Abstract:
A myocardial implant for insertion into a heart wall for trans myocardial revascularization (TMR) of the heart wall. The TMR implant provides for means to promote the formation of new blood vessels (angiogenesis), and has a flexible, elongated body that contains a cavity and openings through the flexible, elongated body from the cavity. The TMR implant includes a coaxial anchoring element integrally formed at one end for securing the TMR implant in the heart wall.

Description:
This is a continuation-in-part of pending application serial number 09/008,695, filed Jan. 19, 1998, now abandoned which was a divisional application of application Ser. No. 08/739,724, filed Nov. 7, 1996, now U.S. Pat. No. 5,810,836. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention is generally directed to the fields of cardiac surgery and interventional cardiology, and particularly, to mechanical devices and methods suited for improving blood flow to a heart muscle by Trans Myocardial Revascularization (TMR). 
     2. Description of Related Art 
     Symptomatic occlusive coronary artery disease that does not respond to medical or interventional treatment is a major challenge for cardiac surgeons and cardiologists. The discovery of sinusoidal communications within the myocardium (Wearns, 1993) has motivated researchers to attempt various methods for myocardial revascularization based on the existence of this vascular mesh network. These methods aimed at the delivery of oxygenated blood to the vicinity of the sponge-like sinusoidal plexus in order to restore blood flow to the ischemic myocardium. Several investigators have attempted to deliver oxygenated blood directly from the left ventricle into the myocardial sinusoids by employing needle acupuncture to create transmural channels. Trans Myocardial Revascularization (TMR) has been employed clinically (Mirhoseini, 1991) by utilizing a CO2 laser for creating transmural channels in the left ventricular myocardium. These channels are typically 1 mm in diameter and extend throughout the wall thickness (15 to 20 mm) of the ventricle. It has been hypothesized that TMR works by providing a fluid conduit for oxygenated blood to flow from the endocardiac surface (heart chamber) to the mycardium inner layers thus providing oxygenated blood to myocardial cells without requiring coronary circulation; as in reptiles. Animal studies in the canine model have demonstrated the feasibility of this approach. In these studies, an increase in survival rate was demonstrated in dogs that had transmural channels and ligated coronary arteries. 
     While clinical studies have demonstrated improvements in patient status following TMR, histological studies indicate that the channels created for TMR tend to close shortly after the procedure. Randomized, prospective clinical trials are underway to examine the merit of TMR compared to medical treatment. In the meantime, research studies are being initiated to provide an understanding of the mechanism by which TMR actually works. 
     It would be desirable to develop means for maintaining the patency of TMR channels within the myocardium. Furthermore, it would be desirable to create channels for TMR without requiring the use of an expensive and bulky laser system, such as currently available CO2 laser systems. This invention provides the desired means for producing trans myocardial channels that are likely to remain patent, and that do not require laser application for generating these channels. 
     Specifically, the objective of the present invention is to generate needle-made channels or space in the ischemic heart wall, and to deliver or place in these channels (or space) an array of implants or stents in order to provide improved means for supplying blood nutrients to ischemic myocardial tissue. Nutrients flow to the stented channels from the ventricular cavity, and diffuse from the side ports of the stent to the myocardial tissue through the needle-made channels. Our disclosed TMR approach of producing stented, needle-made, channels is supported by the recent scientific evidence (Whittaker et al, 1996) that needle-made transmural channels can protect ischemic tissue. Whittaker et al. assessed myocardial response at two months to laser and needle-made channels in the rat model which has little native collateral circulation. They found that channels created by a needle can protect the heart against coronary artery occlusion, and that these channels provide greater protection to ischemic tissue than channels created by laser. The limitation of needle-made channels is early closure (Pifarre, 1969). The disclosed implant approach offers a possible solution to the early closure problem, while taking advantage of simple and effective needle-made channels for TMR. 
     SUMMARY OF THE INVENTION 
     This invention provides implant and needle means for creating and maintaining a patent lumen in the diseased myocardium. This implant provides a conduit for the flow of blood nutrients from the ventricular chamber to the intramyocardial vascular network. This implant can be used as the sole therapy or as an adjunctive therapy to other forms of TMR. Revascularization of the myocardium can be achieved and maintained by creating implanted, needle-made, channels within the myocardial tissue. These channels can allow blood nutrients within the left ventricular cavity to find direct access to ischemic zones within the ventricular wall independent of access through the coronary arteries. 
