Abstract:
Endotension, the continued expansion and tensioning of a blood vessel at an aneurysm site after the repair of the aneurysm by placement of a stent graft therethrough, typically caused by refilling of the aneurysmal location by blood leakage thereto, is detected. The detection is accomplished by locating a detector in the aneurysmal vessel, between the blood vessel wall and the stent graft, and monitoring signals generating therefrom which are indicative of the arrival of fresh blood in the region, and thus a leakage of blood therein. The detector may be an oxygen sensor, and the monitoring can include maintaining a history of periodic blood oxygen signals indicative of the oxygen content of blood between the stent graft and the vessel wall, and the periodic analysis of these signals to determine whether the oxygen level is increasing, indicating the existence of endoleak and thus likely endotension.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to the field of blood vessel repair, more particularly to the field of the detection of leakage of blood past stent grafts placed into blood vessels to enable the repair or bypass of an aneurysm in the blood vessel.  
           [0003]    2. Description of the Related Art  
           [0004]    Aneurysms occur in blood vessels in locations where, due to age, disease or genetic predisposition, the blood vessel strength or resiliency is insufficient to enable the blood vessel wall to retain its shape as blood flows therethrough, resulting in a ballooning or stretching of the blood vessel at the limited strength/resiliency location to form an aneurysmal sac. If the aneurysm is left untreated, the blood vessel wall may continue to expand, to the point where the remaining strength of the blood vessel wall is below that necessary to prevent rupture, and the blood vessel will fail at the aneurysm location, often with fatal result.  
           [0005]    To prevent rupture of the aneurysm, a stent or graft of a tubular construction is introduced into the blood vessel, such as from a remote location through a catheter introduced into a major blood vessel in the leg and pushed through the blood vessel to the aneurysm location, and the stent is secured in a location within the blood vessel such that the stent spans the aneurysmal sac. The outer surface of the stent, at its opposed ends, is sealed to the interior wall of the blood vessel at a location where the blood vessel wall has not suffered a loss of strength or resiliency, such that blood flowing through the vessel is diverted through the hollow interior of the stent, and thus diverted from the blood vessel wall at the aneurysmal sac location. Therefore, the risk of rupture of the blood vessel wall at the aneurysmal location is significantly reduced, if not eliminated, and blood can continue to flow through to the downstream blood vessel without interruption.  
           [0006]    Although the use of stent grafts to treat aneurysms is a well-developed procedure, complications can arise which, if unaddressed, can lead to failure of the aneurysm repair. In particular, there is a risk of endotension, i.e., that the aneurysmal sac will become refilled with blood, at systemic pressure. If this occurs, there is a renewed risk of blood vessel wall failure and thus serious medical complications or death. Typically, blood can enter the aneurysmal sac, after the placement of the stent graft, by virtue of an endoleak, which may include mechanism such as blood introduction by: leakage through the graft material; passage of blood between the stent graft and blood vessel wall through failure of one of the seals between the ends of the stent graft and the blood vessel wall; or, supply of blood by side branch arteries through the weakened blood vessel wall. An endoleak can be difficult to detect. Typical methods include the use of x-rays, ultrasound of CT scan technologies to monitor the status of the aneurysmal sac, and hopefully detect enlargement or refilling of the aneurysmal sac with blood before vessel wall rupture occurs. However, these techniques cannot always detect small changes in the aneurysmal sac, i.e., endotension, since the size or morphology of the aneurysmal sac may not substantially change, or may not provide a visibly detectable change, when fresh blood enters. Thus an endoleak may not be detectable when a high risk for post intervention rupture of the aneurysm exists.  
           [0007]    Therefore, there is a need in the art to enable the detection of endoleak and endotension conditions after the placement of a stent graft to bypass the weakened blood vessel wall, with increased likelihood of early detection of a high-risk condition, without the need to resort to traditional diagnostic techniques.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention generally provides methods and apparatus for detecting endoleaks, and thus the resulting endotension, in an aneurysmal location. In one embodiment, the invention provides a detector, located within an aneurysmal blood vessel, which is responsive to the flow of fresh blood into the aneurysmal region of the blood vessel, and is configured to enable remote sensing of the detector and/or signals emitted by the detector, to evaluate the presence or absence of fresh blood within the aneurysmal blood vessel. One method for determining endoleak or endotension includes the steps of providing a detector responsive to the presence of fresh blood in the aneurysmal blood vessel area, and reading of such detector from a remote location to diagnose endoleak or endotension at the aneurysmal location.  
