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Ann Thorac Surg 2008;85:1828-1836. doi:10.1016/j.athoracsur.2008.01.015
© 2008 The Society of Thoracic Surgeons
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Right arrow Coronary disease

Review

Coronary Connector Devices: Analysis of 1,469 Anastomoses in 1,216 Patients

Willem J.L. Suyker, MDa,*, Cornelius Borst, MD, PhDb

a Division of Cardiothoracic Surgery, Isala Klinieken, Zwolle, the Netherlands
b Heart Lung Center, University Medical Center Utrecht, Utrecht, the Netherlands

* Address correspondence to Dr Suyker, Isala Klinieken, PO Box 10500, 8000 GM Zwolle, the Netherlands (Email: w.suyker{at}isala.nl).


Dr Suyker discloses that he has a financial relationship with iiTech BV, Amsterdam, the Netherlands.

 

   Abstract
Top
 Abstract
Introduction
 Material and Methods
 Statistical Analysis
 Results
 Comment
 Study Limitations
 Disclosure
 Acknowledgments
 References
 
Automated coronary anastomotic devices could be the key to limited or port access procedures. To evaluate their clinical performance to date, 33 studies that included systematic elective angiographic imaging were reviewed, reporting on five proximal and seven distal devices. Marked outcome differences between the technologies were uncorrelated to study type and demographic, operative, and follow-up variables. Significant issues included graft thrombosis, graft kinking, and stenosing intimal hyperplasia inside the connector, limiting clinical applicability of at least three devices. Substantial equivalence to 1-year conventional anastomotic patency standards was found for selected anastomotic devices, which holds the promise of expanded applicability.

In the continuous search for improved myocardial revascularization strategies, interventional cardiologists are striving to enhance the safety and efficacy of percutaneous interventions, whereas cardiac surgeons are exploring ways to make their established procedures less traumatic. Although off-pump coronary artery bypass surgery has matured into a recognized treatment modality [1] since the introduction of suction stabilizing techniques [2], and port access procedures are possible in selected cases [3, 4], mainstream adoption of these procedures is hampered by the difficulty of suturing small vessels. In recognition of this problem, ample resources have been expended in the development of novel concepts for automated anastomotic devices [5]. The potential benefits are compelling: simplified distal anastomosis construction and reduced aortic manipulation with potentially improved neurologic outcomes in open chest beating heart surgery, as well as swifter recovery with reduced hospital stay in closed chest beating heart surgery. Provided that efficacy matches the gold standard of conventional suturing, these advantages may offset the expected cost of the required technology.

However, the quest for an anastomotic solution has proved to be more of a challenge than anticipated. Important lessons are to be learned from the early experience with coronary connectors. For this reason, we have analyzed all clinical data available since the first anastomotic connector was implanted in 1999 [6], and we compared the findings to the results of conventional suturing.


   Material and Methods
Top
 Abstract
 Introduction
 Material and Methods
Statistical Analysis
 Results
 Comment
 Study Limitations
 Disclosure
 Acknowledgments
 References
 
Study Selection and Data Collection
We reviewed clinical studies involving automated coronary anastomotic devices with elective follow-up angiography, multi-detector computer tomography or magnetic resonance imaging from 1999 until August 2007. PubMed (www.ncbi.nlm.nih.gov/sites/entrez/) and CTSNet (www.ctsnet.org/) were searched using key words including anastomosis or anastomotic device, sutureless, connector, and CABG, limiting the results to the English language, but including abstracts from presentations on the recognized international fora. In cases of apparent multiple reports on the same study, the most complete publication was selected.

We followed the guidelines for meta-analysis of observational studies as proposed by the Meta-analysis of Observational Studies in Epidemiology (MOOSE) group [7]. We looked at raw patency data, defining the anastomosis as the entity of study and anastomosis occlusion rate as the outcome. We numbered studies according to publication date, and we assigned them to one of four categories: (1) randomized trials, (2) observational studies, (3) consecutive patient studies, and (4) increased risk studies, the latter involving selective proximal device application in patients with a diseased aorta. We collected data on eight demographic, operative, and outcome variables, including age, gender, realized intention-to-treat, graft type (saphenous vein or arterial), presence of a target vessel size requirement (≥ 2 mm), follow-up compliance, anticoagulation regime, and percentage Fitzgibbon grade B anastomosis. To monitor heterogeneity, we tested demographic and operative variables against the outcome, and we compared study categories at the device level. The relation between publication number and outcome was tested per device. From the controlled studies of both proximal and distal devices, we calculated a reference graft occlusion rate.

