here, smaller venous drainage cannulas are inserted through auxiliary incisions. Standard caval occlusion and venous drainage are usually effective. However, additive active venous suction allows usage of smaller cannulas. (Courtesy of Dr. L.H. Cohn.)

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For a first aortic valve operation, we use a 23F direct right atrial cannula and apply suction venous return. In aortic valve reoperations, we pass a 23F percutaneous femoral venous cannula to the right atrium, using the Seldinger technique and echocardiographic guidance. For minimally invasive mitral valve surgery we always establish bicaval venous drainage using a percutaneous 17F internal jugular cannula and a femoral vein to right atrial catheter (Fig. 44-11).48,49 For safety it is important to use the Seldinger guidewire method with echocardiographic guidance to assure optimal venous catheter tracking and atrial position. Using internal jugular and femoral venous catheters, combined either with caval tapes or balloon occluders, minimally invasive tricuspid surgery can be performed alone or in combination with mitral operations using a 5-cm minithoracotomy. Carpentier designed a specialized percutaneous femoral venous cannula with dual-stage drainage ports (see Fig. 44-6).24 This catheter can be combined with caval snares to perform atrial septal and tricuspid surgery, as well. After heparin reversal both jugular and femoral percutaneous venous cannulas can be removed with local pressure applied for hemostasis.



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FIGURE 44-11 A right internal jugular venous catheter (17F) is combined with femoral-atrial active venous drainage for full bicaval access. This is important during atrial retraction in a near closed chest where the cavae can be kinked with distraction. The Aesop 3000 robotic camera arm is seen in the foreground.

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Assisted venous drainage has been a major advance as this technique enhances the efficiency of smaller cannulas. We prefer to use the Bio-Medicus centrifugal vortex pump to create variable negative pressures for venous drainage. Also, by combining wall suction (less than -40 cm H2O pressure) and a hard-shell cardiotomy reservoir, a safe, simple, and economical assisted venous drainage system can be developed.43 Using these altered cannulation methods and a vortex pump, venous drainage has been excellent for aortic, mitral, and tricuspid surgery.

Myocardial Preservation

Myocardial preservation techniques used with MIHVS are similar to sternotomy-based operations. For both aortic and mitral valve patients, we cool systemically to 28?C, as the ambient cardiac temperature generally is warmer than during conventional valve operations. With either a ministernotomy or minithoracotomy, a retrograde coronary sinus cardioplegia catheter can be inserted directly into the right atrium and position confirmed echocardiographically. Also, Port-Access technology provides a percutaneous retrograde cardioplegia catheter, which is introduced using echo via the internal jugular vein preoperatively (see Fig. 44-7). Although retrograde cardioplegia seems preferable, to assure uniform cardiac cooling and even distribution of cardioplegia solutions, we have found antegrade cardioplegia preferable and efficient. Exposure limitations make direct retrograde coronary sinus catheter insertion more difficult and with less control should sinus complications arise. We prefer cold antegrade blood cardioplegia for both minimally invasive aortic and mitral surgery. During aortic valve surgery, supplemental ostial cardioplegia can be delivered intermittently using a soft catheter. In mitral patients we insert an antegrade cardioplegia/aortic vent catheter into the aortic root directly through the incision. For aortic valve operations, we rarely vent either the left ventricle or pulmonary artery. However, we keep the operative field clear using a small catheter, placed across the valve annulus into the left ventricle. Should additional venting be required, the ministernotomy provides excellent exposure to the superior pulmonary vein. To keep the surgical field clear during mitral surgery, we place a flexible sucker directly into the left atrium.

Aortic Occlusion

For MIVHS most surgeons use a standard cross-clamp, placed through the incision (see Figs. 44-2 and 44-5). Specialized flexible-handle aortic clamps have been developed to increase exposure through the hemisternotomy and minimize inadvertent dislodgement (Fig. 44-12). For minithoracotomy mitral operations, we use a percutaneous, transthoracic aortic cross-clamp. The clamp is inserted through a 4-mm incision placed in the right lateral 3rd intercostal space. The posterior immobile "tine" of the clamp is positioned through the transverse sinus dorsal to the aorta (Figs. 44-3 and 44-13).48 During placement, attention is necessary to prevent injury to the left atrial appendage and right pulmonary artery behind the aorta. This clamp has provided very secure occlusion without any aortic injuries.



