Interactive Cardiovascular and Thoracic Surgery 2:237-240(2003)
© 2003 European Association of Cardio-Thoracic Surgery
Work in progress report - Cardiac general |
Use of nitinol-U clips and flow characteristics of LIMA-LAD anastomoses
Giuseppe D'Anconaa,b,
Tomas A. Salernoc,
Pierre S. Aoukara and
Hratch Karamanoukiana,*
a Quebec Heart Institute, Ste-Foy, Quebec, Canada
b Center for Less Invasive and Robotic Heart Surgery, Buffalo General Hospital, 100 High Street, Buffalo, NY 14203, USA
c University of Miami Medical School, Jackson Memorial Hospital, Miami, FL, USA
* Corresponding author. Tel.: +1-716-859-1080; fax: +1-716-859-4697
lisbon5{at}yahoo.com
Received September 6, 2002;
received in revised form February 1, 2003;
accepted February 10, 2003
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Abstract
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The aim of this study was to compare flow characteristics of LIMA-LAD anastomoses constructed using two different techniques. Thirty patients underwent MIDCAB using either simple continuous suture (20) or separate nitinol U-clips (10). Intraoperative transit time flow measurements were recorded. Preoperative variables were similar in the two groups. Anastomosis time was significantly higher in the U-clipped group (9.9±1.5 min. vs.11.4±1.5 min;  ). Average flow value in the 20 continuous suture LIMA-LAD anastomoses was 26.7±8.8 ml/min versus 36.3±10.6 ml/min in the 10 U-clipped grafts ( ). Pulsatility Index value was significantly lower in the U-clipped group (3.1±0.9 vs. 1.8±0.3,  ) and diastolic flow index was significantly higher (0.7±0.04 vs. 0.8±0.03,  ). Perioperative results were similar in the two groups ( ). No mortality was reported. Postoperative trans-thoracic Doppler confirmed patency of the LIMA in all 30 patients. At short-term clinical follow-up (60±4 days), all patients were in CCSI. Nitinol U-clips can be used to construct LIMA-LAD anastomoses on the beating heart. Flow dynamics of these anastomoses are superior to those of grafts constructed using continuous suture technique. Particularly, total flow is higher and diastolic flow may reach values of 80% of the total measured flow.
Key Words: Nitinol U-clips; TTFM diastolic flow index
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1. Introduction
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The present technique in constructing vascular anastomoses with continuous sutures as described by Alexis Carrel at the beginning of the 20th century [1] has been proven to be reproducible and effective in millions of patients operated upon for both vascular and cardiac surgery procedures. Although satisfactory long-term results have been achieved when using this technique in conventional coronary artery bypass grafting (CABG) surgery, imperative questions regarding technical factors that may directly influence anastomotic patency rates and operative outcomes remain uninvestigated. In this regard differences between continuous and interrupted suture technique as applied to CABG have been poorly investigated. The limited number of studies showing definite advantage of the interrupted suture technique [2,3,4,5] has contributed to a broader adoption of the easier and faster continuous suture technique. On the other hand, the recent introduction and popularization of minimally invasive and endoscopic robotically enhanced coronary surgery [6] has refocused attention on new technologies that may ease construction of coronary anastomoses maintaining good operative results. Many different surgical devices have been investigated and, among them, the coalescent U-clip (Coalescent Surgical, Inc, Sunnyvale, CA) has been safely adopted in animal and human studies [7,8]. This device reproduces the theoretical advantages of the interrupted sutures anastomoses technique in a self-closing stitch that does not need to be manually tied. Although short-term angiographic patency rates of coronary anastomoses constructed with U-clips have been already addressed [7,8], limited information is available concerning the blood flow patterns in U-clipped coronary artery grafts [8]. Furthermore, differences in graft flow characteristics of U-clipped versus conventionally sutured coronary anastomoses have never been investigated.
In this manuscript we report our results in a prospective comparison between intraoperative transit time flow measurement (TTFM) findings of conventionally constructed (continuous polypropylene suture) versus U-clipped left internal mammary artery (LIMA) to the left anterior descending (LAD) coronary artery anastomoses.
