Abstract:
An apparatus is described for treating arterial occlusions combining an intraluminally operable catheter, having an occlusion-crossing working element, with a micro-invasive extraluminally operable locator for imaging the progress of the working element through the occlusion. Conical, abrasive, blunt-dissecting, and sharp-pointed, and steering and non-steering working elements including guide wires are described. Acoustic transducers and a flexible imaging tube are described for the locator. A suction cup is described for removably anchoring the imaging tube to a surface. A signal-emitting working element and cooperating signal-receiving locator are described. A method for treating arterial occlusions is described.

Description:
RELATED APPLICATIONS 
     This application is a division of U.S. Patent Application No. 09/008,033, filed Jan. 16, 1998, now U.S. Pat. No. 6,157,852. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention: 
     This invention relates generally to catheters and more particularly to catheter apparatus for treating arterial occlusions. The invention relates especially to the combination of an intraluminally operable atheroma-penetrating catheter device with an extraluminally operable imaging device to restore blood flow in an occluded coronary artery. 
     2. Background: 
     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. Over time this tissue, known in medicine as an atheroma, hardens and blocks the artery. In the coronary arteries, which supply the heart muscle, this process leads to ischemia (deficient blood flow) of the heart muscle, angina (chest pain), and, eventually, infarction (heart attack) and 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. Unfortunately, the demand for surgical treatment of disabling and life-threatening coronary artery disease will likely increase in the decades ahead. 
     It has been common surgical practice to treat severe coronary artery disease by performing a coronary bypass, in which a segment of the patient&#39;s saphenous vein (taken from the leg) is grafted onto the artery at points upstream and downstream of the stenosis. The bypass often provides dramatic relief. However, this procedure involves not only dangerous open chest surgery, but also an operation on the patient&#39;s leg to obtain the segment of saphenous vein that is used for the bypass. Additionally, there is a long, often complicated and painful, convalescence before the patient is healed. Moreover, within a few years, the underlying disease may invade the bypass graft as well. The bypass can be repeated, but at ever greater peril and expense to the patient. 
     Fortunately, for patients with moderate stenosis, a less traumatic operation is available. A typical mechanical device for such operations is a thin, flexible, tubular device called a catheter. Through a small, conveniently located puncture, the catheter is introduced into a major artery, typically a femoral artery. Under fluoroscopic observation, the catheter is advanced and steered through the arterial system until it enters the stenosed region. At the distal (tip) end of the catheter, a balloon, cutter, or other device dilates the stenosed lumen or removes atheromatous tissue. 
     Cardiac catheterization procedures for treating stenoses include percutaneous transluminal coronary angioplasty (PTCA), directional coronary atherectomy (DCA), and stenting. PTCA employs a balloon to dilate the stenosis. A steerable guide wire is inserted into and through the stenosis. Next, a balloon-tipped angioplasty catheter is advanced over the guide wire to the stenosis. The balloon is inflated, separating or fracturing the atheroma. Ideally, the lumen will remain patent for a long time. Sometimes, however, it will restenose. 
     In directional coronary atherectomy, a catheter, containing a cutter housed in its distal end, is advanced over the guide wire into the stenosis. The housing is urged against the atheroma by the inflation of a balloon. Part of the atheroma intrudes through a window in the housing and is shaved away by the cutter. 
     Stenting is a procedure in which a wire or tubular framework, known as a stent, is compressed onto a balloon catheter and advanced over the guide wire to the stenosis. The balloon is inflated, expanding the stent. Ideally, the stent will hold the arterial lumen open for a prolonged period during which the lumen will remodel itself to a healthy, smooth configuration. Stents are often placed immediately following PTCA or DCA. It must be noted, however, that a severe stenosis may be untreatable by stenting, DCA, or PTCA. The catheters used in these operations are advanced to their target over a guide wire which has already crossed the stenosis. Most guide wires, however, are too slender and soft-tipped to penetrate the calcified tissue of a total occlusion. Additionally, most guide wires have a bent steering tip which is easily trapped or diverted by the complex, hard tissues often found in a severe stenosis. Without a guide wire to follow, neither PTCA nor DCA nor stenting is feasible and the interventionist may have to refer the patient to bypass surgery. Additionally, degeneration makes a saphenous vein graph a risky and therefore undesirable site of intervention. 
     Thus, many patients would benefit from a less traumatic alternative to bypass surgery for restoring circulation in severely stenosed or totally occluded coronary arteries. In particular, interventionists need to do what has so far been difficult or impossible: safely forge a path of low mechanical resistance through the tough, complex tissues of the severely or totally occlusive atheroma so that blood flow can be restored. Instruments have been developed which can penetrate even a total occlusion. However, such a device must make its way through the occlusion without accidentally perforating the artery. Severe dissections and cardiac tamponade can easily result when an unguided working element is diverted by the heterogeneous tissues of the occlusion. What is needed is a way of reliably guiding a working element through the atheromatous tissue. Once a path is made for a guide wire or catheter to follow, a stent can be installed or DCA or PTCA can be performed. However, reliable guidance is needed in order to open this path safely. 
     One guidance system used in coronary catheterization is fluoroscopy, a real-time X-ray technique which is widely used to position devices within the vascular system of a patient. For visualizing a totally occluded artery, biplane fluoroscopy can be used wherein the interventionist observes two real-time x-ray images acquired from different angles. Biplane fluoroscopy, however, is unreliable, costly and slow. 
