Access platform for internal mammary dissection

Abstract: An access platform (10) having a first and a second blade (50,51) interconnected to a spreader member (12) that laterally drives the blades apart or together and a sternal pad (80,81) interconnected to a blade. The superior blade is pivotally coupled to the spreader member such that it naturally rises as the blades are separated. Alternatively, a vertical displacement member is operably interconnected to a blade and the spreader member and is used to vertically displace the interconnected superior blade and, thus, increase a surgeon's working space and visual access for the dissection of an internal mammary artery. A tissue retractor (70,71) is interconnected to the blades to draw the soft tissue around an incision away from the surgeon's working area.

Description: This invention relates to an access platform according to the precharachterizing part of claim 1. Diseases of the cardiovascular system affect millions of people each year and are a leading cause of death in the United States and throughout the world. The cost to society from such diseases is enormous both in terms of lives lost and the cost of treating cardiac disease patients through surgery. A particularly prevalent form of cardiovascular disease is a reduction in the blood supply to the heart caused by atherosclerosis or other conditions that create a restriction in blood flow at a critical point in the cardiovascular system leading to the heart. In many cases, a blockage or restriction in the blood flow leading to the heart can be treated by a surgical procedure known as a Coronary Artery Bypass Graft (CABG) procedure, which is more commonly known as a "heart bypass" operation. In the CABG procedure, the surgeon either removes a portion of a vein from another part of the body to use as a graft and installs the graft at points that bypass the obstruction to restore normal blood flow to the heart or detaches one end of an artery and connects that end past the obstruction while leaving the other end attached to the arterial supply to restore normal blood flow to the heart. Although the CABG procedure has become relatively common, i.e., heart bypass surgery is performed in one of every thousand persons in the United States, the procedure is lengthy and traumatic and can damage the heart, the central nervous system, and the blood supply. In a conventional CABG procedure, the surgeon cuts off the blood flow to the heart and then stops the heart from beating in order to install the graft. Thus, in order to perform the conventional CABG procedure, the surgeon must make a long incision down the middle of the chest, saw through the entire length of the sternum, spread the two halves of the sternum apart, and then perform several procedures necessary to attach the patient to a cardiopulmonary bypass machine to 93 continue the circulation of oxygenated blood to the rest of the body while the graft is sewn in place. The CABG procedure further requires that a connection for the flow of blood be established between two points that "by pass" a diseased area and restore an adequate blood flow. Typically, one end of a graft is sewn to the aorta, while the other end of the graft is sewn to a coronary artery, such as the left anterior descending (LAD) artery that provides blood flow to the main muscles of the heart. This procedure is known as a "free bypass graft." Alternatively, the IMA pedicle is dissected off of the chest wall, while still attached to its arterial supply, and attached to the LAD past the obstruction. This procedure is known as an "in situ bypass graft." In an in situ bypass graft, the IMA must be dissected from its connective tissue until there is sufficient slack in the IMA to insure that the graft does not kink after it is installed. The IMAs, left and right, extend from the subclavian arteries in the neck to the diaphragm and run along the backside of the rib cage adjacent the sternum. During a conventional in situ bypass graft, typically the left half of the sternum is raised to increase the surgeon's access to the left IMA (LIMA) and the heart. A device used for this type of sternal retraction is disclosed in United Kingdom Patent Application No. GB 2267827 A, "A device for Internal Mammary artery dissection." Although several efforts have been made to make the CABG procedure less invasive and less traumatic, most techniques still require cardiac bypass and cardioplegia (stoppage of the heart). The safety and efficacy of CABG procedure could be improved if the surgeon could avoid the need to stop the heart from beating during the procedure, thereby eliminating the need to connect the patient to a cardiopulmonary bypass machine to sustain the patient's life during the CABG procedure and, thus, eliminate the need