Auxiliary device for pulsatile coronary artery bypass

The present invention provides a device for safely and completely performing the anastomosis of the bypass graft to the coronary artery on the beating heart with good patency, which comprises: PA1 a means for rotating a heart to obtain excellent exposure of the target coronary artery to be anastomosed and absorbing the portion of the myocardium to stabilize the anastomosis area without reducing cardiac output; PA1 a means for perfusion to the distal myocardium during the anastomosis of the bypass graft to the coronary artery; and PA1 a means for compressing the coronary artery proximal and distal to the site of the anastomosis at a minimum stress to perform occlusion for obtaining bloodless operative field.

TECHNICAL FIELD
 The present invention relates to a device used for performing the
 anastomosis of a bypass graft to the coronary artery on the beating heart.
 BACKGROUND OF THE INVENTION
 In recent years, interventional treatments, such as percutaneous
 transluminal angioplasty or stent placement for coronary stenosis, have
 been widely applied for patients who suffer from ischemic heart disease
 such as myocardial infarction. Interventional treatments provide shorter
 post-treated hospital stays to patients because methods of these
 treatments are less invasive to patients. However, patients must receive
 observations over a long time after hospital stays because restenosis
 often occurs.
 Meanwhile, coronary artery bypass grafting (hereinafter abbreviated to
 CABG) has been applied for patients. CABG procedures comprise exposing the
 heart, and performing the anastomosis of the bypass graft to the distal
 portion of the coronary stenosis to provide blood flow to distal coronary
 artery. This method offers many advantages to patients in terms of
 potential for no restenosis in the postoperative period.
 CABG, is applicable to many of patients who have some risk factors to the
 interventional treatment. Risk factors are, for example, restenosis in the
 post-treated period of interventional treatments, serious heart failure,
 occlusions or stenosis in a plurality of coronary arteries, calcification
 in ascending aorta, chronic diseases in brain, kidney, respiratory system
 and/or the like, and advancing age of patients. But all of theme risk
 factors to interventional treatments are also risk factors to CABG with
 cardiopulmonary bypass. Cardiopulmonary bypass has allowed all surgeons to
 perform the operation with good patency rate, but deleterious effects of
 cardiopulmonary bypass to patients who have those risk factors are wall
 documented. In fact, those patients have been abandoned.
 If anesthesia and medial sternotomy are able to be applied to those
 patients mentioned above, CABG procedures would be performed on the
 beating heart without cardiopulmonary bypass and cardiac arrest. This less
 invasive technique is called off pump CABG (hereinafter abbreviated to
 OPCAB) and becoming increasingly popular in terms of a means for saving
 such an abandoned patient. The anastomosis of the bypass graft is
 performed under temporary proximal and/or distal occlusion of target
 coronary artery to provide a bloodless operative field.
 Further, the least invasive technique called minimally invasive direct
 coronary artery bypass grafting (hereinafter abbreviated to MIDCAB) is
 applied to patients. The procedures of this technique are performed on the
 beating heart with left or right anterior small thoracotomy and no medial
 sternotomy. in the case of CABG with medial sternotomy for obtaining
 exposure of the coronary artery, patients were obliged to stay in hospital
 for about one month or more and suffered from postoperative pain. In the
 case of MIDCAB with anterior small thoracotomy, however, patients would
 take no pain and have good recovery so that they are able to take a meal
 on the next day after the operation. Thus, MIDCAB offers many advantages
 to patients in terms of shorter postoperative hospital stays, cost
 savings, and superior postoperative appearance resulting from decreasing
 trauma.
 In OPCAB and MIDCAB procedures, it is difficult to perform completely the
 anastomosis of the bypass graft with good patency rate to the target
 coronary artery in a short time because the heart is beating. In order to
 resolve the problem, two types of devices for target area stabilization
 are developed and are in use. One is a compression type stabilizer, and
 the other is a suction type tissue stabilizer.
 The compression type stabilizer comprises, as described in, for example,
 JP-A-10-5203, an arm and fork-shaped two legs attached at the front end of
 the arm. The shape and the number of legs are not restricted thereto.
