U.S. patent application number 10/124530 was filed with the patent office on 2002-12-12 for implantable medical lead having a retraction stop mechanism.
Invention is credited to Bischoff, Thomas C., Helmick, Marc R..
Application Number | 20020188340 10/124530 |
Document ID | / |
Family ID | 23090193 |
Filed Date | 2002-12-12 |
United States Patent
Application |
20020188340 |
Kind Code |
A1 |
Bischoff, Thomas C. ; et
al. |
December 12, 2002 |
Implantable medical lead having a retraction stop mechanism
Abstract
A medical lead having a rotatable helical tip electrode helix
and a retraction stop mechanism for preventing over-retraction of
the helical tip electrode during lead repositioning. The retraction
stop mechanism includes an engaging member positioned along a drive
shaft of the lead and having a front surface, a flange portion
extending along the front surface of the engaging member, and a
retraction flange. Rotation of the drive shaft causes the flange
portion to engage the retraction flange so that rotation of the
drive shaft is absorbed by the conductor.
Inventors: |
Bischoff, Thomas C.;
(Minneapolis, MN) ; Helmick, Marc R.; (Newton,
MA) |
Correspondence
Address: |
MEDTRONIC, INC.
710 MEDTRONIC PARKWAY NE
MS-LC340
MINNEAPOLIS
MN
55432-5604
US
|
Family ID: |
23090193 |
Appl. No.: |
10/124530 |
Filed: |
April 17, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60284430 |
Apr 17, 2001 |
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Current U.S.
Class: |
607/127 |
Current CPC
Class: |
Y10T 29/49227 20150115;
A61N 1/0573 20130101; A61N 1/056 20130101 |
Class at
Publication: |
607/127 |
International
Class: |
A61N 001/05 |
Claims
What is claimed is:
1. A retraction stop mechanism of a medical electrical lead, the
medical electrical lead having an electrode electrically coupled to
a conductor by a drive shaft, the retraction stop mechanism
comprising: an engaging member positioned along the drive shaft and
having a front surface; a flange portion extending along the front
surface of the engaging member; and a retraction flange, wherein
rotation of the drive shaft causes the flange portion to engage the
retraction flange so that rotation of the drive shaft is absorbed
by the conductor.
2. The retraction stop mechanism of claim 1, wherein the drive
shaft and the engaging member are machined as a single
component.
3. The retraction stop mechanism of claim 1, wherein the lead
includes an electrode head assembly housing the engaging member and
the retraction flange, and the retraction flange and the electrode
head assembly are formed as a single molded component.
4. The retraction stop mechanism of claim 1, wherein the drive
shaft of the medical electrical lead includes a distal stem
coupling the drive shaft to the electrode, and wherein the
retraction stop mechanism is positioned proximal to the stem to
enable inspection of the coupling.
Description
REFERENCE TO PRIORITY APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/284,430, entitled "MEDICAL ELECTRICAL
LEAD", incorporated herein by reference in its entirety.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0002] Cross-reference is hereby made to commonly assigned related
U.S. Applications, filed concurrently herewith, docket number
P-10009, entitled "INSULATING MEMBER FOR A MEDICAL ELECTRICAL LEAD
AND METHOD FOR ASSEMBLY"; P-10010, entitled "DRIVE SHAFT SEAL FOR A
MEDICAL ELECTRICAL LEAD"; P-10013, entitled "APPARATUS FOR
TRANSFERRING TRACTION FORCES EXERTED ON AN IMPLANTABLE MEDICAL
LEAD"; and P-10051, entitled "MEDICAL ELECTRICAL LEAD".
FIELD OF THE INVENTION
[0003] The present invention relates generally to a medical
electrical lead and, more particularly, the present invention
relates to a retraction stop mechanism of a medical electrical lead
for preventing over-retraction of a rotatable helical tip
electrode.
