Abstract:
Several embodiments of a battlefield defibrillation system ( 2 ) comprising external defibrillator ( 6 ) and at least one electrode ( 8 ) connected thereto are described. The system includes direct cardiac access-( 8 ), or indirect subcutaneous electrodes ( 30 ). The direct cardiac access electrodes ( 26 ) engage the heart muscle directly via the intercostal space. Indirect subcutaneous electrodes are positioned under patient&#39;s skin. Several design features are implemented to aid precise electrode positioning and facilitate system operation by an untrained personnel.

Description:
FIELD OF INVENTION 
       [0001]    This invention relates in general to cardiac defibrillators, and in particular to external portable defibrillators and systems. 
       BACKGROUND OF INVENTION 
       [0002]    Modern medical care in the forward battlefield environment strives to provide the most advanced and timely diagnosis and treatment to casualties possible, since time factor is often crucial to the successful clinical outcomes. 
         [0003]    One of the trauma encountered in the battlefield is cardiac ventricular fibrillation (VF) which is invariably fatal unless treated promptly. The common way to treat VF is to administer an electric pulse to the heart which shocks the heart muscle and induces it to revert to normal contraction pattern. This procedure is called defibrillation and is effected by an apparatus called ‘defibrillator’. 
         [0004]    There are two types of defibrillators: the external and internal, the latter implanted into a patient&#39;s body. External defibrillators are relatively large and contain a large battery pack and a high voltage generator. The weight of an external defibrillator is in the order of 2-3 lbs (1-1.5 kg). The generated high voltage pulse is administered to a patient via two large conductive paddles positioned on his chest and side, respectively. 
         [0005]    The implantable defibrillator, being very small and light is permanently surgically implanted into a patient&#39;s body, and its electrical lead is inserted into the heart. The outer case of the device is made of metal and acts as a second electrode to complete the path of electrical current through the heart. The implantable defibrillators are used in patients with chronic cardiac disease and their implantation requires a major surgery procedure in a hospital setting. 
         [0006]    In a forward battlefield environment obtaining an external defibrillator on a short notice is problematic, since due to its size and weight it presents a carry challenge to field medical personnel who are frequently over-burdened with equipment. On the other hand, to implant a defibrillator under field conditions and within an extremely short ‘window of opportunity’ is not feasible. 
         [0007]    Still, having a defibrillation capability ‘on-hand’ in a forward battlefield environment is very desirable in view of its potential in saving lives. 
       OBJECTIVES OF THE INVENTION 
       [0008]    Thus, it is the objective of instant invention to provide a small and light defibrillator system which can be easily carried by a field military medic along with other first-aid equipment. 
         [0009]    Another objective is to provide a defibrillator which would be easy to use even by an untrained personnel. 
       SUMMARY OF THE INVENTION 
       [0010]    In accordance with the present invention, a miniature battlefield defibrillation system is described. The system consists of a small external defibrillator equipped with direct cardiac access-, or indirect subcutaneous electrodes. The direct cardiac access electrodes engage the heart muscle directly, preferably via the left 5 th  intercostal space. Several design features are implemented to aid precise electrode positioning and facilitate system operation by an untrained personnel. 
         [0011]    The subcutaneous-type electrodes are positioned below the skin near the patient&#39;s sternum and laterally below the left armpit. Their design also facilitates simplified operation by an untrained personnel. 
       PRIOR ART 
       [0012]    The prior art is comprised by two distinct groups of defibrillators: the external and the implantable ones. The external ones, as was mentioned, are large and heavy for the wide use in the forward battlefield environments. The implantable defibrillators, while very small, are unsuitable in the first-response situations. 
       OBJECTS AND ADVANTAGES 
       [0013]    In contrast to the prior art mentioned hereinabove, the present invention provides a miniature external defibrillator, which, together with the specific electrode system delivers the desired defibrillation action. 
         [0014]    My research showed that a great difference exists between the required defibrillation energy while using an external defibrillator and using an implanted defibrillator. An external defibrillator is required to deliver up to 400 Joules of electrical energy per pulse. The need for high energy output for external defibrillation results in large size and weight of the corresponding defibrillators. In contrast, only 10-50 Joules per pulse are delivered by an implanted defibrillator with a direct intra-cardiac electrode, with satisfactory defibrillation results. 