 While the arm is fixed to a sternum retractor, the two legs compress the
 target area and restrict the motion of the myocardium. In fact, cardiac
 output has decreased as the result of direct ventricular compression with
 reduced stroke.
 The suction type tissue stabilizer, an described in, for example, U.S. Pat.
 No. 5,727,569, immobilizes the target area by providing a sucker to the
 surface of the target area, attaching the surface to the sucker, and
 pulling the sucker with the tissue of the heart. However, internal
 bleeding has been observed in the tissue of the heart surface after
 operation as the result of suction of tissue at the vacuum pressure of
 about -350 mmHg. Since the size of the sucker is large, the operative
 field becomes too small to perform MIDCAB procedure with anterior small
 thoracotomy.
 In OPCAB procedure, it is necessary to rotate the heart to obtain good
 exposure of the target coronary artery. In the case of obtaining proper
 exposure of the left coronary artery by medial sternotomy, it is necessary
 that the heart is rotated to the patient's right. This rotation the heart
 is generally conducted by inserting a gauze pad at the posterior surface
 of the heart. However, it is difficult with this technique to obtain
 excellent exposure of the target coronary artery because degree of the
 rotation is not controlled. Furthermore, sudden reduction in blood
 pressure may occur when the surgeon raise the heart to make a space for
 inserting the gauze pad.
 In OPCAB and MIDCAB procedures, the surgeon has to perform the anastomosis
 in the time for which the blood flow of the target coronary artery can be
 stopped. A long time occlusion of the target coronary artery for the
 anastomosis gives the patient extremely dangerous conditions such an
 ventricular fibrillation or the like. Therefore, the surgeon tries to
 perform the anastomosis in a short time. This, however, may make
 unsuccessful anastomosis to invite occlusion of the bypass graft or
 coronary artery after the operation.
 The stenosis at the point of hemostasis of the coronary artery for the
 anastomosis has often observed in the postoperative period. In order to
 interrupt the blood flow of the target coronary artery in the area to be
 anastomosed, the following technique has been generally used: to place a
 suture around the coronary artery proximal and/or distal to the site of
 the anastomosis; pass each end of the suture through the passage of a
 tube; and slide the tube down while pulling up each end of the suture just
 to the point of hemostasis. However, Endo at. al. report in The Japanese
 Journal of Thoracic Surgery, Vol. 51, No. 8, page 704 that the post
 operative cc:lusiom was observed at the point of hemostasis of the
 coronary artery because the coronary artery would be damaged by receiving
 overload force to compress the coronary artery. In fact, the force t o
 compress the coronary artery is not able to be under control according to
 this technique.
 For such a case, in some proposals a flexible and elastic suture made of
 polyurethane or porous Tefron was used with the purpose of reducing the
 force applied to the coronary artery, or a Silastic tape was used for wide
 contact area with the surface of the coronary artery to compress the
 coronary artery gently. Nevertheless, as a fact, the stenosis or occlusion
 in the postoperative period has been often observed yet.
 In order to reduce the force applied to the coronary artery, the technique
 of passing the suture through surrounding tissue of the coronary artery
 has been proposed. The tissue would play a part of a cushion against the
 force of compression. However, since a needle was used for passing the
 suture through the tissue around the coronary artery, the coronary artery
 itself may be injured with the needle. Further, this technique makes the
 compression force uncertain to occlude the target coronary artery.
 An object of the present invention is to provide a device for safely and
 reliably carrying out OPCAB and MIDCAB.
 Another object of the present invention is to prov,te a device used in
 OPCAB and MIDCAB procedures, which stabilizes anastomosis area without
 decrease of cardiac output.
 Another object of the present invention is to provide a means used in OPCAB
 and MIDCAB procedures, for obtaining excellent exposure of a target
 coronary artery to be anastomosed without decrease of cardiac output.
 Another object of the present invention is to provide a means used in OPCAB
 and MIDCAB procedures, which provides a blood flow to the distal
 myocardium during the anastomosis of a bypass graft to the target coronary
 artery.
 Another object of the present invention is to provide a means used in OPCAB
 and MIDCAB, which controls a load force to compress the target coronary
 artery at a minimum load to stop a blood flow.
