Methods and apparatus for locating body vessels and occlusions in body vessels

This application claims priority under 35 U.S.C. § 120 to U.S. patent application Ser. No. 10/278,531, filed Oct. 23, 2002, which application is incorporated by reference herein in its entirety.

The present invention pertains to methods and apparatus employed to locate body vessels and occlusions in body vessels finding particular utility in cardiac surgery, particularly minimally invasive cardiac surgery to locate cardiac arteries and occlusions in cardiac arteries.

Diseases of the cardiovascular system affect millions of people each year and are a leading cause of death throughout the world. The cost to society from such diseases is enormous both in terms of the number of lives lost as well as in terms of the costs associated with treating patients through traditional surgical techniques. A particularly prevalent form of cardiovascular disease is coronary artery disease (CAD), which is caused by atherosclerosis. Atherosclerosis is a disease in which the lumen (interior passage) of an artery becomes stenosed (narrowed) or even totally occluded (blocked) by an accumulation of fibrous, fatty, or calcified tissue (hereinafter referred to collectively for convenience as an occlusion). Over time, this tissue, known in medicine as an atheroma, hardens and occludes the artery. The partial stenosis or full occlusion of the coronary arteries that supply the heart muscle leads to ischemia (deficient blood flow) of the heart muscle, angina (chest pain), and can lead to infarction (heart attack) or patient death. Although drug therapies and modifications to diet and lifestyle show great promise for preventing and treating atherosclerotic vascular disease, many patients urgently require restoration of blood flow that has already been lost, especially in those having severely or totally occluded blood vessels.

In many cases, a patient suffering such a coronary vessel occlusion undergoes a coronary artery bypass graft (CABG) surgical procedure, more commonly known as a “heart bypass” operation to restore normal oxygenated blood flow to the heart muscle downstream of the occlusion. The heart bypass typically involves surgically attaching a blood vessel harvested from the patient\'s body from a source of oxygenated blood, e.g., the aorta or a site of the obstructed coronary artery proximal to the obstruction, to provide a conduit for oxygenated blood downstream or distal to the occlusion to restore the flow of oxygenated blood to the heart muscle. CABG surgery is generally lengthy, traumatic and subject to patient risk. Among the risk factors involved is the use of a cardiopulmonary bypass (CPB) circuit, also known as a “heart-lung machine”, to both pump blood and oxygenate the blood so that the patient\'s heart can be stopped or arrested during the surgery, with its function performed by the CPB circuit. Recently, beating heart procedures have been developed that eliminate the need for any form of CPB.

In one approach, the surgeon harvests a section of a blood vessel from the patient\'s venous or arterial system, closes any branching vessel openings, and prepares its proximal and distal ends to be attached in a “proximal anastomosis” and a “distal anastomosis” bypassing the occlusion. The proximal or inflow end of such a “free graft” can be attached via a proximal anastomosis at a site proximal or upstream to the occlusion or to another vessel supplying oxygenated blood, e.g., the aorta. Generally, a free graft is a section of the saphenous vein harvested from the patient\'s leg or segment of radial artery harvested from the patient\'s arm.

In another approach, an available blood vessel within the trunk is dissected from supporting tissue while leaving it connected to the source of oxygenated blood so as to provide a source vessel free end. The sites of excision of the “attached” graft are closed to avoid blood loss, and the source vessel free end is anastomosed to the obstructed coronary artery at a distal anastomosis site distally or downstream from the occlusion that obstructs or restricts blood flow.

The trunk hosts a number of potential grafts including, the left internal mammary artery (left IMA), the right internal mammary artery (right IMA), the radial arteries and three visceral arteries, one in the abdomen, and two in the lower abdominal wall, though the latter can be quite short and are generally of limited usefulness. The visceral arteries include the epigastric artery, the gastroepiploic artery and the splenic artery.

The left IMA is best used for bypass to the left anterior descending (LAD) coronary artery and its diagonal branches, whereas, the right IMA can be used for bypass to selected vessels more posterior such as the distal right coronary artery (RCA). The right IMA can also be used for bypass to selected marginal branches of the left circumflex coronary artery. A segment of radial artery harvested from an arm is generally used to revascularize the posterior surface of the heart. The right gastroepiploic artery can be used to revascularize almost any artery on the surface of the heart and is most commonly used for bypass to the distal RCA or the posterior descending coronary artery. In unusual circumstances, the splenic artery is used to revascularize posterior coronary arteries, but it is long enough to reach the marginal branches of the circumflex coronary artery.

