The coronary anastomosis

General aspects

The word anastomosis comes from the combination of two Greek words: Ana and Stoma. Ana is a prefix and means on, upon, or against. A stoma is a noun and means mouth. An anastomosis is the apposition of two mouths or cavities. These cavities can be as well a stomach or a bowel as vascular structures. We will focus on the current clinical and training challenge of an anastomosis in very reduced airspace, angulated, and on an unstable or beating platform. The airspace is the perpendicular distance between the anastomotic surface and the “roof.” On the cardiac anterior wall, the “roof” can be the actual roof of the operating theater; several hundred centimeters distant. But on the cardiac lateral wall, just above the coronary sinus, the “roof” can be the pleura. This space will vary in off-pump coronary surgery by the increase and decrease in cardiac volume during each heartbeat but also by the ventilated lungs. These frequencies are in addition not synchronous, obviously. The airspace will then be reduced to one or two centimeters.

A vascular anastomosis is an anastomosis between two vessels: a graft, usually without disease, and a host, usually with disease; but it can also be between two grafts or two hosts. These graft and host vessels can as well be arteries or veins, as well as biological or prosthetic material. The connection between an internal mammary or thoracic artery and the left anterior descending coronary artery is one example, but a sequential anastomosis of a human umbilical venous graft to the lateral side branches of the circumflex artery is another historical example.

The tools

The connection can be made through suturing both walls together, through stapling and finally through (semi)automated devices. This chapter will address the suturing of both walls.

The suture is used to bring both walls together and keep them together under the arterial or venous pressure; sufficiently long enough in time until they have grown together. The suture normally has a needle and thread. The superelastic suture clip in nitinol looks like a suture but is more frequently classified as a device and will not be discussed.

The needle ( Fig. 17.1 ) has a point, a body, a length, a radius, a chord length, a diameter, and swage area. A needle can have a round or a cutting point. This choice of point is more often based on surgical preference versus scientific evidence. Fragile tissues as liver and kidney are often addressed with round points. Less fragile tissues are addressed with cutting needles with a triangular shape and three cutting edges.

Figure 17.1

The needle.

The needle will always penetrate the wall in a perpendicular angle to the wall. The force ( Fig. 17.2 ) needed for penetration will vary according to the part of the needle that penetrates; this force will increase at each penetration until the needle breaks. To avoid this increase, the needle is coated. Different ( Fig. 17.3 ) coatings have different penetration force effects, but surgeons will have to appreciate that each contact between needle holder/forceps and coated needle will damage the coating and reduce the coating’s benefit.

Figure 17.2

The penetration force.

Figure 17.3

The penetration force with different coatings.

The thread used in vascular suturing is always a nonabsorbable suture since the arterial pressure forces on the anastomosis demand a holding force beyond the normal holding interval of absorbable threads, often only a few weeks. Silk was the first nonabsorbable thread used in vascular anastomoses but Cutler and Dunphy identified that this suture was at risk of fraying and losing its structural integrity. The clinical consequence was called anastomotic or false aneurysms; in abdominal anastomoses sometimes even aorto-enteric fistulae . The current nonabsorbable threads can be nylon, polyester, or polypropylene.

The body of the needle of a vascular anastomosis is rectangular ( Fig. 17.4 ) in shape to provide for the necessary stiffness, even in the very small sizes. Indeed, this stiffness is related to the second power of the height – the more rectangular, the stronger. In consequence, if we want to be able to move the needle in the needle holder, in an effort of optimizing the needle angle, we need to not only unlock but also to control the holding pressure of the needle holder and increase and decrease the holding force on a body of ±150 μm.

Figure 17.4

The body of the needle.

The swage area is the area where the thread is inserted into the needle. A normal process creates a needle-to-suture ratio of 1.7. This means that when the needle has penetrated completely through a surface without memory, then the hole will only partially be filled by the thread. A surface without memory is typically a surface in polytetrafluoroethylene, alternatively a very diseased or calcified vessel. This will result in needle-hole bleeding, certainly in anticoagulated patients. This can be addressed by using a suture with a swage area close to 1.1 .

