Technical Field of the Invention

This invention relates generally to the field of angioplasty, the nonsurgical reconstruction of a blood vessel. In particular, it relates to a method and apparatus for percutaneous transluminal angioplasty for non-surgically enlarging an arterial lumen totally occluded by a stenotic lesion, and to a unique catheter used during that operation. The catheter is constructed to permit distal tip placement very close to an occlusion and to provide a stabilized or anchored pressure platform and arterial section proximal to the occlusion for enhancing the mechanical forces applied to the occluded area. The resulting combined effect of helical and contractile mechanical forces with pulsatile and phasic pressure forces greatly aids in the opening of the occluded region.

Background of the Invention

Atherosclerosis is a disease that is characterized by irregularly distributed lipid deposits, called plaque. Plaque is deposited in the lumen or central portion of large and medium-sized arteries and results in narrowing of the lumen. Atherosclerosis usually occurs in the second or third decade of life and typically affects the entire length of the coronary artery in varying degrees. In some portions of the coronary artery, the arterial lumen exhibits a more severe narrowing called "stenosis". When the stenosis severity reaches across 75-80% of the cross sectional area of the artery, symptoms of myocardial ischemia, the inadequate circulation of blood to the myocardium, the muscular layer of the heart, occur. Myocardial ischemia is sometimes accompanied by angina pectoris, a severe constricting pain in the chest radiating from the chest into the shoulder and down the left arm. Also attendant with the progression from stenosis to total occlusion of the coronary artery are

coronary spasms and the formation of intraluminal coronary thrombi or blood clots.

Plaque consists of acellular fibrous tissue, calcified tissue and amorphous debris that includes cholesterol clefts containing extra-cellular lipid, called pultaceous debris. It is known that plaque morphology varies as a function of cross-sectional narrowing of the artery. That is, the amount of plaque increases as the severity of stenosis increases and at times, produces total occlusion of the coronary artery that requires reconstructive revascularization by the traditional method called coronary transluminal angioplasty.

Percutaneous transluminal coronary angioplasty (PTCA), using a balloon catheter was first introduced in the mid-1970's and has become one of the recognized methods for treating obstructed coronary arteries. The procedure is generally performed by making a needle puncture in the patien s groin to gain access to the femoral artery and a sheath or introducer is inserted into the wound. A guidewire is passed through the sheath and routed through the vascular system imtil the distal end of the wire reaches the coronary ostium, the opening from the ascending aorta into the coronary artery. A guiding catheter is next advanced over the guidewire imtil its distal end exits over the distal end of the guidewire. A special PTCA wire is then advanced through the guiding catheter into the proximal coronary stump, the area between the ostium and the occlusion, up to the origin of the total occlusion. The physician, by manipulating the proximal end of the wire, attempts to pass it across the stenotic lesion that is obstructing the artery. If the physician successfully manipulates the guidewire past the stenotic lesion, a PTCA balloon angioplasty catheter is passed over the guidewire by feeding the distal end of the balloon catheter over the proximal end of the guidewire and then pushing the balloon catheter over the guidewire until the balloon is adjacent to the stenotic lesion. In position, the balloon is inflated to press the occlusion against the wall of the artery thus restoring patency to the artery.

Frequently, however, the traditional method of transluminal angioplasty using a balloon catheter is not successful because it depends on the ability to insert the guidewire through the stenosis. If the stenosis is so dense that the guidewire cannot be inserted through it, the balloon catheter will also not be able to pass through the stenosis. Rather, the balloon can only be advanced up to the tip of the wire, just outside the occlusion, and then inflated. In this case arterial patency will not be restored.

Another problem associated with the traditional method is presented by the fact that total occlusions frequently occur very close to the ostium. Thus a very short area in which the physician may manipulate the balloon is provided (the "coronary stump"). PTCA balloons are commercially available in lengths of at least two centimeters. If the balloon is inflated in a coronary stump of less than two centimeters, it may displace the guiding catheter away from the occlusion and into the arterial wall and the balloon may tear.

In addition, conventional balloon catheters have tapered oval ends with a shaft tip extending three to five millimeters beyond the distal portion of the balloon. If the physician is unable to direct the shaft tip to the ideal location relative to the total occlusion, the tip may bend thereby reducing the extent to which the physician may advance it further into the artery. Furthermore, the shaft tip prevents the balloon from entering the most proximal portion of the total occlusion. If the balloon cannot enter the occlusion, it cannot be inflated directly adjacent to the total occlusion. This reduces the chances of restoring patency to the totally occluded artery.

