Abstract:
An apparatus is described for treating arterial occlusions combining an intraluminally operable catheter having an occlusion-crossing working element, with an extraluminally operable locator for imaging the progress of the working element through the occlusion. Suction coupling means are described for removably anchoring the locator to a surface proximate the heart. A method for treating arterial occlusions is described in which the distal end of the catheter shaft exits a lumen of the locator, penetrates the arterial wall distal to the occlusion, crosses the occlusion retrograde and passes into a separately introduced standard intravascular catheter, whereupon the distal end of the shaft may be manipulated from the proximal end of the standard catheter. The proximal end of the shaft is then released from external attachments and drawn into the artery to perform treatment or guiding functions. Spatial interrelationships are observed real-time via the locator. Conical, abrasive, blunt-dissecting, sharp-pointed and guide-wire type working elements, steerable and non-steering, are described. Acoustic transducers and a flexible imaging tube are described for the locator. A signal-emitting working element and cooperating signal-receiving locator are described.

Description:
This application is a continuation-in-part application of U.S. patent applicaton Ser. No. 09/007,434 filed Jan. 15, 1998, currently issued as U.S. Pat. No. 6,081,738 and is related to U.S. patent application Ser. No. 09/008,033 and issued on Mar. 23, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to catheters and more particularly to catheter apparatus for treating severe or total arterial occlusions. The invention relates especially to the combination of an extravascularly operable imaging and therapeutic device and an intravascular catheter shaft. 
     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 occludes 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 guidewire 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 severe or 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 guidewire 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 the bypass for restoring circulation after a coronary artery has become severely stenosed or totally occluded. In particular, many such patients would benefit from an operation for crossing the severe or total occlusion without inflicting the gross trauma of classical bypass surgery. In particular, such a procedure is needed for safely forging a path of low mechanical resistance through or around the tough, complex tissues of the severely or totally occlusive atheroma so that blood flow can be restored. 
     It would be beneficial if a cardiologist could safely cross an occlusion using instruments deliverable by cardiac catheterization or through a small incision in the patient&#39;s chest. Instruments have been developed which are deliverable to the site of an occlusion by a cardiac catheter and are capable of penetrating the tissues of a severe or total occlusion or piercing the arterial wall. However, penetrating the arterial wall is what cardiac catheterization procedures usually strive to avoid, because perforation can easily lead to cardiac tamponade. What is needed is a way of reliably selecting the points at which the wall of an artery can be safely penetrated by a catheter working element. What is also needed is a way of reliably guiding the working element from that point of penetration through an occlusion and into another patent portion of the arterial lumen. What is also needed is a way of guiding the working element through interstitial tissue to an appropriately selected point of transvascular entry into an artery. 
     Likewise, it would be advantageous to reopen the natural lumen of a severely or totally occluded artery so that a stent can be installed or DCA or PTCA can be performed, preferably without straying into the subintimal space or creating a false lumen. Thus, it would be highly advantageous to have a reliable, accurate way of steering and operating a catheter working element along a safe path through the atheromatous tissues of the occlusion. 
     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 boundaries of the atheromatous tissues of an occlusion, and the structure of the occluded artery as the working element is manipulated. 
     What is needed is an effective combination of a working element and an imaging system for precisely crossing a severe or total coronary occlusion without causing cardiac tamponade. In particular, such a combination is desired which continuously displays a stable image of the atheroma, the structure of the artery, and the working element as the interventionist maneuvers the working element. What is especially needed is such a combination which is deliverable and operable with minimal trauma to blood vessels and surrounding tissues. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to treat severe or total arterial occlusions by minimally invasive means and, more particularly, to cross such occlusions without causing cardiac tamponade, so that the circulation to tissues supplied by the occluded artery is increased with minimal invasiveness and low risk to the patient. It is also an object of the present invention to open a path of low mechanical resistance through the atheromatous tissues of the severely occluded artery so that a guide wire, or PTCA catheter, DCA catheter, or stent delivery catheter can be placed across the occlusion. 
     It is an additional object of the present invention to provide a combination of an effective steerable transvascular working element and a locator device for continuously visualizing the working element and its anatomical environment, so that the working element can be safely directed through the arterial wall and atheromatous tissues as needed to reach and cross the occlusion. 