           [0009]    In another embodiment, the detector is responsive to a gaseous component of blood, such as oxygen or carbon dioxide which would be present in fresh blood entering such anueral sac. In still another embodiment, the detector detects oxygen in the space between an intervention device, such as a stent graft inserted within the blood vessel to span the aneurysmal blood vessel wall area, and the wall of the aneurysmal blood vessel, and a reading and storing mechanism is provided to store a multiplicity of oxygen level readings. A remote reading device is provided to periodically review the stored readings for blood oxygen level in the space, to enable the detection of changed or increasing oxygen levels in the space between the stent graft and the aneurysmal blood vessel wall, and thereby detect the presence of endoleak or endotension. In still another embodiment, a sensor responsive to a different component of blood, such as carbon dioxide or carbon monoxide, is used in place of an oxygen sensor to detect endoleak and endotension.  
           [0010]    In a still further embodiment, the invention provides a method of enabling detection of endoleaks or endotension without the need to resort to MRI, CT scan or ultrasound techniques, by providing an oxygen sensor implantable in the aneurysmal location, providing a time sensitive clocked reading mechanism capable of receiving signals emanating from the oxygen sensor upon placement thereof in the aneurysmal sac location, and instructions on the placement, interconnection and use of signals emanating from the oxygen sensor. In still a further embodiment, the method includes the steps of implanting the oxygen sensor in an appropriate location; interconnecting the oxygen sensor to an implantable reading and recording mechanism, and remotely sensing the reading and recording medium to receive data indicative of oxygen content at the implant location. In still another embodiment, a sensor responsive to a different component of blood, such as carbon dioxide or carbon monoxide, is used in place of an oxygen sensor to detect endoleak and endotension.  
           [0011]    In still a further embodiment, an oxygen sensor is implantable in the aneurysmal location, providing a time sensitive clocked reading mechanism capable of receiving signals emanating from the oxygen sensor upon placement thereof in the aneurysmal location, and instructions on the placement, interconnection and use of signals emanating from the oxygen sensor. A real time monitor can be provided, which includes an alarm circuit responsive to a change in the aneurysmal blood vessel status. In still another embodiment, a sensor responsive to a different component of blood, such as carbon dioxide or carbon monoxide, is used in place of an oxygen sensor to detect endoleak and endotension. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a partial sectional view of an aneurysmal blood vessel, in the specific embodiment shown, an aneurysmal aorta, having a stent graft received therein and bypassing the aneurysmal portion of the vessel;  
         [0013]    [0013]FIG. 2 is a schematic view of the placement of a sensor and controller in the chest of a patient, including a schematic placement of a reader thereby;  
         [0014]    [0014]FIG. 3 is an enlarged view of the aneurysmal blood vessel of FIG. 1, showing a sensor received therein in the space between the stent graft and the aneurysmal blood vessel wall;  
         [0015]    [0015]FIG. 4 is a schematic view of a controller used in the present invention; and  
         [0016]    [0016]FIG. 5 is a schematic view of a remote alarm useful in conjunction with the detector arrangement of FIGS.  1  to  4 .  
