This patent application is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "Medical implantable leads of the above kind are well known in the art and can be employed whenever it is desirable to monitor or control an organ inside a human or animal body by receiving and/or transmitting electric signals from and to the tissue of the organ. One such common application is monitoring and controlling of a heart by means of a pacemaker or an ICD (Implantable Cardioverter Defibrillator), wherein the pacemaker or the ICD is connected to a proximal end of the lead whereas a distal end of the lead and in particular at least one electrode positioned at the distal end or distal portion of the lead is in contact with tissue of the heart. However, it is to be understood that it could be conceivable to electrically monitor and/or control also other organs inside a human or animal body.
"To accomplish electrical monitoring and/or controlling of an organ inside a body, it is common practice to insert the lead into the body through some kind of narrow body canals or vessels. In the case of monitoring and/or controlling of a heart by means of a pacemaker or an ICD, this vessel typically is a vein through which the distal end of the lead can be brought into a ventricle or an atrium of the heart or be placed inside a coronary vein surrounding the heart. The latter is frequently applied when implanting a left ventricular lead (LV-lead) to a heart for the purpose of not causing any blood cloths inside the left ventricle. A blood cloth there could be potentially hazardous for the patient since the left ventricle is in direct connection with the brain and any coagulated blood in the blood flow could cause an obstruction in the small capillaries of the brain. Therefore an LV-lead is usually positioned in one of the coronary veins surrounding the left ventricle of the heart.
"Since a lead of this kind is to be inserted into the body through narrow body vessels, such as veins, an important feature for such a lead is that it should have a small cross sectional dimension to facilitate and even at all allow insertion through the desired vessel. To accomplish this it is common practice to form for example an LV-lead of a flexible tubing, of e.g. silicone, and to arrange one or more cables, i.e. electrically conducting wires surrounded by an electrically insulating layer, inside the tubing which connects the one or more electrodes at the distal portion of the lead with electric contact surfaces at a connector in the proximal end. In order to make the lead sufficiently rigid to be able to insert the lead into a narrow vein, provisions are taken to allow insertion of a stiffening stylet into an inner bore of the tubing, wherein the stylet is inserted into the tubing during introduction of the lead into the vein and is subsequently withdrawn. The outer cross sectional dimension of a lead designed in this way can be kept advantageously small.
"However, it has become more and more common throughout the world to use magnetic resonance imaging (MRI) for diagnosing and examining bodies for various diseases or injuries. The use of MRI is increasing, both as the MRI equipment becomes less expensive, less complicated and smaller but also as the number of applications increase. For a person or animal having a lead relating to the present art implanted into the body, it is of great benefit that the lead is MRI-compatible. MRI-compatible as used herein implies that any heating of electrodes in connection with the distal end of the implantable medical lead caused by a current induced by RF fields of the MRI system is at an acceptable level to thereby not cause or at least reduce the risk of causing significant injuries to surrounding tissue in the subject body or damages to internal lead parts. By a lead which is not MRI-compatible, the magnetic field will induce current in the lead which can lead to an incorrect stimulation of an organ, e.g. a heart, or thermal damage to the tissue closest to the electrodes. It can also render the MRI procedure unusable.
"Over the years it has been suggested different ways to render a medical implantable lead MRI-compatible. One way is to arrange the one or more conductors, which electrically connects the one or more electrodes at the distal end portion of the lead with the connector in the proximal end, in form of one or more coils of one or more electrically conducting wires, each having an electrically insulating layer. A coil formed in this way will act as an inductance coil which will prevent or reduce the induction of high frequent alternating current into the coil. A lead arranged in this way is disclosed in e.g. WO 2010064962 to the present assignee.
"One disadvantage with a lead having an electric conductor in form of a coil is however that it will in most cases have a larger cross sectional dimension in comparison to a corresponding lead being provided with a conductor in form of one or more cables. Moreover, the inductance of the coil, and accordingly also the MRI-compatibility, will increase with an increased diameter of the coil so it is advantageous to try to keep the cross sectional dimension as large as possible. However, even a small increase of the cross sectional dimension can cause problems when it comes to insertion of the lead through narrow veins or other narrow body vessels. The smaller the lead diameter is, the more veins it can be placed in and also the further it can be inserted into a particular vein. For an LV-lead the placement is very important for the effectiveness of the lead function, so being able to position the lead at the most desirable position is very important.