A tapered balloon has the added undesirable effect of allowing the arterial wall in the area adjacent to the total occlusion to recoil, which prevents the development of a cleft. Cleft formation during percutaneous transluminal angioplasty is desirable because it provides the pathway through which the guidewire may be inserted across the total

occlusion. This in turn enhances the successful completion of the procedure.

The success rate of the conventional method is further mitigated by abrupt total occlusion of the artery without tapering, total occlusion of the artery of greater than six months duration, stenotic lesions greater than three centimeters in diameter, and occlusion that is flush at the ostium of the vessel that allows no stump with which to start the procedure.

Objects and advantages of the present invention in achieving these and other goals will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein are set forth by way of illustration and example certain embodiments of the present invention.

Summary of the Invention The problems outlined above that have inhibited successful percutaneous transluminal angioplasty are in large measure solved by the balloon catheter method of percutaneous transluminal angioplasty in accordance with the present invention. The method of percutaneous transluminal angioplasty in accordance with the present invention enables the use of a unique catheter that permits the separation of the arterial wall adjacent to a total occlusion thus forming a "cleft". The formation of a cleft permits the angioplasty wire to readily cross the total occlusion resulting in successful percutaneous transluminal angioplasty.

The balloon and catheter system in accordance with the present invention consists of three complimentary members, a guiding catheter, a guidewire and a balloon catheter. The guiding catheter and guidewire are conventional. The balloon catheter is generally rod shaped similar to an as ^* jm metrical cylinder and includes an elongated tubular member having a double central lumen with a proximal end and a distal end and a balloon portion having a concave distal tip smaller in diameter than the proximal tip. The balloon catheter in accordance with the present

invention is espedally designed for percutaneous transluminal angioplasty of totally ocduded arteries, although advantages may exist for application to partial stenoses.

Percutaneous transluminal angioplasty in accordance with the present invention is preferably performed by inserting a guidewire into the femoral artery and up through the descending aorta. A conventional guiding catheter is positioned over the guidewire and advanced up to the ostium of the ocduded coronary artery. A balloon catheter and PTCA wire are advanced through the guiding catheter and are positioned adjacent to the total ocdusion. The balloon is then inflated, a plaque deft is formed, and the PTCA wire is manipulated to explore the entire surface area of the deft. Once the wire has crossed the deft into the distal patent arterial lumen beyond the total ocdusion, the balloon is deflated and withdrawn leaving the PTCA wire across the newly developed deft. Then, conventional angioplasty is commenced.

One of the advantages of the present invention is that the unique shape of the balloon catheter allows the physidan to advance the balloon to within about one-half a millimeter of a total ocdusion. Inflation of the balloon in dose proximity to the total ocdusion permits the formation of a deft thereby enhancing the success rate of conventional ^■ percutaneous transluminal angioplasty.

The drawings constitute a part of this specification and indude exemplary embodiments with the present invention, while illustrating various objects and features thereof. It will be understood that in some instances relative material thicknesses and relative component sizes and dimensions may be shown exaggerated to facilitate an understanding of the invention.

Brief Description of the Drawings

FIG. 1 is an anterior pictorial view of the heart with a partial cross sectional view of the ascending and descending aorta illustrating a

totally ocduded coronary artery and the placement of the present invention through the aorta;

FIG. 2 is a side sectional view of a prior art balloon catheter in use, with anatomical parts cut away; FIG 2a is similar to FIG 2, but depicts the problems assodated with using a prior art balloon catheter to treat a coronary artery having an ocdusion in dose proximity to the coronary ostium;

FIG. 3 is a side elevation sectional view of a prior art deflated balloon catheter disposed within a totally ocduded artery; FIG. 4 is a view similar to that of FIG. 3 with the prior art balloon catheter inflated;

FIG. 5 is a side elevation view of the balloon catheter configuration according to the present invention;

FIG. 6 is a cross sectional view of the shaft illustrating the balloon inflation lumen and wire lumen according to the present invention;

FIG. 7 is a view similar to that of FIG. 2 illustrating a balloon catheter in accordance with the present invention as it may be disposed during a percutaneous transluminal angioplasty procedure; FIG. 8 is a side elevation sectional view of a deflated balloon catheter in accordance with the present invention disposed within a totally ocduded artery;

FIG. 9 is a view similar to that of FIG. 8 with the balloon catheter inflated; FIG. 10 is a side elevation sectional diagram of the balloon catheter in accordance with the present invention illustrating the range of possible PTCA wire exploration.

