Coronary Artery Disease
Heart disorders are a leading cause of death in developed countries. Such disorders also impair the quality of life of millions of people by restricting activity because of pain, breathlessness, fatigue, fainting spells and anxiety. The major cause of heart disease in developed countries is impaired blood supply. One cause of reduced blood supply to the heart is coronary artery disease.
FIG. 1 is a schematic view of the coronary arteries on the outer surface of the human heart. Though the heart supplies blood to all other parts of the body, the heart itself has relatively little communication with the oxygenated blood supply. Thus, the coronary arteries essentially comprised of the right anterior descending (RAD) coronary artery 100, the left anterior descending (LAD) coronary artery 102 and the circumflex (CIR) coronary artery 103 arise from the aorta 104 beneath the aortic arch 106. The coronary arteries encircle the heart muscle on either side "like a crown" to supply the heart muscle itself with blood.
Coronary artery disease generally involves and results in a narrowing of the coronary arteries due to atherosclerosis. The resulting ischemia or blockage can lead to angina pectoris, a pain in the chest, shoulders, arms or jaw due to a lack of oxygen to the heart, or infarction, death of an area of the myocardium caused by the ischemia.
Coronary artery blockage can be relieved in a number of ways, including drug therapy, utilization of nitrates, beta-blockers, and peripheral vasodilatator drugs (to dilate the arteries) and thrombolytic drugs (to dissolve the clot). Transluminal angioplasty is often indicated--the narrowed part of the artery, clogged with atherosclerotic plaque or other deposits, can be stretched apart by passing a balloon to the site and gently inflating it a certain degree. Additionally, stents or other tubular structures can be implanted during angioplasty to hold the walls of a vessel apart. Risks attendant with angioplasty include blockage of the coronary arteries essentially completely during the time the balloon is being placed and expanded, and also the possibility that portions of the atherosclerotic material can become dislodged which may cause a total blockage at a point downstream of the subject occlusion thereby requiring emergency procedures.
CABG and MIDCAB
Coronary artery bypass grafting (CABG) is a procedure in which the coronary arteries are bypassed for delivering oxygenated blood to myocardium. CABG is the most common and successful major heart operation performed with over 500,000 procedures being performed annually in the United States alone. CABG may be performed as a sternotomy procedure, or more recently, as a MIDCAB procedure (see below). In a sternotomy, a cardiac surgeon makes a sternotomy incision down the center of the patient's chest and the heart is exposed by opening the pericardium. A length of vein is removed from another part of the body, typically the leg. The patient is connected to a heart-lung machine which takes over the function of the heart and lungs during the operation. The section of vein is first sewn to the aorta and then sewn onto a coronary artery at a place such that oxygenated blood can flow directly into the heart. Not only does the procedure typically require the installation of the heart-lung machine but the sternum must be sawed through and the risk of infection is enhanced during the time the chest cavity is spread open.
The use of the cardiopulmonary bypass (CPB) machine has become standard for CABG and other procedures because the beating heart can typically tolerate only about one minute of blood flow interruption before the distal anatomy of the heart reacts to the lack of oxygenated blood and the risk of heart ischemia or infarction increases. The CPB machine takes over the heart's function of pumping oxygenated blood through the rest of the body during surgical intervention, typically 20 minutes up to several hours in duration.
Minimally invasive surgical (MIS) procedures have recently become popular due to the availability of sophisticated materials of construction and smaller designs of surgical and visualization equipment. Minimally invasive direct coronary artery bypass (MIDCAB) is an alternate way to revascularize the coronary vessels using arterial conduits without extracorporeal circulation. Video Assisted Coronary Bypass Surgery by Benetti, et al., J. Card. Surg., 10:620-625 (1995). Various apparatus are recently available for performing such MIS procedures.
FIG. 2 is a representative drawing showing typical locations of sternotomy and thoracotomy incisions. It will be understood that the present invention includes use of these and other incision locations. The MIDCAB procedure replaces the traditional, "open-heart" traumatic vertical sternotomy incision 160, in which the entire chest cavity is opened, with a shorter, more horizontal thoracotomy incision 162 to work on the still beating heart. Typically, no CPB equipment is needed. The thoracotomy exposes the heart over the fifth left intercostal space, or elsewhere as desired by the cardiac surgeon. Using a thorascope in the thorax to enhance visualization via video signal, a portion of the left internal mammary artery (LIMA) is harvested and grafted directly to the left anterior descending (LAD) coronary artery 102. The same procedure can be performed on the right side using the RIMA and the RAD 100, in the center for treating blockages of the circumflex coronary artery 103, or otherwise.
