Abstract:
Systems and methods for detecting and measuring cardiac contractile function of a heart using an acceleration sensor unit inserted within the heart, such as within a vein of the cardiac wall are disclosed. The systems and methods involve detecting the occurrence of electrical events within the patient&#39;s heart by inserting and positioning an implantable lead having an electrode near a cardiac wall as well as detecting mechanical events within the patient&#39;s heart by then inserting and positioning a cardiac motion sensor unit through the inner lumen of the implantable lead. Furthermore, the systems and methods do not require dedicated leads and may be used with preexisting implantable leads.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to cardiac sensing devices. More specifically, the present invention relates to insertable acceleration sensor units that provide signals representative of cardiac mechanical activity.  
         BACKGROUND  
         [0002]    Implantable cardiac sensing and stimulating devices are generally used to manage a variety of heart arrhythmias and conduction system blockages. Heart arrhythmias, such as bradycardia and tachycardia, often prevent the heart from pumping an adequate amount of blood. When the body does not receive enough oxygen-carrying blood, symptoms such as fatigue, shortness of breath, dizziness, and unconsciousness may occur. Furthermore, conduction system blockages in the heart cause slow, asynchronous contractions that reduce the pumping efficiency and lower cardiac output. Implantable cardiac sensing and stimulating devices must be capable of detecting such arrhythmias and decreased pumping efficiency due to conduction system blockages, and the implantable device should respond to the detected arrhythmia or low pumping efficiency by providing therapeutic electrical stimulation.  
           [0003]    Accurate measurement of cardiac activity is needed to deliver effective therapy by an implantable cardiac sensing and stimulating device. Many cardiac sensing and stimulating devices that detect and distinguish among cardiac arrhythmias monitor heart rate, which is usually accomplished by measuring cardiac electrical activity. Furthermore, the functions of the conduction system and synchronization of cardiac wall contractions are assessed by measuring and analyzing cardiac electrical activity. However, electrical activity is not a sufficiently accurate representation of the mechanical function of the heart. Thus, using only electrodes to sense cardiac mechanical activity can have some disadvantages in some circumstances.  
           [0004]    Some implantable cardiac sensing and stimulating devices include implantable leads with built-in accelerometers to measure cardiac mechanical movement representative of cardiac contractile function. However, built-in accelerometers typically require a dedicated implantable lead, which tends to be bulky and hard to handle. Furthermore, these conventional leads with built-in accelerometers are too large to fit within a vein of a cardiac wall and require invasive installation procedures.  
           [0005]    Thus, it is desirable to provide an improved sensing method and system for accurately detecting and monitoring cardiac mechanical activities. Further, it is desirable to provide an improved sensing method and system that has the ability to be implanted without a dedicated lead, such as within a preexisting implantable lead that may be positioned within a vein of a cardiac wall.  
         SUMMARY  
         [0006]    As embodied and broadly described herein, the present invention relates to a method for detecting and measuring cardiac contractile functions using a signal representative of cardiac wall acceleration provided by an acceleration sensor unit. The method involves introducing the acceleration sensor unit into a vein of the cardiac wall and positioning the sensor so that it responds to the acceleration of the cardiac wall and provides a signal representative of the cardiac wall acceleration. The method further involves connecting the acceleration sensor unit to an electronic device.  
           [0007]    Moreover, the present invention also relates to another method for detecting and measuring cardiac contractile functions using a signal representative of cardiac wall acceleration provided by an acceleration sensor. This method involves inserting a guide element along the inner lumen of an implantable lead. The method also involves introducing the implantable lead into a vein of the cardiac wall. The method further involves positioning the implantable lead within the vein using the guide element and then removing the guide element from the inner lumen of the implantable lead. Finally, the method involves inserting the acceleration sensor unit along the inner lumen of the implantable lead.  
           [0008]    In another embodiment, the present invention relates to a method for creating an acceleration sensor. This method involves providing an implantable lead and inserting a cardiac motion sensor along the inner lumen of the implantable lead. This method also involves positioning the cardiac motion sensor within the lumen of the implantable lead so that the cardiac motion sensor remains mobile along the longitudinal axis of the implantable lead.  