 SUMMARY OF THE INVENTION
 The present invention lies in a device for beating coronary artery bypass
 grafting on a beating heart, used for performing anastmosis of a bypass
 graft to a coronary art which device comprises:
 a means for rotating a heart for obtaining good exposure of the coronary
 artery and absorbing motion of the beating heart to provide motion
 reduction of an area of performing the anastomosis;
 a means for providing blood flow to the distal myocardium during the
 anastomosis of the bypass graft; and a means for compressing the coronary
 artery to perform proximal and distal occlusion of anastomosis portion, to
 stop blood flow through the coronary artery to provide a bloodless
 operative field during the anastomosis of the bypass graft.

The numerals in the above drawings refer to the followings.
 1: coronary artery; 2: aorta; 3: stenosis; 4: heart; 5: bypass graft; 7:
 left coronary artery; 8: stabilizer; 11: pad; 12: ribbon; 13: hole; 14:
 sealed part; 15: port; 16: fluid tube; 17: three-way stopcock; 18:
 syringe; 19: connector; 20: perfusion catheter; 22: connector; 23:
 insertion part; 24: trunk part; 25: connection part; 26: tip; 28: rib; 29:
 side passage; 30: occluder; 31: tube; 32: front stopper; 33: spring; 34:
 cylinder; 35: ring-shaped member; 36: back stopper; 37: cap; 38: wire; 39:
 loop; 41: suture; 42: pledget; 43: suture; 44: needle
 DETAILED DESCRIPTION OF THE INVENTION
 The present invention is described specifically below while referring to
 the accompanying drawings.
 The present invention is constituted by three elements, that is, a fluid
 type pad (11), a perfusion catheter (20) and an occluder (30), and shows
 the maximum effect when all the elements are used. Two or one element may
 be used selectively. Explanation is made on each element below.
 Pad
 The pad (11) shown in FIG. 2 has a sealed part (14) at one side; a hole
 (13) is formed at each end of the sealed part (14); and a ribbon (12) is
 inserted into each hole (13). While using the pad, the other ends of the
 ribbons (12) are fixed at the outside of the operative field to prevert:
 the pad from moving to an undesirable due to the beating heart. In the
 present example, two holes are formed, but the number of holes is not
 restricted to two. The ribbons (12) for fixation of the pad are not
 necessary depending upon the site at which the pad is located. In such a
 case, the sealed part (14) or the holes (13) are not required.
 The pad (11) shown in the present example has a tetragonal shape. However,
 the shape of the pad is not restricted thereto and, as shown in FIGS. 3(a)
 to 3(c), various shapes such as circular shape, oval shape, floating ring
 shape, concave shape capable of covering the apex cordis of a heart, and
 the like can be employed depending upon the site at which the pad is
 located.
 The pad (11) has a port (15), and one end of a fluid tube (16) is connected
 to the port (15). A fluid is introduced into the inside of the pad (11) by
 a syringe (18) through the fluid tube (16) to inflate the pad (11). The
 connection of the syringe (18) and the fluid tube (16) is made via a
 connector (19)provided at the other end of the fluid tube (16). Between
 the connector (19) and the syringe (18; is provided a three-way stopcock
 (17). By closing the throe-way stopcock (17), a fluid is held inside the
 pad (11).
 The pad used in the present invention is made of a stretchable flexible
 material and has a thickness of preferably 0.05 to 0.50 mm. A thickness
 smaller than 0.05 mm is not preferred because damage such as pinhole or
 the like may appear during the use of the pad. The thickness larger than
 0.50 mm is not preferred because the pad has neither stretchability nor
 flexibility to absorb the motion of the heart beating for stabilizing the
 anastomosis area.
 The material for the pad used in the present invention is preferred to have
 a tensile elongation of at least 300% and a 100% modulus of 5 to 30
 kg/cm.sup.2. Herein, "tensile elongation" and "100% modulus" refer to
 values measured according to JIS K 6301. In the case that the tensile
 elongation is smaller than 300%, the pad is too hard and too inflexible to
 absorb the motion of the myocardium for stabilizing the anastomosis area.