Follow-up time was divided into three intervals: (1) predischarge, (2) first year (1 to 12 months) and (3) extended (> 12 months), selecting the first year for comparing individual device performance. We investigated described failure modes of underperforming devices, and tested four specific device properties, including implant material, device type (self-expanding, mechanically expanding, or nonexpanding), pulsatility noncompliance, and blood exposed nonintimal surface (BENIS) [8].

Evaluated Devices
The devices were grouped according to their solution to the two essential steps of anastomosis construction: (1) bringing the vessel wall rims together precisely, and (2) bonding them permanently. Three conceptual categories were distinguished: self-expanding, mechanically expanding and non-expanding devices.

Self-expanding devices
Both anastomosis construction steps are achieved by using the remarkable hyperelastic properties of Nitinol [9]. Simple release of the connector at the target site effects spontaneous device expansion, bringing the vessel walls together, and releasing facing connector wings to realize tissue bonding. Graft eversion over the connector, like a sleeve, is required for the CorLink (Bypass Ltd, Herzelia, Israel) [10].

Mechanically expanding devices
Both anastomosis construction steps are achieved by expanding a stainless steel connector using a delivery device. The SJM distal device (St. Jude Medical, St. Paul, MN) uses axial device shortening upon expansion for tissue clamping and realizes these steps concurrently [11]. The PAS-Port system (Cardica Inc, Redwood, CA) requires graft eversion over the connector and first expands the connector, and then deforms the tissue hooks for clamping [12]. The automated anastomotic distal device (AADD, Bypass Ltd, Herzelia, Israel) realizes expansion by sliding down an elliptical, extraluminal ring over initially converging tissue hooks and subsequently clamps the tissue [13]. The Spyder (Medtronic Inc, Minneapolis, MN) uses an expanding applicator to deploy a series of separate Nitinol clips without any connecting ring, and it requires graft eversion as previously described [14].

Nonexpanding devices
This category is more diverse. It includes three subcategories: (1) two equal-sized vessel incisions are clamped from the inside for the construction of a side-to-side anastomosis, either by mechanical means (SJM Symmetry II, St. Jude Medical, St. Paul, MN) [15] or by magnetic attraction (Magnetic Vascular Positioner [MVP], Ventrica Inc, Fremont, CA) [16], (2) matching frames inside and outside the lumen clamp one end of the bypass graft, which are then hooked into the target vessel (Converge Coupler, Converge Medical, Sunnyvale, CA) [17], and (3) the sequence of anastomosis construction is reversed by first bonding the vessel walls with a double row of staples and then making the arteriotomy in between from the inside (C-Port, Cardica Inc, Redwood, CA) [18], a strategy that was pioneered by the neurosurgeon Tulleken [19].


   Statistical Analysis
Top
 Abstract
 Introduction
 Material and Methods
 Statistical Analysis
Results
 Comment
 Study Limitations
 Disclosure
 Acknowledgments
 References
 
Data are presented as median and range, or as weighted mean with 95% confidence interval (CI). All outcome comparisons and variable effects were calculated with the Comprehensive MetaAnalysis program (Version 2.2, 2005; Biostat, Englewood, NJ). To address heterogeneity, random effects modeling was used. The calculated I2-statistic (the degree of heterogeneity across studies that could not be attributable to chance alone) supported this choice. Events were considered dichotomous (patent or occluded graft). If any study had no events, the software automatically added 0.5 to maintain its contribution to the analysis. In all cases, two-tailed p values were calculated. Categorical variables were examined using analog to analysis of variance testing. The effect of continuous variables was assessed using meta regression. In cases of missing data, the specific study was treated as having no impact. A p < 0.05 was considered to indicate a significant difference.