     Another way of imaging the coronary arteries and surrounding tissues is intravascular ultrasound, which employs an ultrasonic transducer in the distal end of a catheter. The catheter may be equipped with an ultraminiature, very high frequency scanning ultrasonic transducer designed to be introduced into the lumen of the diseased artery. Frustratingly, however, the stenosis is often so severe that the transducer will not fit into the part that the interventionist most urgently needs to explore. Indeed, if the occlusion is too severe to be crossed by a guide wire, it may be too difficult to steer the transducer into the segment of greatest interest. Additionally, an attempt to force an imaging catheter into a severely stenosed artery may have undesirable consequences. Alternatively, the intravascular ultrasonic catheter can be placed in a vein adjacent the occluded artery. Because venous lumina are slightly broader than arterial lumina and rarely if ever stenosed, a larger transducer may be employed. Depending on its configuration, a larger transducer may acquire images over greater distances, with finer resolution, or both. However, there is not always a vein properly situated for such imaging. 
     While superior imaging alone is of diagnostic interest, imaging and guidance for effective intervention for severe occlusive arterial disease is what is truly desired. A reliable imaging technique is needed for discerning precisely the relative positions of a therapeutic working element, the atheromatous tissues of the occlusion and the arterial lumen proximal and distal to the occlusion as the working element is operated to cross the occlusion. 
     What is needed is an effective combination of a working element and an imaging system for crossing severe or total occlusions without severely dissecting the artery wall and without causing cardiac tamponade. In particular, such a combination is desired which continuously displays a stable image of the artery, the atheroma and the working element as the interventionist urges the working element through the stenosis. What is especially needed is such a combination which is deliverable and operable with minimal trauma to the patient. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to treat arterial occlusions by minimally invasive means and, more particularly, to open a path of low mechanical resistance through the atheromatous tissues of the severely or totally occluded artery without severely dissecting the arterial wall and without causing cardiac tamponade, so that a guide wire or PTCA or DCA catheter can be placed across the occlusion. 
     It is an additional object of the present invention to provide a combination of an effective occlusion-crossing working element and a system for continuously displaying a stable real-time image of an artery, the arterial lumen, the atheromatous tissues therein, and the working element itself, to effectively guide the crossing element through the occlusion. 
     It is an additional object of the present invention to provide a combination of a catheter shaft, including a steerable intraluminally operable working element, and a locator for guiding the working element, the locator including an extraluminally operable imaging device. It is a related object of the present invention to position the locator proximate the occluded coronary artery through a small incision in the patient&#39;s chest. 
     It is an additional object of the present invention to provide such a combination in which the imaging device can be stabilized with respect to the surface of a beating heart while the imaging and operation are accomplished. 
     It is an additional object of the present invention to provide such a combination having the capability of precisely selecting the point where the working element enters the tissues of the occlusion. It is a related object of the present invention to provide such a combination with the capability of enlarging the path so opened, so that the catheter shaft itself, or other devices of diameter substantially larger than that of a mere guide wire, may be placed in that path. 
     In accordance with the above objects and those that will be mentioned and will become apparent below, an apparatus for treating arterial occlusions in accordance with the present invention comprises: 
     an elongated flexible catheter shaft having a distal end zone and an intra-arterially operable working element disposed in the distal end zone; and 
     an extra-arterially operable locator including an imaging tube and an imaging device operatively disposed in the imaging tube, 
     whereby the locator is positioned proximate the arterial occlusion and guides the working element for effective treatment of the occlusion. 
     An exemplary embodiment of the catheter apparatus according to the present invention includes a steering member including a plurality of steering wires disposed in the catheter shaft. The steering wires are fixed in the distal end zone of the catheter shaft, optionally attached to a retaining ring therein and, also optionally, confined in braided tubes for preventing mechanical interference, and are manipulable from the proximal end of the catheter shaft. The steering wires provide the apparatus of the present invention with the ability to steer the distal end of the catheter shaft, and thus the working element, by applying unequal tension to different steering wires. 
     Another exemplary embodiment of the catheter apparatus according to the present invention includes a plurality of rigid tubes confining the steering wires. The rigid tubes have distal ends some distance proximal to the distal ends of the steering wires, thereby increasing the flexibility of the intervening segment of the distal end zone of the catheter shaft. 
     Another exemplary embodiment of the catheter apparatus according to the present invention includes a working element including a pointed tissue-penetrating wire for crossing an occlusion and for penetrating arteries, veins, and interstitial tissues. This provides the apparatus of the present invention with the ability to precisely select the point of entry of the working element into the vascular, interstitial or atheromatous tissue that is to be penetrated. 
     Another exemplary embodiment of the catheter apparatus according to the present invention includes a working element including a rotatable motor-driven inner shaft having a tissue-penetrating point and an abrasive-coated nose cone. This provides the apparatus of the present invention with the ability to leave behind an enlarged path through an atheroma or other tissue after the working element is withdrawn. 
     Another exemplary embodiment of the catheter apparatus according to the present invention includes a working element including a steerable metal nose cone, disposed on the distal end of the catheter shaft, for urging the catheter shaft itself through tissues. This provides the apparatus of the present invention with the ability to leave behind an enlarged path after the working element is withdrawn and to position the catheter shaft itself in the path made by the nose cone as that path is created. 