         [0015]    I determined that the difference in the required pulse energies is due to the high impedance of the human skin and tissues immediately underneath it, which needs to be overcome by the existing external defibrillators in order to deliver sufficient defibrillation energy to the heart. 
         [0016]    If, however, the heart can be stimulated from within the body, such as done presently with implanted defibrillators, directly to/inside the heart, or from under the skin and thus avoiding its high impedance, the required pulse energy is greatly reduced. 
         [0017]    Thus, it is possible to use a small external defibrillator if its energy is delivered directly to the heart or indirectly subcutaneously, avoiding high losses in the skin and the immediate underlying tissue. 
         [0018]    Indeed, an implantable defibrillator, Model S-ICD® introduced recently by Boston Scientific, Inc. of Natick, Mass., USA utilizes an indirect subcutaneous electrode positioned along the sternum, with the defibrillator itself implanted laterally, below left armpit. The metal case of this defibrillator serves as a second subcutaneous electrode to complete the current path through the patient&#39;s heart. The energy generated by this device is relatively low 80 Joules per pulse but it is sufficient for successful defibrillation. This further supports the low-impedance model of subcutaneous electrode operation. 
         [0019]    Furthermore, in case of external defibrillators, the external electrode pads by necessity are made quite large in order to decrease impedance and current density and avoid burns to the patient&#39;s skin. In case of subcutaneous electrodes, this requirement is reduced due to lower impedance. 
         [0020]    Nevertheless, in several embodiments of the instant system, precautions were taken to decrease current density at electrodes to minimize a chance of an electrical burn injury to the patient. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a perspective view of the defibrillator system of the instant invention with two direct cardiac access electrodes. 
           [0022]      FIG. 2  is a perspective view of the defibrillation system positioned on the patient&#39;s thorax and engaging his heart. 
           [0023]      FIG. 3  is a perspective view of the defibrillator system&#39;s alternate embodiment with three direct cardiac access electrodes. 
           [0024]      FIG. 4  is a perspective view of the defibrillation system&#39;s alternate embodiment positioned on the patient&#39;s thorax and engaging his heart. 
           [0025]      FIG. 5  is a perspective view of a direct cardiac electrode assembly. 
           [0026]      FIG. 6  is a perspective view of the defibrillation system with subcutaneous electrode assemblies positioned on the patient&#39;s thorax. 
           [0027]      FIG. 7  is a perspective view of the subcutaneous electrode assembly in its pre-deployment configuration. 
           [0028]      FIG. 8  is a perspective view of the subcutaneous electrode assembly deployed. 
           [0029]      FIG. 9  is a perspective view of the subcutaneous electrode assembly&#39;s alternate embodiment in its pre-deployment configuration. 
           [0030]      FIG. 10  is a perspective view of the subcutaneous electrode assembly&#39;s alternate embodiment while deployed. 
           [0031]      FIG. 11  is a perspective view of a subcutaneous electrode assembly&#39;s alternate embodiment in its pre-deployment configuration. 
           [0032]      FIG. 12  is a perspective view of a subcutaneous electrode assembly&#39;s alternate embodiment while deployed. 
           [0033]      FIG. 13  is a perspective view of another subcutaneous electrode assembly&#39;s alternate embodiment in its pre-deployment configuration. 
           [0034]      FIG. 14  is a perspective view of another subcutaneous electrode assembly&#39;s alternate embodiment while deployed. 
           [0035]      FIG. 15  is a perspective view of a subcutaneous electrode element in pre-deployment configuration. 
           [0036]      FIG. 15   a  is a perspective view of a subcutaneous electrode element while deployed. 
           [0037]      FIG. 16  is a perspective partial view of a subcutaneous electrode assembly in pre-deployment configuration. 
           [0038]      FIG. 16   a  is a perspective partial view of a subcutaneous electrode assembly while deployed. 
           [0039]      FIG. 17  is a perspective view of a subcutaneous electrode with scimitar-shaped electrode elements. 
           [0040]      FIG. 18  is prior art of implantable defibrillator with indirect subcutaneous electrode. 