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FIGURE 44-12 Flexible arm Cosgrove Aortic Clamp (Allegiance Healthcare Corp., McGaw Park, IL). This mobile arm clamp allows complete aortic occlusion through limited-access incisions, such as the ministernotomy. We have also used it for transthoracic aortic occlusion in mitral surgery.

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FIGURE 44-13 (A) The Chitwood transthoracic aortic cross-clamp (Scanlan International Inc., Minneapolis, MN). The shaft, which is 4 mm in diameter, is passed through the 3rd intercostal space. (Inset) The posterior or fixed prong of the clamp is passed through the transverse sinus, under direct or video visualization to avoid injury to the right pulmonary artery, left atrial appendage, or left main coronary artery. The mobile prong is passed ventral to the aorta as far as the main pulmonary artery. (B) A videoscopic view of the deployed transthoracic aortic clamp (Clamp). The aorta is fully compressed and an antegrade cardioplegia needle is shown (Plegia), in position just distal to the right coronary artery origin.

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Intra-aortic balloon occluders generally are introduced retrograde through the femoral artery. The occlusive balloon should be positioned, under echocardiographic control, just above the tubulosinus ridge in the ascending aorta (Fig. 44-14).5,45 Balloon pressures often approximate 300 torr during complete occlusion, and the catheter tip position must be monitored continuously. Antegrade cardioplegia is given via the catheter central lumen. Balloon dislodgement can cause innominate artery occlusion, resulting in neurologic injury, or prolapse into the left ventricle with inferior myocardial preservation. Thus continuous echocardiographic monitoring is essential to detect balloon migration.



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FIGURE 44-14 Radiograph of an expanded Port-Access balloon occluder in the ascending aorta. Optimal positioning, with the proximal balloon at the aortic tubulosinus ridge and the distal segment below the innominate artery, is confirmed either by angiography or more commonly by transesophageal echocardiography. An echo probe is also seen in this illustration, as is the venous drainage catheter.

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Cardiac Air Removal

Meticulous cardiac air removal is particularly important in minimally invasive valve operations. Difficulty exists in manipulating and de-airing the cardiac apex, as it cannot be elevated. Also, with a right anterolateral minithoracotomy, air tends to be retained along the more dorsal ventricular septum and in the right pulmonary veins. Continuous carbon dioxide (CO2) insufflation has been particularly helpful in minimizing cardiac air and should be begun before cardiac chambers are opened. CO2 is much more soluble in blood than is air and displaces it very efficiently. We infuse CO2 continuously (45 L/min) into the thorax, and prior to cross-clamp release ventilate both lungs vigorously to draw the gas deep into all pulmonary veins. After atriotomy closure and following cross-clamp release, suction is applied to the aortic root vent, and we then compress the right coronary artery origin during early ejection. As the heart beats, nonatherosclerotic aortas are reclamped gently to expel residual air into the vent suction. Constant transesophageal echocardiographic monitoring is essential to assure adequate air removal before weaning from cardiopulmonary bypass.


?? ROBOTIC TECHNOLOGY
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The Aesop 3000 robotic camera manipulator (Computer Motion, Inc., Santa Barbara, CA) has remained a pillar of control during our minimally invasive video-assisted mitral surgery. Figure 44-15 shows how this device is arranged during these operations. Even though video assistance with robotic vision control has proved valuable, surgeons still must operate with long instruments in a two-dimensional operative field. The da Vinci Surgical System (Intuitive Surgical, Inc., Mountain View, CA) is comprised of three components: a surgeon console, an instrument cart, and a visioning platform (Fig. 44-16).49 The operative console is removed physically from the patient and allows the surgeon to sit comfortably, resting the arms ergonomically with his/her head positioned in a three-dimensional (3-D) vision array. The surgeon's finger and wrist movements are registered, through sensors, in computer memory banks, and then these actions are transferred efficiently to an instrument cart, which operates the synchronous end-effector instruments (Fig. 44-17). Through 1-cm ports, instruments are positioned near cardiac operative sites in the thorax, and the camera is passed via a 4-cm working port used for suture and prosthesis passage (Fig. 44-18). Every analog finger movement, along with inherent human tremor at 8 to 10 Hz/sec, is converted to binary digital data, which are smoothed and filtered to increase microinstrument precision. Wrist-like instrument articulation emulates precisely the surgeon's actions at the tissue level, and dexterity becomes enhanced through combined tremor suppression and motion scaling. This allows both increased precision and dexterity, with the surgeon becoming truly ambidextrous. A clutching mechanism enables readjustment of hand positions to maintain an optimal ergonomic attitude with respect to the visual field. This clutch acts very much like a computer mouse, which can be reoriented by lifting and repositioning it to reestablish unrestrained freedom of computer activation.