 A 100% modulus smaller than 5 kg/cm.sup.2 is not preferred because the pad
 is too soft and has no structural strength; a 100% modulus larger than 30
 kg/cm.sup.2 is not preferred because the pad is too hard and too
 inflexible to absorb the motion of the myocardium for stabilizing the
 anstomosis area. There is no particular restriction as to the kind of the
 material as long as there is used a material satisfying the above
 requirements. Referred as the material are, for example, soft polyvinyl
 chloride, polyurethane, polyester, polyamide, silicone rubber, polyolefin,
 natural rubber, synthetic rubbers, and polymer alloys or laminates
 thereof.
 A following technique using the pad is explained to clarify effects of the
 present invention, with reference to FIG. 1 and FIGS. 4(a) to 4(c).
 Illustrated is a heart having a stenosis (3) at the upstream site of a left
 coronary artery (7). The anastomosis of a bypass graft at the downstream
 site in being performed for providing blood flow to the distal myocardium.
 When medial sternotomy is used, the surgeon is unable to obtain good
 exposure of the target left coronary artery (7) because it is located at
 the left to posterior surface of the patient's heart as shown in FIG.
 4(a).
 In order to obtain excellent exposure of the target coronary artery (7) to
 be anastomosed, the pad having a shape shown in FIG. 2 is used. The pad
 (11) is inserted at the posterior surface of the heart as shown in FIG.
 4(a) and fixed by holding ribbons (12) at the outsides of the operative
 field. A fluid is gradually introduced into the inside of the pad (11)
 using syringe (18); thereby, the pad is inflated slowly so as to rotate
 the heart to the patient's right as shown in FIG. 4(b). With this pad of
 the present invention, t surgeon is an,(e to obtain excellent exposure of
 the target left coronary artery (7) because it in possible to adjust the
 heart rotation under control of volume of fluid introduced into the pad.
 Heart rotation must be conducted slowly while observing changes of the
 patient's hemodynamics such as blood pressure, or electrocardiogram. Rapid
 rotation must be avoided because it provides the heart with sudden
 increase of load to reduce blood pressure. According to the present
 invention, however, in the case that blood pressure is reduced in the step
 of heart rotation, it can be recovered easily by immediate deflation of
 the pad (11) to release load applied to the heart. As soon as the recovery
 of the blood pressure has been confirmed, the heart can be carefully
 rotated again.
 In order to stabilize the anastomosis area of the heart, the stabilizer
 described in the background art is used in combination with the pad of the
 present invention. The stabilizer (8) has two fork-shaped legs at the
 front end as shown in FIG. 1. The two legs compress the anastomosis area
 and restrict the motion of the myocardium. Though many types of
 stabilizers are commercially available, a proper stabilizer is selected
 depending upon operative procedure. According to the technique using the
 pad of the present invention, following effects are expected even if any
 type of stabilizer is used.
 The pad (11) is able to deform flexibly in response to the heart beating to
 absorb the motion of the myocardium because it is freely stretchable and
 highly flexible. As shown in FIG. 4(c), while the stabilizer provides the
 target area with motion reduction in the X and Y plains, the pad (11)
 provides target area with motion reduction in the Z plain without reducing
 stroke due to direct ventricular compression by the stabilizer. In
 comparison with the case using the stabilizer alone, this technique
 provides not only excellent stable state of the anastomosis area but also
 less restriction of the myocardial motion. Therefore, this invention is
 useful for a means to stabilize the anastomosis area without increasing
 load provided to the heart and to obtain excellent exposure of the target
 coronary artery to be anastomosed.
 Perfusion catheter
 The perfusion catheter (20) is made of a flexible material and is
 constituted by three parts, that is, an insertion part (23) of small
 diameter to be inserted into a target coronary artery anastomosed, a trunk
 part (24) of large diameter and a connection part (25) which connects the
 insertion part (23) to the trunk part (24). Inner diameter and outer
 diameter of the connection part (25) gradually decrease in a direction
 proceeding from the trunk part (24) toward the insertion part (23) to
 connect the connection part (25) with the insertion part (23). Smooth
 surface is formed at the point of connection between the connection part
 (25) and the insertion part (23), and between the connection part (25) and
 the trunk part (24). The insertion part (23) has a proper outer diameter
 fitted for inner diameter of the coronary artery to be inserted. For
 example, the outer diameter is preferably 0.7 to 1.5 mm for left anterior
 descending artery. Of course, the outer diameter may be changed according
 to the inner diameter of the coronary artery to be inserted.