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2. Patients and methods
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Between October 2001 and May 2002, 30 patients were enrolled in this study at the Buffalo General Hospital. Minimally invasive direct coronary artery bypass grafting (MIDCAB) was performed in all 30 patients. Twenty consecutive procedures using continuous suture were done followed by 10 consecutive procedures using U-clip. Assignment to one of the two groups was mainly done on the basis of U-clip availability. All operations were performed by the same surgeon. The selection criteria used were: requirement for a single vessel LIMA-LAD anastomosis approachable by MIDCAB, and LAD diameter >1.75 mm. Patients with calcified, intramural, and <1.75 mm LAD were excluded from the study. These are the criteria that we normally apply to MIDCAB patients. Use of U-clip technique did not add any further exclusion criterion to the study. LIMA was harvested through a left anterior small thoracotomy in the 4th intercostal space, and the anterior pericardium was opened to expose the LAD. Coronary stabilization was achieved by means of pressure type stabilizer. A 1.75-mm shunt was routinely used and allowed for satisfactory hemostasis. Anastomosis of the LIMA to the LAD was performed in 20 (66.6%) patients on the beating heart using a traditional technique with 7-0 polypropylene simple running suture. In 10 patients (33.3 %) LIMA to LAD anastomoses were performed on the beating heart using nitinol U-clip single armed sutures (Coalescent Surgical, Inc, Sunnyvale, CA). The clip is made of titanium and nickel and has shape-memory properties. The clip is maintained in its U-shape configuration and is connected to a flexible wire with a releasing mechanism in between. The 3-cm long wire has a needle at its other extremity. The needle is passed through the graft and the coronary as in conventional suturing. When the two tissues are properly approximated and the U-clip is placed in the desired position, the clip is deployed by compressing the 1-mm-long release mechanism located between the wire and the clip. At this point, the released clip returns to its original shape as a closed ring connecting the LIMA to the LAD. At the end of each anastomosis intraoperative graft patency verification was performed by means of transit time technology (Medistim, Oslo, Norway). Measurements were performed with the proximal snare applied in order to exclude any possible competition of flow from the native coronary artery. Flow curves, total flow, pulsatility index (PI) (Maximum flow-minimum flow/mean flow), and diastolic index values (mean diastolic/mean total flow) were recorded for each graft after protamine infusion. Cost of continuous suture was approximately $60 (one continuous suture+one additional, in case of placement of hemostatic sutures at $30 each), while the cost of U-clip sutures was $165 (11 U-clips at $15 each).
Demographic and perioperative data were prospectively collected for the two groups (continuous suture vs. U-clip) and statistically compared. Differences between variables were considered significant with a two-tailed P value <0.05. Continuous variables were compared using the unpaired t-test. Discrete variables were compared by using the chi-square test or the Fisher's exact test. Welch t-test was used instead of the unpaired t-test when differences between standard deviations were significant.
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3. Results
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Demographic and preoperative data were comparable in the two groups (Table 1). Average LAD occlusion time was similar in the two groups (11.1±1.9 min continuous suture vs.12.0±1.6 min U-clipped; ). Average anastomosis time was significantly higher in the U-clipped group (9.9±1.5 min continuous suture vs.11.4±1.5 min U-clipped; ). An average of 11±2 clips were used in the U-clipped group. No anastomosis in the U-clipped group was converted to a continuous suture technique. No conversion to full sternotomy or to cardiopulmonary bypass (CPB) was necessary in the two groups.
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Table 1 Preoperative and perioperative data in 30 patients undergoing LIMA-LAD anastomosis (20 continuous suture vs. 10 U-clip)
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Intraoperative TTFM data were compared in the two groups. Although all recorded flow curves appeared to have a diastolic flow pattern, statistically significant differences in the absolute flow, PI, and diastolic index flow values were reported. Data from all three parameters were normally distributed according to the method of Kolmogorov and Smirnov. Average flow value in the 20 LIMA-LAD anastomosed with continuous suture technique was 26.7±8.8 ml/min versus 36.3±10.6 ml/min in the 10 U-clipped grafts (). PI value was significantly lower in the U-clipped group (3.1±0.9 continuous suture vs. 1.8±0.3 U-clipped, ). Standard deviations between the two groups for PI were found to be extremely statistically significant ( ) using the unpaired t-test. Thus the Welch t-test was conducted, yielding a P value of 0.0001. Diastolic flow index was significantly higher in the U-clipped group (0.7±0.04 continuous suture vs. 0.8±0.03 U-clipped, ).
Perioperative data are reported in Table 1.
Postoperative trans-thoracic Doppler confirmed patency of the LIMA with diastolic flow pattern in all 30 patients. At clinical follow-up (60±4 days) all patients were free from angina and EKG stress tests performed 1 month after surgery did not show signs of myocardial ischemia.