BACKGROUND OF THE INVENTION
[0004] A wide assortment of implantable medical devices (IMDs) are
presently known and in commercial use. Such devices include cardiac
pacemakers, cardiac defibrillators, cardioverters,
neurostimulators, and other devices for delivering electrical
signals to a portion of the body and/or receiving signals from the
body. Pacemakers, for example, are designed to operate so as to
deliver appropriately timed electrical stimulation signals when
needed, in order to cause the myocardium to con-tract or beat, and
to sense naturally occurring conduction signals in the patient's
heart.
[0005] Devices such as pacemakers, whether implantable or temporary
external type devices, are part of a system for interacting with
the patient. In addition to the pacemaker device, which typically
has some form of pulse generator, a pacing system includes one or
more leads for delivering generated signals to the heart and for
sensing cardiac signals and delivering those sensed signals from
the heart back to the pacemaker. As is known, pacemakers can
operate in either a unipolar or bipolar mode, and can pace the
atria or the ventricles. Unipolar pacing requires a lead having
only one distal electrode for positioning in the heart, and
utilizes the case, or housing of the implanted device as the other
electrode for the pacing and sensing operations. For bipolar pacing
and sensing, the lead typically has two electrodes, one disposed
substantially at the distal tip end of the lead, and the other
spaced somewhat back from the distal end. Each electrode is
electrically coupled to a conductive cable or coil, which carries
the stimulating current or sensed cardiac signals between the
electrodes and the implanted device via a connector.
[0006] Combination devices are available for treating cardiac
arrhythmias that are capable of delivering electrical shock therapy
for cardioverting or defibrillating the heart in addition to
cardiac pacing. Such a device, commonly known as an implantable
cardioverter defibrillator or "ICD", uses coil electrodes for
delivering high-voltage shock therapies. An implantable cardiac
lead used in combination with an ICD may be a quadrapolar lead
equipped with a tip electrode, a ring electrode, and two coil
electrodes. A quadrapolar lead requires four conductors extending
the length of the lead body in order to provide electrical
connection to each electrode.
[0007] In order to perform reliably, cardiac pacing leads need to
be positioned and secured at a targeted cardiac tissue site in a
stable manner. One common mechanism for securing an electrode
position is the use of a rotatable fixation helix. The helix exits
the distal end of the lead and can be screwed into the body tissue.
The helix itself may serve as an electrode or it may serve
exclusively as an anchoring mechanism to locate an electrode
mounted on the lead adjacent to a targeted tissue site. The
fixation helix may be coupled to a drive shaft that is further
connected to a coiled conductor that extends through the lead body
as generally described in U.S. Pat. No. 4,106,512 to Bisping et al.
A physician rotates the coiled conductor at a proximal end to cause
rotation of the fixation helix via the drive shaft. As the helix is
rotated in one direction, the helix is secured in the cardiac
tissue. Rotation in the opposite direction removes the helix from
the tissue to allow for repositioning of the lead at another
location.
[0008] One problem that can arise with the use of such a lead is
over-retraction of the helix during lead repositioning.
Repositioning of the lead may be required during an implant
procedure if poor electrical contact is made with the targeted
cardiac tissue, resulting in higher than desired stimulation
thresholds or poor sensing. The physician must retract the helix by
applying turns to the coiled conductor in the appropriate
direction. The physician may not have tactile feedback or
fluoroscopic image indicating when the helix has dislodged from the
heart tissue and is fully retracted. In many cases, the physician
will perform additional turns of the coiled conductor in order to
ensure the helix is safely removed from the heart tissue before
applying tension to the lead to relocate it. Excessive turns,
however, can cause deformation of the fixation helix rendering it
unusable. In such cases, the lead must then be removed and replaced
by a new lead.
[0009] To address the problem of over-retraction, a retraction stop
mechanism may be provided within the distal lead head. An exemplary
retraction stop mechanism that includes a fixed stop formed of a
plurality of fixed cam and axial stop surfaces and a movable stop
formed of a like plurality of rotatable cam and axial stop surfaces
is disclosed in U.S. Pat. No. 5,837,006 to Ocel et al.. This stop
effectively prevents over-retraction.
