CA2253476A1 - Implantable cardiac cardioverter/defibrillator with emi suppression filter with independent ground - Google Patents
Implantable cardiac cardioverter/defibrillator with emi suppression filter with independent ground Download PDFInfo
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- CA2253476A1 CA2253476A1 CA002253476A CA2253476A CA2253476A1 CA 2253476 A1 CA2253476 A1 CA 2253476A1 CA 002253476 A CA002253476 A CA 002253476A CA 2253476 A CA2253476 A CA 2253476A CA 2253476 A1 CA2253476 A1 CA 2253476A1
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- emi
- capacitor
- electrode
- frequency range
- predetermined frequency
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/38—Applying electric currents by contact electrodes alternating or intermittent currents for producing shock effects
- A61N1/39—Heart defibrillators
- A61N1/3925—Monitoring; Protecting
- A61N1/3931—Protecting, e.g. back-up systems
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
- A61N1/362—Heart stimulators
- A61N1/37—Monitoring; Protecting
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
- A61N1/372—Arrangements in connection with the implantation of stimulators
- A61N1/375—Constructional arrangements, e.g. casings
- A61N1/3752—Details of casing-lead connections
- A61N1/3754—Feedthroughs
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
- A61N1/362—Heart stimulators
- A61N1/37—Monitoring; Protecting
- A61N1/3718—Monitoring of or protection against external electromagnetic fields or currents
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S128/00—Surgery
- Y10S128/901—Suppression of noise in electric signal
Abstract
An implantable defibrillator (10), which may include cardioversion and pacemaker capabilities, which has EMI filters (46, 54) which are not susceptible to defibrillation shocks and which reduce or eliminate the effects of charging noise on sensing circuits used for continuous confirmation. A first filter capacitor (104) is provided between a sense electrode, which may include pacing capabilities, and a ground reference (106) within a hermetically sealed can (66) containing a pulse/shock generator (62, 68). A second filter capacitor (112) is provided between a sensing/pacing reference electrode, which may also be a high voltage or shock electrode, and the ground reference (106). In addition, there is a third filter capacitor (108) between the ground reference and the can. Preferably, the connections of the first, second and third filter capacitors are physically as well as electrically adjacent to each other. The filter capacitors are housed in the can and in or adjacent to a feedthrough assembly which passes through the can. Most preferably, the filter capacitors are discoidal capacitors mounted in or adjacent to the feedthrough.
Description
CA 022~3476 1998-11-03 WO 97/41923 PCr/US97/07572 Description Imrl~nt~hle Carfli~ rdioverterlDefibrill~tor with Fl~I Suppression Filter with In~ endent Ground S
Technical Field The present invention is directed towards an implantable biomedical device such as a cardiac cardioverter-defibrillator, incorporating an output regulating circuit for controlling energy applied to the heart and a sensing circuit for d~t~cting electrical conditions in the heart, and particularly to filters for suppressing electro-magnetic hlle~relence (EMI) and the effects of defibrillation shocks.
B~rk~ground Art The basic implantable cardioverter/defibrillator system consists of at least one electrode attached to the heart and connected by a flexible lead to a shock or pulse generator. This generator is a c~ billalion of a power source and the microelectronics required for the system to perform its intended function. An implantable cardioverterldefibrillator may also include a p~cem~ker to treat bradycardia. Many cardioverter/defibrillators in current use incorporate circuits and antennae to communicate non-invasively with external instruments called programmers. Implantable cardioverters/ defibrillators have the capability of correcting dangerous arrhythmias and fibrillation by applying selected slim~ tion patterns or high energy shocks. High energy shocks are used primariJy to correct life-thre:ltening fibrillations by e~.senti~lly stopping the heart and allowing an apl.lol)~iate rhythm to re-establish itself.
To achieve reversion to an organized rhythm, it is generally believed that the heart should receive an effective amount of electrical energy, equal to or exceeding a threshold energy. The threshold energy may vary from patient to patient. Consequently, a physician will customarily perform certain tests when implanting a defibrillator and will select an energy level for defibrillating shocks. Implantable defibrillators are configured to deliver electrical energy by controlling the voltage on or applied from output capacitors.