     It is an additional object of the present invention to provide a combination of a catheter shaft, including a steerable transvascular working element, and a locator for guiding the working element, the locator including an extravascularly operable imaging device and being positionable proximate the occluded coronary artery through a small incision in the patient&#39;s chest and being removably attachable to bodily tissues proximate the artery. 
     It is an additional object of the present invention to provide a combination of such a catheter shaft and locator in an apparatus which can be inserted into the body through a single incision. 
     It is an additional object of the present invention to provide such a combination in which the catheter shaft reaches the vascular tissues at a location within the imaging field of the locator. 
     It is an additional object of the present invention to provide such a combination in which the catheter shaft and 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 treat an artery using such a combination in conjunction with a separate intravascular catheter, which has been introduced in the traditional manner, to control a catheter shaft, guide wire or other such elongate device from either end or both ends. 
     It is an additional object of the present invention to permit the release of the proximal end of the catheter shaft or guide wire from any external control apparatus, thus allowing what had been the proximal end to be manipulated or positioned within the arterial system. 
     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: 
     a locator including an imaging tube having a proximal end zone, a distal end zone, a lumen therebetween, and an imaging device operatively disposed in the imaging tube; 
     an elongated flexible catheter shaft, disposed in the lumen of the imaging tube, including a distal end zone and a working element disposed therein, 
     whereby the locator is extraluminally placed proximate the arterial occlusion, the working element is transvascularly operable upon the occlusion, and the locator provides spatial information for effective manipulation of the working element to treat 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 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 the arterial wall to reach the occlusion. 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 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 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 or other tissue. 
     Another exemplary embodiment of the catheter apparatus according to the present invention includes a working element (for example, a guide wire or other tissue penetrating or treatment device) 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 coupling area 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 extravascularly operable imaging tube having a distal end zone. A surface of the distal end zone defines an acoustic window. A catheter delivery lumen terminates in an orifice proximate the acoustic window. This provides the apparatus of the present invention with the ability to view an image of the catheter shaft or guide wire as it emerges from the orifice and as it is advanced through the occlusion or arterial wall. 
     Another exemplary embodiment of the catheter apparatus according to the present invention includes an extravascularly operable imaging tube having a distal end zone having a surface defining an imaging window and a plurality of suction coupling areas disposed peripherally about the window for adhesion to a beating heart. A catheter delivery lumen terminates in an orifice proximate the window. This provides the apparatus of the present invention with the ability to stabilize the imaging device and the catheter shaft with respect to the vessels and the occlusion while viewing an image of both and manipulating the catheter shaft and working element. The multiple peripherally arranged suction coupling areas provide enhanced stabilization without obstructing the imaging device or catheter shaft. 
     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. 
     Another exemplary embodiment of the catheter apparatus according to the present invention includes an array of acoustic transducers disposed in the imaging tube and 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 an ultrasound image of the catheter shaft, working element, occlusion and surrounding vascular and interstitial tissues as the operation is performed without necessarily employing a rotating or translating transducer control shaft. More generally, this provides an expanded imaging field, enhanced image resolution, or both, with reduced need for moving parts. 
     Also in accordance with the above objects and those that will be mentioned and will become apparent below, method for treating an arterial occlusion having a distal boundary and a proximal boundary in a human or animal body in accordance with the present invention comprises the steps of: 
     providing a apparatus for treating an arterial occlusion, the apparatus comprising: 
     a locator including an imaging tube including a proximal end zone, a distal end zone, a lumen therebetween, and an imaging device operatively disposed in the imaging tube; and 
     an elongated flexible catheter shaft, disposed in the lumen of the imaging tube, including a distal end zone and a working element disposed therein; 
     introducing the locator into the patient&#39;s chest, placing the distal end zone of the locator proximate the distal boundary of the occlusion, and activating the locator to discern the anatomical location and position of the working element; 
     while observing the anatomical location and position of the working element via the locator, advancing the catheter shaft into contact with the artery; 
     while continuing the observation, advancing the working element through an arterial wall and into the artery; and 
     while continuing the observation, advancing the working element retrograde within the artery and into and through the occlusion until the working element exits the occlusion via the proximal boundary of the occlusion; 
     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 method according to the present invention, the working element is steerable and is steered within the artery under observation via the locator. 