     Another exemplary embodiment of the catheter apparatus according to the present invention includes a working element including a plurality of slots partially circumscribing the distal end zone of the catheter shaft. This provides the apparatus of the present invention with the ability to deflect the distal end of the catheter shaft with only a gentle force supplied by the steering member, while preserving the axial incompressibility of the catheter shaft and so its suitability for pushing the distal end against and through an occlusion. 
     Another exemplary embodiment of the catheter apparatus according to the present invention includes a working element including an inner shaft disposed in a lumen of the catheter shaft, a nose cone disposed on the distal end of the inner shaft, and a gap between the proximal end of the nose cone and the distal end of the catheter shaft, the gap being spanned by a pair of wires. As the catheter shaft is urged through an occlusion or other tissues and the inner shaft is forced backward into the lumen, the wires bow outward to blunt-dissect the tissues. This applies increased blunt dissecting force to the tissues as the nose cone encounters greater resistance. 
     Another exemplary embodiment of the catheter apparatus according to the present invention includes a working element which emits a signal, and a locator which detects the signal emitted by the working element, whereby a spatial relationship between the working element and the locator is discernible. This provides the apparatus of the present invention with the ability to readily locate the working element. 
     Another exemplary embodiment of the catheter apparatus according to the present invention includes an extravascularly operable imaging tube having a distal end zone defining a surface including a suction cup for adhesion to a beating heart. This provides the apparatus of the present invention with the ability to stabilize the imaging device with respect to the blood vessels and occlusion. 
     Another exemplary embodiment of the catheter apparatus according to the present invention includes an acoustic transducer affixed to a transducer control shaft disposed in a lumen of the imaging tube. The control shaft is mechanically manipulable by external control apparatus. The transducer is operatively coupled to external signal generating and processing apparatus for displaying an image. This provides the apparatus of the present invention with the ability to display a scanning ultrasound image of the catheter shaft, working element, occlusion, and surrounding vascular and interstitial tissues as the operation is performed. 
     Also in accordance with the above objects and those that will be mentioned and will become apparent below, a method for treating an arterial occlusion in a human or animal body comprises the steps of: 
     providing an apparatus for treating an arterial occlusion, the apparatus comprising: 
     an elongated flexible catheter shaft having a distal end zone and an intra-arterially operable working element disposed in the distal end zone; and 
     an extraluminally operable locator including an imaging tube and an imaging device operatively disposed in the imaging tube; 
     introducing the catheter shaft into the arterial system and placing the distal end of the catheter shaft in the lumen of a coronary artery proximate an occlusion; 
     introducing the locator into the chest cavity, placing the distal end of the locator adjacent the artery proximate the occlusion, and activating the locator; 
     operating the working element of the catheter shaft to cross the occlusion while observing the spatial relationships of the working element, the occlusion and the surrounding tissues, 
     whereby the locator, catheter shaft and working element are positioned proximate the occlusion and the working element is operated to cross the occlusion, while the locator reveals the anatomical location and orientation of the working element to accomplish the effective manipulation of the working element. 
     In an exemplary embodiment of the method according to the present invention, the catheter shaft includes a steering member and the method includes the step of operating the steering member to steer the working element when treating the occlusion. 
     An advantage of the present invention is that it permits the use of cardiac catheterization techniques for restoring blood flow to totally occluded coronary arteries previously inaccessible to those techniques. A related advantage is that patients can enjoy relief from cardiac ischemia while avoiding the trauma of coronary bypass surgery. Another related advantage is that the native artery can be preserved and, with it, the artery&#39;s superior blood-carrying characteristics and ability to withstand repeated intervention. 
     An additional advantage of the present invention is the ability to guide a penetrating element through atheromatous tissues of a totally occluded artery without perforating the arterial wall. A related advantage is that access is safely provided for a guide wire or other catheter device across a site of total occlusion. 
     An additional advantage of the present invention is the provision of a stable, real-time image both of the arterial anatomy and of the working element that is being guided therein, allowing accurate determination of the direction and distance from the penetrating element to a point of reentry into the natural arterial lumen beyond the occlusive lesion. 
     An additional advantage of the present invention is the effectively micro-invasive intra-pericardial delivery of the guidance system to the vicinity of the occlusion, requiring only a small, minimally traumatic incision in the patient&#39;s chest. 
     An additional advantage of the present invention is the provision of a scanning ultrasound image of the catheter shaft and its anatomical environment from an imaging device which is stabilized on the surface of a beating heart. Thus, it is easier to visualize important spatial relationships while manipulating the catheter shaft and working element. 
     An additional advantage of the present invention is that the working element and the distal end of the catheter shaft can be steered, the catheter shaft pushed, pulled or twisted, and the working element operated according to its particular design, all while the effect of these actions is immediately and continuously observable via the locator. 
     An additional advantage of the present invention is that the catheter shaft may be provided with a highly flexible distal end zone for precise maneuvering to exploit high resolution imaging available from the extravascularly operable locator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a further understanding of the objects and advantages of the present invention, reference should be had to the following detailed description, taken in conjunction with the accompanying drawings, in which like parts are given like reference numerals and wherein: 
     FIG. 1 illustrates an exemplary embodiment of the apparatus for treating arterial occlusions in accordance with the present invention placed proximate a total coronary artery occlusion. 
