Embolic coil deployment system with improved embolic coil

A medical device for placing an embolic coil at a preselected location within a vessel comprising a positioning catheter having a distal tip for retaining the embolic coil which when pressurized with a fluid expands outwardly to release the coil at the preselected position and in which a plurality of turns at the proximal portion of the embolic coil are spot welded to adjacent turns to prevent this proximal portion of the coil from elongating or stretching while also providing a coil which is very flexible.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a medical device for placing an embolic 
coil at a preselected location within a vessel of the human body, and more 
particularly, relates to a catheter having a distal tip for retaining the 
embolic coil in order to transport the coil to a preselected position 
within the vessel and a control mechanism for releasing the embolic coil 
at the preselected position. 
2. Description of the Prior Art 
For many years flexible catheters have been used to place various devices 
within the vessels of the human body. Such devices include dilatation 
balloons, radiopaque fluids, liquid medications and various types of 
occlusion devices such as balloons and embolic coils. Examples of such 
catheter devices are disclosed in U.S. Pat. No. 5,108,407, entitled 
"Method And Apparatus For Placement Of An Embolic Coil"; U.S. Pat. No. 
5,122,136, entitled, "Endovascular Electrolytically Detachable Guidewire 
Tip For The Electroformation Of Thrombus In Arteries, Veins, Aneurysms, 
Vascular Malformations And Arteriovenous Fistulas." These patents disclose 
devices for delivering embolic coils to preselected position within vessel 
of the human body in order to treat aneurysms or alternatively to occlude 
the blood vessel at the particular location. 
Coils which are placed in vessels may take the form of helically wound 
coils, or alternatively, may be random wound coils, coils wound within 
other coils or many other such coil configurations. Examples of various 
coil configurations are disclosed in U.S. Pat. No. 5,334,210, entitled, 
"Vascular Occlusion Assembly"; U.S. Pat. No. 5,382,259, entitled, 
"Vasoocclusion Coil With Attached Tubular Woven Or Braided Fibrous 
Coverings." Embolic coils are generally formed of a radiopaque metallic 
materials, such as platinum, gold, tungsten or alloys of these metals. 
Often times several coils are placed at a given location in order to 
occlude the flow of blood through the vessel by promoting thrombus 
formation at the particular location. 
In the past, the proximal end of embolic coils have been placed within the 
distal end of the catheter and when the distal end of the catheter is 
properly positioned the coil may then be pushed out of the end of the 
catheter with, for example a guidewire, to release the coil at the desired 
location. This procedure of placement of the embolic coil is conducted 
under fluoroscopic visualization such that the movement of the coil 
through the vasculature of the body may be monitored and the coil may be 
placed in the desired location. With these placements systems there is 
very little control over the exact placement of the coil since the coil 
may be ejected to a position some distance beyond the end of the catheter. 
As is apparent, with these latter systems, when the coil has been released 
from the catheter it is difficult, if not impossible, to retrieve the coil 
or to reposition the coil. 
Numerous procedures have been developed to enable more accurate positioning 
of coils within a vessel. Still another such procedure involves the use of 
a glue or solder for attaching the embolic coil to a guidewire which, is 
in turn, placed within a flexible catheter for positioning the coil within 
the vessel at a preselected position. Once the coil is at the desired 
position, the coil is restrained by the catheter and the guidewire is 
pulled from the proximal end of the catheter to thereby cause the coil to 
be detached from the guidewire and released from the catheter system. Such 
a coil positioning system is disclosed in U.S. Pat. 5,263,964, entitled, 
"Coaxial Traction Detachment Apparatus And Method." 