 According to this invention, 2d&lt;D must be satisfied, where D is inner
 diameter of the trunk part (24) and d is inner diameter of the insertion
 part (23). 2d&gt;D is not preferred because it provides lower pressure
 from the blood flow at the outlet of the perfusion catheter (20) and no
 sufficient blood flow to the distal myocardium. The length L of the
 insertion part (23) is preferably in a range of 10d to 35d. A length
 smaller than 10d is not preferred because the length is not sufficient for
 insertion into the target coronary artery and fixation of the insertion
 part. A length larger than 35d is not preferred because the pressure loss
 of the blood flow through the insertion part (23) is larger and provides
 no sufficient blood flow to the distal myocardium. Lager loss in the
 pressure from the blood flow through the perfusion catheter (20) provides
 hemolysis causing complications such as renal diseases and the like.
 The perfusion catheter (20) is manufactured in the process including
 drawing which is carried out under given conditions. In the drawing
 process, one end of a flexible tube is drawn under the following equation:
EQU D/T=d/t
 where T is the wall thickness of the trunk part (24) and t is the wall
 thickness of the insertion part (23).
 A connector (22) is prepared at the proximal end of the perfusion catheter
 (20) for connection with resources of the blood flow such as blood pump or
 the like. Though any kind of the connector can be used for the perfusion
 catheter, a connector with rotating lure is preferred because connection
 can be hold against the pressure from the blood flow through the perfusion
 catheter.
 The perfusion catheter is preferably formed from fIexible thermoplastics
 having a hardness of 50 shore A or more for good kink resistance. A
 thermoplastic elastomer composed of soft segment and hard segment is
 preferred. For example, polyamide elastomers, polyester elastomers,
 polyolefin elastorners, polyurethane elastomers, and polymer alloys
 thereof can be used, however, the present invention is not restricted
 thereto.
 A crooked shape of the distal end of the perfusion catheter (20) may be
 formed as shown in FIG. 7. The perfusion catheter (20) having the crooked
 shape allows visualization for suturing behind the perfusion catheter (20)
 to be inserted into the coronary artery (7). The crooked shape also makes
 handling of the perfusion catheter (20) easy in the operative field,
 however, the blood flow rate is reduced slightly.
 A length between the distal end and the crooked point is preferably 5 to 20
 mm. In the case of the length smaller than 5 mm, the distal end of the
 perfusion catheter comes out of the coronary artery during perfusion
 because deep insertion cannot be carried out. In the case of the length
 larger than 20 mm, the whole length from the distal and to the crooked
 point cannot be inserted into the coronary artery and the crooked point
 positioned outside the coronary artery interrupts visualization for
 suturing behind the perfusion catheter (20)."
 The distal end of the perfusion catheter (20) may be crooked at the angle
 determined depending upon the site of the coronary artery into which the
 perfusion catheter is inserted. According to the present invention, the
 angle in the range from 80 to 100 degrees is preferred. The angle out of
 the above range is not preferred because the perfusion catheter (20)
 interrupts visualization for suturing.
 A tip (26) may be attached at the distal end of the perfusion catheter
 (20). The tip (26) prevents the perfusion catheter (20) from coming out of
 the coronary artery due to the pressure of the blood flow through the
 perfusion catheter. The tip (26) also performs complete plugging of the
 coronary artery. The shape of the tip is not restricted. For example, a
 spindle shape as shown in FIG. 6(a), or an egg shape as shown in FIG. 6(b)
 may be used. As shown in FIG. 6(b), ribs (28) may be also formed on the
 surface of the tip for higher resistance to disconnection from the
 coronary artery. Of course the present invention is not restricted to this
 shape.
 A side passage (29) may be formed at the distal end of the perfusion
 catheter (20) as shown in FIG. 6(c) for maintaining the blood flow in the
 case that no sufficient blood flow is obtained because the opening at the
 distal end of the perfusion catheter (20) is in contact with the inner
 wall of the coronary artery.