           [0009]    Further, the present invention also relates to a system for detecting and measuring cardiac contractile functions. This system includes an acceleration sensing means disposed at the cardiac wall for providing a signal representative of acceleration of the cardiac wall. This system also includes a conductor means molded into an elongated insulator body for transmitting a signal representative of acceleration of the cardiac wall from the acceleration sensing means to the electronic sensing means. This system further includes a connector means for electrically linking the conductor means to the electronic sensing means.  
           [0010]    The present invention also relates to another system for detecting and measuring cardiac contractile functions. This system includes an acceleration sensing device disposed at the cardiac wall for providing a signal representative of acceleration of the cardiac wall. The system also includes a conductor device molded into an insulated elongate body for transmitting a signal representative of acceleration of the cardiac wall from the acceleration sensing device to the electronic device. This system further includes a connector device for electrically linking the conductor device to the electronic device.  
           [0011]    Advantages of the invention will be set forth in part in the description which follows or may be learned by practice of the invention. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
       
    
    
     DESCRIPTION OF DRAWINGS  
       [0012]    [0012]FIG. 1 is a schematic representation of a typical human heart with acceleration sensor units in accordance with embodiments of the present invention;  
         [0013]    [0013]FIG. 2 depicts an acceleration sensor unit in accordance with an embodiment of the present invention;  
         [0014]    [0014]FIG. 3 illustrates an implantable lead incorporating a guide element and an acceleration sensor unit in accordance with an embodiment of the present invention;  
         [0015]    [0015]FIG. 4 is a flow chart representing an exemplary method into which an embodiment of the present invention may be incorporated. 
     
    
     DETAILED DESCRIPTION  
       [0016]    Various embodiments of the present invention will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies through the several views. Reference to various embodiments does not limit the scope of the invention, which is limited only by the scope of the claims attached hereto.  
         [0017]    Embodiments of the present invention allow detection and measurement of cardiac contractile functions by an acceleration sensor unit inserted within the heart, such as within a vein of the cardiac wall. These embodiments also provide systems and methods that may be used without requiring a dedicated lead for the acceleration sensor. Further, these embodiments provide systems and methods that may be used with preexisting leads. Certain of these embodiments also provide systems and methods that may be removed from implantable leads without disturbing the position of the implantable lead within the heart  100 .  
         [0018]    [0018]FIG. 1 is a schematic representation of a typical human heart with acceleration sensor units in accordance with embodiments of the present invention. In FIG. 1, the heart  100  comprises the upper heart chambers, the right atrium area  106  and left atrium area  102 , and the lower heart chambers, the right ventricle area  108  and left ventricle area  104 . The coronary sinus  110  extends from the opening in the right atrium  106  laterally around the atria to form the great cardiac vein that extends further inferiorly into branches of the great cardiac vein. An electronic device  22  having leads  24 ,  26  is implanted in a human body (not shown) with portions of the implantable leads  24  and  26  inserted into the heart  100  and/or veins of the heart  100 . The device  22  is used to detect and analyze electrical cardiac signals and signals indicative of cardiac wall acceleration produced by the heart  100  and to provide electrical energy to the heart  100  under certain predetermined conditions to treat arrhythmias or conduction system blockages. As shown, the electronic device  22  may be an implantable cardiac resynchronization device for establishing synchronization of ventricular wall contractions, such as for patients with a left bundle branch blockage.  