     
    
     DETAILED DESCRIPTION  
       [0017]    Referring initially to FIG. 1, there is shown in partial section, an aneurysmal aorta  10 , having a stent graft  12  inserted therein to bypass the weakened blood vessel wall at the aneurysmal location, and thereby prevent further expansion or failure of the lumen wall at the aneurysmal location. Stent graft  12  is inserted into the aorta to span the aneurysmal sac in the aorta  10 , such that the opposed ends  16 ,  18  of the stent graft are positioned in sealing engagement with portions of the blood vessel wall which are not implicated in the aneurysmal event, i.e., they are not in a weakened state. The placement of stent graft across the aneurysmal sac  14  causes that portion of the sac  14  to be isolated from the blood flowing through the blood vessel by the presence of stent graft  12 . Thus, the stent graft provides a secure bypass of the aneurysmal blood vessel wall preventing blood flow thereto and thus eliminating systemic pressure which would otherwise result in further extension or failure thereof. The stent graft  12  is preferably introduced remotely, such as by the use of a wire and catheter inserted into a blood vessel at a remote location and then pushed therethrough to the location of the aneurysmal blood vessel, as is well known in the art. Although the stent graft is shown placed in an aorta, other aneurysmal locations, and thus other stent graft configurations and placements are specifically contemplated for use with the present invention.  
         [0018]    After the stent graft  12  is in place, blood supply to the aneurysmal sac  14 , the stent graft  12  isolates the aneurysmal sac  14  such that blood flow thereto should be substantially reduced, if not eliminated. Preferably, no fresh blood should be introduced to aneurysmal sac  14 , because the presence of such blood could result in further expansion or rupture of the weakened blood vessel wall  22  in the aneurysmal sac  14 . Rupture of the aneurysmal aorta  10  could lead to uncontrolled massive hemorrhaging, and patient morbidity and mortality, despite the presence of the stent graft  12  spanning the aneurysmal location.  
         [0019]    Referring now to FIG. 2, there is shown an endoleak and/or endotension detector  18  in situ, comprising an implantable oxygen sensor  20 , positioned on the terminus of a lead  24  extending through the blood vessel wall  22  and terminating within the aneurysmal sac  14  between the stent graft  12  and the weakened blood vessel wall of the aneurysmal sac  14 , and extending outwardly from the aneurysmal sac  14  to an implantable controller  28  preferably maintained in the abdominal cavity at a location adjacent to, but spaced from, the aneurysmal sac  14 . Controller  28  is preferably configured to control the operation of oxygen sensor  20 , record the readings for oxygen concentration or content generated by oxygen sensor  20 , and to be remotely read, such as by a telemetry reader  100 , as will be further described herein.  
         [0020]    Referring now to FIG. 3, the placement of the oxygen sensor within the aneurysmal sac  14  is illustrated. The oxygen sensor  20  is shown, in partial cutaway, located in aneurysmal sac  14 , and is configured to provide a signal, indicative of the level or saturation of oxygen in blood, and includes a sealed body portion  30 , from which lead or leads  24  extend, a lens assembly  34  enabling light transmission inwardly and outwardly of the body portion  30  within which body portion  30  is provided a light source  36  and a light detector  38 . The body portion  30  is preferably substantially miniaturized, such that its diameter is on the order of 3 to 4 mm, and the overall length thereof, non-inclusive of the lead  24 , is on the order of one centimeter. A hook (not shown), or other securement mechanism, may be provided on body portion to secure the body portion  30  against withdrawal from the aneurysmal sac  14 .  
         [0021]    Oxygen sensor  20  operates on the principle that oxygen in blood reflects or absorbs light in certain frequency ranges. Thus, by emitting a known intensity of light in a specific frequency range, and detecting the intensity of light received back at the detector in that specific frequency range, the likely concentration of oxygen in the blood is ascertainable. Specifically, as shown in FIG. 3, the light source  36  preferably includes a first light emitter, preferably an LED,  42 , and a second light emitter, preferably an LED,  44 . First light source  42  is preferably selected to emit light having a first blood oximetry frequency, and second light source is selected to have a second blood oximetry frequency, such that by sequentially powering the light sources  42 ,  44  to emit light at different times, light detector  38  will detect discrete signals corresponding to different blood oximetries. The light sources  42 ,  44 , as well as the light detector  38 , are maintained within sealed body  30  adjacent lens assembly  34 , which preferably includes discrete windows  50 ,  52 , such that light sources  42 ,  44  are positioned adjacent window  50  and light detector  38  is positioned adjacent window  52 . A non-light transmissive element  39  is positioned between the two windows  50 ,  52 , such that light leaving the light sources  42 ,  44  must pass through both windows  50  and  52  before it can reach light detector  38 . As light from light sources  42 ,  44  passes through window  50 , as shown by arrows  83 , it will encounter blood  84  present in the aneurysmal sac  14 . A portion of such light will be directed to window  52 , as shown by arrows  85 , for detection by light detector  38 . Further details of the operation and structure of a oxygen sensor which may be used with the present invention are found in U.S. Pat. No. 6,198,952, hereby incorporated by reference herein.  