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FIGURE 44-15 (A) During minimally invasive video-assisted mitral surgery, the camera is voice activated and positioned by the surgeon using the Aesop 3000 robot. Operative maneuvers are made through the 5-cm incision using long instruments and secondary vision.

(B) Here the Aesop 3000 is attached to a 5-mm 0? two-dimensional telescope. For mitral valve surgery the pericardial edges are retracted using transthoracic sutures.

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FIGURE 44-16 (A) da Vinci Robotic telemanipulation system. The operative console is in the foreground while the instrument cart is at the table. Both the operating surgeon and patient side assistant are shown. (B) da Vinci Robotic mitral valve repair. The surgeon is positioned approximately 10 feet from the patient. The instrument cart is placed on the left side of the tilted patient with arms entering the right thorax.

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FIGURE 44-17 The operating surgeon manipulates instrument tips in the patient's thorax via ergonomic "handpieces" that transfer filtered digitized data into smoothed movements.

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FIGURE 44-18 This thoracic cross section during a da Vinci mitral operation shows how both instrument arms and the visual field converge at the operative plane to effect an unobstructed topographic view with full access to valvular and subvalvular structures.

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The 3-D digital visioning system enables natural depth perception with high-power magnification (10X). Both 0? and 30? endoscopes can be manipulated electronically to look either "up" or "down" within the heart. Access to and visualization of the internal thoracic artery, coronary arteries, and mitral apparatus have been shown to be excellent. The operator becomes ensconced in the 3-D operative topography and can perform extremely precise surgical manipulations, devoid of traditional distractions. Figure 44-19 shows the surgeon's operative field during a da Vinci mitral repair. Perfusion technology is the same as described above for video-assisted operations and a larger minithoracotomy.



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FIGURE 44-19 (A) da Vinci mitral valve repair. The P2 segment of the posterior leaflet is being resected by robotic microscissors. The annulus is reduced and both P1 and P3 approximated. (B) Instrument arms of the da Vinci are tying sutures to secure an annuloplasty band along the posterior annulus.

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?? CURRENT STATUS
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Minimally Invasive Aortic Valve Surgery

Most cardiac surgeons already have the innate abilities needed to perform direct-vision MIHVS. Valve exposure, repair methods, prosthesis insertion, and perfusion technology differ little from traditional aortic operations. The hemisternotomy approach, initially described by Cosgrove, Cohn, Gundry, Koernitz, Machler, von Sagesser, and others, has been the most common incision used by minimally invasive aortic valve surgeons.1,2,12,15,50,51 In a randomized study, comparing the conventional sternotomy (N = 60 patients) to an upper hemisternotomy (N = 60 patients), Machler found the latter to provide reduced trauma, less ventilation requirements, less blood loss, and better cosmesis.50 Comparatively, Aris found no differences in results; however, he used two different hemisternotomy approaches, therefore seemingly confounding his conclusions.52 Christiansen concluded the only benefit remaining 1 year following minimally invasive aortic surgery in 25 patients to be cosmesis.53