Implantable medical devices such as p:lrem~k~rs, defibrillators, and other implantable pulse generators generally comprise one or more electrical leads in electrical communication with the pulse generator which emanate from the housing and typically terminate at a distal location within the patient. The leads transmit electrical signals to and from the device and, as such, are fabricated having a conductor made from a metal alloy to enable good conductivity. Because of their conductive properties, these leads effectively act as an antenna and thus tend to conduct unwanted electromagnetic interference (EMI) signals. These EMI signals may be transmitted to the medical _, .. . . . ... . . . . .. .
CA 022~3476 1998-11-03 device and interfere with normal operations. Sources of EMI signals are prevalent and include, for example, radio and TV transmitters, cellular telephones, medical electrosurgical equipment, microwave devices, welding equipment, security and surveillance systems, and other sources of radio frequency illt~lrele~lce (RFI). In implantable cardioverter/defibrillators, charging and delivery of a defibrillating shock can cause EMI which adversely affects the sensing circuits or the operation of the device.
Two basic a~-oaclles are employed to reduce the effects of u~ nted EMI on implantable medical device operations. In the first approach, the medical device is enclosed in a metallic housing or shield which may be conductively connected to a ground reference of the device. In the second approach, a filtering circuit attenuates potential EMI before it reaches the circuitry of the medical device. The two approaches may be used separately or combined.
Presently, multilayer ceramic type capacitors and, in particular, discoidal capacitors are recognized as an effective alternative for filtering EMI. In a typical construction, these discoidal capacitors form part of a feedthrough filter assembly, which admits patient connections through the hermetic barrier of the device. The feedthrough assembly includes a metallic ferrule connected to the capacitor and a terminal pin hermetically supported from and extending through the ferrule. The metallic ferrule is connected to and hermetically sealed with the medical device. Typically, the discoidal capacitor has two separate electrode plate sets which are embedded within a dielectric substrate. One set of the electrode plates is electrically coupled to the terminal pin. This pin is electrically connf cted at one end to the medical device circuitry and at another end to the lead used to transmit the desired electrical signals to and from the patient. The other set of electrode plates is electrically coupled to a cylindrically shaped ferrule which, in turn, is welded to the housing of the medical device. Generally, the ferrule consists of a conductive material and may have an in.c~ ting material disposed along an inner portion of the outer conductive surface. This insulating material is used to support the terminal pin and rn~int~in it in nonconductive relation with the housing of the medical device.
During signal tr~n.cmis.cion, the discoidal capacitor permits passage of relatively low frequency signals along the lead, through the terminal pin, and to the medical device. Higher frequencies, representative of the spectrum of unwanted EMI, however, are shunted to the housing of the medical device by the capacitor and not permitted to pass into the medical device. As a consequence, interfering signals which could otherwise adversely affect the performance of the device are filtered as they enter the medical device.
Discoidal capacitors, as well as other multilayer ceramic capacitors, are formed of multiple layers of alternating ceramic and metallic materials. Generally, the multilayer ceramics are available CA 022~3476 1998-11-03 W O 97/41923 PCTrUS97/07572 in several different dielectrics and the choice of material depends on the desired capacitance volume efficiency and the operating temperature range. Ceramic capacitors of this nature, however, primarily serve to filter EMI and not protect against voltage transients and surges. For further information regarding discoidal and multilayer capacitors, reference should be made to U.S. Pat. No.
5,333,095 by Stevenson et al., issued July 26, 1994, entitled "Feedthrough Filter Capacitor Assembly for Human Implant", and Ivan G. Sarda and William H. Payne, "Ceramic EMI Filters -A Review," Ceramic Bulletin, Vol. 67, No. 4 (1988), pp. 737-746.
Implantable defibrillators usually produce high voltage, high energy shocks by charging large capacitors. It takes a certain amount of time, depending on the condition of the batteries and other factors, to charge these high voltage capacitors. During this interval, it is possible that the heart may spontaneously revert to a normal sinus rhythm. Since a defibrillation shock is both painful and potentially dangerous, it is desirable to avoid delivering unnecessary shocks. To do this, implantable defibrillators are programmed to continue to monitor the electrical condition of the heart during a capacitor charging interval. If normal sinus rhythm is detecte-l, charging is interrupted and a shock is not delivered. This is soml~times referred to as "continuous collfi.,llalion," m~ning that the existence of a life-threatening tachycardia or fibrillation is constantly detected. It has been observed, however, that the process of charging the high voltage capacitors can be so electrically noisy that the heart's electrical signal cannot be reliably detected. This noise appears as internally-generated EMI, tran.cmirted from high voltage leads or electrodes to a sensing circuit. It is desirable, therefore, to reduce or eliminate this noise so that the sensing circuit can more readily detect the heart's electrical slgnals.