     Various configurations of implants are disclosed; including flexible and rigid implants, screw implants, sleeve implants, and others. Manual or powered devices are disclosed for the delivery or placement of implants into a heart wall. The proximal end of each implant terminates at the epicardial surface and provides mechanical holding means to prevent implant detachment and leakage of blood from the ventricle. Each implant is designed so as to maintain an adequate pressure gradient between the left ventricle and the myocardial tissue in order to maintain the flow from the ventricular cavity to the myocardial tissue of blood nutrients. 
     Furthermore, the disclosed TMR implants may define a cavity, which can be pressurized during operation so as to enhance the flow of blood to myocardial tissue. Each such implant can essentially operate as a mini-pump that is activated by myocardial contraction or by an external energy source. 
     Several embodiments of the implant and delivery systems therefor are proposed. The implants include the following: flexible spring, rigid sleeve, hollow screw, helical screw, and pumping (active) implants. The implants can be prestressed or made from memory metal in order to minimize the size of the implant during the insertion process. The various delivery systems are described below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a TMR implant inserted in a heart wall. The implant is configured as an expandable coil spring having an integral anchoring wire; 
     FIG. 2 is a cross-sectional view of a TMR implant having the configuration of a rigid sleeve having side ports; 
     FIG. 3 is a cross-sectional view of a TMR implant having the configuration of a hollow screw with side ports; 
     FIG. 4 is a cross-sectional view of a TMR implant having the configuration of a wire screw; 
     FIG. 5 is a cross sectional view of a flexible implant having an integral anchoring coil; 
     FIG. 6 is a cross-sectional view of a TMR implant having the configuration of a miniature pump; 
     FIG. 7 shows a TMR delivery device and method for insertion of a TMR implant into a heart wall; 
     FIGS. 8A-8I illustrate an alternate TMR implant and a delivery system for insertion of this TMR implant into a heart wall; 
     FIG. 9 shows a catheter delivery device and method utilizing a percutaneous access for insertion of a TMR implant into a needle-made space within the heart wall; 
     FIG. 10 shows an alternate catheter delivery device and method utilizing a percutaneous access for creating a channel in the heart wall, and for insertion in this channel of a TMR implant; 
     FIG. 11 is a front elevational view of an alternate implant (myocardial stent); 
     FIG. 12 is an end view of the implant of FIG. 11; and 
     FIG. 13 is a front elevational view of a further embodiment of a TMR impant. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following description is provided to enable any person skilled in the art to make and use the invention, and sets forth the best modes contemplated by the inventors of carrying out their invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the generic principles of the present invention have been defined herein specifically to provide for improved implants and an improved delivery system for such elements. 
     FIG. 1 shows a flexible TMR stent (hereinafter “myocardial implant”, or “implant”) having a coil spring body  21  defining a cavity  22  and spacing  23  between the turns of said spring body. In this embodiment, blood nutrients flow from the heart chamber  24  to the heart wall  25  by passage through the coil spring cavity  22  and spacing  23 . An anchoring wire  65  secures the implant to the heart wall. 
     FIG. 2 shows a myocardial implant that comprises a tubular body  1 , cavity  2 , side ports  3 , retainer  4 , and closure  5 . In this embodiment, blood nutrients  6  are transported from the heart chamber (ventricle)  7 , through the cavity  2  and side ports  3 , to the heart wall  8 . 
     FIG. 3 shows a myocardial implant that is configured as a hollow screw having a threaded body  9 , cavity  10 , side ports  11 , closure  12 , and slot  15 . In this embodiment, blood nutrients flow from the heart chamber  13  to the heart wall  14  by passage through the cavity  10  and side ports  11 . 
     FIG. 4 shows a myocardial implant that is a hollow wire screw having an elongated hollow coil body  16 , side ports  17 , and anchor  18 . In this embodiment, blood nutrients flow from the heart chamber  19  to the heart wall  20  by passage through the hollow core of the wire  16  and side ports  17 . 
     FIG. 5 shows a flexible myocardial implant having a coil body  26  and an anchoring coil  27  which is an integral part of the myocardial implant. The anchoring coil prevents detachment of the myocardial implant from the heart wall. 
     FIG. 6 shows a myocardial implant having a cylindrical body  28  defining a cavity  29 . A valve  30 , pumping element  31 , and side ports  32  are situated within the cavity  29 . In this embodiment, blood nutrients flow from the heart chamber  33  to the pumping cavity  29 . The valve  30  is activated and the pumping element  31  operates to displace the blood from the pumping cavity  29  through side ports  32  to the heart wall  34 . 