[0010] However, many considerations are taken into account when
optimizing the design of a lead. For example, minimizing lead size
is important since a smaller device is more readily implanted
within the cardiac structures or coronary vessels of a patient.
Moreover, providing features that make a lead easier to implant and
extract allows the clinician to complete the associated surgical
procedure more safely and in less time. Finally, an optimized lead
design requires a minimum number of parts that may be assembled
using techniques that are relatively simple and low cost. It is
therefore desirable to provide a medical lead having a retraction
stop mechanism that requires a minimal amount of space, can be
constructed from a minimal number of parts, and is easily
manufactured and verified.
SUMMARY OF THE INVENTION
[0011] The present invention is directed to a medical lead having a
helical tip electrode mounted on a drive shaft. The helical tip
electrode and drive shaft are housed within an electrode head
assembly at the distal end of the lead. The electrode head assembly
is bonded to a lead body having at least a center lumen for
carrying a coiled conductor that is coupled at its distal end to
the drive shaft and at its proximal end to a connector pin.
Applying turns to the connector pin effectively turns the coiled
conductor resulting in rotation of the drive shaft and advancement
or retraction of the helical tip electrode. When enough turns are
applied in the appropriate direction to cause full retraction of
the helical tip electrode, a movable flange portion located on the
drive shaft engages a fixed retraction flange located on the
electrode head assembly so that rotation of the drive shaft is
absorbed by a conductor of the lead.
[0012] The movable flange portion is provided as an extension in
the proximal direction from a cylindrical body formed near the
distal end of the drive shaft. The geometry of the movable flange
portion allows it to be incorporated in a one-piece, machined drive
shaft eliminating the need for additional parts, welds, or weld
inspections. The fixed retraction flange is provided as a
protrusion from the distal end of the electrode head assembly. The
fixed retraction flange may be incorporated in a one-piece, molded
proximal electrode head assembly, eliminating the need for
additional parts or bonding processes.
[0013] The present invention thus provides an effective retraction
stop mechanism comprising two components that require a minimal
amount of space within the distal end of the lead. By minimizing
the size of the retraction stop mechanism, over all lead size may
be reduced. Furthermore, the two component retraction stop
mechanism included in the present invention does not require
additional bonding or welding procedures, resulting in a lead
manufacturing process that is easily accomplished at a low
cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a plan view of an implantable cardiac lead that
may be utilized in accordance with the present invention;
[0015] FIG. 2 is a cross-sectional view of a multi-lumen lead body
of the lead shown in FIG. 1;
[0016] FIG. 3 is a side cut away view of a distal end of the lead
shown in FIG. 1;
[0017] FIG. 4 is a perspective view of a retraction stop mechanism
of an implantable cardiac lead according to the present
invention;
[0018] FIG. 4A is a planar view of a front surface of the
retraction stop mechanism of FIG. 4; and
[0019] FIG. 5 is an enlarged, perspective, partially cut-away view
of the retraction stop mechanism of FIG. 4.
DETAILED DESCRIPTION OF THE INVENTION
[0020] FIG. 1 is a plan view of an implantable cardiac lead that
may be utilized in accordance with the present invention, embodied
as a transvenous cardiac defibrillation lead. As illustrated in
FIG. 1, a lead 10 according to the present invention includes an
elongated lead body 12 having a connector assembly 16 at a proximal
end of the lead 10 for connecting to an implantable device, and an
electrode head assembly 14 at a distal end of the lead 10 for
carrying one or more electrodes. Lead 10 is shown as a quadrapolar
lead including a helical tip electrode 30, a ring electrode 50, a
right ventricular (RV) defibrillation coil 38 and a superior vena
cava (SVC) defibrillation coil 40. The helical tip electrode 30 and
ring electrode 50 may be utilized to sense cardiac signals and/or
deliver pacing pulses to a patient. One of the defibrillation coils
38 and 40 serves as the cathode while the other serves as the anode
during delivery of a defibrillation shock to a patient as a result
of a detected tachycardia or fibrillation condition.