"From U.S. pat. No. 5,755,766 it is known a medical implantable lead having a conductor in form of a coil and which has a reduced lead body diameter in a most distal portion. The reduced lead body diameter is achieved by reducing the diameter of the coil in the most distal portion. However, a coil formed in this way will be comparatively expensive and complicated to manufacture."
In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventors' summary information for this patent application: "It is an object of the invention according to a first aspect to provide a medical implantable lead comprising a conductor in form of a coil which is easy to insert through narrow body vessels, such as veins. This object is achieved by a medical implantable lead according to claim 1.
"It is also an object of the invention according to a second aspect to provide a medical implantable lead, which is MRI-compatible, which comprises a conductor in form of a coil and which is easy to insert through narrow body vessels, such as veins. This object is achieved by a medical implantable lead according to claim 10.
"Accordingly, the basis of the invention is the insight that the object according to the first aspect may be achieved by terminating the coil at a termination point on a distance from the distal end to form the lead with a tapered distal portion and to provide a conducting arrangement comprising the coil and an end conductor, in form of a non-coiled electric conductor or an eccentrically positioned small diameter coil, which connects at least one electrode at the distal end with the conducting coil. The object according to the second aspect may be achieved by forming the coil, which is terminated at a termination point on a distance from the distal end, of one or more electrically conducting wires, which each is provided with an electrically insulating layer such that the coil will act as an inductance coil.
"Within the scope of the invention, as defined in claim 1, the invention can be varied and modified in many different ways. In the hereinafter described and illustrated embodiments, the medical implantable lead is designed primarily as a cardiac lead for monitoring and/or controlling of a heart and for this purpose to be connected to a pacemaker or an ICD and more particularly a cardiac lead in form of an LV-lead adapted to be implanted into the coronary veins of the left ventricle of a heart. However, it is to be understood that a lead having the features of the invention also could be employed to be implanted at other areas of a heart and also be employed to monitor and/or control other organs inside a human or animal body.
"The electric end conductor, which connects the most distal or first electrode with the coil, can be formed in many different ways. For example as a cable having an electrically conducting core, e.g. a wire, and an outer electrically insulating layer, as a bare conductor in form of a wire or a strip, as an electrically conducting layer applied on the inside of the distal portion of the tubing, or as an eccentrically positioned small diameter coil. It could also be conceivable to arrange the conductor as a combination of two or more of these for redundancy purpose. According to the embodiments the electric end conductor is defined either as being non-coiled and this expression is intended to be interpreted as a conductor not comprising a close-coiled wire or cable, in contrast to the coil, but does not exclude the provision of a cable or bare wire which forms a few loops along its length, or as a conductor in form of an, in relation to a centre line along the length of the lead, eccentrically positioned small diameter coil. In case of an MRI-compatible lead, a non-coiled electric conductor will not itself be MRI-compatible and an eccentrically positioned small diameter coil can be formed as an electrically insulated coil having an inductance but since the diameter is small the inductance will be comparatively low. However, since the length of the end conductor is short compared to the total length of the lead and since it is connected to a coil having a large inductance the end conductor will not have any detrimental effect on the overall MRI-compatibility of the lead.
