Coronary artery bypass grafting using sequential grafts.

Use of intravascular ultrasound (IVUS) to determine optimal conditions for creation of coronary anastomosis

Rudenko A., Salo S., Galich S., Gavrilishin A.

   Abstract: Intravascular ultrasound (IVUS) of the coronary anastomoses, that constructed using different techniques and suture material of various diameter of thread, allows determining the optimal conditions for increasing the area of anastomosis. According to the results of the investigation: using of suture material with thread “8-0” and relative positioning of internal layers of vascular wall of vessels by “intima-to-intima” and putting stitches in 1 mm along the edge of coronary artery increase the size of longitudinal and transverse diameter and total area of anastomosis that increase the volume blood flow velocity through coronary anastomosis.

   Key words: Ischemic heart disease, intravascular ultrasound, coronary anastomosis.

 

   Background:  One of the actual problems of coronary surgery is the patency of coronary grafts as one of the determinants of long-term outcomes following coronary artery bypass grafting. The graft patency influences the probability of several postoperative complications and life-threatening cardiac events such as cardiac death, myocardial infarction, recurrent angina etc. Accordingly  to the point of view of some investigators, the grafts patency significantly depends on the technique of performing the vascular anastomosis[1,2], and, respectively, on the value of volume blood flow velocity through the graft[3,4]. However, there is no straight list or doctrine of the optimal conditions and rules for performing the graft anastomosis in the worldwide literature. Today, there are many surgical techniques of creation the anastomosis that include the features of preparing the vessel sides that involved in anastomosis, techniques of suturing, position of layers of vessel wall relative to each other in corresponding vessels and type of suture material etc.   

   Aim: To determine optimal conditions for creation of coronary anastomosis with associated maximum volume blood flow velocity.

  Methods: There were series of experiments with coronary anastomosis that were performed by different surgical techniques with suture material of various diameter of thread. After each performing of anastomosis evaluation of volume flow velocity was taken place in association with intravascular ultrasound(IVUS) investigation of internal geometric parameters. Anastomoses were performed between arterial (diameter from 2mm to 3mm) and venous (diameter from 3,5mm to 5mm) vessels with coronary arteries (epicardial arteries of porcine myocardium).

  Evaluation of volume flow velocity was used to assess the blood flow through the anastomosis. Permanent pressure was created by using reservoir with stable liquid column. Special liquid with viscosity identical to blood was used. Measurement  of longitudinal and transverse diameters and area of anastomosis were applied by intravascular ultrasound device(«Boston Scientific iLab Ultrasound Imaging System»). During intravascular ultrasound investigation coronary imaging catheter(CI-catheter) was situated freely in a center of vessel. But during investigation of vessels connected at particular angle, CI-catheter was passed through anterior point of connecting line between the vessels to find most suitable position. After some geometric calculations we can conclude that during ultrasound investigation of vessels connected at an angle of 90°, the position of CI-catheter  approximated to 60° with respect to horizontal coronary artery. Whereas, if the angle between the vessels was 45°, CI-catheter situated at an angle of 30° (figure 1). 

   Figure 1. Position of CI-catheter in the vessels connected at the different angles (45° и 90°, respectively). Maximum size of image of anastomosis is showed by double arrow.

   The maximum size of ultrasound image of internal structure of anastomosis will be recorded at exactly these angles. Having perpendiculars to opposite walls of both vessels, we obtain two triangles in each case. Hypotenuses of both triangles are composing the value of the maximum longitudinal diameter of ultrasound image of anastomosis (С(max)).

   The formula to measure this maximum diameter of anastomosis between vessels connected at 45° angle is:

С(max) = С1 + С2,

, where С – maximum longitudinal diameter, С1- arterial part of longitudinal diameter, С2 - graft part of longitudinal diameter.

С1= d/cos(30°), т.е. С1= 2d/√3

, where ‘d’- intrinsic diameter of artery.

С2= D/sin(75°), т.е. С2= D/0,96

, where ‘D’- intrinsic diameter of graft.

In this way, C(max)=2d/√3+D/0,96

The formula to measure maximum diameter of anastomosis between vessels connected at 90° angle is:

С(max)= С1 + С2,

С1= d/sin(30°), т.е. С1=2d

C2= D/sin(60°), т.е. С2=2D/√3

C(max)=2d+2D/√3

 

   Hence, comparing this two formula with each other and based on the fact that diameter of graft is bigger than diameter of coronary artery, it becomes apparent that connection of vessels at 90° increases longitudinal measure of ultrasound image of anastomosis. However, this type of connection decreases direct longitudinal diameter of anastomosis (С(long)) – the length of arteriotomy, that probably impact on the value blood flow volume too. In case of 90° connection this diameter will correspond to diameter of graft but in case of 45° connection - С(long) = 2D/√2.

   The value of transverse diameter of anastomosis approximates to diameter of graft and never will be more than that and there is no possible to increase it.

   Above mentioned longitudinal and transverse diameters and area are the maximum calculated sizes of anastomosis and creation the proper configuration of anastomosis allows achieve these measures with providing the maximum of volume blood flow velocity through coronary anastomosis.   