   Results
Top
 Abstract
 Introduction
 Material and Methods
 Statistical Analysis
 Results
Comment
 Study Limitations
 Disclosure
 Acknowledgments
 References
 
Clinical Device Studies
A total of 40 publications that included systematic follow-up angiographic imaging were identified. Seven publications were rejected; two because they were incomplete, one referred to an unconventional application, and four referred to studies that were covered more completely by other articles.

Thirty-three publications [6, 10–13, 15–18, 20–43] reported on 1,469 connector anastomoses in 1,216 patients with a maximum number of 3 connectors per patient. Twenty publications reported 1,069 anastomoses in 824 patients using five types of proximal anastomotic devices and 13 studies reported 400 anastomoses in 392 patients using seven types of distal devices, including five different concepts with second-generation iterations in two cases (Table 1). Follow-up angiography, multi-detector computer tomography or magnetic resonance imaging ranged from pre-discharge to 41 months (follow-up compliance 83% [range, 33% to 100%], 572 anastomosis years, Table 2).


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  		Table 1 Automated Anastomotic Device Characteristics
 

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  		Table 2 Included Studies and Details
 
Five studies [10, 23, 32, 35, 43] were prospectively randomized; one was observational [22], but included a separate control group, 19 were observationally uncontrolled [6, 11–13, 15–18, 24, 28, 33, 34, 36–42], five concerned consecutive patients [20, 27, 29, 30] including one with a control group [26], and three [21, 25, 31] concerned increased risk patients. The outcomes of studies on the Symmetry deteriorated with the publication number, and therefore, over time (p = 0.06). For the three other devices with sufficient data to allow this calculation (MVP, Converge Coupler, PAS-Port system), this relation was not significant (p ≥ 0.36).

Patency
The patency outcomes of the 33 publications (Fig 1) were distributed comparably over study categories for individual devices (p ≥ 0.56), except for the PAS-Port, where observational studies reported higher patency rates than the other study categories [31, 32] (p = 0.13). Basic demographic differences had no significant impact on outcome (age, p = 0.49; gender, p = 0.61). Overall pre-discharge patency was reported in 12 studies [12, 13, 18, 20, 23, 25, 26, 29, 33, 34, 36, 38] and was 96% [95% CI, 93% to 97%] for 413 proximal devices (Symmetry and PAS-Port) and 169 distal devices (MVP, C-Port, and automated anastomotic distal device) (p = 0.79). Overall follow-up patency in the first year (1 to 12 months) was 86% (95% CI, 81% to 90%) for 515 proximal and 281 distal devices (p = 0.80). The patency for the extended time frame was 76% [95% CI, 37% to 94%], but contained only three studies [21, 39, 41] for three different devices, with one device showing excellent results (Converge, 93% at 22 months vs MVP, 83% at 19 months and Symmetry, 46% at 41 months; see Table 2).


Figure 1
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  		Fig 1. Patency per device in all 33 studies (follow-up range, pre-discharge to 41 months). Dots represent individual studies according to Table 2.

 
Arterial grafts (ie, internal mammary artery, radial artery, gastroepiploic artery) were used in 5% of cases with three devices (Symmetry, MVP, AADD) [13, 16, 29, 36, 37, 39], but were not associated with improved outcome (p = 0.78) mainly due to underperformance of the MVP (Table 2).

Twenty studies [6, 11–13, 15, 17, 18, 20–24, 26–30, 32, 35, 43] reported the percentage of stenosed, Fitzgibbon grade B anastomoses (luminal diameter stenosis, 50% to 99%). The median incidence was 3% (range, 0 to 56%, all time frames). For the Symmetry, the percentage Fitzgibbon grade B anastomoses correlated with the graft occlusion rate (p < 0.001). For the other devices, this correlation was not significant (p = 0.15), possibly indicating different mechanisms.

Reference Patency
The reference patency for conventionally sutured vein grafts was calculated from the occlusion rates in six control groups, five in the prospective randomized studies [10, 23, 32, 35, 43] and one in the controlled observational studies [22], excluding the one limited to pre-discharge data [26]. Reference graft patency was 94% [95% CI, 89% to 97%] in 174 patients (6 months follow-up [range, 3.8 to 11.4 months], 96 anastomosis years).

