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Ann Thorac Surg 2000;70:218-221
© 2000 The Society of Thoracic Surgeons

Original articles: Cardiovascular

Assessment of patented coronary end-to-side anastomotic devices using micromechanical bonding

Jules S. Scheltes, MSca, Martijn Heikens, BSca, Peter V. Pistecky, MSca, Carolien J. van Andel, MSca, Cornelius Borst, MD, PhDb

a Man-Machine Systems Group, Department of Design, Engineering and Production, Delft University of Technology, Delft, The Netherlands
b Department of Cardiology, Heart Lung Institute, Utrecht University Medical Center, Utrecht, The Netherlands

Address reprint requests to Dr Borst, Experimental Cardiology, Utrecht University Medical Center, Room G02.523, PO Box 85500, 3508 GA Utrecht, The Netherlands
e-mail: c.borst{at}hli.azu.nl


   Abstract
Top
 Abstract
Introduction
 Material and methods
 Results
 Comment
 References
 
Background. Despite multiple patented ideas for vascular end-to-side anastomotic devices, and the growing need for them in minimally invasive coronary bypass procedures, no device has been evaluated clinically yet. This study assessed patents of micromechanical end-to-side anastomotic devices with respect to application in coronary artery bypass grafting.

Methods. Patents were categorized with respect to their micromechanical bonding principle. Calculated values for the wall strain during the construction of an anastomosis were compared with the allowable strain for human coronary arteries.

Results. From 51 patents describing vascular anastomotic devices, 11 ideas, categorized into four groups (staples, clips, mounting systems, and intraluminal stent structures), are serious candidates for coronary end-to-side anastomoses. Most ideas use an anvil for proper application of the bonding elements. For small (1.5 mm) coronary arteries, the calculated wall strain was 0.87, exceeding the breaking strain (0.45) in 60- to 79-year-old patients.

Conclusions. In a coronary anastomotic device, the concept of using an anvil for the application of micromechanical bonding elements is not attractive, because excessive wall strain is likely to occur.


   Introduction
Top
 Abstract
 Introduction
Material and methods
 Results
 Comment
 References
 
Coronary artery bypass grafting (CABG) on the beating heart is making a progressive comeback [1]. To reduce the morbidity of coronary surgical procedures further by limiting access to portholes, alternative ways and means for constructing the distal anastomosis need to be explored. It is likely that true minimally invasive coronary operation by conventional endoscopic means will carry a substantial risk of constructing a distal anastomosis of inferior quality. This would defeat the objectives of minimally invasive CABG [2].

In the pursuit of closed chest CABG on the beating heart, currently two strategies are followed that may ultimately merge. First is the development of master-slave robotic surgery systems [3, 4] that allow conventional suturing in thoracoscopic approach. Second is the development of alternative ways to construct the coronary anastomosis, characterized by reduced technical demand with respect to the total number of manual maneuvers and the required manual dexterity. In the latter strategy, recently reviewed by Werker and Kon [5], three categories may be distinguished: (a) anastomotic devices using micromechanical tissue bonding; (b) laser-assisted vascular anastomosis techniques; and (c) adhesive bonding of donor and recipient vessel.

Many vascular anastomotic devices have been described in the patent literature, but remarkably few ideas for coronary anastomotic devices have reached the development stage of animal testing [6], and none have been evaluated clinically. To our knowledge, no coronary anastomotic device is available commercially.

The aim of this study was to identify fundamental features common to patents of ideas for a micromechanical end-to-side vascular anastomotic device, and to assess these features with respect to application in (closed chest) CABG procedures.


   Material and methods
Top
 Abstract
 Introduction
 Material and methods
Results
 Comment
 References
 
From the Intellectual Property Network (http://www.patents.ibm.com/ibm.html) and the esp@cenet (http://www.european-patent-office.org/espacenet/info/index.htm), patents for coronary end-to-side anastomotic devices using micromechanical bonding elements were collected. The search was restricted to patent documents from the United States and Europe and to patent applications published by the World Intellectual Property Organization. The patents were analyzed by delineating the various steps needed to construct the anastomosis and by categorizing them regarding the bonding principle they used.