           [0041]      FIG. 19  is a perspective view of a linear subcutaneous electrode assembly inside of the introducer prior to insertion. 
           [0042]      FIG. 20  is a perspective view of a linear subcutaneous electrode assembly inside of the introducer, with introducer being removed. 
           [0043]      FIG. 21  is a partial perspective view of a linear subcutaneous electrode assembly inside of the introducer, with introducer penetrating tip closed. 
           [0044]      FIG. 22  is a partial perspective view of a linear subcutaneous electrode assembly inside of the introducer, with introducer penetrating tip open while being extracted. 
           [0045]      FIG. 23  is a perspective view of the defibrillation system with linear subcutaneous electrode assemblies positioned in the patient&#39;s thorax. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0046]    In the foregoing description like components are referenced by the like numerals. 
         [0047]    The preferred embodiment  2  of the defibrillator system is shown on  FIG. 1 . Defibrillator  6  is preferably releasably attached to the reference template  10  containing landmark registration elements  4 . Direct cardiac access electrode assemblies  8  interface with registration elements  4  to ensure proper positioning and direction of the electrodes with respect to the patient&#39;s heart. Reference template  10  further contains apertures  5  and  7  to enable adjustment of registration elements&#39;  4  positions in response to the differences in patients&#39; anatomies. Electrode assemblies  8  are electrically connected to defibrillator  6 . 
         [0048]    As shown on  FIG. 5 , each direct cardiac access electrode assembly  8  comprises a long conductive needle  26  terminating in a sharp tip, which is covered in its entirety, except for the exposed tip, by electrically insulating layer  24 . On the opposite of its sharp tip end, the needle  26  is terminated by a handle  20  used to push the needle into the patient&#39;s body prior to defibrillation and to extract it afterwards. The direction of needle&#39;s  26  movement is controlled by sleeve  22  interfacing with registration element  4  for precise guidance. 
       Operation 
       [0049]    Electrode assemblies  8  are kept retracted prior to the operation. Referring to  FIG. 2 , after adjusting the positions of landmark registration elements  4  according to the patient&#39;s anatomy within apertures  5  and  7 , reference template  10  is positioned onto patient&#39;s upper body  12 , with registration elements  4  preferably engaging the body surface immediately over the 3 rd  and 5 th  intercostal spaces and generally parallel to patient&#39;s sternum  18 . 
         [0050]    Electrode assemblies  8  are then pushed into the patient&#39;s body preferably via the 5 th  intercostal space  15 , between rib  5  denoted  14 , and rib  6  denoted  14   a,  and engage patient&#39;s heart  16  with exposed conductive tips of their needles  26 . The positioning of the needles  26  is such that they penetrate in the lower margin of the intercostal space in order to avoid contact with veins, arteries and nerves present in the upper margin of intercostal space, on the lower edge of the uppermost rib, in this case, the 5 th  rib. 
         [0051]    Defibrillation is then effected by defibrillator  6  generating an electrical pulse of the energy sufficient to defibrillate the patient&#39;s heart, which propagates down electrode assemblies  8  to the heart. After defibrillation pulse electrode assemblies  8  are either withdrawn from the patient&#39;s body, or a subsequent pulse(s) can be delivered in case the first pulse did not succeed. 
         [0052]    Embodiment 2 relies on two-electrode operation where they engage the same or both ventricles, or, by increasing the penetration angle of one of the electrodes, an atrium and a ventricle. 
       Additional Embodiments 
       [0053]    In the foregoing description like components are labeled with like numerals. 
         [0054]    Referring to  FIGS. 3 and 4  an alternative defibrillator system embodiment  2   a  utilizes a three-electrode defibrillation. This scheme, while more complicated than a two-electrode one, offers flexibility to the defibrillation action. For example, one electrode can engage atrium while two others engage same or both ventricles, or one of them is inserted half-way to serve as a common electrode. 
         [0055]    An alternative defibrillator system embodiment  11  utilizing indirect subcutaneous electrode assemblies is shown on  FIGS. 6 through 17 . On  FIG. 6  subcutaneous electrode assemblies  30  are placed onto patient&#39;s skin, with their blade electrodes piercing it to establish a low-impedance current path to the heart. 