     FIG. 2 is an enlarged view of the exemplary embodiment of FIG. 1 placed proximate a total arterial occlusion. 
     FIG. 3 is an enlarged side view of an exemplary embodiment of the apparatus showing a catheter shaft according to the present invention. 
     FIG. 4 is an enlarged side view of an exemplary embodiment of the apparatus showing a locator according to the present invention. 
     FIG. 5 is an enlarged side view of an exemplary embodiment of an apparatus according to the present invention showing a catheter shaft including rings and slots in the distal end zone of the catheter shaft. 
     FIG. 6 is an enlarged side view of an exemplary embodiment of an apparatus according to the present invention showing a catheter shaft including a rotatable abrasive nose cone. 
     FIG. 7 is a side view of an exemplary embodiment of an apparatus according to the present invention showing a catheter shaft including a pair of blunt-dissecting wires. 
     FIG. 8 is a side view of an exemplary embodiment of an apparatus according to the present invention showing a catheter shaft including a pair of blunt-dissecting wires, the wires in a bowed position. 
     FIG. 9 is an enlarged side view of an exemplary embodiment of an apparatus according to the present invention showing a locator including a plurality of suction cups. 
     FIG. 10 is an enlarged sectional view of an exemplary embodiment of an apparatus according to the present invention showing a locator including a plurality of suction cups. 
     FIG. 11 is an enlarged side view of an exemplary embodiment of an apparatus according to the present invention showing the structure of a catheter shaft including a signal-emitting working element. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is now described particularly with reference to a coronary artery having a severe or total occlusion. As illustrated in FIG. 1, an exemplary embodiment of an apparatus in accordance with the present invention is shown placed proximate the occlusion  62  in a coronary artery  60 . The apparatus embodies a combination of two devices which cooperate to safely bypass the occlusion  62 . The first device is an intraluminally operable catheter shaft  100  including a distal end zone  104  having a working element  102  for bypassing the occlusion  62 . The second device of the combination is an extraluminally operable locator  160  for locating the working element  102  with respect to the arterial lumen, the arterial wall and the tissues and boundaries of the occlusion  62 . The locator  160  includes an imaging tube  162  which is introduced through a small incision (not shown) in the patient&#39;s chest and is positioned in the chest cavity adjacent the heart and proximate the occlusion  62 . 
     Continuing with reference to FIG.  1  and now also to FIG. 2, the imaging tube  162  is introduced through an incision (not shown) which need only be large enough to slip the imaging tube  162  into the patient&#39;s chest. The imaging tube is introduced, for example, by thoracotomy, thoracoscopy or sub-xyphoid access, is passed through a puncture in the pericardium, and is advanced until it is adjacent the surface of the heart. The external imaging instruments (not shown) of the locator  160  are then activated to display an ultrasound image. 
     Referring now to FIG. 2, the locator and catheter shaft are operated simultaneously to safely guide and steer the working element of the catheter shaft through the occlusion. Using standard cardiac catheterization techniques, the catheter shaft  100  is introduced through a puncture incision (not shown) into a major artery (not shown) and is advanced and guided intraluminally into an arterial branch which serves a portion of the heart. The distal end zone  104  of the catheter shaft  100  is positioned within the artery lumen and proximal to (upstream of) the total occlusion  62 . The locator  160  is stabilized adjacent the heart and activated to provide an image from a vantage point close to the occluded artery  60  but outside the arterial lumen  71 . It will be appreciated that because only small punctures or incisions are needed in order for the catheter shaft  100  and locator  160  to reach the operation site, the patient can expect a comfortable, uncomplicated recovery. With the present method there is no need to saw through the patient&#39;s sternum or rib cage. 
     Referring now to FIGS. 2 and 3, the catheter shaft  100  and locator  160  are positionable with minimal trauma in the proximity of the occlusion  62  and are simultaneously operable to open a path through the occlusion  62 . The elongated flexible catheter shaft  100  (greatly shortened in FIG. 3) includes a steerable distal end zone  104  and a working element  102  which is carried into the proximity of the occlusion  62  by the distal end zone  104 . The proximal end zone (not shown) of the catheter shaft  100  is connectable to external apparatus (not shown) for manipulating the catheter shaft  100  and working element  102 . The locator  160  includes an imaging tube  162  for placement of the imaging device  168  proximate the occluded artery  60 . The imaging tube  162  includes a proximal end zone (not shown) connectable to external imaging instruments (not shown). The locator  160  also includes an imaging device  168  which is locatable extraluminally near the occlusion  62  and is operatively coupled to the external imaging instruments. 
     Referring again to FIG. 3, the catheter shaft  100  includes a proximal end  110  connectable to external apparatus (not shown), a distal end zone  104  including a distal end  112 , and at least one lumen  114  therebetween. A working element  102  for penetrating tissues is disposed in the distal end zone  104 . A steering member  122  is disposed in the distal end zone  104  for directing the working element  102  at and through the occlusion (not shown). 