"The tapered distal portion of the lead may in a practical embodiment of a cardiac LV-lead have a length of between 10-50 mm, preferably 10-30 mm or most preferred 15-25 mm, but other lengths could be conceivable as well, especially for other types of leads. The tapering could optionally be continuously from the beginning of the tapering to the distal end of the lead, or be performed along one or more shorter sections such that the decreasing of the cross sectional dimension of the lead is done 'stepwise' in one or more shorter tapered portions and have a uniform reduced cross sectional dimension at the rest of the length. However, it is advisable that abrupt changes of the cross sectional dimension is avoided since sudden changes of the outward shape is susceptible to growth of tissue into the inward curved formations, which e.g. might render a possible subsequent retraction of the lead from the body difficult. Normally, it is preferred that the tapering begins at the termination point of the coil but it is of course possible to begin the tapering before as well as after the termination of the coil as seen in the direction towards the distal end of the lead. The decreasing of the outer cross sectional dimension may suitably be in the order of about 20 to 50% or preferably about 30 to 40% at the distal end in relation to the dimension of the lead at a non-tapered section. Since the outer cross sectional dimension of a cardiac LV-lead normally is about 2 mm, the cross sectional dimension at the distal end will suitably be between about 1.0 to 1.6 mm or preferably between about 1.2 to 1.4 mm.
"The medical implantable lead may optionally be unipolar--i.e. comprising only one electrode, bipolar--i.e. comprising two electrodes, or be multipolar--i.e. comprising more than two electrodes. In addition, the conducting arrangement may comprise one or more coils. The number of separate electrically conducting wires in the one or more coils has to be at least as many as the number of electrodes. In hereinafter described and illustrated embodiments of the invention are a bipolar and quadrupolar (having four electrodes) leads disclosed. For a bipolar lead, both of the electrically conducting wires can be provided in one and the same coil, i.e. be coradially arranged in relation to each other, or be provided in two separate coaxially arranged coils. In the latter case the outer cross sectional dimension of the lead will probably be somewhat larger than in the former case. Also, for a quadrupolar lead it could be conceivable to provide all four electrically conducting wires coradially in one common coil, but normally it is more convenient to provide the wires as two coradially arranged wires in two separate coaxially arranged coils, as is disclosed in a hereinafter described and illustrated embodiment. One reason for this is that the inductance of a coil will be higher the more close-coiled each wire is, i.e. the inductance will decrease if all four wires are coradially arranged side by side in the same coil. In case of two separate coils, these can be terminated at different positions along the lead. It is also possible to connect more than one of the electrodes by means of an end conductor formed of a non-coiled conductor or an eccentrically positioned small diameter coil, as is disclosed in embodiments described and illustrated hereinafter.
"The most distal electrode may optionally be positioned in the very distal end of the lead or be positioned a short distance from the distal end as an annular electrode. The second electrode from the distal end, if any, can be positioned at an arbitrary distance from the distal end, preferably where it gives the lead the best performance with regard to the type of lead and the particular application. However, it may be advantageous to terminate the coil at the same region where the second electrode is positioned, e.g. inside the second electrode. In such a case it is easy to connect the second electrode directly to one of the wires in the coil. However, it is to be understood that also the second electrode can be connected to the coil via an end conductor in form of a non-coiled electric conductor, such as a cable, a bare wire or a strip, or an electrically conducting layer on the inside of the tubing, or in form of an eccentrically positioned small diameter coil, similar to the most distal electrode.
"The embodiments described and illustrated hereinafter, comprise also an inner tubing. It should be understood however that this tubing could be dispensed with, especially in case the lead is MRI-compatible and the individual wires of the coil are electrically insulated.
BRIEF DESCRIPTION OF THE DRAWINGS
"The invention will hereinafter be described with reference to exemplary embodiments of the invention as illustrated in the attached drawings, in which:
"FIG. 1 is a partly cut through perspective view of a heart to which an LV-lead is attached by insertion of its distal portion into a coronary vein outside the left ventricle;
"FIG. 2 is a cut through perspective view of a distal portion of a first embodiment of an LV-lead according to the invention;
"FIG. 3 is a longitudinal section through the lead according to FIG. 2;
"FIG. 4 is a side view of the lead according to FIGS. 2 and 3 in a straightened implantation stage having a stylet or guidewire inserted through its inner lumen;
"FIGS. 5-7 are longitudinal sections through a distal portion of different embodiments of quadrupolar leads according to the invention; and
"FIG. 8 is an enlarged longitudinal section through a distal portion of a lead having an end conductor in form of an eccentrically positioned small diameter coil."
URL and more information on this patent application, see: Bjorling, Anders; Sparf, Caroline. Medical Implantable Lead. Filed
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