         [0056]    Referring to  FIGS. 7 ,  8 ,  15 ,  15   a ,  16  and  16   a  subcutaneous electrode assembly  30  comprises several electrode sleeves  38  which contain electrode assemblies  34  contained in a curved inner channel  35  terminating in electrode exit aperture  35   a.  Each assembly  34  contains one or more flexible blade electrodes  34   a  connected to the contact pad  34   b  which in turn is electrically connected to defibrillator  6 . Contact pad  34   b  is also mechanically connected to the deployment handle  32 . Flexible electrode&#39;s  34   a  tip is made to be very sharp to facilitate its easy penetration into the skin. Several sleeve-electrode assemblies are held together by plate  36 . 
         [0057]    Upon placement on the patient&#39;s skin  19 , handle  32  is pressed downwards toward the skin&#39;s surface by the operator. Sleeves  38  internal curved channels  35  terminating in outwardly and radially pointing apertures  35   a  force blade electrodes  34   a  to emerge at a slant angle with respect to the skin surface  19 , penetrating it. One or more electrodes  34   a  are thus inserted simultaneously under the skin enabling a low-impedance current path for defibrillation. 
         [0058]      FIGS. 9 and 10  show an alternate embodiment of the subcutaneous electrode assembly  40 . It is more compact than assembly  30  and utilizes a single sleeve  38  with assembly  34   c  consisting of two electrodes. To stabilize the assembly on the patient&#39;s skin, it is equipped with a rest  36   a  on its bottom. 
         [0059]    Yet another embodiment of the subcutaneous electrode assembly  50  is shown on  FIGS. 11 through 14 . Instead of the flat bottom of the previous assembly, each sleeve  38  terminates in a sharp tip  52 . This construction enables deeper penetration of the skin and subcutaneous layers. The plate  36  serves in this embodiment as a penetration depth limiter. 
         [0060]    Another embodiment of the subcutaneous electrode assembly  70  is shown on  FIG. 17 . It features scimitar-shaped electrodes  72  extending radially from the common contact pad  34   b  attached to handle  32 . The electrodes are inclined to the plane of the handle/contact pad, so when placed on skin  19 , they pierce it when handle  32  is turned, in this configuration, clockwise. Rotating handle  32  counter-clockwise removes electrodes  72  from the skin. 
         [0061]    Another embodiment of the subcutaneous electrode assembly  100  is shown on  FIGS. 19 through 23 . A relatively thin and flexible electrode  102  is positioned inside introducer  104  for subcutaneous insertion. Introducer  104  at its distal end has a sharp penetrating tip  106  which consists of several flexible tangs  106   a.  During insertion tangs  106   a  are held firmly against each other by skin&#39;s resistance, forming a sharp tip  106 . Referring to  FIG. 23  introducers  104  containing electrodes  102  inside are placed under patient&#39;s skin preferably at two locations: one along the sternum  18  and another laterally below left armpit. These locations are customarily selected for external defibrillator electrode pads placement and also shown in the prior art implantable defibrillator system  80  with indirect electrode  82  and implantable defibrillator  86  whose metal case serves as a second electrode, shown on  FIG. 18 . 
         [0062]    When electrode assembly  100  is positioned at the desired position, introducer  104  is withdrawn by the operator&#39;s pulling it back off of the electrode  102 . During this operation the tip of electrode  102  pushes the tangs  106   a  of introducer  104  outwards and causes them to flex, clearing electrode  102 . Introducer  104  is then slid off the electrode  102 , leaving it in place inside patient&#39;s body. Upon completion of defibrillation electrode  102  is withdrawn from the patient&#39;s body by simple pulling. 
         [0063]    Although descriptions provided above contain many specific details, they should not be construed as limiting the scope of the present invention. Several features of distinct embodiments can be combined, for example, the introducer/electrode assembly  100  can be used in the direct cardiac contact embodiments  2  and  2   a,  with an advantage that a thin electrode can be left in place while chest compressions are performed on the patient as a part of a cardio-pulmonary resuscitation (CPR) procedures. 
         [0064]    Thus, the scope of this invention should be determined from the appended claims and their legal equivalents.