         [0019]    The implantable leads  24  and  26  comprise elongate bodies, both having a proximal end,  32  and  36  respectively, and a distal end,  35  and  38  respectively. The implantable leads  24  and  26  further include one or more pacing/sensing electrodes  50 ,  52  respectively and/or one or more acceleration sensor units  46 ,  44 . The implantable lead  26  is passed through a vein into the right atrium chamber  106  of the heart  100 , into the coronary sinus  110  and then inferiorly in the great cardiac vein in a basal region to extend the electrode  52  located at the distal end  38  onto the cardiac wall alongside the left atrium chamber  102  of the heart  100 . In an alternative embodiment, the implantable lead  26  may be extended further into the coronary sinus  110  and anterior and/or lateral veins extending therefrom to extend the electrode  52  located at the distal end  38  onto the cardiac wall alongside the left ventricle chamber  104  of the heart  100 . In one embodiment, the implantable lead  26  is fixed in place by a distal fixation mechanism  70  comprising a plurality of fixation tines well known in the art. When the implantable lead  26  is positioned within the coronary sinus  110 , an acceleration sensor unit  44  is passed through the inner lumen  28  of the implantable lead  26  to extend the cardiac motion sensor  42 , such as an accelerometer, of the acceleration sensor unit  44  alongside preferably either the left ventricle chamber  104  or left atrium chamber  102  of the heart  100 . The acceleration sensor unit  44  may be removed from the inner lumen  28  of the implantable lead  26  without removing the implantable lead  26  from the coronary sinus  110  of the heart  100 .  
         [0020]    In an additional embodiment, the implantable lead  24  is passed into the right atrium chamber  106  of the heart  100  and through the tricuspid valve into the right ventricle  108  where the electrode  50 , located at the distal end  35 , is fixed in place in the interventricular septum by a distal attachment mechanism  62 . The distal attachment mechanism  62  may be a wire shaped into a helical cork-screw like projection, a plurality of fixation tines projecting away from the peripheral surface of the implantable lead  24 , or other structures for attaching the lead  24 . Such distal attachment mechanisms are well known in the art and are intended to embed the distal end of the lead  24  in the tissue of the heart. When the implantable lead  24  is fixed in place, an acceleration sensor unit  46  is passed through the inner lumen  20  of the implantable lead  24  to extend the cardiac motion sensor  40  located at the distal end of the acceleration sensor unit  46  to the interventricular septum. The acceleration sensor unit  46  may be later removed from the inner lumen  20  of the implantable lead  24 , if necessary, without removing the implantable lead  24  from the interventricular septum of the heart  100 .  
         [0021]    The implantable device  22  may detect electrical events as well as mechanical events within the heart  100 . The electrodes  50 ,  52  placed into the heart  100 , including the electrode in the coronary sinus vein branch  110 , sense the naturally occurring depolarization of the cells as the electrical wave travels past the electrode  50 ,  52  down the surface of the heart  100  from the atrium area to the ventricle area. The acceleration sensor units  44 ,  46  inserted through the inner lumens  20 ,  28  of the implantable leads  24 ,  26  sense the cardiac contractile functions by providing a signal indicative of cardiac wall acceleration.  
         [0022]    The illustrated types and locations of implantable leads  24 ,  26 , electrodes  50 ,  52  and acceleration sensor units  44 ,  46  are merely exemplary. It will be understood that one or more other types of endocardial and epicardial leads, electrodes and acceleration sensor units located in or about the right and left chambers of the heart  100  as well as the coronary sinus  110  can be substituted for those illustrated in FIG. 1 described above.  
         [0023]    [0023]FIG. 2 illustrates an example of an acceleration sensor unit in accordance with the present invention. In FIG. 2, the acceleration sensor unit  44  comprises a cardiac motion sensor  42  and a connector  45  coupled together by an elongate body  41 . The elongate body  41  comprises two electrical conductors  43 ,  47  encompassed by an insulator  49  extending longitudinally. The electrical conductors  43 ,  47  electrically connect the cardiac motion sensor  42  located at the distal end of the acceleration sensor unit  44  with the connector  45  located at the proximal end of the acceleration sensor unit  44 . In one embodiment, the insulator  49  of the elongate body  41  is an implantable polyurethane, silicone rubber or other implantable flexible polymer. At the distal end of the acceleration sensor unit  44 , the electrical conductors  43 ,  47  connect with the cardiac motion sensor  42 . At the proximal end of the acceleration sensor unit  44 , the electrical conductors  43 ,  47  connect with the connector  45 . Standard electrical bipolar or unipolar connectors may be used as the connector  45 , which provides mechanical and electrical connections to the electronic device  22 . The electrical conductors  43 ,  47  transmit the signal indicative of cardiac wall motion from the cardiac motion sensor  42  to the electronic device  22 .  