Another coil positioning system utilizes a catheter having a socket at the 
distal end of the catheter for retaining a ball which is bonded to the 
proximal end of the coil. The ball, which is larger in diameter than the 
outside diameter of the coil, is placed in a socket within the lumen at 
the distal end of the catheter and the catheter is then moved into a 
vessel in order to place the coil at a desired position. Once the position 
is reached, a pusher wire with a piston at the end thereof is pushed 
distally from the proximal end of the catheter to thereby push the ball 
out of the socket in order to thereby release the coil at the desired 
position. Such a system is disclosed in U.S. Pat. No. 5,350,397, entitled, 
"Axially Detachable Embolic Coil Assembly." One problem with this type of 
coil placement system which utilizes a pusher wire which extends through 
the entire length of the catheter and which is sufficiently stiff to push 
an attachment ball out of engagement with the socket at the distal end of 
the catheter is that the pusher wire inherently causes the catheter to be 
too stiff with the result that it is very difficult to guide the catheter 
through the vasculature of the body. 
Another method for placing an embolic coil is that of utilizing a heat 
releasable adhesive bond for retaining the coil at the distal end of the 
catheter. One such system uses laser energy which is transmitted through a 
fiber optic cable in order to apply heat to the adhesive bond in order to 
release the coil from the end of the catheter. Such a method is disclosed 
in U.S. Pat. No. 5,108,407, entitled, "Method And Apparatus For Placement 
Of An Embolic Coil." Such a system also suffers from the problem of having 
a separate element which extends throughout the length of the catheter 
with the resulting stiffness of the catheter. 
Still another method for placing an embolic coil is disclosed in co-pending 
U.S. patent application Ser. No. 09/177,848, entitled "Embolic Coil 
Hydraulic Deployment System," filed on Oct. 21, 1998 and assigned to the 
same assignee as the present patent application. This patent application 
discloses the use of fluid pressure which is applied to the distal tip of 
the catheter for expanding the lumen in order to release the embolic coil. 
Various embolic coil designs have been proposed for use with coil 
deployment systems such as the stretch resistant vasoocclusive coil 
disclosed in U.S. Pat. No. 5,853,418, entitled "Stretch Resistant 
Vaso-occlusive Coils," which discloses a helically wound coil having a 
polymeric stretch resisting member extending through the lumen of the coil 
and fixedly attached to both the distal end and the proximal end of the 
coil. While the stretch resisting member prevents the coil from being 
stretched during use, this member which extends throughout the length of 
the coil tends to significantly reduce the flexibility of the coil. In 
order to place vaso-occlusive coils into a desired location it is very 
important that the coil be very flexible. 
SUMMARY OF THE INVENTION 
The present invention is directed toward a vascular occlusive coil 
deployment system for use in placing an embolic coil at a preselected site 
within a vessel which includes an elongated, flexible catheter having a 
distal tip for retaining the coil so that the coil may be moved to the 
preselected position within the vessel. The catheter has a lumen which 
extends therethrough the length of the catheter and also includes a distal 
end which is formed of a material having a durometer such that when a 
fluid pressure of about 90 to 450 pounds per square inch (psi) is applied 
to the interior of the catheter, the walls of the distal tip expand 
outwardly, or radially, to thereby increase the lumen of the distal tip of 
the catheter. The proximal end of the embolic coil is placed into the 
lumen of the distal tip of the catheter and is retained by the distal tip 
of the catheter. A hydraulic injector, such as a syringe, is coupled to 
the proximal end of the catheter for applying a fluid pressure to the 
interior of the catheter. When the coil is placed at a desired position 
within a vessel, fluid pressure is then applied to the interior of the 
catheter by the hydraulic injector to thereby cause the walls of the 
distal tip to expand outwardly to thereby release the coil for placement 
in the vessel. 
In order to prevent the proximal portion of the coil which is held by the 
distal tip of the coil deployment system from stretching and unwinding 
which could cause the premature release of the coil, the proximal portion 
of the coil is modified in a manner "lock" adjacent coils together to 
thereby prevent elongation of the proximal portion of the coil. Such 
elongation will result in the stretching or unwinding of the coil thereby 
reducing the outside diameter of the coil with the result that the coil 
could be prematurely released from the distal tip of the deployment 
system. 