Certain implantable cardioverter/defibrillators have been developed which deliver shocks between an electrode mounted on a lead, preferably an endocardial lead, and a conductive part of the hermetically sealed case or can C.~ i..i.,g the pulse generator. This is sometimes referred to as a "hot can" and is analogous to so-called unipolar operation of a pacemaker, wherein a stin nl~ting pulse is delivered between an electrode and a pacemaker can. The m~gnitude of a shock is, of course, substantially greater than a pacing pulse and presents additional difficulties. In particular, in a "hot can" implantable cardioverter/defibrillator with EMI filters, a shock waveform may be prematurely terminated by a feedback effect. This appears to be attributable to the use of at least two EMI Su~ g capacitor filters, between each pace/sense electrode, which may also be a high voltage or shock electrode, and the can.
This phenomenon can be avoided by removing the EMI su~plessillg capacitor filters or by substantially reducing their capacitance. This, however, renders the device more susceptible to externally generated electromagnetic interference.
... .... .. . .
CA 022~3476 1998-ll-03 It is an object of the invention, therefore, to provide an implantable cardioverterldefibrillator in which the design of EMI suppressing filters is not influenced by the programmed selection of shock delivery path.
It is a further object of the invention to provide an EMI filter configuration for an implantable cardioverter/defibrillator which prevents premature termination of shock delivery.
It is another object of the invention to provide an implantable defibrillator which has continuous confirmation, but which is not susceptible to charging noise.
Disclosure of the Invention The present invention is addressed to an implantable defibrillator, which may include cardioversion and pa~.em~ker capabilities, which has EMI filters which are not susceptible to defibrillation shocks and which reduce or elirninate the effects of charging noise on sensing circuits used for continuous confirmation. A first filter capacitor is provided between a sense electrode, which may include pacing capabilities, and a ground reference within a hermetically sealed can containing a pulse/shock generator. A second filter capacitor is provided between a pacing/sensing reference electrode, which may also be a high voltage or shock electrode, and the ground reference.
In addition, there is a third filter capacitor between the ground reference and the can. Preferably, the connections of the first, second and third filter capacitors are physically as well as electrically adjacent to each other. In the preferred embodiment, the filter capacitors are housed in the can and in or adjacent to a feedthrough assembly which passes through the can. Most preferably, the filter capacitors are discoidal capacitors mounted in or adjacent to the feedthrough.
Bri~f Pescription of Drawings FIG. 1 is a block diagram of an implantable pac.em~ker/defibrillator.
FIG. 2 is a block diagram of an output circuit for use in the defibrillator of FIG. 1.
PIG. 3 is a schematic diagram of a prior art EMI filter circuit.
FIG. 4 is a scl~m~tic diagram of an EMI filter circuit according to the invention.
FIG. 5 is a perspective view of a combined hermetic feedthrough and filter circuit according to the invention.
FIG. 6 is a through section plan view of a first embodiment of the feedthrough and filter circuit of FIG. 5.
FIG. 7 is a through section plan view of a second embodiment of the feedthrough and filter circuit of FIG. 5.
FIG. 8 is a through section plan view of a third embodiment of the feedthrough and filter circuit of FIG. 5.
Best Mode for Carryin~ Out the Invention . ., . _ _ , .
~M 363 ~T
FIG I is a block diagrarn illustrating a rate adaptive pacern~rldefibrillator 10 according t~ the invention. A micropr~cessor 12 preferably provides p.lcent~er control ~n~ ccmp\lta~ion~l facilities. It will be appreciated that other form~ of circ~litry, such as analog or discrele digital circui~ry c~n bc used in place ~f rnicroprocessor 12. Ho~ever, a microprocessor is preferred for its miniature size and its tlexibility, ~oth of which are of critical importance in the imri~f~ble systen~s in which it is envisioned the invention will find use. A particulally energy efficient microproc~sscr ~hich i9 designed 6pecifically for use with imr~ t~le medical device~ i~ fuily describdd i;l Gor~on, ~r ~1., U.S. Pa~ent N~. 4,404,g72, which i5 also assi~ned to the assignee.
l'he micmprocessor 12 has ~nput~output ports conr~ec~ed in ~ conventional rnanner via bidirectinrlal bu~ 1~ t~ a n~ernory 15, an .~-V interva] timer 18, ~nd a p2~ing interval ~m~er 20. I~
~- addition. ~he A-V interval t~mer 18 and pacing inter-~a~ timer 20 each has an output connected individually to a COr~eSpQlldiIlg input pQrtofthe mlcroprocess~r 12 by lines 22 and ~4 respecti~ely.