The most frequently used needle holder for vascular anastomoses is the Castroviejo needle holder, even though some surgeons still use a Mayo-Hegar one. The Castroviejo needle holder is commercially available with flat or with rounded rough controlling surfaces. Since the needle holder will guide the needle when it follows a curved pathway through a wall, the needle holder will rotate as primary movement. In simulation training and in clinical practice, we therefore use needle holders with rounded surfaces. Even with the rounded surfaces, the needle holder will never be round, at best oval; therefore minute corrections will be needed during the rotational process. The Castroviejo needle holder has a rough zone where the fingers control (not hold) the instrument. By controlling the needle holder at the beginning of this rough zone, starting from the tip of the holder, the needle holder becomes balanced in the hand. Holding force is replaced by controlling force. The surgeon will stabilize his hand and the needle holder needs to cover the distance between the tip of the fingers of the stabilized hand, controlling the holder at the beginning of the rough zone, and the anastomotic site. So sometimes a longer needle holder is needed, sometimes a shorter one. In conclusion, there is no optimal needle holder length, just a perfectly stabilized hand and a covered distance. Needle holders come with and without a lock. The lock allows the needle holder to block a needle in a certain position whilst the needle holder changes hands or position. In anastomotic training we always use a lock, whereby we train the scholar to mandatory open it during needle-angle optimization and during tissue penetration.

The forceps changed function over the last decades. Originally, it had only two functions: exposure and guidance of the needle beyond the penetrated wall. Today, for example, two forceps are used in off-pump coronary surgery for shunt insertion in extremely reduced airspaces. This demands very fine control and rotational capacity. If the points are too thin, the shunts cannot be manipulated. So, forceps with rounded off bodies are preferred, very similar in length to the Castroviejo used. Both hands will probably find stabilization at similar distances. The choice of the tip of the forceps (open eyes or just rough contact zones) will be influenced by its use. Certain forceps tips create a difficult interaction when they are only allowed to touch the needle to optimize the needle angle. But it is perfectly possible to use different forceps for shunt manipulation and insertion.

The dawn of anastomotic techniques

Carrel , the 1912 Nobel Prize winner, introduced in 1902 vascular anastomoses and proposed a triangular-shaped anastomosis. He started the anastomosis by distributing three separate sutures between the two vessels, each at 60 degrees of the anastomotic circle. The triangulation was proposed to locate and oppose correctly the margins of both sides of the anastomosis. He continued in everting the edges of both anastomotic margins to avoid the contact of blood with any other surface but the endothelized inner surface of the vessels.

Technical criteria of an anastomosis

The coronary anastomosis performed in coronary bypass surgery without the support of an extracorporeal machine has the same criteria as the one performed with the support of the machine. But, in addition, it needs to be adapted to three additional criteria: very reduced airspace, angulated perspective, and performed on an unstable or beating surface. The optimal anastomosis is the one that provides very long-term patency through minimal wall trauma and wall stress and an optimized internal flow. In sequential anastomosis, it will be important that the anastomosis creates no negative effect on the further flow downstream in the graft.

Several authors have tried to bring numerical analysis , computational flow dynamics and modeling to identify the optimal technical anastomosis. Indeed, a vascular anastomosis is at risk of intimal hyperplasia, restenosis, and early occlusion. They have tried the Navier–Stokes equation, the continuity equation, the momentum equation, the Womersley parameter, the Reynolds number, the wall compliance, the wall shear stress, the dynamic viscosity, the Newtonian fluid laws, the Rayleigh dissipation theory, the Boussinesq approximation, the vorticity, the velocity profile, the pressures, etc. They concluded that geometric features are important as well as graft to artery diameter, anastomotic angle, junction shape, vessel curvature. Also, that geometric features vary according to the coronary hosting system and the source of the graft flow, but uncertainty remains about the optimal anastomosis geometry, the graft length, and the transitional curvature.

The wall sheer stress (WSS) seems very important for atherosclerotic progression. Low WSS segments develop greater plaque, necrotic core progression and constrictive remodeling, high WSS segments develop a greater necrotic core, calcium progression, a regression of fibrous and fibrofatty tissue, and excessive expansive remodeling. So as well very high as very low WSS need to be avoided. The WSS varies according to the place of measurement. At the outlet bottom, the longer the anastomosis, the higher the WSS in the end-to-side anastomosis. At the inlet bottom the highest WSS was identified in the diamond shape anastomosis. At the inlet top, the WSS was lower in the diamond shape anastomosis and even lower in the parallel anastomosis. At the outlet top, the WSS was highest in diamond anastomoses, then in the parallel and lowest in the end-to-side anastomosis.