     FIG. 7 shows the construction and method of use of one embodiment of a delivery device for creating a pathway in the heart wall and for placement of a myocardial implant in this pathway. In this first embodiment, a needle obturator  36  carries a myocardial implant  35  having an anchoring wire  37 , which may be offset from the myocardial implant, as shown in FIG. 7, or aligned with the myocardial implant, as shown in FIGS. 11 and 12. The obturator and myocardial implant are inserted through the heart wall  38  until the endocardiac surface is reached. After the endocardiac surface  39  of the heart wall is reached, the obturator  36  is removed, as by turning or unscrewing the same, thereby leaving the myocardial implant  35  embedded in the heart wall. Additional improvements include a fluid channel  66  that is formed in the obturator body to provide an indication that the obturator&#39;s distal end  67  has crossed the endocardiac surface  39 . 
     FIGS. 8A through 8I show the construction of an alternate myocardial implant and a second embodiment of a delivery system for placement of the alternate implant in a heart wall. FIG. 8A shows a delivery system having a pin  40  and handle  41  having a locking device  42 . An obturator  43  is mounted in the pin  40 . The obturator  43  has a recess  44  (FIG. 8B) to engage the distal end of a myocardial implant  45 . The pin  40  has a recess  46  (FIG. 8B) to engage the proximal end of the implant  45 . 
     The method of use involves the placement of the implant  45  over an obturator  43 . The pin  40  is then rotated to create a radial stress on the TMR implant  45  (FIG.  8 D). The pin  40  is locked to the handle  41  (FIG.  8 C). Advancement through the heart wall  50  of the obturator and TMR device  45  is achieved by pressing the obturator through the heart wall (FIGS. 8E,  8 F). The pin  40  is released from handle  41  by withdrawing the locking device  42  (FIGS. 8G,  8 H). This causes the implant  45  to be released from the obturator  43 . The obturator  43  is then pulled back from the heart wall  50  leaving the implant  45  imbedded in the heart wall (FIG.  8 I). 
     FIG. 9 shows a catheter  58  having a slidable wire  59  which terminates at its distal end in a needle point  60 . A myocardial implant  61  is mounted proximal to the needle point. Advancing the needle spreads the heart wall tissue and positions the implant  61  into that tissue. Withdrawal of the needle releases the implant  61  in the heart wall. 
     FIG. 10 shows a catheter  62  which incorporates a slidable wire  63  that terminates at its distal end into a drill or other mechanical attachment  65  for making holes in the heart wall tissue. A myocardial implant  64  is mounted proximal to the drill  65  on the slidable wire  63 . Advancing the drilling tool creates a channel in the tissue and positions the implant  64  in this channel. Withdrawal of the drilling tool releases the implant  64  in the heart wall. 
     FIG. 11 shows a myocardial implant having an anchoring ring retainer or holding means  73  that is coaxial to a main body  70  of a flexible coil. Preferably, the anchoring ring is fabricated as an integral part of the main body of the coil at one end thereof. Preferably, the proximal end of the coil body  70  is formed into a straight wire  72 , which is shaped into the anchoring ring  73 . Securing elements  71 , such as one or more spot welds, join the distal or open end of the coil body  70  to the remainder of that coil. The welds  71  form a joint, which facilitates advancement of the myocardial implant into cardiac tissue, and limits the positioning of the implant on a delivery system. 
     FIG. 12 is a side view of the myocardial implant of FIG. 11, showing securing elements  74 , such as spot welds, that join the open end of the anchoring ring  73 . The anchoring ring may have one or more concentric rings with adjacent rings secured together by one or more spot welds  74 . The spot welds  74  enhance the integrity of the anchoring ring  73 . 
     FIG. 13 is a side view of a myocardial implant  75  having a tapered configuration having a first or larger end  76  and a narrower end  77 . The larger end  76  provides a self-anchoring means in order to retain the implant  75  in the myocardium. The entire body of the tapered implant  75  is intended to be inserted and held entirely within the myocardium, thus eliminating the need to have an anchoring element, such as a ring protruding outside the heart wall. The second smaller end may include adjacent coils or rings having one or more spot welds holding them together. 
     The disclosed myocardial implants are expected to incorporate a cavity having a diameter in the range of 1-5 millimeters and a length in the range of 10-30 millimeters. The bodies of the myocardial implants are preferably made of a biocompatible material; such as stainless steel. The myocardial implants may also be coated with a material that promotes angiogenesis (formation of new blood vessels). The myocardial implants may also be made from carbon, gold, platinum, or other suitable materials. 
     The number of myocardial implants required to be used for each patient depends on the size of the implants and the surface area of the heart segment that is being revascularized. For example, a small segment may require only one myocardial implant, while a large segment may require 10 implants to be implanted in the heart wall. 
     Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiments can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.