 The tip (26) is preferably formed from flexible thermoplastics having a
 hardness of 30 to 100 Shore A for plugging the coronary artery without
 providing any load thereto. A hardness smaller than 30 Shore A is not
 preferred because the tip (26) breaks easily during the use. Fragments of
 the broken tip remain in the coronary artery to occlude in the
 postoperative period. A hardness larger than 100 Shore A is not preferred
 because the tip (26) is so hard. The coronary artery may be damaged by
 inserting the hard tip into the coronary artery. There is no restriction
 as to the kind of the material as long as the above requirements are
 satisfied. For example, silicone rubber, polyamide elastomers, polyester
 elastomers, polyolefin elastomers, polyurethane elastomers, and polymer
 alloys thereof can be used for this invention.
 A following technique using the perfusion catheter is explained to clarify
 effects of the present invention, with reference to FIGS. 10(a) to 10(d).
 As shown in FIG. 10(a), a suture (41) with a pledget (42) is placed around
 the coronary artery proximal and distal to the site of the anastomosis to
 be tightened for stopping the blood flow through the coronary artery and
 arteriotomy is carried out. Following arteriotomy, as shown in FIG. 10(b),
 the distal suture is slightly loosed and the distal end of the perfusion
 catheter (20) is inserted into the distal coronary artery. The tip (26) is
 inserted beyond the point of the suture placement Successfully, then the
 suture is gently applied at the back and of the tip (26) to fix the
 perfusion catheter (20). After the insertion, the connector (22) of the
 perfusion catheter (20) is connected to a resource of the blood flow which
 has been placed at the femoral artery. The distal coronary artery as
 perfused through the perfusion catheter (20) depending upon blood pressure
 of the femoral artery. For occlusion of the coronary artery and fixation
 of the perfusion catheter, use of an occluder to be described later is
 preferred because of no damaging of the coronary artery.
 As shown in FIG. 10(c), the bypass graft (5) is anastomosed to the coronary
 artery (1) under perfusion to the distal coronary artery. The perfusion
 catheter maintains the blood flow to the distal coronary artery and
 prevents myocardial ischemia during the anastomosis. According to the
 present invention, it is possible to take a sufficient time for the
 anastomosis, and the surgeon is able to perform the anastomosis safely and
 completely.
 Right before suturing is secured, the perfusion catheter is removed as
 shown in FIG. 10(d). As described above, it is clear that the perfusion
 catheter of the present invention is useful for OPCAB or MIDCAB procedure
 as a means for perfusion to the distal myocardium during the anastomosis
 of the bypass graft to the coronary artery.
 Occluder
 A cylinder (34) is inserted into the passage of a tube (31) at the back
 end, and fixed. A ring-shaped member (35) is inserted into the passage of
 the cylinder (34). The ring-shaped member (35) is held in such a state
 that it can slide in the passage of the cylinder (34) in the lengthwise
 direction of the cylinder. A back stopper (36) is provided on the
 circumference of the back end of the ring-shaped member (35), and a front
 stopper (32) is provided on the circumference of a tube site near the back
 end of the tube (31). A spring (33) is provided between the front stopper
 (32) and the back stopper (36). The two ends of the spring (33) are fixed
 to the front stopper (32) and the back stopper (36). Thus, the ring-shaped
 member (35) is fixed to the tube (31) via the spring (33); and the range
 in which the ring-shaped member (35) can slide in the lengthwise direction
 of the cylinder (34), is restricted by the length and elastic deformation
 range of the spring. The front stopper (32) and the back stopper (36) have
 been described here in order to explain a means for fixing the spring
 (33); however, the means for fixing the spring (33) is not restricted
 thereto and, depending upon the fixation means employed, it is not
 necessary to provide the front stopper (32) and the back stopper (36).
 To the back stopper (36) may be fitted a cap (37) engageable to the
 ring-shaped member (35). The function of the cap (37) is described later
 at a section regarding the way on use of an occluder.