In most CABG or MIDCAB procedures, however, either before or at the time an incision is made in the coronary artery itself, blood flow through the coronary artery must be arrested using pressure, suction or a silastic band or clamp, or by placing stay sutures proximal to the bypass site and tightening the sutures to provide a dry field. Placement of these stay sutures is not always a simple matter, since as the heart is beating vigorously movement of the entire heart muscle makes precise placement of such stay sutures difficult.
FIGS. 3A and 3B are representative perspective views showing alignment of a portion of a vessel for CABG with an incision in the coronary artery, and the attached portion sewn into place onto the coronary artery, respectively. As described, during the typical CAB procedure, a vessel graft 200 is harvested from another portion of the vasculature. The proximal end, not shown, can be attached directly to the aorta, or the vessel to be grafted to the coronary artery 202 can be a segment of a nearby artery like the LIMA or the RIMA. The LIMA or RIMA can be severed at only one point somewhat distal from the uppermost portion of the LIMA where it originates adjacent the aorta, and grafted directly to the coronary artery at a point distal to the stenosis or other occlusion.
Various conventional methods are used for temporarily blocking blood flow through the coronary artery for performing CABG or MIDCAB. It will be understood that unless the coronary artery is completely blocked, blood will flow out of the coronary artery 202 at the point of the incision 204. For this reason, before the vessel graft 200 can be sutured into place, a section of the coronary artery 202 must be occluded. This can be done in a number of ways. In a simple method, the coronary artery 202 can be occluded by exerting pressure across the coronary artery 202 with a blunt instrument 210. Alternatively, a suction tube (not shown) can be operatively positioned adjacent the incision 204 in the coronary artery 202 to eliminate excessive blood loss in the operative field using a vacuum (also not shown). Once a portion of vessel graft 200 is made available, an incision 204 is made directly in the coronary artery 202 at a point distal to the stenosis or other occlusion. The distal end 206 of the vessel graft 200 is sutured 208 directly to the coronary artery 202 so as to provide communication of oxygenated blood through the vessel graft 200 into the coronary artery 202 directly.
FIG. 4 is a representative perspective view of the double stay suture method of occluding the coronary artery. As shown, a third solution is to clamp the coronary artery with one or more stay sutures, such as silastic bands 214 or other suitable clamps. After the anastomosis is created, the stay sutures 214 can be removed. Additionally, the stay sutures may be releasable and re-tightenable. This gives the cardiac surgeon the ability to occlude the vessel, attach the anastomosis, and release the stay sutures in order to determine the integrity of the anastomosis. In the event said anastomosis is inefficiently attached, poorly placed, leaks blood, etc., the stay sutures can be re-tightened and additional stitching or attachment of the vessel graft to the coronary artery can be achieved.
Cardiovascular Systems of Allen, Texas manufactures at least one type of elastic stay suture which is designed to occlude the coronary artery in a less traumatic manner. These stay sutures are formed of silastic tubing, filled with air or other fluid, and sealed at each end. By using this type of stay suture, less trauma is caused to the coronary arteries by virtue of its larger diameter and elastic/soft surface with cushion of air which distributes the occluding forces developed over a larger area.
Various devices have been described for assisting the cardiac surgeon attach the vessel graft to the coronary artery. United States Surgical Corporation (USSC) has recently announced a "Mini-CABG Access Set". USSC Cardiovascular Marketing Newsletter, Vol. I, Number 1, November, 1996. The newsletter describes the "VCS Clip Applier" which applies a non-penetrating titanium clip to the everted edges of co-apposed vessels. The apparatus is used to perform vascular anastomosis in AV fistulas, femoral bypasses, organ transplants, pediatric surgery as well as coronary artery bypass procedures.
U.S. Pat. Nos. 5,389,102 issued Feb. 14, 1995 and 5,573,541 issued Nov. 12, 1996, both to Green et al. teach apparatus and methods for subcuticular stapling of body tissue. These patents teach hand-held devices with pistol-type grips with members which grasp the edges of two body tissue portions to be connected together. As the spring-loaded apparatus is manually actuated, rod-like fasteners are moved into position to clamp or staple the two body tissue portions together.
