Abstract:
An endovascular graft having one or more sensors attached to its internal and external surface, one or more power sources attached to its external surface and one or more transmitters attached to its external surface, the sensors capable of measuring pertinent parameters and each transmitter capable of transmitting signals containing pertinent parameters to one or more receiving devices located outside the patient&#39;s body. The sensors may measure pressure, temperature, blood flow, electrical potential, or any combination thereof. The sensors may be attached at specific locations on the graft material, thereby providing pertinent parameters from critical points inside the vasculature, or may be attached to form an array of sensors over the internal and external surface of the graft material, thereby providing a complete profile of pertinent parameters throughout the vasculature covered by the endovascular graft.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to the treatment of body lumens and, more particularly, to the endovascular placement of a prosthetic graft within vasculature for the purpose of repairing the same.  
         [0002]     Ruptured abdominal aortic aneurysms (AAA) are a leading cause of death in the United States. Treatment options to repair AAA include conventional open surgery and implantation of an endovascular graft. Conventional open surgical repair of AAA involves major abdominal surgery with associated high rates of morbidity. Endovascular grafts have been developed to endoluminally bypass abdominal aortic aneurysms through minimally invasive surgery. Many patients that are unacceptable surgical risks for open repairs are eligible for endovascular graft implantation. Deployment of transfemoral, endovascular grafts to treat AAA is appealing for many reasons: avoidance of an abdominal incision, lack of aortic cross clamping, the potential for regional anesthesia, and a shortened hospital stay.  
         [0003]     Untreated AAA has been shown to continue to expand until rupture, with an associated high mortality rate. Implantation of endovascular grafts have also been associated with high complication rates, including perioperative death, conversion to open repair, the need for further intervention, the need for hemodialysis, a failure to cure the AAA, and wound complications.  
         [0004]     The inability to obtain or maintain a secure seal between the vessel wall and the endovascular graft is a complication unique to endovascular aneurysm exclusion. Because the term “leak” has been associated with aneurysm rupture following conventional surgery, the term “endoleak” has been proposed as a more definitive description of this complication. It is believed that persistent endoleaks result in continued aneurysm expansion, which may eventually lead to aneurysm rupture. Aneurysms that have been successfully excluded have shown a tendency towards a reduction in aneurysm diameter. Failure to properly exclude the aneurysm from systemic arterial blood pressure keeps the patient at risk of impending rupture. Endoleaks have been classified according to the source of the leaks. Current classifications of endoleaks include four categories. Type I endoleaks are “perigraft” or “graft-related” leaks that involve a persistent channel of blood flow due to inadequate or ineffective sealing at the ends of the endovascular graft, or between overlapping components of a modular system. Type II endoleaks are retrograde flow into the aneurysm sac from patent lumbar arteries, the inferior mesenteric artery, or other collateral vessels. Type III endoleaks result from fabric tears, graft disconnection, or graft disintegration. Finally, Type IV endoleaks are flow through the graft fabric associated with graft wall porosity or permeability. Preoperative patent side branches are not a good predictor of postoperative endoleaks.  
         [0005]     A number of reported cases of aneurysm rupture following implantation of an endovascular graft have been reported. Some of the ruptures occurred in patients without a documented endoleak.  
         [0006]     A number of studies have focused on measurement of pressure within the aneurysm sac following implantation of an endovascular graft, both in the human patient, an animal model, or an in vitro model. Properly implanted endovascular grafts have been shown to reduce the pressure within the aneurysm sac while an endoleak, with or without detectable blood flow, continues to pressurize the sac at pressures equivalent to the systemic arterial pressure. Animal studies utilizing a predictable rupturing aneurysm model have shown that non-excluded aneurysms will rupture. Thrombosed aneurysm sacs may still receive pressurization from a sealed endoleak and this continued pressurization keeps the aneurysm at risk for rupture.  
         [0007]     Current methods of patient follow-up include arteriography, contrast-enhanced spiral computed tomography (CT), duplex ultrasonography, abdominal X-ray, and intravascular ultrasound. All of these methods are costly and involve invasive procedures that have associated morbidity. None of the imaging methods are completely successful in detecting endoleaks. Therefore, the potential exists for an endoleak to go undetected until eventual rupture. An increase in aneurysm diameter is detectable, and should be considered an indication of endoleak. To avoid aneurysm rupture an increase in aneurysm diameter must be detected in a timely fashion to identify patients in need of corrective surgical procedures.  