Accordingly, the embolic coil takes the form of a tightly wound helical 
coil having a distal end, a proximal end and a lumen extending 
therethrough also includes a seal plug disposed in fluid tight engagement 
within the coil lumen at the proximal end of the coil. At the proximal 
portion of the coil several turns of the coil are spot welded to adjacent 
turns to thereby prevent elongation of this proximal portion of the coil. 
In accordance with another aspect of the present invention, the series of 
spot welded points between adjacent coils forms a straight line which is 
parallel to the longitudinal axis of the coil. 
In accordance with another aspect of the present invention, the series of 
spot welded points form two straight lines both of which are parallel to 
the longitudinal axis of the coil. 
In accordance with still another aspect of the present invention, the 
series of spot welded points form a helical path with respect to the 
longitudinal axis of the coil. 
In still another aspect of the present invention, the proximal portion of 
the coil having turns of the coil spot welded to adjacent turns is of a 
length in a range of about 0.5 to 4 millimeters and the entire length of 
the coil is in a range of about 1.5 to 30 centimeters. Preferably, the 
length of the proximal portion of the coil having turns which are spot 
welded to adjacent turns is of a length of about 2.5 millimeters or about 
1 percent of the length of the coil. 
In accordance with another aspect of the present invention, the flexible 
catheter is comprised of a proximal section and a relatively short distal 
section. The proximal section is formed of a material which is 
sufficiently flexible to be passed through the vasculature of the human 
body and is of a durometer which essentially resists outward expansion 
when a fluid pressure on the order of about 90 to 450 psi is applied to 
the interior of the catheter. The distal section of the catheter is formed 
of a material which is also sufficiently flexible to be passed through the 
vasculature of the body, yet is of a durometer which is significantly 
lower than the durometer of the proximal section and exhibits the property 
of expanding outwardly, or radially, when such a fluid pressure is applied 
to the interior of the catheter to thereby permit the release of the 
embolic coil. 
In accordance with still another aspect of the present invention, the 
distal section of the catheter has a durometer in a range of between about 
25D and 55D. 
In still another aspect of the present invention, the embolic coil is 
comprised of a helical coil having a proximal end, a distal end, and a 
lumen extending therethrough. A seal plug is disposed within the lumen of 
the proximal end of the coil in fluid-tight engagement. The proximal end 
of the coil is disposed in a fluid-tight engagement within the lumen of 
the distal section of the catheter and is retained by the lumen of the 
catheter for subsequent release. 
In another aspect of the present invention, the hydraulic injector for 
applying a fluid pressure to the interior of the catheter takes the form 
of a syringe which is coupled to the proximal end of the catheter for, 
upon movement of the piston, creating a fluid pressure which is applied to 
the interior of the catheter to thereby cause the release of the embolic 
coil. 
In accordance with another aspect of the present invention, the embolic 
coil may take the form of other types of implantable devices, such as a 
vascular filter. 
In another aspect of the present invention, there is provided a method for 
placing an embolic coil with a selected site within a vessel of the body 
comprising the steps of advancing a catheter through the vasculature of 
the body to place an embolic coil which is retained within the lumen of 
the distal tip of the catheter to a preselected site, applying a fluid 
pressure to the interior of the catheter to thereby cause the distal tip 
of the catheter to expand radially outwardly to release the embolic coil 
at the preselected site, and withdrawing the catheter from the vasculature 
system. 