     In another exemplary method according to the present invention, the working element, which may be, for example, a steerable catheter, a simple catheter, or a guide wire, is passed retrograde, through the occlusion, into a lumen of a separate intravascular catheter which has been placed in the arterial lumen proximal to the occlusion via femoral arteriotomy. The distal end of the catheter shaft or guide wire is passed through the separate intravascular catheter to the proximal end thereof and coupled to external control apparatus, such that both ends may be simultaneously externally controlled. 
     In another exemplary method according to the present invention, the proximal end of the catheter shaft or guide wire is then released from its attachments and drawn into the artery to perform a therapeutic or guiding function while being controlled from the distal end. 
     An 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. 
     An additional advantage of the present invention is that it permits the use of cardiac catheterization techniques for restoring blood flow to severely or 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 surgical intervention. 
     An additional advantage of the present invention is the ability to guide a working element through the tissues of a severe or total occlusion, and into the artery through the artery wall to reach the occlusion, without causing uncontrolled hemorrhage or tamponade. A related advantage is the ability to provide safe access for a guide wire or other catheter to cross a severe or total occlusion. 
     An additional advantage of the present invention is the provision of a stable, real-time image of the vasculature, the disease and the working element that is being guided therein, allowing accurate determination of the spatial relationships of the working element, the boundaries of the occlusion, and the structures of the artery and interstitial tissues. Thus, the working element can safely and accurately penetrate the occlusion. 
     An additional advantage of the present invention is the effective micro-invasive placement of the locating device in the vicinity of the occlusion, requiring only a small, minimally traumatic incision in the patients 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 the provision of a catheter shaft which is viewable via the imaging device immediately upon its emergence from the orifice in the imaging tube, so that it is always possible to know what tissues the working element is in contact with and what tissues lie ahead. 
     An additional advantage of the present invention is the simultaneous stabilization of both the imaging device and the catheter shaft with respect to the surface of the beating heart, so that conditions are optimized for precise placement of the working element through tissues. 
     An additional advantage of the present invention is the ability to simultaneously control both ends of a catheter shaft or guide wire which is placed in an artery. 
     An additional advantage of the present invention is the ability to introduce a catheter shaft or guide wire into an artery trans-luminally, pass the distal end of the catheter shaft or guide wire retrograde to a separate point of access to the arterial system, and either directly control both ends of the catheter shaft or guide wire simultaneously, or detach the proximal end and draw the free proximal end into the artery by directly manipulating the distal end. 
    
    
     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 in accordance with this invention placed in a human chest cavity proximate a coronary artery having an occlusion. 
     FIG. 2 is an enlarged view of the exemplary embodiment of FIG. 1 placed proximate the occlusion. 
     FIG. 3 is an enlarged side view of an exemplary embodiment of an apparatus according to the present invention showing a catheter shaft. 
     FIG. 4 is an enlarged side view of an exemplary embodiment of an apparatus according to the present invention showing a locator and a catheter shaft disposed in a lumen of the locator. 
     FIG. 5 is a cut-away view of an exemplary embodiment of an apparatus according to the present invention proximate an occluded artery. 
     FIG. 6 is a cut-away view of an exemplary embodiment of an apparatus according to the present invention operating transvascularly to cross an arterial occlusion. 
     FIG. 7 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 rings and slots in the distal end zone of the catheter shaft. 
     FIG. 8 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 coupling surface features. 
     FIG. 9 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 coupling surface features. 
     FIG. 10 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 an occlusion. As illustrated in FIGS. 1 and 2, an exemplary embodiment of the catheter apparatus in accordance with the present invention is shown placed proximate the occlusion  62  in the coronary artery  60 . The apparatus of the present invention embodies a combination of two devices which cooperate to safely bypass the occlusion  62 . The first device is an imaging locator  160  including an imaging tube  162  and an imaging device  168 . The imaging tube  162  is introduced through a small incision (not shown) in the patient&#39;s chest and positioned adjacent the heart and proximate the occlusion  62 . The imaging tube  162  includes a catheter (or guide wire) delivery lumen (not shown). The second device is a catheter shaft  100  including a distal end zone  104  and a steerable tissue-penetrating working element  102 . The catheter shaft  100  is disposed in the catheter delivery lumen (not shown) of the imaging tube  162 . During the operation, the catheter shaft  100  and work element  102  are advanced from the catheter delivery lumen and steered and manipulated through the patient&#39;s tissues while being imaged by the locator  160 . 