Individual Device Performance
For comparing device performance, increased risk studies were excluded. Corrected for patients lost from follow-up, 699 evaluated anastomoses remained for the first year. Overall patency for the 418 proximal and 281 distal anastomoses was comparable (85% [95% CI, 77% to 91%] versus 88% [95% CI, 77% to 94%], respectively, p = 0.69, 333 anastomosis years, exclusively vein grafts, except for the MVP). Individual device patency ranges are shown in Figures 2 and 3. Go For completeness, the 19-month MVP study concerning arterial anastomoses almost exclusively was added to this analysis [39]. The Symmetry, the MVP, and the SJM distal Easyload connector showed a significantly lower patency rate than the conventionally sutured reference group. A marked difference between the highest patency and the weighted mean existed for the Symmetry and the MVP (18% and 23%, respectively), indicating that these two devices suffered from a larger than average susceptibility to interfering factors. For other devices, if applicable, this difference was < 10%. Realized intention to treat using the device was specified in 13 studies [10, 11, 13, 16–18, 29, 30, 35, 36, 38, 42, 43] and ranged from 57% to 100%, including up to 14% device misfiring, but was not associated with different outcomes (p = 0.98). Small vessel size leads to reduced patency [44]. Studies exclusively targeting relatively large coronary arteries (≥ 2 mm) showed better patency (p = 0.05), which blurs the interpretation of the good performance of the involved devices: the Converge Coupler and the SJM distal 2.5 mm connector, both being designed for larger vessels only.


Figure 2
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  		Fig 2. Proximal device performance comparison, weighted mean, and 95% confidence interval, based on follow-up data up to 1.0 year, excluding pre-discharge data and increased risk studies. Symbol size is proportional to anastomosis numbers. The p values indicate the significance of the difference with the conventionally sutured reference group (upper line). The horizontal axis is logarithmic: logit x = ln [x/(1 – x)]. (SJM = St. Jude Medical.)

 

Figure 3
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  		Fig 3. Distal device performance comparison, weighted mean, and 95% confidence interval, based on follow-up data up to 1.0 year, excluding pre-discharge data. Symbol size is proportional to anastomosis numbers. The p values indicate the significance of the difference with the conventionally sutured reference group (upper line). The horizontal axis is logarithmic: logit x = ln [x/(1 – x)]. (MVP = Magnetic Vascular Positioner [Ventrica Inc, Fremont, CA]; SJM = St. Jude Medical.)

aOne 19-month data point included.

 
The anticoagulation regimes were specified in 14 studies [11, 12, 15–18, 22, 23, 27, 32, 35, 39, 42, 43] and were grouped according to the medication received by the majority of the patients. No patency disadvantage was found for regimes limited to acetyl-salicylic acid (p = 0.81). For proximal devices, daily acetyl-salicylic acid was used either exclusively [12, 15, 22, 23, 32, 35] or in combination with warfarin [27] (p = 0.65). For distal devices, daily acetyl-salicylic acid was used either exclusively [11, 18, 42, 43] or in combination with a period of clopidogrel [16, 17, 39] (p = 0.61).

Devices were pooled according to specific characteristics, but no significant impact on outcome was detected (Table 3). This reflects the observation that each tested device characteristic was encountered in at least one device showing satisfactory to excellent results.


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  		Table 3 Significance of Impact of Device Properties on Outcome
 
Reported Failure Modes
Four failure mode categories for anastomoses can be distinguished: (1) flawed initial geometry, (2) thrombotic occlusion, (3) surgery related issues, and (4) progressively stenosing intimal hyperplasia. The first three tend to show up early, the fourth takes months.

Geometry
Device designs are optimized for creating a widely patent anatomy. However, graft eversion as required for most proximal devices may cause orifice stenosis due to the resulting tissue duplicature [10]. Owing to the absence of a supporting ring, this phenomenon is especially relevant for the Spyder [14].