[0021] The lead body 12 takes the form of an extruded tube of
biocompatible plastic such as silicone rubber. Multiple lumens
located within lead body 12 carry four insulated conductors from
the connector assembly 16 to the corresponding electrodes 30, 50,
38 and 40 located at or near the distal end of the lead 10. The
multi-lumen lead body 12 may correspond generally to that disclosed
in U. S. Pat. No. 5,584,873 issued to Shoberg et al. Three of the
insulated conductors carried by lead body 12 are preferably
stranded or cabled conductors, each electrically coupled to one of
the ring electrode 50, the RV coil 38 and the SVC coil 40. The
cabled conductors may correspond generally to the conductors
disclosed in U.S. Pat. No. 5,246,014, issued to Williams et al.,
incorporated herein by reference in its entirety. A fourth, coiled
conductor extends the length of the lead body 12 and is coupled to
the helical tip electrode 30.
[0022] In this embodiment, the helical tip electrode 30 functions
as an electrode for cardiac pacing and/or sensing and as an active
fixation device for anchoring the lead 10 in a desired position. In
other embodiments that may employ the present invention, a helical
tip may function only as an active fixation device. Reference is
made to U.S. Pat. No. 4,217,913 to Dutcher, incorporated herein by
reference in its entirety. Therefore, the helical tip electrode 30
may also be referred to herein as a "fixation helix".
[0023] The connector assembly 16 has multiple connector extensions
18, 20, and 22 arising from a trifurcated connector sleeve,
typically formed of silicone rubber. The connector extensions 18,
20, and 22 couple the lead 10 to an implantable medical device such
as an implantable cardioverter defibrillator (ICD).
[0024] Connector extension 20 is shown as a bi-polar connector
including a connector ring 24 and a connector pin 25. Connector
extension 20 houses the cabled conductor that is electrically
coupled to the connector ring 24 at its proximal end and to the
ring electrode 50 at its distal end. The connector extension 20
also houses the coiled conductor that is electrically coupled to
the connector pin 25 and extends to the tip electrode 30. During a
lead implant or explant procedure, rotation of the connector pin 25
relative to the connector assembly 16 causes corresponding rotation
of the coiled conductor and advancement or retraction of the
helical tip electrode 30 in the fashion generally described in U.S.
Pat. No. 4,106,512 to Bisping et al., incorporated herein by
reference in its entirety. By advancing the helical tip electrode
30, the electrode 30 can be actively fixed in cardiac tissue. A
stylet 32 may be advanced within an inner lumen of the coiled
conductor to the distal end of the lead 10 to aid in lead placement
during an implant procedure.
[0025] The connector extension 18 carries a single connector pin 52
that is electrically coupled to an insulated cable extending the
length of the lead body 12 and electrically coupled to the RV coil
38. The connector extension 22 carries a connector pin 42 that is
electrically coupled to a respective insulated cable that is
further coupled to the SVC coil 40.
[0026] FIG. 2 is a cross-sectional view of a multi-lumen lead body
of the lead of FIG. 1. As illustrated in FIG. 2, the lead body 12
is provided with four lumens 102, 122,124, and 126. Lumen 102
carries the coiled conductor 26 that is coupled to the helical tip
electrode 30. In accordance with the present invention, the
conductor 26 is shown surrounded by an insulation tubing 120. A
stylet 32 may be advanced within the lumen 34 of the coiled
conductor 26. Lumen 122 carries an insulated cable 110 that is
electrically coupled at a proximal end to the connector ring 24 and
at a distal end to the ring electrode 50. Lumen 124 carries an
insulated cable 112 that is electrically coupled at a proximal end
to the connector pin 52 and at a distal end to the RV coil 38.
Lumen 126 carries an insulated cable 114 that is electrically
coupled at a proximal end to the connector pin 42 and at a distal
end to the SVC coil 40.