     Continuing with reference to FIG.  1  and now also to FIG. 2, the imaging tube  162  is introduced through an incision 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) are then activated to display an ultrasound image. 
     Referring to FIG. 2, the two devices are operated simultaneously to safely guide and steer the working element  102  of the catheter shaft  100 . The locator  160  is stabilized adjacent the heart and activated to provide an image of the occlusion  62  from a vantage point close to the occluded artery  60  but outside the arterial lumen  71 . The catheter shaft  100  emerges from the lumen  187  of the imaging tube  162 . It will be appreciated that because only a small puncture or incision is needed in order for the imaging tube  162  to place the imaging device  168  and catheter shaft  100  at the heart surface, the patient can expect a comfortable, uncomplicated recovery. With the present invention 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 direct the working element  102  through the arterial wall  72 , into the artery  60 , and 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 by the distal end zone  104 . The proximal end zone  106  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 micro-invasive extravascular placement of the imaging device  168  proximate the occluded artery  60 . The imaging tube  162  includes a proximal end zone  164  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 now 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 tissues. 
     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, isolating 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 isolating 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 through the occlusion  62 . 
     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 No. 08/775,264, filed Feb. 28, 1997, 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 tissues 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, 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 tissues near the artery  60  having the occlusion  62 . 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  can be made 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. This 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 catheter delivery lumen  187  including a proximal  189  in the proximal end zone  164  of the imaging tube  162  and a distal end  191  in the distal end zone  186  of the imaging tube  162 . The catheter shaft  100  is slidably disposed in the lumen  187  so that, after the imaging tube  162  is stabilized on the heart surface, the catheter shaft  100  can be advanced from the lumen  187  into the appropriate bodily tissues while a stabilized image of the catheter shaft  100  and its anatomical environment is displayed via the locator  160 . 
     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 match the flexibility of 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. 
     Continuing still with reference to FIG. 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 patter 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 FIG. 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 a signal (for example, an electrical signal generated or modulated by the transducer or provided for driving the transducer) 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 generally 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  170  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 FIG. 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 artery  60  and occlusion  62  is ascertained. The locator  160  is manipulated until its position is ideal for imaging the vessels and tissues to be penetrated. The locator  160  is then stabilized. Optionally, the imaging tube  162  has an exterior surface  172  which including 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. 
     Referring back to FIGS. 3 and 4 and now also to FIG. 5, it is seen that the catheter shaft  100  and locator  160  are placed proximate the occlusion  62 . The catheter shaft  100  includes a distal end  112 , a working element  102 , and a proximal end (not shown in FIG.  5 ). 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 penetration of the arterial wall  72  for entry into the artery  60 . The point of entry  70  will have been identified in the image provided by the locator  160 . The image is also studied to determine an appropriate path through or around the atheromatous tissues of the occlusion  62 , yet staying within the artery  60 . 
     Although a catheter shaft  100  including a steering member  122  and a tissue penetrating wire  116  is shown in FIG. 3, it should be understood that the catheter delivery lumen  187  may be adapted for the insertion of a catheter of simpler construction, or of a catheter lacking a steering member or discrete work element, or even for the insertion of a guide wire, into the artery. Likewise, a catheter, wire or the like so inserted may be withdrawn and another substituted in its place. Thus, although much of this discussion refers to a catheter shaft as shown in FIG. 3, the invention is not limited to such a catheter shaft and the method of using the invention is not limited to the exact steps in the order described. 
     Continuing now with reference to FIGS. 3 and 4 and now also to FIG. 6, 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 along the path that has been planned though extravascular tissue, then through the arterial wall  72  into the arterial lumen  71  distal to the occlusion  62 , and then in a retrograde direction through the occlusion  62  until the working element  102  is observed to cross the occlusion  62  and re-enter the arterial lumen  71  proximal to the occlusion  62 . FIG. 6 illustrates the catheter shaft  100  and working element  102  entering the artery  60  immediately distal to the occlusion  62  and crossing the occlusion  62  in the retrograde direction. 