These aspects of the invention and the advantages thereof will be more 
clearly understood from the following description and drawings of a 
preferred embodiment of the present invention:

DESCRIPTION OF A PREFERRED EMBODIMENT 
FIG. 1 generally illustrates the vascular occlusive coil deployment system 
100 which is comprised of a hydraulic injector or syringe 102, coupled to 
the proximal end of a catheter 104. An embolic coil 106 is disposed within 
the lumen of the distal end 108 of the catheter. The proximal end of the 
coil 106 is tightly held within the lumen of the distal section 108 of the 
catheter 104 until the deployment system is activated for release of the 
coil. As may be seen, the syringe 102 includes a threaded piston 110 which 
is controlled by a handle 112 for infusing fluid into the interior of the 
catheter 104. Also as illustrated, the catheter 104 includes a winged hub 
114 which aids in the insertion of the catheter into the vascular system 
of the body. 
FIG. 2 illustrates in more detail the distal end of the catheter 104. The 
catheter 104 includes a proximal section 116 and the distal section 108. 
The proximal section 118 of the embolic coil 106 is disposed within the 
distal section 108 of the catheter and is tightly held within the lumen 
120 of this distal section 108 prior to release of the coil. As may be 
appreciated, FIG. 2 illustrates the vascular occlusive coil deployment 
system prior to activation of the piston of the syringe and prior to 
release of the coil. 
The embolic coil 106 may take various forms and configurations and may even 
take the form of a randomly wound coil, however, with the helical wound 
coil as illustrated in FIG. 2, the coil is provided with a weld bead or 
seal plug 122 which is disposed in a lumen 123 which lumen extends 
throughout the length of the coil 106. The seal plug 122 serves to prevent 
the flow of fluid through the lumen of the coil 106 so that when the coil 
106 is placed in fluid-tight engagement with the lumen 120 the coil serves 
to provide a fluid-tight seal at the distal end of the catheter 104. 
Adjacent turns of the coil 106 at the proximal end 118 of the coil are 
preferably continuously welded together so that the welded turns of the 
coil in conjunction with the plug seal 122 provide a generally unitary 
structure with the coil being very flexible with the proximal end of the 
coil being stretch resistant. The plug seal 122 serves to plug or seal the 
distal end of the catheter in a fluid tight relationship. 
Preferably, the proximal section 116 and the distal section 108 of the 
catheter 104 are formed of materials having different durometers. The 
proximal section 116 is preferably formed of Pebax material having a 
durometer in a range of about 62D to 75D. The proximal section is 
sufficiently flexible to transverse the vasculature of the human body, but 
is sufficiently rigid such that when a fluid pressure of approximately 90 
to 450 psi is applied to the interior of this section of the catheter 
there is very little, if any, radial expansion of the walls of this 
section. On the other hand, the distal section 108 of the catheter is 
preferably formed of polymer material with a relatively low durometer 
which, exhibits the characteristic that when a fluid pressure of 
approximately 90 to 450 psi is applied to the interior of the catheter the 
walls of the distal section 108 expand radially, somewhat similar to the 
action of a balloon inflating, to thereby release the proximal end 118 of 
the coil 106. As may be appreciated, there are numerous materials which 
could be used to fabricate the proximal section 116 and distal section 108 
of the catheter 104, however, the distal section 108 is preferably formed 
from a block copolymer such as Pebax having a durometer of between 25D and 
55D with a durometer of 40D being the preferred durometer. 
FIGS. 3 and 4 generally illustrate the coil release mechanism in action for 
the vascular occlusive catheter deployment system. More particularly, as 
shown in FIG. 3, when a hydraulic pressure is applied to the interior 124 
of the catheter 104 the relatively low durometer distal section 108 of the 
catheter begins to expand radially, much as a balloon expands during the 
process of inflation. As the distal section 108 continues to expand 
radially there comes a point as illustrated in FIG. 4 in which the coil 
106 becomes disengaged from the lumen of the distal section 108 and the 
coil is then released from the catheter and is deployed at that location 
within the vessel. 
As illustrated in FIG. 5, when the coil 106 has been released from the 
catheter 104 the catheter may then be withdrawn leaving the coil 
positioned at the desired site. 