Surgeons typically complete bypass grafts to the following coronary arteries in a patient undergoing multiple bypass surgery in roughly the following order: posterior descending coronary artery (PDA), RCA, obtuse marginal branch, circumflex coronary artery, diagonal branch, and LAD. More generally, surgeons typically revascularize the three coronary systems in the following order: right, circumflex, and anterior descending. However, the order can vary depending on whether the procedure is performed on a beating heart or an arrested heart. About three to four bypass grafts, of which one to three are free grafts, are generally performed per procedure when the heart is arrested. In contrast, about two to three bypass grafts, of which zero to two are free grafts, are generally performed per beating heart procedure. In general, one free graft is used per beating heart procedure.

Two anastomoses are performed when a saphenous vein or other blood vessel is used as a free graft in a CABG procedure; one to the diseased artery distal to the obstruction (outflow end) and one proximally to the blood vessel supplying the oxygenated blood (inflow end). End-to-side anastomotic techniques described further herein are usually performed, although end-to-end or side-to-side anastomotic techniques described further herein are performed at times. For example, sequential graft techniques or “jump” grafts which use side-to-side anastomoses can be used to conserve the amount of blood vessels required when more than one graft is required in any of the three coronary systems for complete revascularization of the heart.

The majority of surgeons will complete the distal anastomosis of a free graft prior to completion of the proximal anastomosis. The small percentage of surgeons who do complete the proximal anastomosis first usually do so to allow antegrade perfusion of cardioplegic solution through the graft during revascularization.

Construction of an anastomosis begins by first precisely locating the occlusion within the target coronary artery. Then, the anastomosis site(s) of the target coronary artery are isolated from the epicardial tissues and overlying fatty layers. Typically, blunt, rounded #15 scalpel blades are employed to dissect these tissues and layers away from the target coronary artery. Blood flow in the target coronary artery can be interrupted by, for example, temporary ligation or clamping of the artery proximal and distal of the anastomosis site. The target coronary artery wall is opened to form an arteriotomy, that is, an elongated incision at the anastomosis site extending parallel to the axis of the coronary vessel and equally spaced from the sides of the coronary artery that are still embedded in or against the epicardium. The arteriotomy is typically created by use of a very sharp, pointed, #11 scalpel blade to perforate the target coronary artery wall, and the puncture is elongated the requisite length using scissors. The length of the incision generally approximates the diameter of the graft or source vessel, e.g., a typical incision for a saphenous vein is about 4 to 5 mm. A “perfect arteriotomy” is an incision that has straight edges, that does not stray from the axial alignment and equal distance from the sides of the coronary artery, and is of the requisite length. A variety of techniques and devices may be used to form an arteriotomy and/or aortotomy, i.e., an incision in the aorta. For example, devices that can cut tissue may be used to form an incision in a vessel. Devices that can cut tissue include mechanical devices, e.g., scissors, scalpel, knife or punch, radio frequency (RF) devices, e.g., electrocautery devices, laser devices and ultrasound devices.

Next, it is necessary to prepare the attachment end or ends of the graft or source vessel by cutting the source vessel end to an appropriate angle for an end-to-side anastomosis or by closing the source vessel end and forming an elongated arteriotomy in the source vessel wall of a suitable length that is axially aligned with the source vessel axis for a side-to-side anastomosis. In an end-to-side anastomosis, it is necessary to prepare the attachment end of the source vessel by beveling its severed end typically at about 30 to 45 degrees. Generally, the surgeon uses surgical scalpels and scissors to shape the source vessel end or make the elongated arteriotomy slit in the source vessel, and sutures to close the open severed end. One method of forming an elongated arteriotomy of a suitable length axially aligned with the source vessel axis for a side-to-side anastomosis is shown, for example, in U.S. Pat. No. 5,893,369.