         [0022]    Referring again to FIG. 2, oxygen sensor  20  is connected, via lead  24 , to controller  28 . Lead  24  preferably has a diameter of approximately 3 to 4 mm (of the same approximate diameter as the detector body  30 ), and a length on the order of about 12 cm, which enables the placement of lead  24  through the aneurysmal blood vessel wall  22 , such as by puncturing the wall  22  to create an opening  120  (best shown in FIG. 3) and inserting oxygen sensor  20  therethrough to position the sensor  20  in the aneurysmal sac  14  and extending the lead  24  therefrom and through the opening  120  and to the controller  28  remotely located from the aneurysmal blood vessel wall  22  location as shown in FIG. 2.  
         [0023]    Referring now to FIG. 4, the Controller  28  is shown in a schematic form, and is provided to operate the sensor  20 , and to maintain a record of the readings provided thereby of blood oxygen content for further review. The controller  28  generally includes a power supply  60 , a timer/clock  62 , a recording memory  64 , a microprocessor  66  and a telemetry system  68  interconnected on a board  70  to enable the control of oxygen sensor  20  for detecting of oxygen content in aneurysmal sac  14 , and to maintain a time based record of such measured values for later interpretation. In operation, microprocessor  66  receives a timing signal from the timer/clock  62 , which is read by microprocessor  66  to establish a time gap over which to initiate a reading of oxygen content in aneurysmal sac  14 . The time gap between measurements is selected to allow a maximum number of measurements to be taken and stored in memory  64  while simultaneously allowing sufficient time between remote reading of memory  64  such that memory  64  can be overwritten with new oxygen content measurements after the recorded measurements are read or otherwise used. A typical controller has sufficient memory to enable oxygen sensor  20  to make readings at 15-second intervals for 6 months, before the memory will begin re-writing over previously stored data. When microprocessor  66  has received sufficient clock signals indicative of an appropriate time interval, microprocessor  66  initiates a measure signal which opens and then closes gates or switches to pass a signal through lead  24  to sequentially power the LED&#39;s  42 ,  44  (FIG. 3), the period between their opening and closing being controlled such that each sequential pulse of light emitted from LED&#39;s  42 ,  44  is of the same time duration, typically on the order of 0.1 seconds. Opening and closing of the gates causes a connection and disconnection of light sources  42 ,  44  to power supply  62 , such that each light source is powered to emit light in a desired frequency range for a select duration of time, such that the light from each light source  42 ,  44  reaches detector  38  (FIG. 3) at distinct separate periods of time. Preferably lead  24  includes at least two conductors therein, such that one conductor is connected to each LED, and the signals emitted by the light detector  38  may be returned down one or either such conductor, the light detector  38  being protected from the incoming signals from the controller  28  by circuit elements, such as a diode (not shown). Upon the sending of the signal to one or the other LED  42 ,  44 , the microprocessor  66  also simultaneously opens gates or switches to connect detector  38  to memory  64 , such that a first signal corresponding to light reaching detector  38  from first light source  42  is recorded at a first memory location and a signal corresponding to light reaching the detector  38  from the second light source  44  is recorded at a second memory location. Each recorded signal includes address information providing a time of recording linked to the recorded sensor value. Microprocessor  66  also monitors the memory  62 , to detect the return of signals corresponding to the light pulses emitted from light sources  42 ,  44 . Although the invention has been described in terms of emitting light in separate frequency ranges at separate times, the oxygen sensor could be configured to emit light in only one frequency, or, where multiple frequencies are emitted from sources  42 ,  44 , the light detector  38  can be configured to discriminate between frequencies received, and send separate signals to the memory  62  indicative of each frequency range detected. Likewise, a plurality of light detectors, each capable of detecting light in a discrete frequency range not overlapping with the frequency range of the other may be used. Additionally, the microprocessor may be programmed to alternately power the LED&#39;s  42 ,  42 , such that every other signal recorded will be indicative of light received at the first frequency, and thus every intervening signal recorded will be indicative of light intensity in the second frequency range  
         [0024]    Once signals corresponding to such light pulses are received at memory  62 , or, if no signal is received after a time out period corresponding to an expected return signal period is passed, the switch or gate from light detector  38  to memory  62  is closed, to prevent the recording of spurious signals in memory  62 . Power supply  60  is preferably a battery selected to supply sufficient energy to power the system for a period of one to two years.  