As illustrated in FIG. 5 and 6, the vaso-occlusion or embolic coil 106 is 
formed by winding a platinum alloy wire into a tightly wound helical 
configuration. The diameter of the wire is generally in the range of about 
0.0015 to 0.008 inches. The outside diameter of the coil 106 is preferably 
in the range of about 0.006 to 0.055 inches. While the particular embolic 
coil 106 illustrated in FIG. 6 and 7 is shown as being a straight coil it 
should be appreciated that embolic coils take the form of various 
configurations and may for example, take the form of a helix, a random 
shape configuration or even a coil within a coil configuration. 
With the embodiment of the coil deployment system disclosed in this 
application it may be noted that the proximal end of the embolic coil is 
retained or held by the distal tip of the coil deployment system as the 
coil is moved into a target position. Often times it is necessary to move 
the coil to a certain position within the vasculature and then to withdraw 
the coil back to a more proximal position within the vasculature. During 
the movement of the coil through the vasculature, particularly when the 
coil is withdrawn, it is possible to stretch or unwind the turns of the 
coil. If the turns of the coil which are held or restrained by the distal 
tip of the deployment catheter or stretched or unwound the result is that 
the outside diameter of the coil in this area decreases. With a decrease 
in the outside diameter of the coil in the proximal portion of the coil it 
is possible for the coil to be prematurely released from the deployment 
system. 
In order to prevent such premature release caused by the stretching or 
unwinding of the proximal portion of the coil, adjacent turns of the 
proximal portion of the coil are spot welded together in order to prevent 
separation of these turns with the result in stretching of the coil. The 
length of the embolic coil is about 1.5 to about 30 centimeters and the 
length of the proximal portion of the coil having adjacent coils spot 
welded is preferably in a range of about 0.5 to 4 millimeters. In a 
preferred embodiment, the length of the proximal portion of the coil 
having adjacent turns welded together is about 2.5 millimeters. 
Preferably the line of points formed by spot welding of adjacent coils 
forms a single line which extends generally parallel to the longitudinal 
axis of the coil, but the weld points may extend along two parallel lines 
which extend generally parallel to the longitudinal axis of the embolic 
coil as illustrated in FIG. 5. Alternatively, the spot welding points may 
be arranged to form a generally helical configuration on the outside 
surface of the coil with respect to the longitudinal axis of the coil as 
illustrated in FIG. 6. 
A liquid silicon material (not shown) may be injected to fill the lumen of 
the proximal portion of the coil. The silicone material is then allowed to 
cure in order to further seal the proximal end of the coil to prevent 
fluid leakage through the turns of the coil. Also, as may be appreciated, 
instead of spot welding adjacent turns of the coil, the adjacent turns may 
be bonded by various other means such as, for example, by glueing or being 
attached by wrapping with thread. 
With the coil design of the present invention the embolic coil is prevented 
from stretching over the proximal portion of the coil, however, the coil 
remains very flexible as is required for proper placement of an embolic 
coil. 
With the vascular occlusive coil deployment system of the present invention 
it is possible to place an embolic coil very precisely at a desired 
location within a vessel. Once the coil has been placed in that location 
by use of the catheter, the catheter may be activated by applying a 
hydraulic pressure to the interior of the catheter to thereby cause the 
catheter to release the coil and deposit the coil very accurately at the 
desired location. 
As is apparent, there are numerous modifications of the preferred 
embodiment described above which will be readily apparent to one skilled 
in the art, such as many variations and modifications of the coil 
including numerous coil winding configurations, or alternatively other 
types of implant devices, such as a vascular filter. Also, there are 
obviously variations of the syringe arrangement for applying a fluid 
pressure to the interior of the catheter, including many other fluid 
pressure generating systems for increasing the pressure within the 
interior of a catheter in order to cause the distal section of the 
catheter to expand. These modifications would be apparent to those having 
ordinary skill in the art to which this invention relates and are intended 
to be within the scope of the claims which follow.