 In the present example (FIG. 8(a)), a cylinder (34) and a ring-shaped
 member (35) are located in the passage of a tube (31). However, it is
 possible that the cylinder (34) is fixed on the circumference of the tube
 (31) and the ring-shaped member (35) is fixed on the circumference of the
 cylinder (34). In this case as well, the ring-shaped member (35) is fixed
 to the tube (31) via a spring (33) and the ring-shaped member (35) is
 slidable in the lengthwise direction of the tube (31).
 The tube (31) must be made of a flexible material and must have appropriate
 strength and flexibility. Any material is used as long as it satisfies the
 above requirements. There can be used, for example, polyvinyl chloride,
 polyurethane, silicone, polyamide, polyester, polyolefin,
 polytetrafluoroethylene, copolymers or polymer alloys thereof, natural
 rubber and synthetic rubbers.
 The front end of the tube (31) can be formed simply by cutting the tube so
 that the cross section formed by the cutting becomes perpendicular to the
 lengthwise direction of the tube. Preferably, the edge of the front end is
 rounded so that the front end gives no damage to the coronary artery. More
 preferably, as shown in FIGS. 8(b) and 8(c), the front end is squeezed
 inwardly, or a ring-shaped member is fitted to the front end so that the
 front end can have a larger contact area. With this enlarged contact area,
 the stress applied to the coronary artery when the coronary artery is
 compressed and blood flow is stopped, can be dispersed; and the
 probability of coronary artery damaging can be reduced.
 In the present invention, the static friction coefficient .mu. between the
 ring-shaped member (35) and the cylinder (34) is preferably 1.0 or less.
 Herein, "static friction coefficient .mu." is a frictional resistance at
 which an object made of a material A, placed on a slope made of a material
 B begins to slide when the inclination angle .theta. of the slope is
 gradually increased, and is a value represented by .mu.=tan .theta.. A
 static friction coefficient larger than 1.0 is not preferred because the
 slidability of the ring-shaped member (35) is lower and the quantitative
 control of the force applied for compressing of the coronary artery is
 impossible.
 As long as the static friction coefficient between the ring-shaped member
 (35) and the cylinder (34) is 1.0 or less, there is no particular
 restriction as to the kinds of the materials for the ,above two
 constituent members. There can he preferably used, for example, a
 combination of two stainless steels, or a stainless steel and a
 polytetrafluoroethylene, or two polytetrafluoro-ethylene. Alternatively, a
 fluororesin or a p-xylylene resin may be coated on the surfaces of the
 cylinder (34) and the ring-shaped member (35) for obtaining higher surface
 lubricity.
 In the present example, slidability is secured by using the cylinder (34).
 However, the cylinder (34) may be omitted when the tube (31) per se can
 satisfy the above-mentioned requirements for the cylinder. The objects of
 the present invention can be achieved also when the cylinder (34) and the
 ring-shaped member (35) are omitted and only a spring is provided at the
 back end of the flexible tube (31); however, since with no use of the
 ring-shaped member (35), deflection appears when the spring (33) is
 compressed, making it difficult to control the tension applied to the
 blood vessel, it is preferred to use these members.
 In the present invention, a spring is used as a source which generates a
 stress necessary for compressing of a coronary artery and resultant
 stoppage of blood flow. The spring (33) has a compression spring constant
 of preferably 0.001 to 0.015 kgf/mm. A compression spring constant smaller
 than 0.001 kgf/mm is not preferred because no stress sufficient for
 compressing of the coronary artery and stoppage of blood flow is obtained.
 A compression spring constant larger than 0.015 kgf/mm is not preferred
 because fine adjustment of the stress required for compressing of the
 coronary artery is impossible and, moreover, too high a stress may be
 applied, which may incur damaging of the coronary artery.
 In the present invention, the stress generated when the spring is
 compressed completely, that is, the highest generatable stress is
 preferably not higher than 200 g and is preferably in a range of 80 to 160
 gf. Compressing the coronary artery at a stress larger than 200 gf is not
 preferred because it may invite damaging of the coronary artery. A
 generatable stress smaller than 80 g is not preferred because even
 complete compression of the spring may not be able to occlude the coronary
 artery. A minimum required stress should be applied for occlusion with no
 damaging of the coronary artery, and a generatable stress higher than 160
 gf is not preferred because the coronary artery may receive excessive
 stress.