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4. Discussion
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More than three decades have passed since the basic techniques adopted for CABG were firstly described [9,10,11]. Although many changes and advancements have been introduced through the years to improve outcomes of the operation, considerable issues regarding physiological and technical factors involved in the construction of coronary anastomoses remain unanswered. In this regard only a limited number of comparative studies have objectively addressed differences between anastomoses constructed with continuous or interrupted suture technique [2,3,4]. Using cast models, Young et al. [2] reproduced the internal configuration of saphenous vein to coronary artery anastomoses and examined the effects of different technical factors. The authors observed that, although the external appearance of the anastomosis was not a reliable indicator of its internal configuration, interrupted suturing consistently produced an internal configuration of the anastomosis with minimal deformities [2]. Shioi et al. [4] investigated the internal configurations of sequential anastomosis constructed with interrupted and continuous suturing technique. Interrupted sutures produced a larger anastomosed area for the incised length than other suture techniques. Furthermore, fine suturing spacing appeared to be less critical when interrupted sutures were used and an average of six to eight sutures per side appeared to produce well formed anastomoses. In a more recent experimental study, Baumgartner et al. [3] compared the effects of continuous vs. interrupted polypropylene (stiff) and polybutester (compliant) sutures on the luminal dimension and compliance of vascular anastomoses. End-to-end anastomoses constructed with continuous polypropylene, continuous polybutester, and interrupted sutures had respectively cross-sectional areas of 70%, 90%, and 107% of that of the native coronary ( ). The authors concluded that interrupted suture line should be used when constructing end-to-end anastomoses in small vessels. In spite of the theoretical superiority of the interrupted sutures technique, construction of vascular anastomoses with continuous simple sutures has increasingly gained popularity and has become standard practice in coronary surgery thanks to its advantages in terms of ease and speed of use. The recent popularization of minimally invasive coronary surgery and particularly the introduction of endoscopic robotically enhanced CABG [6] has focused interests in rethinking the technique of vascular anastomoses construction. In an attempt at eliminating long suture handling and knot tying, that may became a real challenge especially during endoscopic surgery, and with the aim of speeding anastomosis construction on the beating heart, many alternative ingenious techniques and technologies have been proposed [7,8,12,13,14,15]. Use of non-penetrating titanium clips to construct coronary anastomoses has been proposed by Nataf et al. [12]. Successful application of the clip requires eversion of the coronary and graft tissues and cannot be easily performed with calcified vessels [12]. A one-shot anastomotic clip device has been proposed by Heijmen et al. Accurate removal of the periadventitial tissue of the LITA should be performed to allow for appropriate release of the clips [13]. Gundry et al. [14] and Buijsrogge et al. [15] have successfully used biologic adhesives to construct coronary anastomoses in animal models. The nitinol U-clip device has been successfully used to perform vascular anastomosis in animal [7] and human [8] studies. Hill et al. successfully created right internal mammary to coronary anastomosis on the beating heart and repaired carotid arteriotomies in 13 consecutive calves. Patency was confirmed at angiography and neointimal resurfacing of the anastomoses was found at histopathologic evaluation [6]. More recently, Ono et al. reported successful U-clip construction of LIMA-LAD anastomoses in 14 patients operated upon with or without CPB [7].
In the present study we focused our attention on the comparison between intraoperative TTFM findings of LIMA-LAD grafts performed with continuous suture versus interrupted U-clips. Although physiological and anatomical differences between anastomoses constructed with interrupted versus continuous sutures have been partially addressed [2,3,4], functional studies investigating differences in coronary graft flow characteristics are lacking. TTFM findings in the present study confirm that U-clipped anastomoses on the beating heart can be safely performed, considerably improving flow dynamics of the newly constructed grafts when compared to the traditional single continuous suture technique. Performances of U-clipped anastomoses in terms of flow dynamics are satisfactory and diastolic flow averages 80% of the total flow value (diastolic flow index 0.8±0.03). On the other hand, although continuous single suturing technique for LIMA-LAD anastomoses construction has also demonstrated satisfactory clinical results, its flow dynamics are significantly different when compared to the U-clip technique. Total flow value is significantly less when using the continuous suturing technique (26.7±8.8 ml/min continuous suture vs. 36.3±10.6 ml/min U-clip, ) and more importantly the percentage of diastolic flow is significantly lower (0.7±0.04 continuous suture vs. 0.8±0.03 U-clip, ). As confirmation of the superior hemodynamic performance of the U-clip group, mean PI value was significantly lower than in the continuous suture anastomoses (3.1±0.9 continuous suture vs. 1.8±0.3 U-clip, ).
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5. Conclusion
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Superior hemodynamic performances of the U-clipped anastomoses have been reported in our study with a particular emphasis on the superior values of total diastolic flow and diastolic flow ratio. Although these findings are interesting and confirm at least the theoretical advantages offered by separated suture over continuous suture anastomoses, there has not been any clear difference in clinical outcome when using U-clips.
Lack of angiographic controls and adequate mid-term follow-up are present limitations that will be specifically addressed in the future developments of this study.
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Acknowledgements
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We thank Mrs Judy Bassini for her precious help in collecting and analyzing the data.
doi:10.1016/S1569-9293(03)00035-5
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References
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Abstract
1. Introduction