Ann Thorac Surg 2005;79:1372-1376
© 2005 The Society of Thoracic Surgeons
New technology
Robotic Mitral Valve Annuloplasty With Double-Arm Nitinol U-Clips
Clifton C. Reade, MD*,
Curtis E. Bower, MD,
B. Marcus Bailey, MD,
David M. Maziarz, MD,
Saqib Masroor, MD,
Alan P. Kypson, MD,
L. Wiley Nifong, MD,
W. Randolph Chitwood, Jr, MD, FACS
Division of Cardiothoracic Surgery, The Brody School of Medicine at East Carolina University, Greenville, North Carolina, USA
Accepted for publication February 18, 2004.
* Address reprint requests to Dr Reade, Department of Surgery, The Brody School of Medicine at East Carolina University, 600 Moye Blvd, Greenville, NC 27858, USA.
readec{at}mail.ecu.edu
Presented at the Video Session of the Fiftieth Annual Meeting of the Southern Thoracic Surgical Association, Bonita Springs, FL, Nov 13–15, 2003.
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Abstract
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PURPOSE: Robotic mitral valve repair increases precision however operative times are longer. Prior studies have indicated that robotic knot tying is time consuming and it is without potential room for improvement. We therefore investigated tissue approximation devices that may shorten operative times.
DESCRIPTION: A 67-year-old female was approached through a right mini-thoracotomy with the da Vinci Robotic Surgical System (Intuitive Surgical, Sunnyvale, CA). Using 12 nitinol U-clips (Coalescent Surgical, Sunnyvale, CA) an annuloplasty band was placed under robotic guidance. Clip placement and deployment times were recorded and statistical comparisons were assessed to prior suture annuloplasties.
EVALUATION: Clip placement time was 1.3 ± 0.9 (minutes ± standard deviation), statistical comparison with first, most recent, and all prior suture annuloplasties proving no significance. Clip deployment time was 0.5 ± 0.2, whereas knot-tying times and respective statistical comparison for first, most recent, and all prior suture annuloplasties were 2.0 ± 0.7 (p = 0.003), 1.2 ± 0.4 (p = 0.0004), and 1.6 ± 0.6 (p < 0.00001). Follow-up echocardiography performed postoperatively, at 3 months, and at 9 months revealed valvular structural integrity with only minimal mitral regurgitation.
CONCLUSIONS: U-clips considerably reduce time for annuloplasty over conventional suture and may help reduce operative times as well.
Abbreviations: AH = arrested heart • CDT = clip deployment time • CPB = cardiopulmonary bypass • CPT = clip placement time • KTT = knot tying time • RMVR = robotic mitral valve repair • RMVR-AVG = average of all prior robotic mitral valve repairs (using suture) • RMVR-1 = first patient receiving robotic mitral valve repair (using suture) • RMVR-69 = 69th patient receiving robotic mitral valve repair (using suture; performed one week prior to reported case) • SPT = suture placement time • TEE = transesophageal echocardiography • VAMVR = videoscopic assisted mitral valve repair
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Introduction
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Since 1996 minimally invasive technologies and techniques regarding mitral valve surgery have achieved a stepwise progression [1]. Initially the conventional sternotomy incision was modified to a mini or partial sternotomy. Next this incision was changed and reduced to a 5-cm right mini-thoracotomy using manual video assistance. With the introduction of AESOP (automated endoscopic system for optimal positioning) (Intuitive Surgical, Sunnyvale, CA), voice-activated robotic assistance replaced the manual camera guidance of an assistant. Finally the da Vinci Surgical System (Intuitive Surgical, Sunnyvale, CA) has allowed almost complete endoscopic repair of the mitral valve.
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Technology
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The progression to video-assisted mitral valve repair (VAMVR) using AESOP has led to substantial decreases in blood loss, ventilator time, and hospital length of stay without increases in patient morbidity or mortality [2]. Robotic mitral valve repair (RMVR) using da Vinci yields comparable results but allows tele- and micro-manipulation in a three-dimensional (3D) working environment enabling greater precision [3].