         [0008]     An endovascular graft with the ability to measure pressure within the aneurysm sac and provide feedback to the physician could identify those patients with persistent pressurization of their aneurysm, and subsequent risk of rupture. Some physicians are advocating that the follow-up examinations of AAA patients focus on pressure measurements, but that this is not currently clinically feasible.  
         [0009]     Accordingly, there exists a need for an endovascular graft that facilitates non-invasive measurement of pressure, as well as other pertinent parameters, within the aneurysm sac and along the endovascular graft itself as a means for identifying patients at risk for aneurysm rupture after the endovascular graft is implanted. The present invention addresses these and other needs.  
       SUMMARY OF THE INVENTION  
       [0010]     Briefly and in general terms, the present invention is embodied in an endovascular graft with sensors attached thereto. The device will have the ability to be delivered endovascularly and measure pertinent parameters within the excluded AAA. The endovascular graft would have the ability to transmit data about intra-sac parameters to an external monitoring device. Patient follow-up would be less costly (conducted in the physician office), non-invasive, and more accurate, allowing prompt intervention in those patients most at risk for acute rupture. The invention would also allow for more frequent patient follow-up, increasing the potential to diagnose and treat aneurysms at risk before acute rupture. The invention is applicable to all applications of endovascular grafts to treat aneurysmal segments of blood vessels. It is contemplated that the invention may be used with all shapes of endovascular grafts known within the art.  
         [0011]     In one embodiment, sensors are attached to the endovascular graft at the superior end, inferior end and midsection. Measurements of pertinent parameters and comparison of those measurements may allow early identification of areas of the patient&#39;s vasculature at risk for aneurysm rupture, thrombus formation, infection, inflamation or other anomalies without the need for invasive procedures.  
         [0012]     In another embodiment, a pattern of sensors are attached to the endovascular graft such that they cover the interior and exterior of the graft. The pattern of sensors allow a complete profile of pertinent parameters along the endovascular graft to be obtained. Such a profile may provide more accurate identification of anomalies.  
         [0013]     Sensors with pressure measurement capability may be used to detect pressure changes external the endovascular graft, in the aneurysm sac or in blood flow through the interior of the endovascular graft indicative of graft failure, graft kinking, or endoleak due to an inadequate seal between the endovascular graft and the vasculature. Sensors with temperature measurement capability may be used to detect temperature differentials associated with “hot spots” related to inflamation, infection or thrombus formation in the vessel. Sensors with the capability to measure oxygen and other blood constituents such as enzymes, proteins, and nutrients, may be used to detect minute blood flow indicative of endoleak. Sensors with the capability to measure electrical potential may be used to detect differences in potential associated with areas of the vessel at risk for thrombus formation.  
         [0014]     An antenna or other data transmitter and a power source may be attached external the endovascular graft, allowing a physician or technician to monitor graft and vessel health without the need for an invasive procedure. The transmitter transmits measurements made by the sensors to a receiver located outside the patient&#39;s body.  
         [0015]     Other features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a partial cross-sectional view of one embodiment of the invention showing a generally tubular endovascular graft implanted across an aneurysm sac;  
         [0017]      FIG. 2  is a partial cross-sectional view of an alternate embodiment of the invention shown in  FIG. 1  showing a partially assembled bifurcated endovascular graft; and  
         [0018]      FIG. 3  is a perspective view of another embodiment of the invention showing a bifurcated endovascular graft having an array of sensors on the external and internal surfaces of the graft material.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     As shown in the exemplary drawings and for purposes of illustration, the invention is embodied in a prosthetic endovascular graft implant having the ability to measure pertinent parameters inside and outside the graft material and transmit the measurements to a receiver located external the patient within whom the endovascular graft is implanted. In one aspect, the invention includes a graft with sensors mounted on the external and internal surface that measure parameters such as pressure, temperature or voltage. In another aspect the invention includes a transmitter and energy source which facilitate transmission of parameters measured by the sensors to a receiver located outside the patient&#39;s body.  