The higher the energy efficiency, the smoother the flow. An optimal end to side anastomosis for an end to end anastomosis is around 6 mm in length, since this length is associated with the highest energy efficiency.

The trauma of the vessel wall will be minimalized at penetration by having always the needle holder unlocked or by using a needle holder without lock. In the beating heart anastomoses, this will allow the upward and downward movement of the vessel (even only microns) without impact on the penetration trauma. A second mandatory process is selecting needle with the smallest possible body in relation to the vessel wall disease. A 7 zero needle has a body of around 250-μm width, an 8 zero needle has a body of around 150-μm width. If the wall still has memory, the residual hole will be less. But any drift of the needle holder at rotation, even a 1 mm drift will increase the penetration trauma with 1000 μm. So, needle holder control training in simulation toward reduction of this drift (see later) will become mandatory. The frequency of the stitches needs to be appropriate to avoid bleeding. A general rule in coronary anastomoses is a spacing between stitches of 1 mm. More stitches will increase unnecessarily the trauma of the wall with the possibility of disease progression, less increases the risk of bleeding. At the tip of the anastomosis, the distances at the outer edge will be further apart, at the inner edge closer apart.

The stitching has the intention to bring both sides together. Therefore we need to place suture points on both edges. The bites from the edge will be in relation to the fragility of the edge. A normal bite is around 1 mm from the edge. Just as Carrel made sure to evert the suture lines to guarantee opposing the endothelial inner layers of the vessels, one needs to avoid inversion. Inversion will create an inward ridge or spur, create massive turbulence in the anastomosis and lead toward early graft occlusion. In addition, it increases the risk of suturing both sides together, by approximating one side closer to the other side. The WSS will be optimized by a radial distribution of the suture points ( Fig. 17.5 ). This will demand that the needle is continuously changed in angle, in relation to the radiary disposition. In the presence of reduced airspace, this will have an impact on the anastomotic technique. The stitching on the diseased vessel will always be from the inside toward the outside. This will avoid dislodging an atherosclerotic plaque.

Figure 17.5

The radiary positioning of the suture points.

Most surgeons use a continuous suture line, some surgeons prefer intermittent sutures. Outside of the financial aspect of using so many sutures, the issue of stricture of the anastomosis of the continuous suture line is probably overrated. In simulation training with the appropriate graft material, any exaggerated tension on the knot is immediately reflected on the exterior aspect of the graft, showing an excavation. In simulation training, assessed using an Objective Structure Assessment of a Technical Skill (OSATS) (see later), the knot is a major component of the anastomosis, demanding the strictest attention.

The incision in the host vessel, parallel, or diamond shape

The geometry of the anastomosis can take different patterns with different effects. It is possible to just incise or excise a section. Excision is rarely done due to the reduced sizes of the vessels in coronary surgery. An exception could be a small, unexpected plaque or a previous anastomosis as in redo coronary surgery.

Usually it is an incision in both vessels. Here two major possibilities ( Fig. 17.6 ) exist. Either the incisions are parallel in three-dimensional space (A). This is usually done when both vessels are in the same axis. If the vessels are in a perpendicular axis versus one another, then this solution does not open the anastomosis (B) but creates a natural tendency toward approximation of the anastomosis axes. The alternative is a diamond-shaped anastomosis. Here both vessels receive an incision in their axis (C). So, in the creation of the anastomosis the anastomosis is pulled open (E) and (F). The risk is that if one or both incisions are too long, the anastomosis is then pulled open too far and the cobra head is flattened. Therefore the 6 mm rule is not valid anymore, but any incision of one of the two vessels will never exceed the width of the smallest of the two vessels. Matsuura identified that the parallel anastomosis provided more flow to the native outlet and the diamond shape anastomosis more flow to the bypass outlet. This diamond shape anastomosis issue is valid for single as well as sequential anastomoses.

Apr 6, 2024 | Posted by in CARDIOLOGY | Comments Off on The coronary anastomosis

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