As required, detailed embodiments of the present invention are disdosed herein. It is to be understood, however, that the disdosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details herein are not to be interpreted as limiting, but ratiier as a basis for

the daims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed system or structure.

Detailed Description of the Invention Figure 1 depicts a human heart 10. The heart 10 is the bodily organ that pumps blood throughout the body. The interior of the heart 10 is divided into four compartments, two upper atriums 12, 14 and two lower ventrides 16, 18. Blood is pumped into the right atrium 12 of the heart 10 via the vena cave 20. It travels into the right ventride 16 and is then forced into the pulmonary artery 22 which takes it to the lungs (not shown) where it is oxygenated. From the lungs, the blood flows to and enters the left atrium 14. From there it passes into the left ventride 18. When the left ventride 18 contracts, the blood is driven out into the aorta 24 and is drculated throughout the body to supply oxygen to other parts of the body.

The aorta 24 is a large artery that is divided into three parts, the ascending aorta 26, the aortic arch 28 and the descending aorta 30. The descending aorta 30 stems through the central trunk of the body and branches into the femoral artery (not shown), which supplies oxygenated blood to the legs. The ascending aorta 26 branches into the right coronary artery 34 and the left coronary artery 36. The right and left coronary arteries 34, 36 surround the heart 10 and supply blood to its muscular walls, the myocardium 38. The right coronary artery 34 supplies oxygenated blood to the musde wall 40 of the right ventride 16. The right coronary artery 34 branches into several descending branches 42,44. The left coronary artery 36 supplies oxygenated blood to the musde wall 46 of the left ventricle 18 and divides into two branches, the drcumflex artery 48 and the anterior descending branch 50.

A total plaque ocdusion 52 may occur in either the right 34 or left 36 coronary artery but frequently occurs within 10 to 20 millimeters of the coronary ostium 54. The area located between the origin of the

coronary ostium 54 and the total ocdusion 52 is called the right or left coronary artery "stump" 58. Partial plaque ocdusions 52 can be successfully treated by a non-surgical procedure such as percutaneous transluminal angioplasty. If not treated, a partial ocdusion may develop into a total ocdusion 52 which can result in myocardial infarction, and permanent irreplaceable injury to the myocardium. Natural bypasses may occur, however, allowing the preservation of the myocardium notwithstanding the existence of a totally ocduded coronary artery. In the setting of a totally ocduded coronary artery serving functional myocardium, resultant myocardial ischemia may necessitate revascularization to relieve symptoms or prevent death.

Figures 2, 2a, 3, and 4 depict the balloon catheter 60 used in conventional percutaneous transluminal angioplasty. hi the prior art method, a needle puncture is made in the patient's groin to gain access to the femoral artery. A guidewire (not shown) is passed through the femoral artery, up the descending aorta 30 until it reaches the coronary ostium 54. A guiding catheter 62 is advanced over the guidewire until it exits over the distal end of the guidewire adjacent to the coronary ostium 54. The guidewire is removed and a PTCA wire 63 is advanced through the guiding catheter 62 into the coronary stump 56 up to the origin 64 of the total ocdusion 52. If the physidan successfully manipulates the PTCA wire 63 past the total ocdusion, the prior art balloon catheter 60 may be passed over the PTCA wire 63 and conventional transluminal angioplasty carried out. If the PTCA wire 63 cannot be manipulated across the total ocdusion 52, the balloon catheter shaft 65 is advanced up to the tip of the wire 63 and inflated. This often results in displacement of the guiding catheter 62 rearwardly of the ostium presenting the possibility that the balloon will be torn by the head of the guiding catheter 62. Moreover, referring to Figure 2a, when the ocdusion is in close proximity to the coronary ostium, the balloon cannot fully enter the artery and inflation of the artery will cause the sloped forward portion of the balloon to engage the artery sidewall. Expulsion of the balloon from the artery may result.