         [0020]     Referring to  FIG. 1 , an embodiment of the invention is shown in which a generally tubular, including flared or tapered, endovascular graft  10  having a superior end  12  and inferior end  14  is implanted in a body vessel  30  across an aneurysm sac  32  with the superior end  12  secured above the aneurysm and the inferior end  14  secured below the aneurysm. The endovascular graft  10  has sensors  16  attached external the superior  12  and inferior  14  ends. Additionally, the endovascular graft  10  has sensors  18  attached internal the superior  12  and inferior  14  ends. Furthermore, the endovascular graft  10  has sensors  20  attached external the midsection. Moreover, the endovascular graft  10  has a transmitter  22  and power source  24  attached external the graft material in the area where the graft traverses the aneurysm sac  32 . The sensors  16 ,  18 ,  20  measure pertinent parameters inside and outside the endovascular graft and the power source  24  provides power for the transmitter  22  which transmits the measurements to a receiver (not shown) located outside the patient&#39;s body.  
         [0021]     The transmitter  22 , power source  24  and receiver (not shown) may be of any type known in the art of surgical implants or other systems utilizing miniaturized power sources and transmitters. The power source  24  and transmitter  22 , for example, may be of the type used in pacemaker technology or passive power sources such as ultrasonically chargeable capacitors.  
         [0022]     The sensors  16 ,  18 ,  20  of the invention shown in  FIG. 1  may measure pressure. These measurements may be used as an aid in endovascular graft  10  placement or to identify anomalies that occur after endovascular graft  10  implantation before aneurysm rupture occurs.  
         [0023]     The sensors  16  external the superior  12  and inferior  14  ends of the endovascular graft  10  may be used to detect changes in pressure resulting from blood leakage between the endovascular graft  10  and the vessel wall  30 , an endoleak resulting from an inadequate seal between them. It is contemplated that sensors  17  may be located around the entire circumference of the superior  12  and inferior  14  ends of the endovascular graft  10 , thereby allowing the exact location of an endoleak to be determined.  
         [0024]     The sensors  18  internal the superior  12  and inferior  14  ends of the endovascular graft  10  may be used to measure inlet and outlet pressure of blood flow therethrough. A pressure drop indicates an anomaly such as kinking of the endovascular graft  10  or endoleak due to fabric tears or graft material disintegration. It is also contemplated that sensors  19  may be located around the entire circumference of the superior  12  and inferior  14  ends of the endovascular graft  10 .  
         [0025]     The sensors  20  external the midsection of the endovascular graft  10  may be used to measure pressure resulting from blood flow into the aneurysm sac  32 , an indication that endoleak has occurred and there is a risk of aneurysm rupture. Because the sensors  20  are located in the area of the aneurysm sac  32 , there are multiple sensors  20  disbursed over the graft material outer wall since local thrombus or calcification may shield one or more of the sensors  20  from blood pressure and render their measurements erroneous.  
         [0026]     Referring to  FIG. 2 , the embodiment of the invention shown in  FIG. 1  is applied to a bifurcated endovascular graft  110  of the type known within the art. The bifurcated endovascular graft  110  is assembled in-vivo from a tubular trunk portion  40  and two limb portions  50  (only one is shown). The bifurcated endovascular graft  110  is implanted in a body vessel  30  across an aneurysm sac  32  and into the contra-lateral  34  and ipsi-lateral  36  arteries using methods known within the art.  
         [0027]     The trunk portion  40  has a superior end  42  adapted to be secured above the aneurysm and an inferior end  44  adapted to accept the limb portions  50 . The trunk portion  40  has a transmitter  22 , power source  24 , and sensors  16 ,  17 ,  18 ,  19 ,  20  similar to those described with reference to  FIG. 1 .  
         [0028]     Each limb portion  50  has a superior end  52  adapted to mate with the trunk portion  40  inferior end  44  and an inferior end  54  adapted to be secured to the ipsi-lateral  34  or contra-lateral  36  iliac artery. Each limb portion  50  also has a transmitter  122 , power source  124 , and sensors  116 ,  117 ,  118 ,  119 ,  120  similar to those described with reference to  FIG. 1 . The transmitter  122  and power source  124  facilitate transmission of parameters measured by the sensors  116 ,  117 ,  118 ,  119 ,  120  to a receiver (not shown) outside the patient&#39;s body.  