     Continuing with respect to FIG. 3, the steering member  122  includes a plurality of steering wires  124  slidably disposed in the catheter shaft  100 . The steering wires  124  have proximal ends  126  manipulable from the proximal end  110  of the catheter shaft  100  and distal ends  128  fixed in the distal end zone  104  of the catheter shaft  100 . Optionally, braid-reinforced tubes  130  slidably confine the wires  124  to prevent the wires  124  from interfering with other parts of the catheter shaft  100 . Also optionally, the steering wires  124  may be affixed to a retaining ring  132  disposed in the distal end zone  104  of the catheter shaft  100 . Also optionally, rigid tubes  136  may be disposed about braid-reinforced tubes  130 , the rigid tubes  136  having distal ends  138  some distance proximal to the distal ends  128  of the steering wires  124 . Between the distal ends  138  of the rigid tubes  136  and the distal end  112  of the catheter shaft  100 , the absence of the rigid tubes  136  increases the flexibility of the distal end zone  104  to facilitate steering. 
     As can be seen from FIG. 3, unequal tension on the steering wires  124  will deflect the distal end zone  104  of the catheter shaft  100  toward a wire  124  having greater tension. It can also be appreciated that, for example, the distal ends  128  of four steering wires  124  may be fixed in the distal end zone  104  of the catheter shaft  100  at ninety degree intervals about the longitudinal axis of the catheter shaft  100 , with the result that the distal end  112  of the catheter shaft  100  can be deflected in two dimensions somewhat independently by manipulating the steering wires  124  in combination. 
     Continuing still with reference to FIG. 3, the working element  102  is steered by deflecting the distal end zone  104  of the catheter shaft  100 . Because the working element  102  is carried in the distal end zone  104 , the distal end zone  104  will impart to the working element  102  the deflection imparted to the distal end zone  104  by the steering member  122 . In conjunction with the guidance provided by the locator  160  (discussed in detail below), this deflection enables an operator of the present invention to guide the working element  102  along a chosen path into and through the occlusion. 
     Although the embodiment described includes the steering member, a catheter or working element without a discrete steering member and a catheter or working element without a steering function are also within the scope and spirit of the present invention. For example, the apparatus may include a guide wire and the guide wire may include a deflected distal end which functions to steer the guide wire. Likewise, the introduction of a working element into a vascular system and the operation thereof to treat an occlusion without the specific step of steering the working element during treatment is also within the scope and spirit of the method according to the present invention. 
     The present invention can incorporate a wide variety of working elements. For example, a blunt-dissecting working element of the kind described in copending U.S. patent application Ser. No. 08/775,264, filed Feb. 28, 1997 now U.S. Pat. No. 5,968,064 issued Oct. 19, 1999, the entire disclosure of which is incorporated herein by reference, may be used. 
     Continuing with reference to FIG. 3, an exemplary embodiment of the present invention is shown in which the working element  104  includes a tissue-penetrating wire  116  disposed in a lumen  114  of the catheter shaft  100 . The tissue-penetrating wire  116  includes a proximal end  118 , manipulable through the proximal end  110  of the catheter shaft  100 , and a sharp distal end  120  projectable from the distal end  112  of the catheter shaft  100 . The tissue-penetrating wire  116  may, for example, be disposed in the lumen  114  of the catheter shaft  100  much as a trocar is disposed in a cannula. Under guidance provided by the locator  160  (discussed below), pressure is applied to the proximal end of the tissue-penetrating wire  116 , urging the wire  116  into and through the occlusion as the catheter shaft  100  and steering member  122  are manipulated to direct the wire  116 . 
     Referring again to FIG.  2  and now also to FIG. 4, the locator  160  includes an imaging device  168  (in this embodiment, an acoustic transducer  170 ), an imaging tube  162  for placing the imaging device  168  extraluminally proximate the occlusion  62 , and one or more external imaging instruments (not shown) operatively coupled to the imaging device  168  for discerning the spatial interrelationships of the working element  102 , occlusion  62 , arterial lumen  71  and arterial wall  72 . Optionally, the imaging tube  162  has an exterior surface  172  which forms one or more suction cups  174  for stabilizing the imaging tube  162  on a surface proximate the occluded artery  60 . Also optionally, the imaging tube  162  has a suction cup activator  176  for selectively activating the suction cup  174 . As illustrated in FIG. 4, the activator  176  includes a lumen  178  having a distal end  180  communicating with a suction cup  174  and a proximal end  182  communicating with a pressure-modulating device (not shown). The activator  176  may, however, encompass an aspirator, a mechanical means of activating the suction cup  174 , or any other convenient way of establishing and interrupting a vacuum to temporarily stabilize a surface of the imaging tube  162  upon a surface proximate the artery  60  and occlusion  62 . Generally, the suction cup may take the form of any other suction-coupling area or feature, defined by a surface  172  of the imaging tube  162 , which affords adhesion to a surface. 
     Continuing with reference to FIG. 4, it will be appreciated that the imaging tube  162  is flexible, enabling the distal end zone  186  of the imaging tube  162  to be secured adjacent a beating heart while the proximal end zone  164  of the imaging tube  162  remains connected to external instruments (not shown) for support and control. The flexibility of the imaging tube  162  contributes to its micro-invasive quality by reducing the trauma inflicted upon tissues and by permitting the tube  162  to conform to the natural contours of bodily surfaces. As alternative ways of reducing trauma and increasing the ease of use, the imaging tube  162  may be given a shape well suited to the route of entry into the chest, or may be stabilized or flexibly supported by external apparatus at its proximal end  188 . 