[0027] FIG. 3 is a side cutaway view of the distal end of the lead
10 showing a detailed view of the electrode head assembly 14 and
the electrodes 30, 50 and 38. The molded, tubular electrode head
assembly 14 includes two members, a distal electrode head assembly
113 and a proximal electrode head assembly 111. The distal and
proximal electrode head assemblies 113 and 111 are preferably
formed from a relatively rigid biocompatible plastic. For example,
assemblies 113 and 111 may be fabricated from molded polyurethane.
The proximal electrode head assembly 111 is coupled to the
multi-lumen lead body 12, typically formed from a relatively more
compliant plastic such as silicone rubber, at a joint 140. The
lumen 104 within the proximal electrode head assembly 111
communicates with the lumen 102 within the lead body 12 for
carrying the coiled conductor 26 extending between the tip
electrode and the connector ring 24. In FIG. 3, the ring electrode
50 is shown coupled to the cable 110, and the RV coil 38 is shown
positioned on the outer diameter of the proximal electrode head
assembly 111 and the lead body 12.
[0028] FIG. 3 further shows the helical tip electrode 30
electrically coupled to the coiled conductor 26 via a drive shaft
100. The electrode 30 and drive shaft 100 are preferably fabricated
of a biocompatible metal such as platinum iridium alloy. The coiled
conductor 26 extends to the proximal connector assembly 16.
Rotation of the connector pin 25 at the proximal end of coiled
conductor 26 causes corresponding rotation of the distal end of the
coiled conductor 26 to, in turn, cause rotation of the drive shaft
100. This rotation results in extension or retraction of helical
tip electrode 30. A guide 28 actuates the helical tip electrode 30
as the helical tip electrode 30 is advanced or retracted. The lead
10 may include a drive shaft seal 109 encircling the drive shaft
100. The drive shaft seal 109, which may be formed of silicone or
any other elastomer, is housed within the electrode head assembly
14.
[0029] FIG. 4 is a perspective view of a retraction stop mechanism
of an implantable cardiac lead according to the present invention.
FIG. 4A is a planar view of a front surface of the retraction stop
mechanism of FIG. 4. As illustrated in FIG. 4, the drive shaft 100
includes a distal stem 44 for coupling to the helical tip electrode
30. A proximal stem 46 is provided for coupling to the coiled
conductor 26. As illustrated in FIGS. 4 and 4A, an axial stop
surface, or flange portion 240 extends in a proximal direction from
a front surface 107 of a movable stop, or engaging member 106, that
is formed as a cylindrical body near the distal end of the drive
shaft 100. The drive shaft 100 and engaging member 106 with the
flange portion 240 may be machined as one component, eliminating
additional parts, welding processes or weld inspections needed for
providing a movable retraction stop.
[0030] As illustrated in FIGS. 3 and 4, the distal end of the
proximal electrode head assembly 111 includes a fixed retraction
flange 242 that includes an axial stop surface 246. The fixed
retraction flange 242 is a distal protrusion positioned within the
electrode head assembly 14. The electrode head assembly 14,
including the fixed retraction flange 242 may be formed as a
single, molded polyurethane component. Therefore, implementing the
fixed retraction flange 242 in lead 10 does not require additional
parts or bonding procedures during lead assembly.
[0031] FIG. 5 is an enlarged, perspective, partially cut-away view
of a retraction stop mechanism according to the present invention.
As illustrated in FIGS. 3 and 5, as the connector pin 25 at the
proximal end of coiled conductor 26 is rotated in a first,
clockwise direction so as to retract the helical tip electrode 30,
this rotation of the connector pin 25 in the first direction causes
the drive shaft 100 to rotate in the first direction. As the drive
shaft 100 rotates, the electrode 30 and the engaging member 106 are
also rotated in the first direction. As the electrode 30 is rotated
in the first direction, the electrode 30 advances through the guide
28, causing the electrode 30 to be advanced through the electrode
head assembly 14 in a direction shown by arrow A, so as to be
advanced towards the electrode head assembly 14, thereby retracting
the electrode 30 from the cardiac tissue and within the electrode
head assembly 14.