         [0029]     The functions of some of the sensors are slightly different than those previously described with reference to a tubular endovascular graft. The sensors  116  external the superior  52  end of a limb portion  50  may be used to detect pressure changes resulting from blood leakage between the limb portion  50  and the trunk portion  40 , an endoleak resulting from an inadequate seal between the limb portion  50  superior end  52  and trunk portion  40  inferior end  14 . The sensors  116  external the inferior  54  end of a limb portion  50  may be used to detect pressure changes resulting from blood leakage between the limb portion  50  and the ipsi-lateral  34  or contra-lateral  36  iliac artery wall, an endoleak resulting from an inadequate seal between the limb portion  50  inferior end  54  and vessel  30 . The sensors  118  internal the superior  52  and inferior  54  ends of a limb portion  50  may be used to measure inlet and outlet pressure of blood flow therethrough, with a pressure drop indicating an anomaly such as kinking of the limb portion  50  or endoleak due to fabric tears or graft material disintegration. The sensors  120  external the midsection of the limb portion  50  may be used to measure pressure resulting from blood flow between the limb portion  50  and the wall of the ipsi-lateral  34  or contra-lateral  36  iliac artery, an indication that endoleak has occurred due to inadequate mating of the limb portion  50  superior end  52  and the trunk portion  40  inferior end  44 .  
         [0030]     Alternatively, the sensors of the invention shown in  FIGS. 1 and 2  may measure temperature. Differences in temperature may identify “hot spots” associated with infection, inflammation, thrombus formation or other anomalies that indicate an increased risk for aneurysm rupture. Methods known in the art of pathology and physiology may be used to relate temperature to changes in the vessel walls within which the endovascular graft is implanted.  
         [0031]     Alternatively, the sensors of the invention shown in  FIGS. 1 and 2  may detect blood flow by measuring oxygen or other constituents, such as enzymes, proteins and nutrients, which are altered by the presence of blood flow. Such sensors may allow detection of minute blood flow, often missed by conventional imaging modalities, and, therefore, allow endoleaks to be detected earlier. One method is to obtain a baseline of the constituents upon implantation of the endovascular graft. Thereafter, changes in the amount of the measured constituents may be used to identify anomalies.  
         [0032]     Alternatively, the sensors of the invention shown in  FIGS. 1 and 2  may measure electrical potential. Changes in electrical potential may identify areas of the patient&#39;s vasculature that are at risk for thrombus formation.  
         [0033]     It is contemplated that the number of transmitters, power sources and sensors shown in  FIGS. 1 and 2  may be varied to meet the requirements of the individual patient. It is further contemplated that sensors which measure different pertinent parameters may be used together. Moreover, it is contemplated that the invention shown in  FIGS. 1 and 2  may be utilized in any type of endovascular graft implant known in the art.  
         [0034]     Referring to  FIG. 3 , another embodiment of the invention is shown in which miniature sensors  216 ,  218  are arranged as an array covering the interior and exterior of the surface of the endovascular graft  210 . The array of sensors  216 ,  218  provides a complete profile of pertinent parameters over the entire surface of the endovascular graft and, therefore, facilitates better identification of anomalies. The transmitter  222 , power source  224  and external receiver (not shown) allow the measured parameters to be received and monitored outside the patient&#39;s body. The array of sensors  216 ,  218  may spiral around the graft material in between the weaves of fabric and consist of a strip of sensors, continuous strip of wire or other apparatus known in the art.  
         [0035]     It is contemplated that the location and number of transmitters, power sources and sensors shown in  FIG. 3  may be varied to meet the requirements of the individual patient. It is further contemplated that the array of sensors  216 ,  218  may contain sensors capable of measuring pressure, temperature, blood flow, electrical potential, or any combination thereof. Moreover, it is contemplated that the invention shown in  FIG. 3  may be utilized in any type of endovascular graft implant known in the art.  
         [0036]     While several particular forms of the invention have been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.