Currently, at the Cleveland Clinic 90% of aortic valve patients undergo a minimally invasive operation.54 By early 2002 Dr. Cosgrove's team had performed a total of 607 MIS aortic operations, of which 76% either had homograft, mechanical, or xenograft tissue replacements and 24% were repairs. A number of these were combined with ascending aortic root operations. Only 1.7% required conversion to a full sternotomy, and the most common reason was for adjunctive coronary revascularization. Interestingly, only 2 patients were converted for poor exposure and none for bleeding. Cardiac arrest and perfusion times averaged 60 and 70 minutes, respectively, and these data were similar to his conventional aortic valve operations. Their overall mortality for minimally invasive aortic valve operations was 0.8%. Complications included bleeding (4.9%), respiratory insufficiency (1.5%), stroke (2.5%), and wound problems (0.7%). Of these patients 11% required transfusions, and the average hospitalization was 6.2 days with 30% being discharged before the fourth postoperative day. Mortality and length of stay data have been superior to risk-adjusted cohorts from the STS National Adult Cardiac Surgery Database for conventional aortic valve operations, which were 4% and 7 days, respectively. Since minimally invasive aortic surgery was first introduced in 1996 at the Cleveland Clinic, perfusion times have fallen there more than cross-clamp intervals, indicating learning curves to be related more to optimizing perfusion technology and aortic valve exposure than the actual repair/replacement. For aortic valve surgery the upper hemisternotomy has supplanted both parasternal and trans-sternal incisions at most institutions.

Independently, Cohn began performing minimally invasive aortic valve surgery at the Brigham and Women's Hospital in June of 1996.1,14,33 First he preferred the parasternal approach, but for the last five years he has used the upper hemisternotomy.14,44,55 His series of 425 aortic valve operations has yielded equally impressive results to those described above. Nearly all patients underwent valve replacements with pericardial prostheses dominating the series and bileaflet pyrolytic carbon prostheses used next in frequency. The operative mortality was 2.4% and complications included bleeding (3.1%), stroke (1.6%), heart block (5.2%), and wound problems (2.6%). In this series 50% of patients were transfused, and the average length of hospitalization was 7 days. Of these patients 11% were minimally invasive aortic valve reoperations, which were facilitated by avoiding patent internal thoracic arterial graft clamping.55,56 The mean age was 10 years older in reoperative patients, and complications and operative mortality (6.4%) were higher than for first operations.

Other surgeons with smaller series have reported results similar to those of Cosgrove and Cohn. Using a lower hemisternal incision (8-cm), Bonnachi found significant cosmetic benefits, compared with conventional sternotomies (24-cm incision), and noted reduced transfusions, ventilator time, pain management, and hospital stay. In both cohorts he reported similar perfusion and cross-clamp times as well.57 In contradistinction, Ferdinand found no difference between conventional and MIHVS with three different types of stentless aortic valve replacements.58 Using modified Port-Access methods, the New York University group performed 153 aortic valve replacements with a conventional cross-clamp placed through a right second ICS incision.38 In this series both a 6.5% perioperative mortality and a 2.6% stroke rate were reported. They had good surgical access but found mild or greater aortic insufficiency by echocardiography in 24% of their postoperative patients. In a parallel editorial, Chitwood concluded that the second intercostal minithoracotomy might have limited their exposure, resulting in more residual leaks than expected.59

For aortic valve surgery our group has preferred a small incision and either an upper sternotomy with deviation to the right or near complete sternal division with simple spreading of each upper half, "springing" the lower part without division. From these series we can conclude that the upper hemisternotomy provides excellent exposure for simple aortic valve operations and most surgeons can master this technique easily without compromising results. More complex operations involving the aortic root and/or Ross autograft method can be done by this route but should be reserved for surgeons who are very experienced with minimally invasive techniques.

Minimally Invasive Mitral Valve Surgery

Again, Cosgrove and Gundry have been consistent proponents of using the ministernotomy for mitral surgery. They have considered the ministernotomy technique more reproducible for surgeons with variable experiences and abilities. Both complex replacements and repairs have been done through this incision and to date few operative failures have resulted from this exposure. Between 1996 and early 2002, Cosgrove and his Cleveland Clinic group had done 1427 minimally invasive mitral operations, using direct vision, upper hemisternotomy, and modified perfusion methods. As noted earlier, the extended atriotomy, used by Cosgrove, apparently has not eventuated in additional atrial arrhythmias. Of these patients, 82% had degenerative and 9% had rheumatic disease. Of all mitral valves, 90% were insufficient and nearly all were repaired, with 98% having a band annuloplasty and 85% undergoing leaflet resections. Perfusion and aortic occlusion times averaged 80 and 60 minutes, respectively. These times are shorter than those of many experienced surgeons using a full sternal approach. As seen earlier in their aortic operations, perfusion times have fallen more significantly than arrest times since 1996. This mitral valve series presents an impressive mortality (0.3%) and complication rate (bleeding [3.1%], strokes [1.8 %], respiratory insufficiency [0.8%]). Conversions to a full sternotomy have fallen at the Cleveland Clinic from 5 % in 1997 to 0.5% in 2002 (1.5% overall), and most of these have been related to poor exposure, not bleeding. Only 7% of patients were transfused, and the mean hospitalization was 6.5 days, with 20% being discharged in less than 4 days.