Moreover, as can be seen in Figures 2 and 2a, the tip of wire 63 extends beyond the forward end wall of the balloon, preventing balloon expansion diredly adjacent to the total ocdusion 52. This in turn inhibits and often prevents the formation of a deft through which the PTCA wire 63 may be passed. For the above reasons, a total ocdusion is not in all instances treatable with conventional balloon catheters, leaving surgical bypass as the only treatment option available.

U.S. Patent 4,351,341 to Goldberg et. al. disdoses a balloon catheter, in particular an embolectomy catheter, having an elongated coil spring with and defining a catheter lumen. A silicone extensible sheath covers the coil spring, and in combination with the spring forms an elongatable support structure. If excessive stretching forces are applied in withdrawing the silicone rubber balloon, it tends to extend longitudinally in a pear shaped configuration, further limiting shear stress and the concomitant danger of vessel damage. The Goldberg balloon catheter can become disfigured when excessive fluid pressure and over distension is developed within the balloon. Typically, this occurs when pulling forces are applied to the catheter in drawing the balloon through a body passage. Under these conditions the balloon, when pulled, tends to elongate to form a pear shape. A strain relief collar actuates if excessive strain or fluid pressure occurs. The shear stress on passage wall, and the radial pressure of the balloon on the body passage is limited or reduced.

U.S. Patent 4,364,394 to Wilkinson disdoses a combined sump drainage and irrigation device insertable through a patient's abdominal wall into the peritoneal cavity. An outer inflatable bladder surrounds the tube structure of the device. The bladder is disposed centrally intermediate the opposite ends of the tube structure. The bladder is structured in a manner whereby inflation thereof immediately inward of the indsion prevents acddental withdrawal of the tube structure.

U.S. Patent 4,575,371 to Nordqvist et. al. disdoses a urinary balloon catheter which, when inflated, expands in a direction obliquely

forward past the catheter tip. In one embodiment, an expandable balloon comprises two chambers which are arranged on opposite sides of the catheter tube which expand in front of the tip to prevent the tip from contacting the wall of the urinary bladder, thereby avoiding trauma and infection.

U.S. Patent 4,781,681 to Sharrow et. al. disdoses a fransliiminal balloon laser catheter with a distal tip having an annular generally planar distal face section and a gradually tapered section which converges proximally. This structure allows positioning of the balloon adjacent an ocdusion to be treated. An alternate embodiment catheter distal tip comprises a conical distal face section shaped like a truncated cone, converging proximally. This embodiment also affords a dose positioning advantage in that the distal end of the catheter can be placed diredly against the ocdusion for purposes of laser application, hi particular, the concave portion of the balloon is created such that the laser energy is dissipated off the sapphire lens in a cone fashion so as to make the penetrating power and ability of the system limited such that it will not penetrate or perforate the arterial wall and curved areas beyond the segment being worked on. U.S. Patent 4,886,059 to Weber disdoses an endotracheal tube with an asymmetric balloon. A single balloon cuff is asymmetrically disposed about the axis of the tube to simultaneously seal the trachea, securely position a probe in the trachea, and urge a transducer assembly against the tracheal wall in proximity to a selected artery. Figures 5, 6, 7, 8, 9, and 10 depict the balloon catheter 70 in accordance with the present invention. Balloon catheter 70 broadly indudes an elongated flexible tubular member 72 and balloon member 74. The generally rod-shaped tubular member 72 indudes shank 76, bifurcated distal end 78 and bifurcated proximal end 80. The generally rod shaped elongated central shank 76 indudes a central lumen 90 consisting of an upper balloon inflation lumen 92 and a lower wire lumen 94. The two lumens are separated by a lumen wall 96 that extends along the horizontal

axis of the tubular member 72. The central shank 76 may be made from any number of medical grade plastics used in the manufacture of intravascular catheters induding, by way of example, polyurethane, polyethylene, tetrafluorethylene fluorocarbon polymer, nylon or other suitable materials.

Bifurcated proximal end 80 indudes PTCA wire port 98 and balloon inflation port 100. PTCA wire port 98 indudes a generally elongated hollow cylindrical shaft 102, first wire port end 104 and second wire port end 106. The first end of PTCA wire port 104 is connected to lower wire lumen 94 at junction member 108. Hollow shaft 102 provides means for introducing PTCA wire 63 through shank 76.