Initially VAMVR and RMVR increased cardiopulmonary bypass (CPB) and arrested heart (AH) times over conventional sternotomy [2, 3]. Previous studies have indicated that extended AH time contributes to postbypass depressed myocardial function [4, 5]. Factors that contribute to extended times with RMVR include robotic set-up time, port planning, robotic arm insertion, and patient-side surgeon expertise. However we have observed that all of these times decrease continuously as more procedures are performed. In contrast suture knot tying using da Vinci is quickly learned and this time plateaus early in the surgeon's robotic operative experience with no statistical improvement after 20 cases.
To improve existing RMVR techniques suture placement and knot tying during annuloplasty were evaluated as possible areas to expedite time efficiency. On average 10–12 sutures are placed in the annuloplasty ring, which requires an extensive amount of time using repetitive robotic instrument movements [3]. Existing suture technology does not decrease annuloplasty ring placement time despite increased operative experience. Therefore we investigated the use of a novel self-closing clip.
Nitinol U-clips (Coalescent Surgical, Sunnyvale, CA) have been available for use in performing coronary anastamoses since the year 2000. More than 35,000 anastamoses have been performed to date. The clip is made of nitinol, an alloy with superelastic properties that allow the material to return to a preformed pattern. Recently a double-arm U-clip has been introduced that allows placement of a mattress stitch for annuloplasty band placement (Fig 1). We tested this clip extensively in both acute and chronic animal models and previously reported our findings [6]. Clip deployment times were considerably faster than knot tying and total clip placement was considerably faster than total suture placement. No clip fractures or dislodgements were demonstrated. Six-month postoperative echocardiography revealed preservation of mitral competence and no clip fracture, migration, or dehiscence. In response to these encouraging results regarding the animal studies, nitinol double-arm U-clips have recently been FDA-approved for tissue approximation in humans.
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Fig 1. Double-armed nitinol U-clips (left) before release, (middle) after one arm released, and (right) after both arms released.
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Technique
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The first patient to receive nitinol U-clips was a 67-year-old female bearing a past medical history extensive for chronic atrial fibrillation and severe mitral insufficiency with an ejection fraction (EF) of 30% as demonstrated by transesophageal echocardiogram (TEE). Her condition had deteriorated to New York Heart Association (NYHA) class IV.
A ten-minute video highlighting the procedure can be viewed on ctsnet.org at http://www.ctsnet.org/realmedia/vidgal/vg2003_reade.ram.
The patient underwent a standard RMVR and a microwave mini-maze atrial fibrillation ablation procedure through a 5-cm right mini-thoracotomy in the fourth intercostal space (Fig 2). Peripheral arterial and venous cannulation was achieved through the right femoral vessels. After institution of CPB aortic cross-clamping was achieved via a transthoracic clamp and arrest of the heart was achieved via antegrade cold blood cardioplegia. The left atrium was entered through the interatrial groove and the roof was elevated using the Cardiovations retractor (Ethicon, Somerville, NJ). Inspection of the mitral apparatus confirmed a dilated annulus as the cause of mitral regurgitation.
A total of 12 nitinol U-clips were used to secure a #28 Cosgrove-Edwards band (Edwards Lifesciences, Irving, CA) to the posterior mitral annulus. These were placed individually starting with the right fibrous trigone and progressing sequentially to the left fibrous trigone. Individual clip placement times (CPT) as well as clip deployment times (CDT) were recorded, the definitions of which are included in Table 1. These times were compared with suture placement times (SPT) and knot-tying times (KTT) from the first patient receiving RMVR (using suture) (RMVR-1) to the previous 69th patient receiving RMVR (using suture) (performed 1 week before reported case) (RMVR-69) and the average of all prior RMVRs (using suture) (RMVR-AVG). A t test was used for statistical significance with p less than 0.05 proving significance.
After repair of the mitral valve a saline test was performed to determine the adequacy of the repair. The atrium was closed, air was removed from the heart, and the patient was weaned from CPB. TEE confirmed a satisfactory repair.
