Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical energy applicator
Reexamination Certificate
1999-07-26
2001-02-13
Evanisko, George R. (Department: 3737)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical energy applicator
Reexamination Certificate
active
06188931
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a single lead adapted to be used with an implantable active device, such as a pacemaker, in dual pacing and/or sensing.
2. Description Of The Prior Art
Conventionally, dual chamber sensing/pacing has required one lead for the atrium and one lead for the ventricle, i.e. two leads have been implanted into the heart.
Different approaches has been made in order to make possible a good sensing signal from the atrium, which requires essentially a good contact between the sensing/pacing electrode and the inner wall of the atrial cavity. The atrial electrode has for instance been anchored in the atrium or be kept in close contact with the atrial wall mechanically by means applied on the outside of the body until the electrode has been fastened by ingrowth.
More recently, several approaches with single leads have been made.
In German Patentschrift 30 49 652, corresponding to PCT Application WO 80/02801 a bent lead is described which partly has the form of a spiral. The entire bent part has a form that is adapted to the inner cavity wall of the atrium. Apart from the bent part there is a second part which may have a dimension which is smaller than the dimension of the bent part. The shape of the bent part is such that a part thereof is kept in contact with the atrial wall. When the lead is in place it will be kept there until a layer of fibrin has covered the lead, which means that the lead actually will be fastened to the atrial wall.
Another solution is described in U.S. Pat. No. 4,154,247 in which the lead comprising a layer of a repeatable thermally-activated material, is heated before implantation and thereafter the lead is shaped into a non-linear configuration, reforming the lead into a linear configuration, inserting the lead to make electrical contact with the body organ and discontinuing the straightening of the pacer lead. Thus the lead is devised with more geometric variations at the atrial electrode. For example in one embodiment the electrode lead is laid in a circle to enable the atrial electrode to establish continuous contact with atrial tissue.
Yet another solution is described in the U.S. Pat. No. 5,476,499 where a single lead having an atrial electrode at a distal end for implantation in the atrium before the electrode lead is advanced deeper into the heart so a ventricular electrode in-line with and preceding the atrial electrode along the lead, is connectable in the ventricle of the heart. The ventricular electrode is affixed to the ventricular trabecular network. The part of the electrode distal to the ventricular electrode, i.e. the part between the ventricular electrode and the atrial electrode is made significantly thinner than the rest of the electrode lead. This lead has to pass through the tricuspid valve twice.
The greater part of the atrium inner wall from the vena cava superior and downwards does not exhibit any trabecular network which conventionally may be used for the fastening of the electrode or electrodes the wall is smooth.
SUMMARY OF THE INVENTION
An object of the invention is to achieve a lead which can easily be implanted in a heart and which simply and effectively ensures electrical contact between atrial tissue and the atrial electrode/-s.
The above object is achieved in accordance with the principles of the present invention in an implantable lead for an active implantable device, such as a pacemaker, the lead having a proximal end adapted for electrical and mechanical connection to the device and a distal end opposite the proximal end, with a ventricular electrode carried on the lead at the distal end and an atrial lead carried on the electrode between the proximal end of the lead and the ventricular electrode, wherein the distal portion of the lead has a first part with a first predetermined length between 9 and 13 cm and having a first stiffness, with a second part adjacent to the first part exhibiting a second predetermined length which exceeds 15 cm and having a second stiffness, the second stiffness of the second part: providing the overall lead with a stiffness so as to force the atrial electrode into contact with the atrial wall when implanted, and the second stiffness being greater then the first stiffness. The lead further has a transition point between the first and second parts, at a proximal end of the first part. The second part has a radius of curvature which exceeds 20 cm. Preferably the length of the second part is 25 cm and the radius of curvature of the second part is 25 cm.
In contrast to the previously described electrode leads of the ventricular tip and atrial electrode type the present invention takes the specific anatomy of the atrium into account for anchoring the atrial electrode in the atrial tissue.
It fixes the atrial electrode in a simple and secure manner such that the electrode will achieve efficient electrical contact with the atrial wall.
The atrium comprises a specific site on the lower atrial wall that is situated inferior to the exit of the coronary sinus. The inventors have found that this site may be used in the implantation of the atrial electrode. According to the invention, it has been shown that a lead, as defined above, which has a stiffer portion with a length of more than approximately 15 cm and which is situated proximal and adjacent to a part of the lead with a lesser stiffness and a length of approximately 9-13 cm at the distal end of the lead, when implanted in the heart will easily be placed in such a position that the transition point between the two parts with different stiffness will stay in the above defined site.
The less stiff, distal part of the lead should be very flexible with a length of approximately 9-13 cm in order to avoid mechanical forces on the atrial electrode(s) being transferred from the distal part, for instance caused by the movements of the heart. The stiffer proximal portion of the lead should be straight or at least have a radius of curvature exceeding 20 cm in the non-implanted and non-loaded condition of the lead. It should be noted that the minimum stiffness of the proximal part of the lead is stiff in an assymmetrical way, the minimum stiffness of the proximal part should exceed the stiffness of the proximal part. It is however preferred that the stiffness of the lead is symmetrical, i. e. that the lead has the same stiffness in all directions.
The portion of the lead in the subclavian vein, in vena cava superior and in the atrium above this defined site is thus according to the invention intentionally made stiff, and for this reason the ring electrode(s) will be forced in contact with atrial tissue during the ingrowth period. Direct contact will provide good pacing and sensing performance and is also necessary for the electrode ingrowth.
The implantation of the lead is conducted using a stylet and as a first measure the lead having the ventricular electrode at the distal end thereof is introduced and fastened at the appropriate place in the ventricle. The stylet is then retracted to a position proximal to the transition point. The lead will then move outwardly against the atrial wall since the stiff part, which is deflected by the veins and the atrium into a curve having a smaller radius of curvature than the radius of curvature in the non-implanted condition, will strive to resume its original, straighter shape because of its inherent greater stiffness. The transition point then can will then be placed in, or can easily be slid along the atrial wall into, the site above described as being located inferior to the coronary sinus.
To avoid long term irritation the inflexibility/stiffness of the proximal part of the lead is preferably made to decline in about a week when the ring is fixed. This can be attained by using an inner or outer polymer in the lead of the type which softens by time in the body due increased temperature or water content. Alternatively the lead be a standard lead covered with an additional layer of bioresorbable material initially stiffening the lead. When
Holmstrom Nils
Obel Martin
Evanisko George R.
Pacesetter AB
Schiff & Hardin & Waite
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