     Continuing still with reference to FIG. 4, the imaging tube  162  includes a proximal end  188 , a lumen  190  originating in the proximal end  188 , and a motor assembly (not shown) proximate the proximal end  188 . A transducer control shaft  194 , rotatably and translatably disposed in the lumen  190 , includes a proximal end  196  coupled to the motor assembly (not shown), a distal end  198  coupled to the transducer  170 , and a signal conducting path  200  operatively coupling the transducer  170  to the external imaging instruments (not shown). The transducer control shaft  194  is flexible enough to bend with the imaging tube  162 . In this embodiment, the external imaging instruments (not shown) include an acoustic signal generator-processor (not shown) and video display device controlled by a suitably programmed general purpose computer. 
     Referring to FIGS. 2 and 4, the locator  160  in this exemplary embodiment provides a scanning ultrasound image of the environment of the occlusion  62 . The imaging tube  162  is stabilized on the heart adjacent the artery  60  containing the occlusion  62 . The motor assembly (not shown) drives the transducer control shaft  194  within the lumen  190  of the imaging tube  162  in a scanning pattern appropriate for producing an image. For example, the motor assembly (not shown) may drive the transducer control shaft  194  in a repeating reciprocating pattern while at the same time rotating the shaft. In this way, the transducer  170 , which is coupled to the transducer control shaft  194 , describes a two-dimensional scanning pattern which may be registered by appropriate measuring devices as combinations of a rotational angle θ and a longitudinal position Z within the imaging tube  162 . 
     Continuing still with reference to FIGS. 2 and 4, as the transducer  170  describes the scanning pattern, the acoustic signal generator-processor (not shown) causes the transducer  170  to emit acoustic energy. A signal conducting path  200  carries an electric signal from the external instruments (not shown) (which include, in this illustration, a signal generator-processor, also not shown) to the transducer  170 , which may include a piezoelectric crystal or other device for producing acoustic energy. This acoustic energy is of the type referred to as ultrasonic or ultrasound, although these terms may encompass a variety of acoustical signals embodying a variety of frequencies. The energy passes through the surface  172  of the imaging tube  162  and into the occluded artery  60  and surrounding tissues. The transducer  170  and acoustic signal are configured such that the energy is emitted in a narrowly focused beam  202  in a known direction (at a known value of the angle θ) from a known position (at a known value of Z) with respect to the imaging tube  162 . The transducer  107  also functions as a similarly directional acoustic signal detector, converting acoustic energy reflected by features in the environment of the imaging tube  162  to a signal which is conducted back to the signal generator-processor and measured accordingly. As are the emitted signals, the detected signals are associated with values of θ and Z. 
     Continuing still with reference to FIGS. 2 and 4, a third dimension, which shall be referred to as depth or as radius from the transducer  170  and given the letter r, is computable as a function of the time elapsed between the emission of a given signal by the transducer  170  and the detection of the echo of that signal. The value detected at any given time is a function of the intensity of the echo. With appropriate signal processing, this intensity can be reported via suitable video equipment as a two or three dimensional image of the environment of the imaging tube  162 . General purpose computers are programmable to accomplish this function. U.S. Pat. No. 4,794,931, the disclosure of which is incorporated herein by reference in its entirety, describes a computer and instrument system implementing such a function. 
     Alternatively, a rotating or translating scanning transducer may be supplanted by an array of directional transducers (not shown), a phased array of transducers (not shown) or other appropriately energized and interrogated set of transducers operatively connected to the external signal generator-processor for displaying the desired image. 
     Referring to FIGS. 2,  3 , and  4 , the locator  160  provides an image of nearby anatomical features so that the position of the locator  160  with respect to the arterial wall  72  and lumen  71  and occlusion  62  is ascertained. The locator  160  is manipulated until its position is ideal for imaging the penetration of the occlusion  62 . The locator  160  is then stabilized. Optionally, the imaging tube  162  includes an exterior surface  172  having one or more suction cups  174  for stabilizing the imaging tube  162  on tissues near the occluded artery  60 . With the locator  160  positioned and functioning, the positions of the distal end  112  of the catheter shaft  100  and the distal end  120  of the working element  102  are ascertained. The contours of the occlusion  62  and the artery  60 , as revealed by the locator  160 , are also evaluated. 
     Continuing with reference to FIGS. 2,  3  and  4 , it is seen that the catheter shaft  100  and locator  160  are placed proximate the occlusion  62 . With the locator  160  positioned and functioning, the catheter shaft  100  and steering member  122  are manipulated to direct the working element  102  and the catheter shaft  100  at a point of entry (not shown) into the occlusion  62 . The point of entry will have been identified in the image provided by the locator  160 . The image provided by the locator  160  is also studied to plan an appropriate path through the occlusion  62 . The working element  102  is then steered and advanced along that planned path under continuous observation via the locator  160 . While control of the working element  102  and catheter shaft  100  is maintained via the steering member, the working element  102  and catheter shaft  100  are urged and steered though the occlusion  62  until the working element  102  is observed to re-emerge from the occlusion  62  into the arterial lumen  71 . 
     Continuing with reference to FIGS. 2,  3  and  4 , as the working element  102  and catheter shaft  100  are advanced, their positions with respect to the occlusion  62  and arterial wall  72  are carefully noted from the image provided by the locator  160 . The steering member  122  is manipulated to direct the working element  102  away from any contact perceived as likely to perforate or severely dissect the artery  60 . When the distal end  120  of the working element  102  reaches the distal boundary  63  of the occlusion  62 , a path will have been created through the occlusion  62 . The interventionist may successfully cross the occlusion  62  with a guide wire and follow up with DCA or PTCA or install a stent. 