 There is no restriction as to the material for the spring (33) as long as
 the above requirements are satisfied. There can be used a spring made of a
 metal (e.q. stainless steel), a plastic or a rubber; or an air type
 sprtnc.
 Next, description is made on the way in which the occluder of the present
 invention as used, referring to FIGS. 9(a) to 9(c), and the effects of the
 present invention are clarified. Further, an auxiliary device used
 together with the occluder is described.
 The auxiliary device is formed from a wire (38) having a loop (39) at the
 front end, and is beforehand passed through the passages of the tube (31),
 cylinder (34) and ring-shaped member (35) of the occluder. At this time,
 the loop (39) is held in a state that it is projected from the front end
 of the tube (31).
 Preferably, the loop (39) and the wire (38) show neither breakage nor
 elongation larger than 10% when a tensile stress of 1 kgf or more is
 applied thereto, because such breakage or tensile elongation may make
 impossible that the suture (41) is passed through the passage of the
 occluder in the technique later described. There is no particular
 restriction as to the materials for the loop (39) and the wire (38) as
 long as the above-mentioned requirements are satisfied. There can be used
 preferably, for example, a metal wire, a polyamide fiber, or a polyester
 fiber.
 The following technique is used for the occluder of the present invention:
 the suture (41) is placed around the target coronary artery (1) proximal
 and distal to the site of the anastomosis; the both ends of the suture
 (41) are passed through a pledget (42) made of Tefron, then put into the
 loop (39) as shown in FIG. 9(a); the suture (41) is passed through by
 pulling the wire out of the passage of the occluder as shown in FIG. 9(b);
 while pulling up ends of the suture through the passage of the occluder,
 the occluder with pledget (42) is slid down just to the point of
 hemostasis to compress the coronary artery; the suture (41) is interposed
 between the cap (37) and the ringshaped member (35) to maintain the
 occlusion as shown in FIG. 9(c). Other methods for fixing the suture can
 be applied for the occluder of the present invention.
 The pledget (42) prevents direct contact of the front end of the tube (31)
 with coronary artery (1) and protects the coronary artery. A nonwoven
 fabric, a porous material such as sponge, or a sheet formed from
 polyurethane or silicone rubber is preferably used for the pledget. Though
 there is no restriction as to the suture (41), an elastic suture made of
 polyurethane or a Gore-tex suture in preferred.
 In the present invention, the force necessary for compressing coronary
 artery (1) can be set as desired by controlling the amount of slide of
 ring-shaped member (35). As the ring-shaped member (35) is forced deeper
 into the passage of the cylinder (34), the stress given by the spring (33)
 is larger and the compressing force becomes larger. However, the stress
 for compressing the coronary artery is not larger than said highest
 generatable stress.
 The relationship between the amount of the slide and the stress given by
 the spring is in direct proportion and is determined by the
 above-mentioned spring constant of the spring. For example, a spring
 having a spring constant of 0.005 kgf/mm generates an stress of 0.005 kgf
 every time when the ring-shaped member (35) is inserted into the cylinder
 (34) by 1 mm. The stress of the spring is equal to the tension of the
 suture (41), that is, the stress for compressing the coronary artery (1).
 As clear from the above, the present invention can quantitatively control
 the force for compressing a coronary artery and can stop blood flow at a
 minimum required stress and, therefore, is very suitable as a means for
 occlusion of the coronary artery.
 As clear from the above, the present invention includes a means for
 rotating a heart to obtain excellent exposure of the target coronary
 artery to be anastomosed without reducing cardiac output; a means for
 stabilizing the anastomosis area; a means for perfusion to the distal
 myocardium during the anastomisis of the bypass graft to the coronary
 artery; a means for controlling the force compressing the target coronary
 artery quantitatively for occlusion at a minimum stress, and is very
 useful for carrying out OPCAB and MIDCAB safely and completely.
 INDUSTRIAL APPLICABILITY
 The present invention is utilized as devices for carrying out anastomosis
 of the bypass graft to the coronary artery on the beating heart.