Balloon inflation port 100 indudes a generally elongated hollow cylindrical stem 110, first balloon port end 112 and second balloon port end 114. Balloon inflation port first end 112 is conneded to balloon inflation lumen 92 at junction member 108. Second balloon inflation port end 114 indudes a connedor mechanism 116, well-known in the prior art, for connecting stem 110 to a conventional air source (not shown). Hollow stem 110 provides the pathway for introducing air into balloon inflation lumen 92, which in turn introduces balloon inflation air into balloon member 74 at balloon inflation lumen outlet 117. The predse location of balloon inflation lumen outlet 117 may vary within the scope of this invention.

Referring particularly to Figures 5 and 10, balloon member 74 is generally trapezoidal shaped in longitudinal cross section and indudes inner surface 118, outer surface 120, hollow chamber member 122, distal portion 124 and proximal portion 126. The outer diameter of balloon 74 is smaller than the inner diameter of guiding catheter 62. Balloon member 74 is preferably made from polyethylene terephthalate or other suitable materials. Balloon member 74 is conneded to shank 76 by welding, heat pressing or other suitable means. Inner surface 118 of balloon member 74 contains gold or other suitably radiopaque markers 128, well-known in the

prior art, for monitoring the location of balloon catheter 70. Markers 128 may be alternately located along shaft 76 or hollow chamber member 122.

Inner surface 118 surrounds and is molded to hollow chamber member 122 in an air-tight relationship. Hollow chamber member 122 extends along the longitudinal axis of balloon member 74 from proximal portion 126 to distal portion 124 and indudes flared or trumpet shaped mouth 129. The inner diameter of chamber member 122 is larger than the outer diameter of PTCA wire 63. Chamber member 122 is conneded to shank 76 at connector 130. Distal portion 124 has rounded concave surface 132 with blunt edges 134, 136 formed by drcumferential intersection with substantially linearly shaped longitudinal outer surface 120. Concave surface 132 and concave trumpet shaped mouth 129 of chamber member 122 allow for greater PTCA wire 63 exploration of ocdusion surface 133 (shown in Figures 7, 8, and 9). Concave surface 132 and blunt edges 134, 136 are designed to allow balloon member 74 to be advanced to a location substantially diredly adjacent (within approximately .5 millimeters) of the total ocdusion.

Proximal portion 126 has an inflated diameter that is greater than that of distal portion 124. Preferably the surface area of proximal portion 126 is 10-30 percent greater than distal portion 124, with a figure of 20 percent providing excellent results. This structure enables balloon member 74 to exert outward pressure on the musde wall 131 of coronary artery 34. The larger diameter of proximal portion 126 in conjunction with concave surface 132 and blunt edges 134, 136 of distal portion 124 ensure the formation of distally direded deft 138, while also providing structural braking means for discouraging unwanted retrograde expulsion of balloon member 74.

In particular, the ability to position balloon member 74, which may be referred to as a pressure platform, adjacent the total ocdusion results in a phenomenon previously unrecognized in the field of PTCA technology. In many instances, the structure and operational theory

of prior art devices adually teaches away from the present invention. The larger diameter proximal portion 126 functions as a mechanical braking means. Other brake/braking means embodiments may indude frictional, ribbed, or other proximal surfaces of different structure, although a preferred braking means structure is as depicted in Figure 10. Thus, proximal portion 126 also engages the arterial wall and stabilizes that arterial section adjacent total ocdusion 52. This unique feature permits the arterial section distal to total ocdusion 52 to experience the normal helical/shear and contradile forces as the blocked arterial section sits upon the surface of the contracting ventride.

Stated in another manner, the unique braking means of balloon member 74 affords substantially less chance of retrograde expulsion or slippage of the balloon. This improved reliability substantially reduces the risk of creating undesired shear forces which could traumatize the endothelial tissue. The shape of the preferred embodiment disdosed in Figure 10 creates an improved means for opening total ocdusion 52 by placement immediately proximal to the ocdusion and by creation of a mechanical wedge designed to create a deft in the ocdusion. The deft is created in an improved manner over prior art devices by employing the leverage mechanical advantage of a wedge, determinable by formulae known in the mechanical-mathematical fields such as the co-tangent of the angle of the wedge or by dividing the wedge run by the wedge height, etc. Also, generally, the greater the length over which the inflated balloon is in contad with the expanded arterial wall, a substantially correspondingly greater mechanical force will be produced over a greater length of the arterial wall experiendng the plaque ocdusion. Moreover, because of the directional manner in which preferred balloon member 74 creates cleft 170, with proximal portion 126 having the largest diameter of inflated balloon member 74, deft 170 is generally ensured of opening in a direction distal to rather than proximal to the balloon. This substantially avoids the risk of a deft or fissure traveling back to the ostium of the vessel by placement of balloon member 74 immediately