         [0024]    In accordance with the present invention, a preferred embodiment of the cardiac motion sensor  42  is constructed as an accelerometer that is particularly sized for incorporation within a vein of a cardiac wall of the heart  100 . In another embodiment, the cardiac motion sensor  42  is constructed as an accelerometer that is particularly sized for incorporation in an implantable lead within a vein of a cardiac wall of the heart  100 . Suitable accelerometers include, for example, the miniaturized accelerometer provided by Ball Semiconductor Inc. (see U.S. Pat. No. 6,197,610) and others that has a diameter of approximately 1 millimeter. The cardiac motion sensor  42  can be an accelerometer formed by any available technology such as piezoelectric, piezoresistive, capacitive, inductive, or magnetic. The cardiac motion sensor  42  detects and measures cardiac wall motion and provides a signal representative of cardiac wall acceleration to the electrical conductors  43 ,  47  which then transmit the signal to the electronic device  22 .  
         [0025]    [0025]FIG. 3 illustrates an implantable lead  26  incorporating a guide element  60  and an acceleration sensor unit  44  in accordance with the present invention. The implantable lead  26  comprises a cylindrical lead  34  with a conductor used for sensing cardiac electrical activity and delivering stimulation to the cardiac wall. The cylindrical lead  34  is concentrically encompassed by a second cylindrical lead  30  possessing a similar conductor, and the cylindrical lead  34  has an inner lumen  28 . The conductor of the cylindrical lead  34  and second cylindrical lead  30  may be an electrically conductive metal, as known in the art, formed into an insulated coil configuration such as the Guidant EASYTRAK lead, or in other configurations such as a woven conductor. Moreover, the cylindrical lead  34  and second cylindrical lead  30  may have tapered distal ends.  
         [0026]    The implantable lead  26  is adapted to receive a guide element  60  along the inner lumen  28  of the implantable lead  26  for stiffening and shaping the implantable lead  26  during the insertion of the implantable lead  26  into the heart  100 . Preferable guide elements include, for example, standard percutaneous transluminal coronary angioplasty guide wires. Once the guide element  60  is used to position the implantable lead  26  within the heart  100  or veins of the heart  100 , the guide element  60  is removed from the inner lumen  28  of the implantable lead  26 .  
         [0027]    In an embodiment of the present invention, acceleration sensor unit  44  is passed through the inner lumen  28  extending along the longitudinal axis of the implantable lead  26  after the implantable lead  26  is positioned within the heart  100 , such as within the coronary sinus  110 . The acceleration sensor unit  44  is extended into the implantable lead  26  to optimally position the cardiac motion sensor  42  of the acceleration sensor unit  44 . For example, the sensor  42  may be positioned adjacent to the left atrium chamber  102  or left ventricle chamber  104  of the heart  100 . Once an optimal position for the cardiac motion sensor  42  is achieved, the acceleration sensor unit  44  is fixed relative to the longitudinal axis of the inner lumen  28  of the implantable lead  26  by connecting connector  45  to the electronic device  22 . In this embodiment, the connector  45  may be disconnected from the electronic device  22 , and the acceleration sensor unit  44  may be removed from the inner lumen  28  of the implantable lead  26  without removing the implantable lead  26  from the heart  100 .  
         [0028]    [0028]FIG. 4 illustrates the steps representing a method into which the present invention may be incorporated. At Step  200 , a guide element  60  is inserted along the inner lumen  28  of an implantable lead  26 . At Step  205 , the implantable lead  26  is introduced into the heart  100 , such as within the coronary sinus vein  110  of a cardiac wall. At Step  210 , the implantable lead  26  is positioned within the heart  100 , such as within the coronary sinus vein  110 , using the guide element  60 . At Step  215 , once the implantable lead  26  has been sufficiently positioned within the heart  100 , the guide element  60  is removed from the inner lumen  28  of the implantable lead  26 . At Step  220 , the acceleration sensor unit  46  is inserted along the inner lumen  28  of the implantable lead  26 . Subsequently, should it be necessary, the acceleration sensor unit  46  may be removed from the lead  26  while the lead  26  remains installed in the heart  100 .  
         [0029]    While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made therein without departing from the spirit and scope of the invention.