Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a transvenously implantable electrode
for a cardiac pacemaker, the end of this electrode on the heart side being
spiral-shaped for its fixation, which is achieved by screwing this spiral
end into the heart muscle by means of a rotational motion applied to the
other end.
Pacemaker electrodes represent the electrical link between the
pulse generator and the heart tissue which is to be excited. Two methods
are known for the long-lasting implantation of such electrodes: (W. Hager,
A. Seling, Praxis der Schrittmachertherapie; F.K. Schattauer Verlag 1974 -
Practice of pacemaker therapy; F.K. Schattauer publishers, 1974~.
1. Following thoracotomy and pericardiotomy, the electrode is sewed ~
onto the myocardium tissue, or else screwed from outside into this tissue -
with the help of a special device. This technique requires relatively
; important surgery, with the corresponding risks, so that it is not always
applied, particularly in the case of elderly patients.
2. With the transvenous implantation method, which can also be made
under local narcosis, the electrode is pushed into the heart through a vein.
Difflculties arise with this method from the tendency to a dislodging of
non-fixable electrode heads as a result of heart movements and blood flow.
More particularly, when the electrode is to be fixed in the atrium, this
being often desirable from the medical point of view, the risk of dislodging
~ls high, because of the smoothness of the vestibule muscles.
On account of this, it has been proposed to use other types of
electrodes which are designed so as to be firmly anchored in the heart by
;~ means of ~echanlcal fixation devlces in the form of metal or plastic hooks. :
With one of these systems, the electrode carries on its end a wire ~:
countsr-hook; this requires the electrode to be pushed through a voluminous
guide tube. The selection of the stlmulating location in the heart is
rendered much more difficult by the stiffness of the guide tube; similarly,
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pulling back the electrode is possible only with the help of the guide tube,
because the wire hook is protruding.
With other hook systems, use is made of the pressure of a guiding
wire (mandrel) placed inside the electrode, to drive and to push into the
heart tissue a hook device which must be retracted during the introduction
phase. Various embodiments of this system are using either nylon brushes or
small steel hooks, but these have no real "counter-hook" effect. A secure
firm hooking is achievable with all these systems only when the electrode
head lies perpendicular to the tissue. If electrodes of this type come to
rest at an acute angle, it can happen that only one of the hooks will grip9
and that the electrode will be dislodged by forces oriented in a correspond-
ing direction, such as may result from blood flow or heart motions.
When such electrodes have to be withdrawn from the heart, the hook
device must be pulled back with a nylon thread, according to one system, or
else, with another type of electrode, the electrodes are pulled back together
with the released hooks. It is therefore an objective for the electrode
according to the present invention to be easily implanted through a vein and
without requiring an auxiliary device. It should above all, to meet the
requirements of an optimal electrotherapy of the heart, provide for a reliable
fixation in the smooth wall of the vestibule. If the need should arise, dur-
ing the implantation, to place the electrode in a location other than the one
found at first, the electrode according to the invention should then be
~ released easily after its fixation, so as to be shifted to another location.
;~ According to the invention, there is provided a transvenously
~ implantable electrocLe for a cardiac pacemaker, comprising a helically-wound
; flexible conductor including a first portion which is closely wound and a -
loosely wound end portion which is adapted to be located inside the heart,
said conductor being contalned within a protective sheath having means adapted
to cooperate with said~helically-wound conductor upon rotation thereof to
cause said end portion to extend from said sheath.
; In this manner, operating like a flexible transmission shaft, the
inner member, preferably, of the coaxial-shaped electrode is twisted against
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the outer member.
Accordin~ to a preferred embodiment of the invention, the electrical
conductor is constituted by the closely wound conductor which is placed
inside an insulating flexible tube.
According to a further embodiment of the invention, an element lo-
cated in the electrode head operates for driving the helix part of the elec-
trode out of a protection sheath, or to retract it inside it, according to
the sense of rotation. Through a mechanical limitation of the rotation angle
and/or through markings identifiable by X-rays, which show clearly the posi-
tions of the protection sheath and of the helix, respectively to each other,
it is ensured that the helix is screwed into the tissue only to the provided
extent (about 2-4 mm).