Thrombotic occlusions
The thrombotic balance is primarily determined by anticoagulation level, BENIS size, and flow. Graft thrombosis represents some risk for all technologies, including conventional suturing [24, 45]. High BENIS devices have to rely on intensive anti-platelet therapy. Smaller vessels (1.5 mm) appeared to pose a risk for the MVP, as reported by Vicol and colleagues [39]. In addition, chronic medication introduces a long-term risk of noncompliance [46].

Surgery related issues
Most proximal devices require construction of the proximal anastomosis first, which is counterintuitive to many surgeons and easily results in inadequate graft length. In addition, the fixed 90° graft take-off angle may not optimally fit the anatomy without specific provisions. Both issues can cause stenoses or occlusion due to graft kinking [20, 26–28, 30].

Deployment procedures that are not fully automated increase the risk of surgical error. Vicol and colleagues [39] reported the necessity to avoid > 10% tissue inside the anastomosis orifice. Eckstein and colleagues [42] described the inadvertent capture of the target coronaries' back wall by the connector hooks, resulting in an obstructed upstream vessel [42]. Finally, an often overlooked issue is rigorous graft denudation, which may inflict tissue trauma.

Stenosing intimal hyperplasia
This failure mode is primarily caused by tissue trauma or by local hemodynamics [47] and to date appears to be unique for the Symmetry device [21, 22, 48–53]. The pathogenesis has not been fully clarified. Farhat and colleagues [54] reported acute, serious vascular wall trauma resulting from the deployment procedure, but Verma and colleagues [28], in contrast, reported unchanged endothelium dependent vasorelaxation, a sensitive marker of endothelial damage. Flow dynamics appeared not to be relevant as shown by Redaelli and colleagues [55]. A source of chronic stress is found in the radially expanding force of the spring-like connector, but marked variations in study outcomes imply a second factor (Fig 1). Surgical preferences may effect increased levels of graft denudation at the site of the connector, compromising the potential of the vessel wall to overcome the stress. Device properties in combination with surgical preferences may thus explain differences in results.


   Comment
Top
 Abstract
 Introduction
 Material and Methods
 Statistical Analysis
 Results
 Comment
Study Limitations
 Disclosure
 Acknowledgments
 References
 
The principal findings of this analysis are: (1) individual devices showed marked performance differences in the first year, with two currently available devices showing satisfactory to good results that matched suturing; (2) devices with unsatisfactory performance either showed marked patency variations between studies or overall low performance; and (3) implant material, pulsatility noncompliance, expansion mode, and high BENIS did not correlate to patency.

Our analysis shows that substantial equivalence to the gold standard of tailor-made, hand-sewn anastomoses is possible for intrinsically standardized automated systems. The currently available PAS-Port and C-port systems hold the promise of matching conventional results in expanded ranges of patients over prolonged periods of time.

Despite encouraging pre-discharge data, inconsistent results characterized the performance of both the MVP and the Symmetry, indicating susceptibility to interfering factors. In general these factors are: (1) specific device properties resulting in versatility limitations and (2) surgery related issues. Versatility limitations translate into a reduced range of compatible environmental characteristics like vessel size and quality, access requirements, and anticoagulation levels. Surgery-related issues include the learning curve and the probability of unfavorable deviations from the standardized deployment technique. For the MVP, versatility issues appeared to limit applicability to large vessels. For the Symmetry, device properties possibly in combination with deployment preferences resulted in unpredictable efficacy ranges, limiting overall safety. General low performance as detected for the SJM distal Easyload indicated serious technology limitations.

Owing to the standardized nature of automated devices, some surgery-related issues are relevant for all devices. The suboptimal performance of the PAS-Port in Lahtinen and colleagues' [32] small randomized trial is likely related to the requirement of proximal anastomosis construction first and to the 90° graft take-off angle. Expanded follow-up data are required to improve our understanding of the patency issues, in particular the observed Fitzgibbon B anastomoses that are not necessarily progressive. This applies to the Spyder as well.

Compared with coronary stenting, anastomotic devices represent a significantly more difficult technical challenge. Vessel sizes are smaller and flows are lower, stressing precision requirements and decreasing the tolerance to thrombogenity and tissue trauma. This is reflected by the considerable technical complexity of current and next generation devices, as opposed to the simplicity of first generation concepts. Single-device properties could not be correlated to outcome and indicate that multiple interacting factors determine the fate of an anastomosis.