After initially using a right parasternal incision with bicaval cannulation and left atrial entry via the interatrial septum, Cohn et al now prefer modified hemisternal approaches for mitral valve surgery. Of the 411 mitral patients operated between 1996 and early 2002, 201 had hemisternotomies and 201 had parasternal incisions, with 8 having a minithoracotomy. Myxomatous (81%), rheumatic (10%), and endocarditic (4%) were the most common etiologies. In 88% repairs were done, and in the remaining 12%, replacements were done using mechanical valves (84%). Their operative mortality was an impressive 0.2% with no deaths in the repair group. Bleeding occurred in 2% and 38% were transfused with an average of one packed cell unit per patient. Strokes occurred in 2.2% of patients, with myocardial infarctions in 1.0%. Patients were hospitalized for a mean of 6 days and 8.3% required additional rehabilitation prior to discharge.

Grossi et al at New York University compared 100 minimally invasive mitral operations, done through a 6- to 8-cm minithoracotomy using direct-vision and Port-Access methods, to a cohort of 100 conventional mitral operations.39 They reported a perioperative mortality of 1.0%. In these patients 80% had a posterior leaflet procedure and 30% had an anterior leaflet reconstruction. This ratio did not differ from that of their full sternotomy patients, nor did the status of repairs 1 year following surgery. Their results suggest minimally invasive mitral operations can be done safely using Port-Access methods with similar results as conventional operations and with no added mortality or morbidity. At the same time they had fewer transfusions, shorter lengths of stay, and less septic complications, despite longer cardiopulmonary bypass times. In a multi-institutional analysis of 491 Port-Access mitral repairs from 104 centers, Glower reported that 86% of all valves were repaired with aortic cross-clamp times of 90 minutes and perfusion times of 137 minutes.60,61 The overall mortality for repairs was 1.6% and was 5.5% for replacements. Age was the only independent predictor of strokes (2.7%) in these patients. Neurologic complications associated with early use of this technique have diminished with the advent of better devices and more experience. The overall length of stay for this large group of mitral patients was 7 days.

In early 2001 the East Carolina University (ECU) group reported their 128 successful video-assisted mitral valve operations.26 At first patients with anterior leaflet pathology and annular calcification were avoided. However, now we consider these patients within the realm of video-assisted surgery. Table 44-3 details our current criteria for patient selection. In our series repairs have included quadrangular resections, annuloplasties, and complex chordal operations. The majority of the patients had myxomatous disease, and 61% of the total group underwent a repair. Figure 44-20 shows a videoscopic bileaflet repair utilizing two (P1 and P2) sliding plasties as well as a P2 segment transfer to A2 for Type 2 anterior leaflet prolapse. When the early series is combined with the subsequent 100 video-assisted mitral operations, repairs have been done in 81% of patients at ECU. The operative and 30-day mortalities for our entire series have been 0.4% and 1.7%, respectively. After implementing the Aesop 3000 robot to voice-direct the endoscopic camera, cross-clamp and perfusion times fell secondary to improved visualization and reduced lens cleaning. However, in the latter half of the early series cross-clamp (90 minutes) and perfusion (143 minutes) times still remained longer than conventional operations. Currently, cardiac arrest and perfusion times have fallen to 70 and 100 minutes, respectively. Interestingly, we have seen no difference in bleeding and transfusion requirements between our conventional and MIHVS patients. However, the hospital lengths of stays have averaged 4.9 days compared to 8 days for conventional operations. Of these 228 patients, there have been two conversions to a sternotomy, two strokes, and no aortic dissections. We have had one vena caval injury during cannulation. Included in this series are 28 patients having had either prior coronary or mitral surgery. These patients underwent video-assisted reoperations with a 3.5% mortality and markedly less blood loss than conventional reoperations.