     Continuing with particular reference to FIG. 6, a separate intravascular catheter  103  is placed in the lumen  71  of the artery  60  proximal to the occlusion  62 . This separate intravascular catheter  103  may be introduced using traditional techniques (for example, via femoral arteriotomy). The separate intravascular catheter  103  has a distal end  107 , a proximal end (not shown) and at least one lumen  109  therebetween. The catheter shaft  100  with work element  102  (or catheter shaft, or guide wire, as the case may be) is advanced retrograde into the lumen  109  of the separate intravascular catheter  103  and is then advanced substantially to the proximal end of the separate intravascular catheter  103 . At the proximal end of the separate intravascular catheter shaft, the distal end  112  of the catheter shaft  100  is then grasped and controlled by external apparatus (not shown). 
     The proximal end  110  of the catheter shaft  100  (shown in FIG. 6) is released from any external connections. By moving the distal end  112  of the catheter shaft  100  in the retrograde direction (indicated by arrow  105 , toward the femoral arteriotomy), the interventionist draws the free proximal end  110  of the catheter shaft  100  (or guide wire, as the case may be) out of the catheter delivery lumen  187 , through the point of entry  70 , and into the artery  60  until the proximal end  110  of the catheter shaft  100  is positioned in the lumen  71  of the artery  60  distal to the occlusion  62 . In this way, the catheter shaft  100  (or guide wire, as the case may be) is placed across the occlusion  62  and can be used to treat the occlusion  62  or to guide other over-the-wire devices into and through the occlusion  62 . 
     Continuing with reference to FIGS. 5 and 6, as the working element  102  and catheter shaft  100  are advanced along this path, their positions with respect to the arterial anatomy, the occlusion  62  and the separate intravascular catheter  103  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 cause cardiac tamponade or other unintended trauma. The distal end  112  of the catheter shaft  100  is guided through the occlusion  62  and into the separate intravascular catheter  103 . 
     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 interventionist to guide the working element  102  into and through the occlusion  62  while knowing the anatomical location and orientation of the catheter shaft  100  and maintaining control thereof via the catheter shaft  100  and steering member  122 . Thus, the occlusion  62  can be crossed safely and efficiently. Additionally, it is seen that the same cooperation enables the interventionist to pass the catheter shaft (or a guide wire) into a separately introduced intravascular catheter, providing a greater range of options for controlling and exploiting the catheter shaft or guide wire. Finally, it is seen that the same cooperation allows the use of what was originally the proximal end zone of the catheter shaft or guide wire to treat the occlusion or to guide other treatment devices. 
     After the operation, the suction cups  174  may be released, the apparatus withdrawn from the patient, and the incision 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 that would be inflicted upon in the patient by a traditional bypass operation. 
     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 opening 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 tissues, the nose cone  134  reduces the resistance encountered by the catheter shaft  100 . Progress is observed via the locator  160 . 
     Referring back to FIG.  2  and now particularly to FIG. 7, 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. 7, 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 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 back to FIG.  2  and now particularly to FIGS. 8 and 9, an exemplary embodiment of the present invention is shown in which the imaging tube  162  of the locator  160  includes an exterior surface  172  defining a plurality of suction cups  174 . 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. 8, the imaging window  206  includes an acoustically transparent portion of the imaging tube  162  adjacent the lumen  190 . As can be seen in FIG. 8, the transducer  170  has a view through the window  206  unobstructed by the suction cups  174 . 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  162  on the heart surface. Additionally, the catheter delivery lumen  187  terminates proximate the imaging window  206 , so that the working element  102  and the distal end zone  104  of the catheter shaft  100  can be observed via the imaging device  168  as they emerge from the lumen  187 . In this way, it is possible to shorten the distance the catheter shaft  100  must traverse to reach from the catheter delivery lumen  187  to the artery  60  and thus to the interventionist&#39;s control over the catheter shaft  100 . 
     Referring back to FIG.  2  and now also to FIG. 10, 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  262  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  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. 1 0 ; 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. 
     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, optical, thermal, 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.