for the lengthy and traumatic surgical procedures necessary to connect the patient to a cardiopulmonary bypass machine. In recent years, a small number of surgeons have begun performing CABG procedures using surgical techniques especially developed to enable surgeons to perform the CABG procedure while the heart is still beating. In such procedures, there is no need for any form of cardiopulmonary bypass, no need to perform the extensive surgical procedures necessary to connect the patient to a cardiopulmonary bypass machine, cardioplegia is rendered unnecessary, the surgery is much less invasive and traumatic, and the entire procedure can typically be achieved through one or two comparatively small incisions (thoracotomies) in the chest. Despite these advantages, the beating-heart CABG procedure is not widely practiced, in part, because of the difficulty in performing the necessary surgical procedures with conventional instruments while the heart is still beating. If specially designed instruments were available so that the CABG procedure could more easily be performed on the beating heart, the beating-heart CABG procedure would be more widely practiced and the treatment of cardiovascular disease would be improved in a significant part of the cardiovascular disease patient population. Since the "beating-heart" CABG procedure is performed while the heart muscle is continuing to beat or contract, an anastomosis is difficult to perform because the blood continues to flow and the heart continues to move while the surgeon is attempting to sew the graft in place. The surgical procedure necessary to install the graft requires placing a series of sutures through several extremely small vessels that continue to move during the procedure. The sutures must become fully placed so that the graft is firmly in place and does not leak. It is also important that the procedure be performed rapidly because the blood flow through the artery may be interrupted or reduced during the procedure to allow the graft to be installed. This can cause ischemia, which should be minimized. Also, the surgeon's working space and visual access are limited because the surgeon may be working through a small incision in the chest or may be viewing the procedure on a video monitor, such that the site of the surgery is viewed via a surgical scope. The "beating-heart" CABG procedure could be greatly improved if the surgeon's working space and visual access to the heart and the IMA were increased and improved. Current methods to increase and improve the surgeon's working space and visual access include laterally spreading or retracting the ribs with a conventional rib spreader/retractor, and then vertically displacing one of the retracted ribs relative to the other retracted rib to create a "tunnel" under the rib cage. To vertically displace one of the retracted ribs, some force external to the rib spreader must be applied to the rib. Typically, a surgeon's assistant will push or pull upwardly on the rib with a device having a rib blade inserted under the rib. However, the surgeon's assistant must then hold the rib in a vertically displaced position for the duration of the IMA dissection, resulting in an undesirable addition of another set of hands around the surgical area. Another method used by surgeons to vertically displace the retracted rib is to insert a rib blade under the retracted rib and then attach the rib blade to a winch located above the patient. The winch is then operated to pull upwardly on the rib and hold it in a vertically displaced position. However, it is not at all uncommon for the patient to be raised off the operating table by the winch. This is undesirable because if the rib begins to crack or break, the weight of the patient's body will cause the rib to continue to break until the patient reaches the operating table. While using these methods to vertically displace one of the retracted ribs, it may be desirable to further increase a surgeon's working space and visual access by depressing the sternum or the other retracted rib. However, depression of the sternum or the other retracted rib undesirably adds further sets of hands around the surgical site. Furthermore, these methods and devices tend to limit where the thoracotomy can be performed. For example, if the thoracotomy is performed on the lateral side of the chest, the conventional rib spreader would tend to "stand-up" vertically from the ribs it is retracting such that it would intrude on the surgeon's working space. In addition, if a winch is used to offset the ribs, the lifting action of the winch will tend to rotate the patient to an undesirable and often unstable position for performing the IMA. Equally important to improving the "beating heart" CABG procedure, is the ability to retract the soft tissue