     Referring again to FIG. 2, it is seen that the catheter shaft  100  and the locator  160  of the present invention cooperate to enable the operator to guide the working element  102  into and through the occlusion  62  while knowing and maintaining control of the anatomical location and orientation of the catheter shaft  100  and working element  102 . Thus, the occlusion  62  can be crossed while avoiding perforation, severe dissection or other unintended trauma to the artery  60 . After the occlusion  62  has been crossed, the suction cups  174  may be released, the apparatus withdrawn from the patient, and the incisions closed. Importantly, the micro-invasive locator  160  provides the necessary spatial information for guidance of the working element  102  while completely avoiding the gross trauma inflicted by traditional bypass operations. 
     Referring again to FIG. 3, an exemplary embodiment of the present invention is shown including the above-described locator  160 , catheter shaft  100 , lumen  114 , steering member  122 , and tissue-penetrating wire  116 . A metal nose cone  134  is included in the distal end  112  of the catheter shaft  100  and defines a distal orifice through which the tissue-penetrating wire  116  can project from the lumen  114 . As the tissue-penetrating wire  116  is urged through tissues, the catheter shaft  100  can be steered via the steering member  122  and urged into the tissues along the path made by the wire  116 . As the catheter shaft  100  follows the wire  116  through the occlusion  62 , the nose cone  134  reduces the resistance encountered by the catheter shaft  100 . Penetration of the occlusion  62  is observed via the locator (not shown). 
     Referring again to FIG.  2  and now also to FIG. 5, an exemplary embodiment of the present invention is shown including the above-described locator  160 , catheter shaft  100 , lumen  114 , steering member  122 , and tissue-penetrating wire  116  (other work elements may be used, as will be described below). The distal end zone  104  of the catheter shaft  100  also includes a plurality of rings  140 . The rings  140  define paths  141  for the steering wires  124  (described above) of the steering member  122 . 
     One or more of the rings  140  may serve to anchor the distal ends  128  of the steering wires  124 . The distal end zone  104  of the catheter shaft  100  also includes a plurality of slots  142  inscribed therein for increasing the steerability of the distal end zone  104 . 
     Continuing with reference to FIG. 5, unequal tension on the steering wires  124  will deflect the distal end zone  104  and the working element  102  toward a wire having greater tension. The slots  142  in the distal end zone  104  of the catheter shaft  100  reduce the force required to compress one side of the distal end zone  104  and extend the opposite side. A steering wire  124  can thus more easily deflect the distal end zone  104 . Because the slots  142  only partially circumscribe the distal end zone  104  of the catheter shaft  100 , they do not appreciably reduce its axial stiffness. As a result, the distal end  112  of the catheter shaft may still be pushed firmly against a tissue surface at a point where the working element  102  is intended to enter. 
     Referring again to FIG.  2  and now also to FIG. 6, an exemplary embodiment of the present invention is shown including the above-described locator  160 , catheter shaft  100 , lumen  114  and steering member  122 . The working element  102  includes an inner shaft  144 , rotatably disposed in the lumen  114  of the catheter shaft  100 , having a proximal end  146  drivenly coupled to an external motor (not shown) proximate the proximal end  110  of the catheter shaft  100 . The inner shaft  144  also includes a sharp pointed distal end  150  projecting from the distal end  112  of the catheter shaft  100 , a nose cone  152  proximal to the sharp pointed distal end  150 , and an abrasive coating  154  disposed on the nose cone  152  for boring into tissues. 
     Continuing with reference to FIG. 6, after the locator (not shown) is activated to provide an image and the steering wires  124  and catheter shaft  100  are manipulated to urge the working element  102  at a selected point of entry (not shown) into the occlusion  62 , the external drive motor (not shown) is activated, rotating the inner shaft  144  and nose cone  152 . As the sharp pointed distal end  150  of the inner shaft  144  advances through the tissues (not shown), the abrasive coating  154  of the nose cone  152  grinds away tissue to open an enlarged path for the catheter shaft  100  to follow. By removing tissue, the abrasive nose cone  152  reduces the resistance of the tissues to the catheter shaft  100  and enlarges the path created through the occlusion  62 . 
     Referring now to FIG. 7, an exemplary embodiment of the micro-invasive catheter apparatus is shown in which the catheter shaft  100  includes the above-described steering member  122 , a proximal end  110 , a distal end  112 , a lumen  115  originating in the distal end, and a working element  102  disposed in the lumen  115 . The working element  102  includes an inner shaft  230 , slidably disposed in the lumen  115 , having a distal end zone  232  projecting from the distal end  112  of the catheter shaft  100 , a sharp pointed distal end  234  for penetrating the occlusion  62 , and a nose cone  236  proximal to the sharp pointed distal end  234 . The nose cone  236  has a proximal end  238 . The inner shaft  230  projects from the catheter shaft  100  so that a gap exists between the distal end  112  of the catheter shaft  100  and the proximal end  238  of the nose cone  236 . A plurality of dissecting wires  240  span the gap. The dissecting wires  240  have a proximal end  242  fixed in the distal end zone  104  of the catheter shaft  100 , a distal end  244  fixed in the proximal end  238  of the nose cone  236 , and a medial portion  246  therebetween. 