Our reference patency for conventional suturing of 94% at 4 to 11 months appeared to belong to the top of the range of what can be expected from vein grafts. For example, Khan and colleagues [56] reported a comparable 95%, but Perrault and colleagues [57] observed 85%, both at 3 months, and Desai and colleagues [58] and Fitzgibbon and colleagues [59] reported 86% and 81% at 1 year. After the first year, occlusion rates have been reported to come down to 1% to 2.5% per year [59]. The current generation of anastomotic devices is expected to follow this trend, but larger, preferably randomized trials with extended follow-up are necessary to confirm this report.

In summary, establishing a widely open geometry with a low BENIS and minimized tissue trauma holds the promise of excellent results, provided that the deployment procedure is standardized and designed to avoid user inflicted damage. From this perspective, resilient, spring-like devices are at a disadvantage, as well as circumferential vessel denudation, but pulsatility noncompliance does not appear to be critical. As more systems become available, different versatility profiles may serve different situations. Experience to date, revealing the small margin of error, should help to make surgeons realize that the results of applying an intrinsically standardized connector system will still depend on skilful hands for some time to come. After all, it took decades for small vessel anastomosis suturing to mature to the current level.

Current Developments
On the distal side, the encouraging results of the C-port device are further improved with the next iteration, the C-port xA. Several technology refinements (including an increased number of deployed staples) have improved the reliability and decreased the incidence of leakage, but a suture is still required to close the small arteriotomy used to insert the anvil. Recently, the C-Port xA Flex, a version with a flexible shaft for improved maneuverability, received 510(k) clearance from the Food and Drug Administration and Conformité Européenne or European Conformity (CE) mark in Europe, bringing truly minimally invasive bypass surgery several steps closer, including port access anterior wall revascularization. Such a procedure may offer an attractive alternative to the best stent techniques [3, 4].

On the proximal side, the PAS-Port is increasingly being adopted. Having European Conformity approval, a multi-center trial is currently being conducted for Food and Drug Administration approval. A next iteration of the Spyder is expected to become available in the near future. Maintaining several principles of the original device, this design iteration is expected to improve versatility and reduce user issues.


   Study Limitations
Top
 Abstract
 Introduction
 Material and Methods
 Statistical Analysis
 Results
 Comment
 Study Limitations
Disclosure
 Acknowledgments
 References
 
Our findings should be interpreted in light of limitations that arise from analyzing uncontrolled observational studies. Because vein graft patency is known to vary considerably, historical control groups are of limited value. However, new anastomotic technologies are almost invariably evaluated in low-risk patients. The marked homogeneity of the six control groups supported this view and served to build a reference frame.

Technologies beyond initial evaluation, notably the Symmetry when it was commercially available, may have been exposed to higher risk conditions as well, potentially accounting for some performance loss. A positive performance bias may apply to all distal devices, because these are generally not used on the smallest and most diseased vessels. For several devices, limited numbers of patients were available or only one study, but these were included for completeness of this review.


   Disclosure
Top
 Abstract
 Introduction
 Material and Methods
 Statistical Analysis
 Results
 Comment
 Study Limitations
 Disclosure
Acknowledgments
 References
 
Dr Suyker advises iiTech BV (Amsterdam, the Netherlands) regarding automated anastomotic devices, but none are described in this review.


   Acknowledgments
Top
 Abstract
 Introduction
 Material and Methods
 Statistical Analysis
 Results
 Comment
 Study Limitations
 Disclosure
 Acknowledgments
References
 
We acknowledge the constructive support of Ingeborg van der Tweel, PhD (Utrecht University, Centre for Biostatistics, the Netherlands) and the valuable comments by Bas van Zaane, MD (University Medical Center Utrecht, the Netherlands) on the statistical methodology.


   References
Top
 Abstract
 Introduction
 Material and Methods
 Statistical Analysis
 Results
 Comment
 Study Limitations
 Disclosure
 Acknowledgments
 References
 

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