         [0025]    Controller  28  is preferably housed in a generally cylindrical biocompatible housing  80 , having a generally thin wall  82  and configured to receive board  70 , with the controller circuitry such as microprocessor  66 , etc., therein. A sealed aperture  84  enables lead  24  to extend through wall  82  and thus be connected to board  70  for interconnection to the elements of controller  28 . Controller  28  is preferably positioned in a sub-dermal abdominal location spaced from the aneurysm location.  
         [0026]    To evaluate the status of the aneurysmal sac  14 , a medical practitioner can read the data stored in the memory  66 . Referring again to FIG. 2, a reader  100 , linked via an electrically conducting cable  102  to a computer or processor  104 , is positioned over the sub dermal location where controller  28  is positioned. To enable reading of memory through the skin of a patient, controller telemetry system  68  includes an antenna  78 , which is linked through the board  68  and microprocessor  66 , to memory  62 . Likewise, reader  100  includes a read antenna  106 , which is connected through cable  102 , to processor  104 . To initiate reading of the data stored in memory  62 , the practioner first locates or creates a file in processor  104  corresponding to the downloading of the stored data. The program can be individual patient or person specific, and may include means for generating an ID signal which corresponds to a key in controller microprocessor  66  which will only allow reading of data from memory  62  upon first supplying the ID. The processor  104  sends a signal, through cable  102 , to read antenna  106 , which transmits a corresponding rf or other radio signal which is picked up by antenna  78  and transmitted through the interconnections on board  68  to microprocessor  66 . Microprocessor  66  decodes the signal, and if appropriate, begins reading the oxygen sensor readings and transmitting them, through appropriate rf or other radio signals, through antenna  78  to read antenna  106 , and thus to processor  104 . An appropriate program in processor then tabulates the data, and converts the readings of the photo detector  38  into readings indicative of the oxygen content in the fluid in the aneurysmal sac  14  between the stent graft  12  and the aneurysmal wall  22  at the aneurysm  10  locations. The data can be presented in tabular full data form, graphical form, or as distinct summaries or averages of data over specified time periods, or as excursions from a tabulated norm, median or mean of all the data and corresponding times at which such excursion occurred. From the data, and from the results of the data, the practitioner evaluating the data can determine if further investigation of the conditional of the aneurysmal sac is warranted. The placement and design of controllers and readers, as well as telemetry devices capable of allowing reading of the stored memory through the skin, is well known to those skilled in the art of placement and use of implantable devices, in particular implantable devices used for the monitoring and control of the heart, such as pacemakers.  