The structure according to the invention has a number of important
advantages: the helical shape of the electrode tip provides for a reliable
fixation in the heart tissue; its removal is only possible by unscrewing it.
A repeated fixation attempt can be made immediately after unscrewing, without
- having to pull back the electrode from inside the heart. After fixation,
forces from practically any direction can apply to the electrode head, with-
out the electrode becoming dislodged.
The lnsertion of the electrodes, the diameter of which is not
different from that of non-fixable electrodes, requires no guide tube. The
fixation operation does not require a guide wire (mandrel) which would impair
the flexibility of the device; the angle at which the electrode should come
to rest against the tissue is to a large extent without any influence and :
there is no need to take care of securing an anchoring of small hooks on all
sides.
The invention will be further described while referring to the
appended drawings, Figures 1, 2 and 3, which are cross-sectional views of
preferred embodiments. ;
~ In all three Figures, the helix (3) is shown in its retracted
position. Figure 1 represents an axial cross-section of the electrode head,
with the helix (3) lying inside the protection tube (2). Pre~erably, an
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electrode of this type is designed in such manner that the inner conductor
(1) serving simultaneously as electrical conductor is formed of helically
~losely wound wire, and that at its end (3) inserted in the heart, it is
coiled loosely on about 10 mm length, that is with a longer winding pitch.
The external sheath of the electrode consists preferably of a flexible tube
(2) made of insulating material, inside which the inner conductor (1) can
be easily rotated. The insulating tube (2) serves simultaneously as an
electrode head and as a protective sheath for the loosely wound portion (3)
of the electrode, which must not cause any lesions during the introduction
phase through the veins and heart valves. Preferably, the forward end of the
helix (3) is ground so as to form a sharp point. The insulating tube com-
prises also, at the electrode head, the device (5) which causes the helix to
be driven axially when the internal conductor is rotated. This effect can
be achieved for instance, as shown in Figure 19 by forming this device (5)
as a cylinder of silicone rubber provided with grooves in which the wider
portlon of the helix (3) can easily rotate.
Figure 2 shows another embodiment of the electrode head, seen in ;
longitudinal cross-section. The conversion of the rotary motion into an axial
motion is obtained here by means of a plastic rod (6) which i9 helically
wound with the same pitch as the portion (3) of the coiled inner conductor.
This plastic rod (6) is inserted inside the insulating tube (2) to which
its ends are welded, forming small butts (8) which hold it in place and
prevent its sliding out.
.
A ring (4), preferably metallic, is attached to the end of tube t2)
by~means of a silicone sheath (7). This ring (shown only in ~igure 1) serves
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in both embodiments of Figure 1 and Figure 2, to ascertain by X-ray examin-
ation, how far the portion (3) of the inner conductor (1) has been screwed
beyond the protection sheath. The outer cover (7) serves further, in the
embodiment of Figure 2, to mask the butts (8) so as to prevent the formation
of a thrombosis.
Figure 3 shows a further preferred embodiment of the electrode
head, also in longitudinal cross-section. Here is again shown the inner
conductor (1) which simultaneously provides the electrical connection from
the pulse generator to the electrode head. The forward end of this conductor
is again wound with a long pitch, so as to allow it to be screwed into the
tissue. As an additional feature, the diameter of the helix ~3) can be
increased, as well as that of an external helix (9) at the distal end of the
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electrode. The axial motion is achieved by bringing the inner conductor (1)
in sliding contact over a certain length with an external conductor (9)
` which is similarly closely wound into an helix having a larger diameter than
conductor (1), so that a screwing effect is made possible. At the front end
~` of the electrode head, the external helix (9) terminates into a ring (10)
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~ which is not insulated by the silicone cover (2), so that the tissue may
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already be stimulated through this ring before the helix (3) is screwed
lnto the tissue.
In order to keep as small as possible, in each embodiment of the
invention, the area df conductive material contacting tissues, the invention
further provides covering with an insulating layer, preferably of silicone
rubber, those surfaces of the helically wound portion (3) of the electrode
head which are not needed for the electrical stimulation.
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