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Clinical Experience
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All clips were placed easily, functioned appropriately, and sustained no misfires or abnormal clip deployment (Fig 3). The patient was extubated within 8 hours and was transferred out of the intensive care unit (ICU) on postoperative day 1. The chest tubes were removed on postoperative day 2 after 540 mL of drainage and discharge occurred on postoperative day 3. Follow-up echocardiography at 3 and 9 months revealed the valve to be structurally intact with only minimal mitral regurgitation via color Doppler. Left ventricular function had improved from a preoperative EF of 30% to a 9-month postoperative EF of 55%.
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Fig 3. Placement of nitinol U-clips. The needle is passed through the annulus (A, B), each needle is passed sequentially through the band (C), and then each needle is released from the U-clip (D, E). Completed U-clip placement (F).
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Comparisons of intraoperative times are indicated in Table 2. CPT was 1.3 ± 0.9 minutes (mean ± standard deviation [SD]), whereas CDT was 0.5 ± 0.2 minutes. SPT and percent change versus CPT for RMVR-1, RMVR-69, and RMVR-AVG were 3.3 ± 2.9 minutes (60% reduction), 1.1 ± 0.6 minutes (20% increase), and 1.7 ± 1.4 minutes (27% reduction), respectively. None of these groups proved statistically different from CPT. Associated KTT and percent change for RMVR-1, RMVR-69, and RMVR-AVG were 2.0 ± 0.7 minutes (73% reduction), 1.2 ± 0.4 minutes (55% reduction), and 1.6 ± 0.6 minutes (67% reduction), respectively. Statistical significance was observed when comparing CDT which indicated p values of 0.003, 0.0004, and less than 0.00001, respectively.
When performing the annuloplasty on RMVR-1, the surgeon observed an increase in time of 4% (3.4–3.5 minutes) from first to last suture placement, whereas a decrease of 57% (3.3–1.4 minutes) occurred in KTT. With the first U-clip patient the same surgeon observed an 81% decrease in time (3.6–0.7 minutes) with first to last U-clip placement, whereas a 26% decrease (0.6–0.4 minutes) occurred in CDT.
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Comment
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Placement of the double-arm nitinol U-clip is easily learned. Because a single surgeon has performed all of the da Vinci repairs at our institution, equal comparisons can be assessed between clip and suture placement. When RMVR-1 was performed 2 years before this reported case, SPT averaged 3.3 minutes. Over the course of 2 years this surgeon became more efficient with regard to suture placement as RMVR-69 time was reduced to 1.1 minutes, a reduction of 67%. In previous studies we have indicated that SPT continues to decrease as more RMVRs are performed. Therefore we have reason to believe that suture placement with double-arm nitinol U-clips will illustrate similar decreases in time as robotic manipulation of the clip is learned.
Deployment of the nitinol clip provides the greatest time reduction. Knot tying is a tedious process with repetitive motions necessary to secure the suture. From RMVR-1 to RMVR-69, KTT only decreased from 2.0–1.2 minutes, a reduction of only 40%. We have demonstrated in previous studies that this 40% drop in KTT occurs in the first 20 cases with inconsequential gains occurring thereafter. However with nitinol U-clips considerable decreases in CDT are noted versus RMVR-1, RMVR-69, and RMVR-AVG.
Intracase learning curves illustrate differences in suture and clip use as well. SPT associated with RMVR-1 indicated a SD of 2.9 minutes, whereas U-clip placement in our reported patient indicated a SD of 0.9 minutes. With a much lower SD CPT did not range substantiallyfrom the mean of 1.3 minutes, whereas initial SPT indicated a much higher variance. Also there was no appreciable gain in speed associated with SPT on RMVR-1 as times actually increased 4% by the time the last suture was placed in the ring. In contrast when comparing the respective first patients, KTT indicated a 57% decrease in time from first to last knot, whereas CDT only indicated a 26% decrease. However for RMVR-1, KTT indicated a SD of 0.7 minutes, whereas for CDT the SD was only 0.2 minutes. The decreased variance associated with CDT highlights the speed with which one gains with regard to the ease of deployment. These findings support the notion that although knot tying is a skill that all cardiac surgeons have already established, a certain amount of familiarization with da Vinci is required to transmit these skills to the patient. However with clip deployment no familiarization is necessary as first CDT and last CDT were within 0.08 seconds of the overall mean and a minute SD.