around the incision in the chest to draw the soft tissue away from the surgeon's working area. However, none of the methods or devices described above provide the ability to perform soft tissue retraction. Thus, in view of the shortcomings of these devices and methods for increasing a surgeon's working space and visual access during a "beating-heart" CABG procedure, it would be desirable to have a device that is capable of laterally spreading the ribs and vertically displacing opposing retracted ribs relative to each other, that is capable of depressing the sternum, that is self-contained such that the force necessary to spread and vertically displace the ribs, and the force necessary to depress the sternum, is applied by the access platform itself rather than through additional external devices, that does not limit the location where a thoracotomy can be performed, and that is capable of soft tissue retraction. A further access platform is known from EP 0 356 410. It is an object of the invention to overcome the shortcomings in prior art and create an access platform by means of which the ribs of the patient can be spread effectively in order to obtain access to a patient's heart. This is achieved by the features according to claim 1. Advantageous further developments are claimed in the subclaims. The access platform of the present invention serves to facilitate the dissection of an internal mammary artery (IMA), including both proximal and distal dissection, and access to the heart during a "beating heart" Coronary Artery Bypass Graft (CABG) procedure by increasing the surgeon's working space and visual access. The access platform of the present invention is preferably capable of laterally spreading the ribs, vertically displacing the opposingly retracted ribs relative to each other and depressing the sternum to cause a "tunnel" effect under the retracted ribs. Moreover, it is preferably self-contained such that the force necessary to spread and vertically displace the ribs is applied by the access platform itself rather than through additional external devices. The superior blade is pivotally mounted to the spreader member at a pivot point above the blade. The superior blade is naturally lifted as a spreading force from the inferior blade is transmitted to the superior blade through the pivot. In the following a preferred embodiment of the invention is described by referring to the drawings. Figure 1 is an isometric view of an embodiment of the access platform of the present invention. Figure 2 is a partial front elevation view of the access platform in Figure 1. Figure 3 is an isometric view of a tissue retractor assembly for an access platform. Figure 4 is a top view of a spreader member drive assembly of the access platform in Figure 1. Figure 5 is an isometric view of a clutch assembly of the drive assembly in Figure 4. Figure 6 is a partial cross-sectional view of the clutch assembly in Figure 5. Figure 7 is a partial top schematic of the clutch assembly in Figure 5. A preferred embodiment of an access platform 700 of the present invention, as shown in Figures 1 and 2, comprises an elongated spreader housing 702 with a block and tackle type drive mechanism 970 located therein (see Figures 4-7 discussed in detail below). A lever 701 interconnected to the drive mechanism 970 extends upwardly from the spreader housing 702. A blade arm 705 connected to an inferior blade 706 is mounted to a base 704 fixedly received in the housing 702. The blade arm 705 extends outwardly and then downwardly from the spreader housing 702 to the inferior blade 706. The inferior blade 706 includes a tissue retractor 707 extending therefrom. A drive block 708 coupled to the drive mechanism 970 in the spreader housing 702, extends outwardly from the spreader housing 702 in a normal direction to the housing 702. As the lever 701 is rotated, the drive mechanism 970 slidably carries the drive block 708 along the drive slot 703 of the spreader housing 702. A blade arm 711 is attached at its lower end to a superior blade 712 with a tissue retractor 713 extending therefrom. At its upper end, the blade arm 711 is rotatably coupled to an upper end of an elongated arcuate pad arm 715. The pad arm 715 is attached at its lower end to a sternal pad 714. The upper end of the pad arm 715 forms a forked hub 716. The blade arm 711, pad arm 715 and sternal pad 714 assembly is releasably and rotatably mounted on a cylindrical shaft 710 attached to the drive block 708. The access platform 700 incorporates an offset positioning assembly 717 that comprises a pawl 719 pivotally mounted in a recess 723 of the pad arm 715 at a pivot 722 and a ratchet 718 formed on the upper end of the blade arm 711. The pawl 719 includes a pawl nose 721 that engages the ratchet 718 and a pawl lever 