         [0027]    In an additional embodiment, a portable excursion monitor  200  as shown in FIG. 5 may be provided, which is configured to be carried on a patient in a location adjacent to the sub dermal location of controller  28 , and is able to send and receive signals therefrom. In this embodiment, the excursion monitor  200  includes all of the interactive features of the processor  102  and reader  100 , but need not include the analysis enabled by processor  104 . Specifically, monitor  200  is configured to include an antenna  202 , interconnected through a monitor board to a monitor microprocessor  204 , a monitor memory  206  and a monitor timer/clock  208 , and an alarm  210 , all powered by a battery  212 . In operation, microprocessor  204  periodically, at specified times set by the user or medical practitioner and set in an addressable memory  206 , reads the memory  62  of readings of oxygen sensor  20  and establishes an average, mean, median or other analytical value thereof as well as a deviation for the readings. If a reading deviates from the average, mean, median or other analytical value of the just read, or previous readings of the oxygen sensor values, in a direction and quantity which indicates that fresh blood is entering the aneurysmal sac  14  existing between the stent graft  12  and the aneurysmal wall  22 , the microprocessor  204  generates a signal and routes it to alarm  210 , thereby activating the alarm  210  and providing the patient, or a caregiver, an early warning of the need for imminent medical attention. Alternatively, the monitor  200  circuitry could be modified, such that the controller  28  provides the analysis of the blood oxygen readings, and supplies an alarm signal though antenna  78  to antenna  202 , which signal is routed to alarm  210  to activate the alarm in the event that sensor readings indicate the presence of fresh blood in the aneurysmal sac  14 .  
         [0028]    The placement of the endoleak/endotension detector  18  is accomplished surgically. Initially, a stent graft  12  is located in the blood vessel as shown in FIG. 1, in which the aneurysmal sac  14  is located, spanning the weakened aneurysmal region of the blood vessel wall  22  and having opposed ends  16 ,  18  in sealed contact, about the perimeter of the stent graft  12 , to the internal surface of healthy blood vessel tissue. The stent graft  12  is placed by medically accepted techniques, typically through passing a catheter, with the stent graft  12  therein, in a leg blood vessel and pushing the stent graft  12  through the vessel to a desired location where it is positioned to span the aneurysmal sac  14 . The placement and sealing of stent grafts  12  in place is well known to those skilled in the art.  
         [0029]    Once the stent graft  12  is properly positioned, the extent of extension of the blood vessel at the aneurysmal site can be evaluated, and a determination made of the need to place an oxygen sensor into the aneurysmal sac  14  formed between the stent graft  12  and the blood vessel wall. Upon a determination that the oxygen sensor is appropriate, an incision is made through the patients&#39; skin, and an endoscope (not shown) is used to direct the oxygen sensor  20  into a location adjacent the exterior of the aneurysmal blood vessel wall  22 . The endoscope preferably includes a needle actuable at the distal end thereof, which needle is used to puncture the wall and thus create an aperture  120  (as shown in FIG. 3) through the blood vessel wall having a relaxed diameter slightly smaller than the diameter of lead  24 . The puncture location is chosen to be a location in the blood vessel wall which is not significantly effected by the aneurysm, i.e., it has not yet suffered significant stretching or loss of resiliency. The oxygen sensor  20  is then manipulated at the end of the endoscope to be inserted through the aperture  120 , such that the oxygen sensor  20  is fully received in the aneurysmal sac  14 , and lead  24  extends therefrom, as shown in FIGS. 2 and 3. The endoscope is removed and the controller  28 , linked to the free end of lead  24 , is then located in a sub-coetaneous location as shown in FIG. 2, and sutured into place. The incision is then closed, and the patient allowed to recover. Preferably, the operation of the oxygen sensor  20  is checked immediately before implantation into the body. Over a relatively short period of time the blood vessel wall  22  will heal to seal aperture  120  about lead  24 . At a later date, the resulting values for oxygen detected in the blood in the aneurysmal sac  14  are evaluated, and if an elevated oxygen content indicative of new or fresh blood entering the space is found, intervention steps may be taken to prevent further deterioration of the aneurysm. Alternatively, a sensor such as a carbon dioxide or carbon monoxide sensor can be used in place of oxygen sensor, to likewise detect changes in that gas content in the fluid in the aneurysmal sac  14  indicative of fresh blood supply thereto.  
         [0030]    Although the invention has been described specifically in terms of the use of an oxygen sensor to evaluate the possibility of blood leakage or supply to the aneurysmal sac  14 , it is specifically contemplated that other sensors, such as carbon dioxide or carbon monoxide detectors can be used to detect fresh blood incursion into the aneurysmal sac  14 .