In our observation annuloplasties performed with U-clips did not require more clips for approximation than prior performed annuloplasties using suture. We specifically did not use annuloplasty approximation time as a variable because annulus size and ring size dictate the number of sutures or clips used. Spacing on the annulus is correlated to needle size and the surgeon's interpretation of an adequate interval. Hence because both suture and clip patients were performed by the same surgeon any difference should be negated.
Double-arm U-clips also provide a low-profile appearance. Knot tying of suture leaves a "stack" of knots on top of the band that are continuously exposed to blood. In addition to this interaction and potential for unravel and slippage, the "stack" impairs optimal viewing of the valve on echocardiography by creating shadows through the annulus. Nitinol U-clips, as illustrated in Figure 4, do not extend upward from the band. Although at this time we have no supporting evidence with a lower profile U-clips may offer improved flow dynamics and reduce the surface area of possible sources for hemolysis. No difference in durability until fibrous in-growth has been indicated between suture and clips. Prior animal studies with explanted histology at 6 months have demonstrated that annuloplasties performed with U-clips indicate complete fibrous in-growth with preservation of U-clips [6]. In fact the low-profile shape may potentially speed fibrotic in-growth of the ring by reducing impedance.
Currently RMVR increases CPB and AH time even though blood transfusions, postoperative mechanical ventilation time, and length of stay are decreased. With added AH time the patient is put at increased risk for postoperative arrhythmias and myocardial dysfunction. As more patients demand sternal sparing surgery and as more surgeons move toward the employment of endoscopic techniques, novel devices, such as the nitinol U-clip, will begin to dictate a more prominent role with regard to mitral valve surgery.
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Disclosures and Freedom of Investigation
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The tested technology for this study was donated, however the authors maintained full control over the research design, facilitated methods, outcome parameters, analysis of data, and production of the written report.
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Disclosures and Freedom of Investigation
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The tested technology for this study was donated; however, the authors maintained full control over the research design, facilitated methods, outcome parameters, analysis of data, and production of the written report.
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Acknowledgments
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Wiley Nifong, MD, and W. Randolph Chitwood, Jr, MD, are nonpaid instructional consultants for Intuitive Surgical, Inc (Sunnyvale, CA).
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Footnotes
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The Society of Thoracic Surgeons, the Southern Thoracic Surgical Association, and The Annals of Thoracic Surgery neither endorse nor discourage use of the new technology described in this article.
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References
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- Chitwood WR Jr. Robot-assisted mitral valve surgery. Franco KL. Advanced Therapy in Cardiac Surgery. 2nd ed. New York: BC Decker; 2003. p. 220–229
- Felger JE, Chitwood WR Jr, Nifong LW, et al. Evolution of mitral valve surgery: toward a totally endoscopic approach. Ann Thorac Surg. 2001;72:1203–1209[Abstract/Free Full Text]
- Nifong LW, Chu VF, Bailey BM, et al. Robotic mitral valve repair: experience with the da Vinci system. Ann Thorac Surg. 2003;75:438–443[Abstract/Free Full Text]
- Buckberg GD, Olinger GN, Mulder DG, et al. Depressed postoperative cardiac performance: prevention by adequate myocardial protection during cardiopulmonary bypass. J Thorac Cardiovasc Surg. 1975;70:974–988[Abstract]
- Nelson RL, McConnell DH, Goldstein SM, et al. The effects of profound topical cardiac hypothermia on myocardial blood flow, metabolism, compliance and function. Surg Forum. 1975;26:261–262[Medline]
- Reade CC, Bower CE, Maziarz DM, et al. Sutureless robot-assisted mitral valve repair: an animal model. Heart Surg Forum. 2003;6:254–257[Medline]
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Top
Abstract
Introduction