   Results: Results of investigation are presented in table 1

   Tabel 1

 

Feature

Diameter of graft and coronary artery (respectively)

Number of experiments

Volume flow velocity  (ml/min)

Diameter longitudinal (mm)

Diameter transverse (mm)

Area of anastomosis (mm²)

Length of anastomosis (mm)

(С(long))

(calculated)

Calculated

(C(max))

Real

1

8-0 (45°)

- 3,5 мм

- 3,0 мм

 

n=10

240±10

 

7,1

5,5±0,2

3,5±0,2

15,5±1,0

4,7±0,2 (3,5:0,7=5)

6-0 (45°)

200±10  

4,9±0,2

3,1±0,2

12,4±0,4

3,2±0,2

2

8-0 (45°) 1 мм

- 3,5 мм

- 3,0 мм

 

n=7

200±10

 

7,1

4,9±0,3

3,4±0,2

14,1±0,3

4,6±0,2 (3,5:0,7=5)

8-0 (45°) 2 мм

180±10

5,0±0,4

2,7±0,2

10,7±0,7

4,2±0,2

3

8-0 (45°)

 

- 5,0 мм

- 3,0 мм

 

 

n=6

240±10

 

8,7

6,2±0,2

3,6±0,2

18,0±1,0

5,0±0,2 (5,0:0,7=7,1)

8-0 (3мм) (45°)

240±10

6,0±0,2

3,9±0,2

18,0±0,7

4,1±0,2

4

8-0 (45°)

 

- 3,5 мм

- 2,5 мм

 

 

n=4

320±10

 

6,5

4,9±0,2

2,9±0,2

12,0±0,8

3,2±0,2

(3,5:0,7=5)

7-0 (45°) (adventitia)

200±10

4,3±0,3

2,4±0,2

7,9±0,5

Difficult to determine

5

8-0 (90°)

 

- 2,5 мм

- 2,5 мм

 

 

n=6

 

120±10

 

7,9

5,1±0,2

2,4±0,2

13,0±1,0

4,2±0,2

 

6-0 (90°)

50±5

4,7±0,3

1,8±0,2

8,2±0,3

3,2±0,2

 

6

8-0 (90°)

 

- 4,0 мм

- 3,0 мм

 

n=9

170±10

 

10,7

6,2±0,3

3,9±0,3

20,0±1,5

3,4±0,2

 

6-0 (90°)

140±10

6,5±0,2

3,3±0,2

16,7±1,0

2,0±0,2

 

 

   Results of investigation showed that use of suture material with thinner thread, particularly, preferring number “8-0” than “6-0”, most closely approximates the internal geometric parameters of the anastomosis to the calculated values. Furthermore use the thinner thread increases longitudinal (to 8,5% - 12,3%) and transverse (to13% - 30%)  diameter which is reflected in area of anastomosis that enhanced to 20%-50%.

   Putting stitches in 3mm along the edge of coronary artery decreases size of anasomosis: shortens length of anastomosis C(long) and diameter transverse, hence, it decreases the area of anastomosis to decreased 20-25%.

  Method with relative positioning of layers of vascular wall of both vessels by “adventitia-to-adventitia” significantly decreases longitudinal and transverse diameters to 10%-13% and 15%-17%, respectively, that decreases area of anastomosis to 30%-35%.

  Accordingly to data from table 1, diameters of anastomosis influence on value of area of anastomosis and value of volume flow velocity through the anastomosis in direct ratio. Thereby affecting the dimensions of diameters, seeking to increase their maximum values, one can increase the volume flow velocity through anastomosis, that increase longevity of coronary graft.

  Conclutions: Using of suture material with thread “8-0” increases longitudinal (to 8,5%-12,3%) and transverse (to 13%-30%) diameters of anastomosis and it increases the area to 20%-50% comparing with use of suture material with thread “6-0”. This increased area leads to increasing of value of volume flow velocity to 20%-25%.

  Method of performing the coronary anastomosis with relative positioning of internal layers of vessels by “intima-to-intima” increases the area of anastomosis to  40%-50%, that leads to increasing of value of volume flow velocity to 50%-60% comparing with method “adventitia-to- adventitia”.

  Putting stitches in 1 mm along the edge of coronary artery increase the size of longitudinal and transverse diameter and total area of anastomosis (to 25%-30%) and volume flow velocity through anastomosis to 10%-15%, comparing with putting stitches in 3 mm along the artery edge.

  Literature:

1.  Velocity distribution and intimal proliferation in autologous vein grafts in dogs/ S.E. Rittgers et al.// Circ.Res. -1978.-Vol.42 p-792-801

2.  A lumped parameter model to evaluate the fluid dynamics of different coronary bypasses/ R. Pietrabissa [et al.]// Med. Eng.Phys. -1996.Vol.-18.-p.-477-484.

3.  Intraoperative Imaging Techniques to Assess coronary artery bypass graft patency\\ L. Balacumaraswami, D.Taggart\\Ann Thorac Surg 2007;83:2251-7

4.  Intraoperative graft assessment during coronary artery bypass surgery// Toshihiro Fukui// General Thorasic and cardiovascular Surgery// 06January 2015

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