For the patents that use an anvil to construct the anastomosis, the strain that occurs in the arterial graft and the recipient coronary artery during the construction of the anastomosis was calculated using the following formulas and assumptions:

A. Strain in graft = (diameter of outside rim of everted graft - inner diameter of relaxed graft)/inner diameter of relaxed graft;

B. Strain in arteriotomy = (circumference stretched arteriotomy - circumference relaxed arteriotomy)/circumference relaxed arteriotomy;

C. Wall thickness remains equal during construction;

D. Wall thickness is approximately 1/6th of the inner diameter of the artery;

E. Wall thickness of anvil tube is 0.1 mm;

F. Width of anvil rim is 0.5 mm;

G. Inner diameter tube = 0.88 inner diameter graft (when graft is folded in anvil tube);

H. Circumference of relaxed (round or longitudinal arteriotomy) equals the outer circumference of the tube;

I. Graft and recipient artery are of equal dimensions.

This was done for arteries of 1.5, 2.0, and 2.5 mm inner diameter. The strain values were compared with values for the maximal allowable strain for coronary arteries [7] and donor arteries, because arterial grafting is preferred [1].

Soft tubes (inner diameter 15 mm, outer diameter 20 mm) cast from silicone (Elastocil M4500; Wacker Silicone, Munich, Germany) functioned as 10:1 scale models to visualize the apposition of the arterial walls when anastomotic devices would be used.


   Results
Top
 Abstract
 Introduction
 Material and methods
 Results
Comment
 References
 
Inventory of patents
After discarding 17 patents for end-to-end anastomoses and 12 patents for the proximal anastomosis between the thin-walled vein graft and the thick-walled ascending aorta, 22 patents remained that described a micromechanical anastomotic device for a vascular end-to-side anastomosis between equally sized arteries, such as the anastomosis between the internal mammary artery and the coronary artery. After discarding duplicate patents, the 22 patents were reduced to 11 ideas [8–18].

Categorization of patented ideas
In all patents, intima–intima or abutting (rim–rim) contact between the recipient and the donor artery is established. The fundamental difference in the design of the anastomotic devices is found in the bonding principle used to secure the intima–intima or abutting contact. Four different types of bonding principles can be distinguished: staples [8–12], clips [13], mounting systems [14–16], and intraluminal stent structures [17, 18]. Figure 1 presents an overview of the four different bonding principles.



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  		Fig 1. Examples from patents to illustrate four categories of bonding principles.

 
Anvil-based anastomotic devices
Except for the intraluminal stent structures [17, 18] and the idea of Spence and colleagues [15], all ideas have in common that an anvil is used to construct the anastomosis. In the latter approach, five construction steps can be distinguished (illustrated in Figure 2): (a) introduction of the distal end of the graft into the bore of a tube-shaped anvil; (b) eversion of the graft over the anvil; (c) introduction of the anvil (with everted graft) into the lumen of the coronary artery; (d) fixation of the bonding elements; and (e) removal of the anvil by splitting the anvil into two parts.



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  		Fig 2. Five steps during the micromechanical construction of an end-to-side anastomosis between an internal mammary artery graft and a coronary artery. Silicone tubes (inner diameter 15 mm, outer diameter 20 mm), have been used to improve the visibility on the apposition of the vessel walls. (a) Introduction of distal end of the graft into the bore of a tube-shaped anvil. (b) Eversion of the graft over the anvil to expose the intimal layer. (c) Introduction of anvil with everted graft into the lumen of the coronary artery to obtain intima–intima apposition. (d) Fixation of bonding elements to secure apposition of donor and recipient artery wall. (e) Removal of the anvil from the lumen of the coronary artery. (f) Resulting anastomosis.

 
Functions of the anvil
Everting the graft establishes the preferred intima–intima apposition between the donor artery and the recipient artery.

Next to this apposition function, the anvil is also used to create enough overlap between the two arteries for easy application of the bonding elements. In most patents, the anvil additionally prevents the wall segment to move when the bonding elements are lowered into the wall, and it enables the bonding elements to be deformed, so that they are fixated. The four functions of the anvil are sketched in Figure 3. There is, however, a fundamental problem when an anvil is used in small arteries like the internal mammary artery and the coronary artery.



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  		Fig 3. Sketch of the four functions of the anvil: (a) to obtain proper intima–intima apposition, (b) to create enough overlapping area for easy application of bonding elements, (c) to prevent movement of wall segment when bonding elements penetrate the vessel wall, and (d) to enable the bonding elements to be fixated by deformation.