[0032] At the same time, the rotation of the drive shaft 100 in the
first direction also causes the engaging member 106 to be rotated
in the first direction, while at the same time, the movement of the
electrode 30 through the guide 28 causes the engaging member 106 to
also be advanced within the electrode head assembly 14 in the
direction A. Furthermore, the rotation of the drive shaft 100 in
the first direction results in the engaging member 106 being
rotated about the drive shaft 100 so that as engaging member 106
advances in the direction A, the flange 240 engages against the
fixed retraction flange 242 upon complete retraction of the helical
tip electrode 30, so that the torque resulting from extra turns
applied to the connector pin 25 after the helical tip electrode 30
is completely retracted within distal assembly 113 will, therefore,
not be transmitted to the helical tip electrode 30. Rather,
additional torque is absorbed by the coiled conductor 26.
Deformation of the helical tip electrode 30 is thereby avoided,
allowing repositioning of the lead 10.
[0033] As the connector pin 25 at the proximal end of coiled
conductor 26 is rotated in a second, counterclockwise direction in
order to advance of the helical tip electrode 30 within the cardiac
tissue to secure the lead, this rotation of the connector pin 25 in
the second direction causes rotation of the drive shaft 100 in the
second direction. As the drive shaft 100 rotates, the electrode 30
and the engaging member 106 are also rotated in the second
direction. As the electrode 30 is rotated in the second direction,
the electrode 30 advances through the guide 28, causing the
electrode 30, to be advanced through the electrode head assembly 14
in a direction shown by arrow B, away from the electrode head
assembly 14, so that the electrode 30 is advanced outward from the
distal end of the electrode head assembly 14 and is inserted within
the cardiac tissue.
[0034] At the same time, the rotation of the drive shaft 100 in the
second direction also causes the engaging member 106 to be rotated
in the second direction, while at the same time, the movement of
the electrode 30 through the guide 28 causes the engaging member
106 to also be advanced within the electrode head assembly 14 in
the direction B. Furthermore, the rotation of the drive shaft 100
in the second direction results in the engaging member 106 being
rotated about the drive shaft 100 so that as engaging member 106
advances in the direction B, the flange portion 240 disengages from
against the fixed retraction flange 242. As a result, when the
drive shaft 100 is rotated in the in the second direction, opposite
the first direction, the retraction stop mechanism of the present
invention does not prevent rotation of the engaging member 106,
allowing advancement of the helical tip electrode 30 through the
electrode head assembly 14 in the direction B.
[0035] According to the present invention, the flange 240 and the
axial stop surface 246 are compact such that little space within
the electrode head assembly 14 is required to provide a retraction
stop mechanism. Furthermore, the fixed retraction flange 242 and
the engaging member 106 have geometries that may be incorporated
directly into the molded electrode head assembly 14 and the
machined drive shaft 100, respectively, without requiring
additional parts or bonding or welding procedures. The retraction
stop mechanism of the present invention is advantageously located
proximal to the stem 44 allowing the welded joint between the
helical tip electrode 30 and the stem 44 to be easily inspected.
Thus, the assembly procedures for a lead having a retraction stop
mechanism in accordance with the present invention are kept simple
and are easily verified, resulting in a more reliable lead.
[0036] The lead described above employing a retraction stop
mechanism in accordance with the present invention is a quadrapolar
high-voltage lead of the type that may be used for pacing,
cardioversion and defibrillation. However, it will be understood by
one skilled in the art that any or all of the inventive aspects
described herein may be incorporated into other types of lead
systems. For example, one or more of the aspects of the retraction
stop mechanism described herein may be included in any unipolar or
multipolar pacing lead having a rotatable fixation device and any
combination of one or more tip, ring or coil electrodes for use in
pacing, sensing, and/or shock delivery. Alternatively, any
drug-delivery or other electrical stimulation lead that benefits
from having a retraction stop mechanism may employ aspects of the
present invention. As such, the above disclosure should be
considered exemplary, rather than limiting, with regard to the
following claims.
* * * * *