U.S. Pat. No. 5,490,856 issued Feb. 13, 1996 to Person et al. teaches a purse string stapler. The apparatus includes scissors-type handles and a stapling assembly for emplacing a suture and staples into tissue as a purse string suture.
Unfortunately, the prior art is does not solve the problem of immobilizing the heart during placement of stay sutures prior to forming the anastomosis. Prior to the advent of MIS technology, stabilization of the heart muscle was often accomplished with an assistant, manually holding the heart muscle from underneath with one hand, while the cardiac surgeon formed the anastomosis.
FIG. 5 is a representative perspective view of a fork-type stabilizer 220 mounted on an MIS sternotomy collar 222. With MIS, use of a fork-type stabilizer 220 is prevalent, either held in place by an assistant, clamped separately to the operating table or other stationary object, or otherwise fixed in place relative to the chest cavity of the patient (as shown). The device has at least two tines 224 which are placed transverse to a selected portion of LAD or other portion of coronary artery 202. By pivoting the device about its point of attachment 226 on handle portion 228, the tines 224 Will press across the coronary artery and block any (at least as much as desired) blood flow therethrough. Furthermore, releasing the pressure from the fork stabilizer 220 will allow continued movement of the heart, resulting in loss of original position of the fork stabilizer 220 on the coronary artery.
FIG. 6 is a representative perspective view of a "bull dog"-type clamp 230 commonly used to occlude vessels in cardiac surgery. The clamp 230 has a pair of adjustably positionable soft jaws 232 which clamp gently across a vessel as desired. Drawbacks to this type of clamp 230 include the need to manipulate a small nut-type head to release the occluding force across the coronary artery 202. Additionally, the clamp alone, unless associated with other structure, cannot provide sufficient stabilizing effect on the heart muscle. Without the stabilizing effect of the present invention, the task of suturing an anastomosis to a coronary artery is quite a bit more difficult.
FIG. 7 is a representative perspective view of a stabilizing fork device 240 associated with a ring base-type sternotomy collar 242. The USSC newsletter mentioned above also describes the "Universal Ring Base", an oval-shaped platform which offers 360.degree. access to the surgical site. The apparatus comes fitted with a range of positionable retractors and a gear-toothed profile around the extremity of the ring base for positioning the retractors as well as suture organizing equipment in a non-slipping configuration. A similar approach to MIDCAB is disclosed by Cardio Thoracic Systems (CTS). An access platform apparatus, similar at least in function to the ring base by USSC, provides limited access and certain visualization capability to the cardiac surgeon.
The stabilizing collar 242 clamps into place with clamp means 244 within the thoracotomy incision with a pair of adjustable, locking spreading arms 246 which, typically, would lift and spread the ribs apart providing access to the beating heart. The apparatus provides a platform for securing a conventional fork-type stabilizer 240 in place. As described above, the rigid tines of the fork-type stabilizer 240 are placed directly on top of a coronary artery to occlude a portion of the coronary artery therebetween, in order to effect anastomosis of the vessel between or adjacent the times.
A simple "hemostat"-type clamp which is designed for atraumatic occlusion is described by U.S. Pat. No. 4,821,719 issued Apr. 18, 1989 to Fogarty. This clamp, however, is much less desirable than a simple stay suture since it is considerably larger than a suture and therefore needs to be supported somehow. Additionally, once released, the clamp will need to be repositioned, thus taking additional operating room time and increasing the overhead cost of the procedure.
One problem with the prior art, therefore, is that none of the described devices are particularly suited to place an occlusion such as a stay suture, perform some procedure on the occluded vessel, allow removal of the blockage, and then permit re-blocking the vessel in order to alter the anastomosis somehow or for some other reason. Another drawback of the prior art is that when conventional stay sutures are used, the angle at which they pull across the coronary artery often causes trauma to the artery.
As is evident by a review of the prior art, the stay suture method lifts the heart for immobilizations and the fork type devices all tend to develop a downward force on the heart. In a typical open-heart surgery, the heart is supported by the hands of the cardiac surgeon or an assistant from underneath. Both of these support modes are helpful, but there is no single device which will achieve both. It would be very desirable, therefore, to provide an apparatus and method to temporarily occlude the coronary artery precisely where desired. It would also be desirable to provide a device and method for compressing, supporting and immobilizing the heart, for occluding a blood vessel and simultaneously applying a releasable stay suture.