 
Excessive wall strain
Using a tubular anvil to obtain proper intima–intima apposition will stretch the distal end of the graft when it is everted around the anvil. The arteriotomy in the coronary artery also will be stretched when the anvil with everted graft is introduced through the (round or longitudinal) arteriotomy into the lumen. These two strain situations are illustrated in Figure 4.



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  		Fig 4. Location of maximal strain (arrow) when (a) an internal mammary artery graft has been everted around an anvil, and (b) when the everted internal mammary artery graft is introduced into the lumen of the coronary artery. The silicone 10:1 models in this figure represent a donor and recipient artery with an inner diameter of 1.5 mm, an outer diameter of 2.0 mm, and a wall thickness of 0.25 mm. The round arteriotomy is 1.6 mm in diameter (equal to the outside diameter of the tube). The anvil inner diameter is 1.4 mm, the diameter of the outer rim of the anvil is 2.6 mm. Maximal strain is 1.02 (a) and 0.87 (b).

 
Calculated values for the wall strain in both the everted graft and the arteriotomy are listed in Table 1 for arteries with inner diameters of 2.5, 2.0, and 1.5 mm. For 1.5-mm arteries (the size of small human internal mammary and coronary arteries), the wall strain reached high values (1.02 for the graft and 0.87 for the recipient artery), that is, the vessel wall was stretched by a factor 2.


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  		Table 1. Wall Strain in Donor and Recipient Artery When (A) the Graft Is Everted Around the Tube-Shaped Anvil and (B) Is Introduced Into the Lumen Through a Round or Longitudinal Arteriotomy

 
Other anastomotic devices
Spence and coworkers [15] described a device with which both donor and recipient artery are prepared by mounting them to their own frame structure (Fig 1). Then both frames are connected in a way that abutting contact is obtained. The frames are mounted on the arteries with the aid of an anvil, but the difference with the other ideas is that the donor artery is not everted. As a result, less wall strain will occur in both the graft and recipient artery.

In the ideas for intraluminal stent structures [17, 18], the strain in the arteriotomy is avoided by using expandable stent structures. The structures are introduced into the recipient artery when they are folded. Once they are positioned correctly, they unfold.


   Comment
Top
 Abstract
 Introduction
 Material and methods
 Results
 Comment
References
 
Eleven ideas were found that were considered serious candidates for an end-to-side coronary anastomotic device using a micromechanical bonding principle, and eight use an anvil to construct the anastomosis. With the exception of the device of Manzo and colleagues [13], which was tested by Heijmen and colleagues [6], no animal studies with these devices have been reported. Coronary anastomotic devices that have been tested in the past constructed end-to-end anastomoses between the internal mammary artery and the coronary artery [19, 20]. Other vascular anastomotic devices were usually tested on veins [5].

Heijmen and colleagues [6] tested the device of Manzo and colleagues [13] by constructing in the pig 14 end-to-side anastomoses between the left internal mammary artery and the left anterior descending coronary artery. Although the coronary occlusion time was shortened with the device, excessive adventitial stripping was necessary to evert the mammary artery over the tip of the clip cartridge. After 2 days, in 2 of 7 cases local coronary dissection was observed. Both aspects are probably related to overstretching of the recipient artery.

Downscaled prototype devices that comply with the smallest size of human internal mammary and coronary arteries (1.5 mm) will prove to be even more problematic. The wall strain of donor and recipient artery, caused by eversion of the graft around an anvil and introduction of the anvil through an arteriotomy into the lumen of the recipient artery, increases drastically when the size of the artery decreases. For 1.5-mm arteries, the calculated strain in the graft was 1.02, and in the coronary artery 0.87. These values far exceed the maximally allowable strain for (coronary) arteries at age 60 to 79 years, according to Yoshimatsu [7] (Table 2). The report by Yoshimatsu [7], however, is the only source of information we could find, and no data were provided on the degree of arteriosclerosis. For the internal mammary artery, no corresponding values have been found in the literature.


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  		Table 2. Ultimate Strain Before Rupture of Human Coronary Arteries

 
In conclusion, an end-to-side vascular anastomotic device that uses the concept of an anvil for application of micromechanical bonding elements is not attractive because it will induce wall strain in both graft and recipient arteries that exceeds the maximally allowable strain for arteries in coronary artery grafting.


