4,953,564
3 4
MCRD 30 swells in use, an expansion space 40 is pro- within the scope of the invention. For example, the ring
vided proximal to MCRD 30. In general, MCRD 30 and electrode may be positioned on housing 10, as illus
housing 32 function in the same manner as the corre- trated in the above-cited article by Doring and Flink, to
sponding structures disclosed in U.S. Pat. No. provide a bipolar stimulation and sensing lead. Addi
4,506,680, issued to Stokes, incorporated herein by ref- 5 tional alternative embodiments in which the guide 26 is
erence in its entirety. conductive and serves as an electrode, and in which one
In its retracted position, the distal tip of helix 18 is or both of helix 18 and housing 32 are non-conductive
located within electrode guide 26, or extends only are also believed to be within the scope of the invention,
slightly therefrom. In use, the distal end of the lead is As such, the disclosure herein should be considered
placed adjacent the tissue to be stimulated and conduc- 10 exemplary, rather than limiting with regard to the fol
tor 14 is rotated, screwing helix 18 out of the distal end lowing claims. In conjunction with the above specifica
of the lead and into the tissue to be stimulated. As illus- tion,
trated, it is desirable that housing 32 be located such I claim:
that at the maximum extension of helix 18, housing 32 is 1. An electrical medical lead comprising:
roughly adjacent the distal end of the lead. This allows 15 an elongated insulative lead body having a proximal
the drug to be delivered directly to the tissue being end and a distal end;
stimulated. Because the distal end of electrode guide 26 an elongated conductor, mounted within said lead
is positioned adjacent the tissue to be stimulated, it helps body, said conductor having a proximal end and a
to restrict elution of the steroid to the immediate vicin- distal end;
ity of the distal end of the lead. 20 an electrode assembly mounted at the distal end of said
FIG. 2 shows an alternate embodiment of a fixation insulative lead body, said electrode assembly com
helix carrying a monolithic controlled release device. In prising an electrode head member having a lumen
this embodiment, the helix 118 includes a segment of open to the distal end of said lead body; a fixation
close wound coil 120, which serves as the housing for helix mounted within said lumen of said head
the monolithic controlled release device 130. Adjacent 25 member, said fixation helix having a proximal end
close wound coils may be welded to one another, if and a distal end, said fixation helix mounted in said
desired. Located at the distal end of the close wound lumen of said head member such that said helix is
coil segment 120 of helix 118 is a porous, sintered plug advanceable from a first, retracted position within
122, which functions as an elution path for the steroid said lumen of said head member in which the distal
within MCRD 30 and allows for elution of the steroid 30 end of said helix is adjacent the distal end of said lead
to the tissue being stimulated. At the proximal end of body to a second, advanced position in which the
the close wound coil segment 120 is a plug 124 which distal end of said fixation helix projects distally of the
retains steroid 130 within the helix 118. As in FIG. 1, distal end of said lead body, said electrode assembly
above, an expansion space 126 is provided into which further comprising a drug release device having a
MCRD 130 may expand as it imbibes body fluid in use. 35 proximal end and distal end and having means for
As illustrated in FIG. 1, it is desirable that the distal end releasing a drug contained within said drug release
of the porous cap 122 should be approximately even device at least adjacent the distal end of said drug
with the distal end of electrode guide 26 when fixation release device, said drug release device mounted to
helix 118 is fully extended. said fixation helix such that when said fixation helix
FIG. 3 shows a second alternative embodiment of a 40 is in said first, retracted position within aid lumen of
fixation helix and drug elution device. In this case, fixa- said head member, the distal end of said drug release
tion helix 218 carries a porous plug 230, which has been device is located within the lumen of said electrode
soaked in or otherwise impregnated with the drug to be head member and such that when said helix is
delivered. As in the case of FIG. 1, the distal end of advanced to said second, extended position, the
plug 230 should be roughly adjacent the distal end of 45 distal end of said drug release device is adjacent the
the lead when fixation helix 218 is fully extended. distal end of said lead body, the distal end of said
In all of the above drawings, porous structures are helix extending distally of the distal end of said drug
used in conjunction with the drug elution function. release device, said electrode assembly further
These structures may be made by any one of a number comprising at least one conductive electrode surface
of known, commercially available sintering techniques 50 coupled to the distal end of said elongated conduc
which fall into the general category of powder metal- tor; and
lurgy. Alternatively, ceramic, plastic or other non-met- means for advancing said fixation helix from said first,
allic porous structures may be used to serve as elution retracted position to said second, extended posi
bores and/or drug retention mechanisms. tion.
In the embodiment illustrated in FIG. 1, it is antici- 55 2. A lead according to claim 1 wherein said electrode
pated that electrode guide 26 will be fabricated of a surface comprises the distal end of said drug release
non-conductive material, such as a biocompatible plas- device.
tic and that helix 18 and housing 32 would be fabricated 3. A lead according to claim 1 or claim 2 wherein said
of a conductive biocompatible metal, such as platinum, electrode surface comprises said fixation helix,
titanium or MP35N alloy. In such case, the porous sur- 60 4. A lead according to claim 3 wherein said fixation
face of housing 32 would serve as an electrode in con- helix is advanced from said first, retracted position to
junction with helix 18. However, helix 18 may also be said second, extended position by rotation of said helix,
provided with an insulative coating, allowing the po- and wherein said means for advancing said helix com
rous surface 36 of housing 32 to function as the sole prises said elongated conductor, said elongated conduc
electrode. 65 tor being rotatably mounted within said electrode head
As illustrated, the lead takes the form of a unipolar member,
lead. However, alternative embodiments in which the 5. A lead according to claim 1 wherein said drug
lead carries additional electrodes are believed to be release device comprises a conductive housing having