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TABLE 44-3 Current patient selection: videoscopic or video-assisted mitral valve surgery

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FIGURE 44-20 Videoscopic (Aesop 3000) complex mitral valve repair. Here, both the anterior and posterior leaflets are redundant with severe type 2 prolapse. The posterior part of P2 was resected, leaving the anterior quarter of the leaflet with chords attached along the coapting edge. This segment of P2 is then transferred along the coapting edge of A2. Securing mattress sutures are being placed. Finally, a height-reducing sliding plasty is done for both P1 and P3 before central approximation. A band annuloplasty is done last. We have found this method very effective for treating severe anterior prolapse minimally invasively.

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Mohr et al reported on 154 video-assisted mitral valve operations using Aesop 3000 robotic camera control.23,28,62 In these patients the aortic cross-clamp and perfusion times were similar to his conventional operations, and the operative mortality was 1.2%. He considered three-dimensional visualization to be the key to excellent results during videoscopic valve reconstructions. In a study comparing the Port-Access technique to transthoracic clamping, Wimmer-Greinecker obtained similar repair results but with faster operations, less technical difficulties, and lower cost using the clamping method.63 In early 2002 Vanermen reported success in 187 patients undergoing totally endoscopic repairs using the Port-Access method and no rib spreading. He used a holder-mounted, two-dimensional endoscopic camera and performed complex repairs with excellent results at follow-up 19 months later.41 The hospital mortality was 0.5%, and there were two conversions to a sternotomy for bleeding. Freedom from reoperation was 95% at four years. Over 90% of patients had minimal postoperative pain. Although this and other series have not been randomized, there are strong suggestions that mitral valve surgery has entered a new era and that video techniques can facilitate these operations.

Robotic Mitral Valve Surgery

At our institution, as part of an FDA trial, mitral repairs have been performed in 50 patients using the robotic da Vinci Surgical System.29,30 Quadrangular leaflet resections, leaflet sliding plasties, chordal transfers, PTFE chord replacements, and annuloplasty band insertions have been done with facility. Difficult commissural and trigone sutures dissolved into simple efforts using da Vinci. Robotic repair and total operating times decreased from 1.9 and 5.1 hours, respectively, for the first 25 patients to 1.5 and 4.4 hours, respectively, in the last 25 patients. Excepting times required to place annuloplasty bands, all time intervals decreased significantly with experience. In the last cohort, cross-clamp and perfusion times were 1.8 and 2.7 hours, respectively. This time course paralleled improvements experienced with our videoscopic series reported above. We have had no major complications and the mean length of stay has been 3.8 days. Two valves were replaced either because of hemolysis (19 days) or a new grade 3 leak (2 months). Mohr has successfully completed 22 mitral repairs in Leipzig with da Vinci.28 Lange in Munich has performed a totally endoscopic mitral repair using only 1-cm port incisions.32 A multicenter da Vinci trial, enlisting approximately 120 patients, is nearing completion and to date demonstrates efficacy and safety in performing these operations by multiple surgeons at various centers. To date aortic and tricuspid valves have not held widespread interest for robotic surgeons.


?? CONCLUSIONS
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The above information suggests that minimally invasive valve surgery is well on the way to reality. Although operative philosophies, patient populations, and surgeon abilities differ between centers, the compendium of recent results remains very encouraging. The advent of true three-dimensional vision with tactile instrument feedback will be the major bridge to truly "tele-micro-access" operations. Also, to perform these operations optimally, "extracorporeal" surgeons and engineers will need to improve methods by which instruments are directed by computers. Recent successes with direct-vision, videoscopic, and robotic minimally invasive surgery all have reaffirmed that this evolution can be extremely fast, albeit through various pathways. In fact catheter-based technology is even moving toward treating aortic valve disease, and mitral annuloplasties have been done experimentally through the coronary sinus.64

Patient requirements, technology developments, and surgeon capabilities all must become aligned to drive these needed changes. In addition we must work closer with our cardiology colleagues in these developments. This is an evolutionary process, and even the greatest skeptics must concede that progress has been made. However, curmudgeons and surgical scientists alike must continue to interject their concerns. Caution cannot be overemphasized. Traditional valve operations enjoy long-term success with ever-decreasing morbidity and mortality, and remain our measure for comparison. Surgeons and cardiologists must remember that less invasive approaches to treating valve disease cannot capitulate to poorer operative quality or unsatisfactory valve and/or patient longevity.


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