   Acknowledgments
 
Jules S. Scheltes, Martijn Heikens, Carolien J. van Andel, and this research were supported by the Technology Foundation STW (grant UGN 66.4183), the applied science division of the Netherlands Organization for Scientific Research (NWO), and the technology program of the Ministry of Economic Affairs.


   References
Top
 Abstract
 Introduction
 Material and methods
 Results
 Comment
 References
 

  1. Borst C., Gründeman P.F. Minimally invasive coronary artery bypass grafting. Circulation 1999;99:1400-1403.[Free Full Text]
  2. Bonchek L.I., Ullyot D.J. Minimally invasive coronary bypass. Circulation 1998;98:495-497.[Free Full Text]
  3. Shennib H., Bastwisy A., McLoughlin J., Moll F. Robotic computer-assisted telemanipulation enhances coronary artery bypass. J Thorac Cardiovasc Surg 1999;117:310-313.[Abstract/Free Full Text]
  4. Reichenspurner H., Damiano R.J., Mack M., et al. Use of the voice-controlled and computer-assisted surgical system ZEUS for endoscopic coronary artery bypass grafting. J Thorac Cardiovasc Surg 1999;118:11-16.[Abstract/Free Full Text]
  5. Werker P.M., Kon M. Review of facilitated approaches to vascular anastomosis surgery. Ann Thorac Surg 1997;63:S122-S127.
  6. Heijmen R.H., Hinchliffe P., Borst C., et al. A novel one-shot anastomotic stapler prototype for coronary bypass grafting on the beating heart. J Thorac Cardiovasc Surg 1999;117:117-125.[Abstract/Free Full Text]
  7. Yoshimatsu N. Study of strength of parts of human heart. J Kyoto Pref Med Univ 1958;641:553. Cited in: Yamada H, Evans FG, eds. Strength of biological materials. Baltimore: Williams & Wilkins, 1970: 113.
  8. Barak JH, inventor; Abiomed Inc, assignee. Surgical stapler. EP patent 0384647. 1990 Aug 29.
  9. Heck CR, Bolduc LR, inventors; Heartport Inc, assignee. Surgical anastomosis apparatus and method thereof. US patent 5,881,943. 1999 Mar 16.
  10. Hinchliffe PWJ, Ratcliff K, Toso KE, inventors; United States Surgical Corporation, assignee. Anastomosis instrument and method thereof. US patent 5,833,698. 1998 Nov 10.
  11. Kapitanov NK, Ippolitov VV, Adreeva GD, Petrova NP, Rabotnikov VS, inventors. Surgical instrument for suturing vessels with metal staples. US patent 4,076,162. 1978 Feb 28.
  12. Tzakis AG, inventor; Tzakis, assignee. Apparatus for anastomosis. EP patent 554990. 1993 Aug 11.
  13. Manzo SE, Gresham RD, Sniffin K, Hinchliffe PWJ, inventors; United States Surgical Corporation, assignee. Anastomosis instrument with detachable loading unit. EP patent 885595. 1998 Dec 23.
  14. Rygaard AJ, inventor; Oticon A/S, assignee. Method, instrument and anastomotic fitting for use when performing and end-to-side anastomosis. WO patent 9517128. 1995 Jun 29.
  15. Spence PA, Williamson WP, Christakis G, inventors; Guidant Corporation, assignee. Means and methods for performing an anastomosis. US patent 5,868,763. 1999 Feb 9.
  16. Walsh DJ, Lougheed WM, Gentili F, Fazl M, inventors; Walsh Manufacturing Limited, assignee. Anastomosis devices, kits and method. EP patent 303767. 1989 Feb 22.
  17. Berg TA, Peterson AA, Boldenow GA, inventors; Vascular Science Inc, assignee. Tubular medical graft connectors. WO patent 9819630. 1998 May 14.
  18. Ducksoo K, inventor; Beth Israel Deaconess Medical Center, assignee. Catheter apparatus and method using shape-memory alloy cuff for creating a bypass graft in vivo. WO patent 9807399. 1998 Feb 26.
  19. Abe K., Main F.B., Gerbode F. Internal mammary-coronary artery anastomoses. J Thoracic Cardiovasc Surg 1966;51:808-820.[Medline]
  20. Carroll S.E. Experimental anastomosis of the left internal mammary artery to the divided circumflex coronary artery using the NRC-vogelfanger stapling device. Can J Surg 1964;7:463-469.[Medline]
Accepted for publication January 20, 2000.




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