The prepared end or elongated arteriotomy slit of the bypass graft or source vessel is attached or anastomosed to the target coronary artery at the arteriotomy in a manner that prevents leakage of blood. The inner, endothelial layer, vessel linings are less thrombogenic than the outer epithelial layers. So, in one approach, the attachment of graft to target artery is made by everting and applying the interior linings of the bypass graft or source vessel and the target coronary artery against one another and suturing the everted linings together. Surgeons can construct the anastomosis via a ten-stitch running suture using 7-0 polypropylene suture material. The ten-stitch anastomosis typically comprises five stitches around the “heel” of the source vessel and five stitches around the “toe” of the source vessel. The five stitches around the heel of the graft comprise two stitches to one side of the apex of the graft and the artery, a stitch through the apex and two stitches placed at the opposite side of the apex. The graft is generally held apart from the coronary artery while the stitches are constructed using a needle manipulated by a forceps. Suture loops are drawn up and the suture pulled straight through to eliminate purse-string effect. The five stitches around the toe of the graft also comprise two stitches to one side of the apex of the graft and the artery, a stitch through the apex and two stitches placed at the opposite side of the apex. Again, suture loops are drawn up, the suture is pulled straight through to eliminate purse-string effect, and the suture ends are tied.

The proximal anastomosis of a saphenous vein free graft to the aorta, i.e., an aortosaphenous vein anastomosis, is formed by first removing the pericardial layer that covers the aorta. An occluding or side-biting clamp can be placed on the aorta at the anastomosis site. A small circular or elliptical portion of the ascending aorta is excised forming a small opening, or aortotomy, 4 to 5 mm in diameter. An aortic punch typically facilitates this procedure. The opening for a right-sided free graft is made anterior or to the right lateral side of the aorta, whereas an opening for a left-sided free graft is made to the left lateral side of the aorta. The opening is made proximal on the aorta if the free graft is to supply blood to the right coronary artery. If the free graft is to supply blood to the anterior descending coronary artery, the opening is made in the middle on the aorta. And, if the free graft is to supply blood to the circumflex artery, the opening is made distal on the aorta. The right graft opening is placed slightly in the right of the anterior midpoint of the aorta and the left graft opening slightly to the left. The end of the saphenous vein free graft is cut back longitudinally for a distance of approximately 1 cm. A vascular clamp is placed across the tip of the saphenous vein free graph to flatten it, thereby exposing the apex of the vein. Five suture loops of a running suture using 5-0 polypropylene are then placed around the heel of the saphenous vein free graft and passed through the aortic wall. Two stitches are placed on one side of the apex, the third stitch is placed precisely through the apex of the incision in the saphenous vein free graft, and the final two stitches are placed on the opposite side of the apex. Suture traction is used to help expose the edge of the aortic opening to ensure accurate needle placement. Stitches include about 3 to 5 mm of the aortic wall for adequate strength. Suture loops are then pulled up to approximate the vein graft to the aorta. The remaining stitches are placed in a cartwheel fashion around the aortic opening thereby completing the remainder of the anastomosis.

Left-sided grafts are oriented so the apex of the incision in the heel of the saphenous vein free graft will face directly to the left side. The stitches are placed in a clockwise fashion around the heel of the graft and in a counterclockwise fashion around the aortic opening. Right-sided grafts are oriented in a caudal fashion. The stitches are placed in a counterclockwise fashion around the heel of the graft and in a clockwise fashion around the aortic opening. Five suture loops complete the heel portion of the graft and an additional five or six are necessary to complete the toe of the graft. Finished proximal anastomoses tend to have a “cobra-head” appearance.

It is essential for the surgeon to take steps to minimize the possibility of thrombosis, narrowing and/or premature closure of the anastomosis due to technical errors. Some surgeons feel the proximal anastomosis must have a take-off angle of 45 degrees while other surgeons believe the take-off angle is not critical. In addition, it was felt that intima-to-intima contact of the vessels at the anastomosis was critical for endothelization to occur, thereby making an ideal union of the vessels. However, most surgeons now feel intima-to-adventitia contact is acceptable. The main objective of the surgeon is to create an anastomosis with an expected long-term patency rate of greater than 5 to 10 years. The creation of an anastomosis takes approximately 10-15 minutes.

Adequate exposure that affords acute visualization of the vessel walls is an essential requirement for creating a sutured anastomosis without error. Acute visualization of the vessel walls is mandatory in order to properly place each stitch and avoid inadvertently including the back wall of the vessel in a stitch, which in effect narrows or completely occludes the vessel. Most surgeons employ blood-less field devices such as shunts, snares, and misted blowers to achieve the required exposure.