proximal to ocdusion 52. The above mentioned advantages accrue and are further complemented by resulting wire control advantages. For example, the doseness to ocdusion 52 reduces the length of PTCA wire 63 which must be extended beyond mouth 129 and therefore increases the force and control available to the wire. Also, the shape of mouth 129 permits increased area of the ocdusion to be exposed to proximal pulsatile arterial pressure, therefor aiding the deft creation process naturally.

Figures 2, 3, and 4 disdose common problems experienced with use of conventional PTCA balloon catheters. Such catheters are particularly ill-suited for treatment of resistant chronic total ocdusion for several reasons. First, a 3-5 millimeter shaft tip 66 typically extends beyond distal portion 68 of the deflated balloon. This prevents the balloon from entering the most proximal portion of the total ocduded artery. Second, prior art balloons are tapered distally and thereby permit recoil of the arterial wall 131 in the area adjacent to the total ocdusion, thus inhibiting or preventing deft development. Third, the most proximal portion 68' of the balloon is also tapered more narrowly proximally. When additional force is required to advance a PTCA wire across a total ocdusion, expulsion of the balloon proximally can occur with the prior art design, and the chances of a proximal coronary dissection are increased. Fourth, the standard balloon length of 2 centimeters or greater is frequently longer than the available coronary stump length.

Accordingly, the preset balloon catheter 70 invention, shown in Figures 1, 5, 6, 7, 8, 9, and 10 solves the problems of prior art devices by several means. First, balloon catheter 70 comprises a blunt distal end portion which provides coronary arterial luminal widening diredly adjacent to a total ocdusion 52. Cleft separation is thereby formed whidi permits a PTCA wire to be manipulated therethrough, facilitating subsequent angioplasty to be performed. Second, balloon catheter 70 provides distal end structure means which permits exit of a PTCA wire from hollow chamber member 122 mouth 129. The exit location is accordingly distanced from the ocdusion. This permits improved

manipulation of PTCA wire tip 63 to explore and seek out the area of newly formed plaque separation and enhances pulsatile mechanical deft formation. Third, a preferred balloon member 74 may comprise a balloon member having a size which is short enough to fit a short coronary stump, i.e. approximately less than 2 centimeters. Fourth, retrograde expulsion is limited by providing balloon member proximal portion 128 with a blunt configuration having braking means configured to engage arterial wall 131 in a manner suffident to discourage such expulsion, as well as to provide further backup support to wire manipulation across a new area of plaque separation. Fifth, the arterial section proximal to the ocdusion is stabilized by the structure of balloon member 74 while permitting the arterial section distal to the ocdusion to experience the pulsatile, helical, phasic, and torquing forces created by the related adjacent organs and arterial pressures. This promotes further mechanical opening of deft 170 - particularly when combined with the novel wedge action of balloon member 74.

Figures 3, 4, 8, and 9 provide dear illustrations of the operational differences between conventional PTCA wire, balloon catheter devices designed for partial coronary stenosis, and the present invention developed more spedfically for the total ocdusion. In Figure 3, the deflated conventional balloon wire 60 is advanced as dose to the total ocdusion 52 as possible. The balloon is inflated, but the tapered distal balloon with the shaft tip extension 63' remains at a distance from total ocdusion 52. Moreover, the plaqued arterial wall 131' distal to the balloon recoils inward preventing deft separation. Efforts to medianically force wire 63 into total ocdusion 52 may produce coronary perforation, dissection, or retrograde displacement of the balloon.

In contrast, the present balloon catheter 70 may be advanced to within about .5 millimeter of total ocdusion 52. Then, the blunt and substantially non-tapered distal portion 124, and assodated corner portions, provides improved means for deft formation, improved wire

support, and enhanced wire exploration of the entire surface area of the total ocdusion until the deft 170 is entered and crossed.

The invention accordingly consists in the features of the construction, combinations of elements, and construction of parts which will be exemplified in the construction described and of which the scope of the invention would be indicated in the following daims. It is to be understood that while certain embodiments of the present invention have been illustrated and described, the invention is not to be limited to these specific forms or arrangements of parts herein described and shown.