720 that is depressed to pivot the pawl 719 about pivot 722 to disengage the pawl nose 721 from the ratchet 718. With the pawl nose 721 engaged, the pad arm 715 can only rotate in a clockwise direction relative to the blade arm 711. The pawl 719 prevents the hub 716 of the arm 715 from rotating in a counterclockwise direction relative to the blade arm 711. With the pawl nose 721 disengaged from the ratchet 718, the pad arm 715 can freely rotate relative to the blade arm 711 in a counterclockwise direction. In operation, with the superior blade 712 and sternal pad 714 assembly separated from the rest of the access platform 700, the superior blade 712 and sternal pad 714 assembly is positioned on the patient's chest. Initially the angle between the blade and pad arms 711 and 715 is large or nearly flat. The superior blade 712 is then inserted into an incision in the patient's chest wall and slid under the superior ribs adjacent to the incision. With the superior blade 712 properly positioned within the incision, the sternal pad 714 is adjusted downwardly on top of the patient's chest wall by rotating the pad arm 715 relative to the blade arm 711 in a clockwise direction to decrease the angle between the pad arm 715 and blade arm 711. Next, the rest of the access platform 700 with the inferior blade 706 attached, is aligned on the patient's chest. The inferior blade 706 is then inserted into the incision in the patient's chest. The blade arm 711 and pad arm 715 assembly is then rotatably mounted on the shaft 710. The access platform 700 is now fully assembled and the blades 706 and 712 are in parallel alignment. The handle 701 is rotated to spread the blades 706 and 712. Because the shaft 710 is located above the superior blade 712 and because the superior blade 712 and sternal pad 714 assembly pivots freely around the shaft 710 a lifting of the superior blade 712 and ribs naturally occurs as the blades 706 and 712 are separated. The spreading force from the inferior blade 706 is transmitted to the superior blade 712 through the shaft 710 located above the superior blade 712. With the blades 706 and 712 offset, the surgeon can harvest the IMA. Upon completion of the IMA harvest, the handle 701 is rotated in a reverse direction to bring the blades fully together. With the blades 706 and 712 together, there is substantially no spreading force being exerted on the superior blade 712 and sternal pad 715 assembly. The pawl lever 720 can then be depressed to disengage the pawl nose 721 from the ratchet 718. With the pawl 719 disengaged, the sternal pad 714 and pad arm 715 are raised allowing removal of the access platform 700 from the incision. As shown in Figure 3, the tissue retractor 707, 713 alternatively includes a plurality of malleable retractor fingers 101A, 101B and 101C extending upwardly from the throat section 55 of the blade 706, 712. The retractor fingers are preferably constructed from annealed sheet metal approximately 0.9 mm (0.035 inch) thick. The fingers 101A, 101B and 101C are preferably welded onto the blades 706 or 712. Prior to operation, the retractor fingers 101A, 101B and 101C extend relatively vertically from the blade 706 or 712. Once the blade 706 or 712 is in position, the retractor fingers 101A, 101B and 101C are bent over the patient's rib cage to retract the soft tissue adjacent to the incision area out of the surgeon's working space. Because of the thickness of the sheet metal, the retractor fingers 101A, 101B and 101C are easily deformed and retain their position once deformed. Referring to Figures 4-7, a drive mechanism 970 preferably comprises a modified block and tackle assembly. The drive mechanism 970 includes a pulley 971 mounted in the spreader housing 702 at a first end, two intermediate pulleys 972 and 973 mounted on the drive block 708 which is interconnected to a superior blade and slidably positioned within the housing 702, and a pulley 974 and a clutch 976 mounted in the housing at a second end-adjacent the base mount 704 which is interconnected to an inferior blade and fixedly mounted within the housing 702. A cable 988 is conventionally wrapped around the pulleys 971, 972, 973 and 974 and clutch 976 to transversely drive the drive block 708 away from the base mount 704 to spread the superior and inferior ribs. The two ends of the cable 988 are tied to a tensioning spring 987 mounted in the drive block 708. The cable tensioning spring 987 provides a preload force (preferably about 13.3 N, i.e. three pounds) necessary to maintain a sufficient preload tension on the drive cable 988. Referring to Figures 5-7, the clutch mechanism 976 includes a clutch housing 977 having a cylindrical capstand 978 mounted therein and a hub 979 coaxially positioned within the capstand 978. A hub shaft 980 extends upwardly