     Continuing with reference to FIG.  7  and now also with reference to FIG. 8, as the catheter shaft  100  is urged through an occlusion (not shown), the nose cone  236  of the inner shaft  230  will encounter resistance and the inner shaft  230  will tend to slide backward into the lumen  115 . As this sliding movement narrows the gap spanned by the dissecting wires  240 , the medial portion  246  of each dissecting wire  240  will be forced to bow outward. As the bowed dissecting wires  240  pass through the tissues of the occlusion (not shown), they blunt-dissect the tissues, leaving behind an enlarged passage. The greater the resistance offered by the tissue, the greater the lateral pressure exerted by the dissecting wires  240  upon the tissues. 
     Referring back to FIG.  2  and now particularly to FIGS. 9 and 10, an exemplary embodiment of the present invention is shown in which the imaging tube  162  of the locator  160  includes an elastomeric flared portion  173  having an exterior surface  172  defining a plurality of suction cups  174 . The elastomeric flared portion  173  can be rolled around the imaging tube  162  to reduce the profile of the imaging tube  162  for insertion into the patient. The suction cups  174  are arrayed in two roughly parallel rows  204 . Between the rows  204  is a region of the surface defining an imaging window  206 . In the exemplary embodiment illustrated in FIG. 10, the imaging window  206  includes an acoustically transparent portion of the imaging tube  162  adjacent the lumen  190 . As can be seen in FIG. 10, the transducer  170  has a view through the window  206  unobstructed by the suction cups  174  (alternatively, the imaging window  206  may be located on a portion of the surface  172  of the imaging tube  162  which also defines a single enlarged suction area). The imaging tube  162  optionally includes a suction cup activating lumen  178  having a distal end zone  180  communicating with the suction cups  174  and a proximal end  182  coupled with a pressure modulating device (not shown). The lumen  178  and pressure modulating device permit rapid, minimally traumatic temporary stabilization of the imaging tube  160  on the heart surface. 
     Referring back to FIG.  2  and now also to FIG. 11, an exemplary embodiment of the present invention is shown including the above-described locator  160 , catheter shaft  100 , lumen  114  and steering member  122 . In this embodiment, the working element includes a tissue-penetrating working element  102  having a distal end  260 . A signal emitter  262  is disposed in the distal end  260 . A signal generator (not shown) is operatively coupled to the signal emitter  262 . In this embodiment, the signal generator is external to the body and is coupled to the emitter through an electrically conductive path  266  originating in the proximal end zone  106  of the catheter shaft  100  and terminating at the emitter  262 . As illustrated, the electrically conductive path  266  includes an outer conductor  268  disposed in the catheter shaft  100 , a tubular dielectric layer  270  therein, and an inner conductor  272  disposed within the dielectric layer  270 . However, any other energy-delivering or converting means can be employed to energize the emitter  262 . When the locator  160  and emitter  262  are activated within the body, the locator  160  selectively detects the signal emitted by the emitter  262  in order to discern a spatial relationship between the working element  102  and the locator  160 . Alternatively, the signal emitter  262  and the associated conductive path  266  may be disposed in the distal end of a guide wire (not shown). 
     Alternatively, the signal emitter  262  may be disposed in a working element which is essentially a guide wire, optionally steerable. Likewise, the catheter shaft may be of a simpler design than the one shown in FIG. 11; in particular, a catheter shaft without a steering member, and a signal-emitting guide wire distal end not surrounded by a separate catheter shaft, are both within the scope of the present invention. 
     While the foregoing detailed description has described several embodiments of the invention, it is to be understood that the above description is illustrative only and not limiting of the disclosed invention. Particularly, the imaging device need not be an acoustic transducer and need not accomplish its imaging by scanning or mechanical movement in any particular manner. The imaging device may be operatively coupled to external instruments by any appropriate mechanical, electromagnetic, optical, wave guide or other path. The image that is displayed may be computed by any of a variety of algorithms for extracting one-, two-, or three-dimensional information from energy reflected, scattered or absorbed within tissues. The imaging tube may be stabilized proximate the occlusion  62  by any appropriate mechanical, pneumatic, hydraulic or other means. Additionally, the locator  160  need not approach the heart in the particular manner described; alternative routes may be taken. 
     It will also be noted that, depending on the configuration and support of the working element, either the catheter shaft or the working element or both may be placed in the path created by the working element. Also, either the working element or the catheter shaft may be left in the path so created to serve as a conduit or for some other purpose. The catheter shaft may include a lumen to facilitate blood flow in the bypass. The catheter shaft or work element may include a balloon for stabilization, for interruption of flow, or for other purposes. 
     Likewise, the steering member may include more or fewer than the two wires illustrated in the drawing figures. The working element  102  may include any mechanical, thermal, optical, chemical or other device for penetrating tissues, treating an occlusion or delivering a medicament. The catheter shaft  100  and working element  102  may be configured such that only the working element  102  traverses certain tissues or, alternatively, the catheter shaft  100  itself may follow along with the working element  102 . It will be appreciated that the embodiments discussed above and the virtually infinite embodiments that are not mentioned could easily be within the scope and spirit of the present invention. Thus, the invention is to be limited only by the claims as set forth below.