from the hub 979 out of the spreader housing 702 where it is coupled to the lever 701 (see Figure 1). Two opposing dowel pins 985 and 986 reside longitudinally along the circumference of the hub 979. The dowel pins 985 and 986 are partially captured in longitudinal recesses 989 and 990 formed in the interior of the capstand 978 and in a slot 981 bored through the hub 979. A spring mechanism comprising three parallel springs 982, 983 and 984 resides in the slot 981 and biases the dowel pins 985 and 986 outward with a force F1. The amount of drive or output force that can be exerted on the superior blade is dictated by the diameter of the capstand 978 and the number of times the cable 988 is wound around the capstand 978. Thus, as the diameter of the capstand 978 is increased, the amount of force that can be exerted by the drive mechanism 970 on the blades is decreased. In addition, as the number of times the cable is wound around the capstand 978 increases, the amount of force that the drive mechanism 970 can exert on the blades is increased. Preferably, the drive mechanism 970 provides about 222.5 N (50 pounds) (±10-15%) of drive force on the blades with a minimum force of preferably about 44.5 - 89 N (10 to 20 pounds) being applied to the lever 701. Only about 133.5 - 178 N (30-40 pounds) of drive force is necessary to spread the ribs on the heaviest of patients. The clutch 976 advantageously provides a slip or overdrive mechanism which ceases the drive force on the blades. This slip force (F slip) is preferably about 222.5 N (50 pounds). At the prescribed slip force, enough torque is transmitted by the capstand 978 on the dowel pins 985 and 986 to overcome the spring bias F1 on the dowel pins 985 and 986 and push the dowel pins 985 and 986 within the slot 981 of the hub 979 such that the hub 979 slips within the capstand 978. As the hub 979 slips within the capstand 978, the blades are prevented from being spread any further and, thus, advantageously prevented from accidentally breaking any of the ribs.

Claims: An access platform comprising: a spreader member (702), an inferior blade (706) an inferior blade arm (705) connected to said spreader member (702) and said inferior blade (706), a superior blade (712), and a superior blade arm (711) connected at a first end thereof to said superior blade 712, characterized by said superior blade arm (711) being pivotally coupled at a second end to said spreader member (702) at a pivot (710), and wherein said superior blade is freely rotatable about said pivot (710) such that said superior blade (712) rises relative to said inferior blade (706) as a spreading force from said inferior blade (706) is transmitted to said superior blade (712) through said pivot (710). The access platform of claim 1 further comprising: a sternal pad (714), and a sternal pad arm attached to said sternal pad at a first end and rotatably coupled to said superior blade arm (711) adjacent said pivot (710) at a second end. The access platform of claim 2 further comprising: a ratchet formed on said superior blade arm (711) adjacent said pivot (710), and a pawl (719) pivotally mounted on said sternal pad arm and operably coupled to said ratchet. The access platform of one of claims 2 to 3 further comprising a drive block (708) operably coupled to said spreader member 702, and a cylindrical shaft extending from said drive block; said superior blade arm (711) and said sternal pad arm being rotatably and releasably mounted on said shaft. The access platform of one of claims 1 to 4, further comprising a drive block (708) operably coupled to and slidably movable along said spreader member (702), wherein said pivot (710) comprises a cylindrical shaft extending from said drive block (708), said superior blade (712) being freely and upwardly rotatable about said shaft to enable said superior blade (712) to vertically and laterally separate from said first blade as said drive block (708) is driven along said spreader member (702). The access platform of claims 1 to 5, further comprising a tissue retractor (713 or 707) mounted to said superior blade (712) or said inferior blade (706). The access latform of claim 6 wherein said tissue retractor (713 or 707) comprises a plurality of interconnected fingers.

Inventors: ALDRICH WILLIAM N, BENETTI FEDERICO J, FERRARI RICHARD M, GINN RICHARD S, MATHENY ROBERT G, MOREJOHN DWIGHT P, REGAN BRENT, REIS EUGENE E, SEPETKA IVAN, TAYLOR CHARLES S, WITT WILLIAM F, ALDRICH, WILLIAM N., BENETTI, FEDERICO J., FERRARI, RICHARD M., GINN, RICHARD S., MATHENY, ROBERT G., MOREJOHN, DWIGHT P., REGAN, BRENT, REIS, EUGENE E., SEPETKA, IVAN, TAYLOR, CHARLES S., WITT, WILLIAM F.
Applicants: CARDIOTHORACIC SYS INC, CARDIOTHORACIC SYSTEMS, INC.
Application year: 1997
Main classification: A61B17
IPC codes: A61B17, A61B19