Memory 1~ preferably in~;ludes ~oth ~OM arld RAI~!~. The microproce~sor 12 m~y also 1 j contain ~ itionsl RG~f and RAhI as aescribed ~n the G~r~o~, e~ al. ~r.s. Pa~ent ~o. 4,404,~, 2.
~he paeema~er op rating rout~ne is stored in ROM The RA-~ stores v~rious prognrr~ le parameters and l/~riables.
The A ~' and pac~ng inte~al timers 18 2nd ~0 may be ex~ernal to the rnicroproces~or I,, as illustrate-l, or int~rnal thereto. as described in the Gordon, et al. U.S. Patcnt No. 4,~ 72. The Jl~) hmess l~ 20 are suitable con~er~tional up or down counter~ of tlle type that are i~i~ially loaded with a count value and count up to or down from the value and output a roll~ver bit upon co~pleting ~.e pro~rarrlnled coun~. The initial count value is loaded ~Ilto the timers 18, 20 on bus 14 and ~e respective rol~ ver bi~s are ~utput to t~e n~icroprocessor 12 on lines 22, 24.
The micro,~roces~or 12 preferably also has an input/output port cc)nrlecte~ to a telemetry ~5 lr.te.face 26 by IjLA~e f~O. ~hC de,~brill&tor, -w-hen impl~n~u, is ~us abie io receiYe pacing, arrhy~nmia t~r~py, and rate controL parameters fr~m an ~xterIIal program~er and send data to an exterDal receiver if desired. Many suitable telemetry s!~stems are known to those skilled in the arl. One ~u~h syst m and encoding arrangernent is d~cribed i~.4r7nstrong a~d Co,~, U.S. Patent No. 5,3S3,91' whi~ is al~o as~igned to the a~signee.
The ll,icr.~ uees~or output ports are &onn~t~d to inputs of an atrial sti~ulu~ pulse generator 30 and a ventricle stirn~lus pul~e generator 32 b~ ~ontrol lines 34 an~l 36 rcspectiYely. The microprocessor I2 ~ansmi~ pul e para~neter data, such as arnplitude and width, as well ~s enable/disable and puise initiatioxl codes to the g~ ators 30, 32 on the respec~iVe control lines. The microproce~sor 12 also has input ports co~n~ct~d to outputs of an atr~al ~ensc amplifier 38 and a ~Ç~ 3 S~
o K~ L. ~ t. ~ , r~J ~ J ~ J ~C~.~ . f~ I ~J
~ -36~CT -6-venIricular sense a!r.pli~ier 40 by lin~s 42 and 44 respe~tively. Tbe ~tIial and ven~ricular scnse amplifiers 3&. 10 detect elec~rical conditions irl the hea~t ~ncluding ~brill~tion and occurrences of P-waYes ar~ R-waves. The atrial sense an~p'ifier 38 output~ a sigrlal on liIle 42 co the microproc~ssor 1~ whe~ ic de~ec~s a P-wave. This sign~l is latched to the microproces~or 12 input port by a S conventional la~ch (r.ot ~houn) ~he ~entr.cular sense arnpl~fier 40 outputs a ~ignal on llne 44 to the microprocessor 12 when it det~cts an R-wave. Thi~ signal ~s also latched tQ the microproce~sor 12 IrlpUt port by a conventional latch (not shown).
~he ~r~put of the atrial sense arnplifier 38 and the ourput of the atrial stirnulus pulse get~erat~r 30 are cormected ~ conductors through a first ~MT filter,ng feedthJorl,~h 4b, and through a con~entional first lead 48 to a paticnt's heart ~0. Lead ~8 i~ inserted mto ~he pahent's heart 50 intra~e~ously or in ~.ny other suitabl~ 2~anner. The lead 4~ has an el~ctric,ali~ conduc~i~e t~ pacing/sensing ~ip C2 or tip and ritlg at its dis~a' ~nd which is electric~lly colm~cted to the conductors in lead 48. 'rhe paeingJsensing tip 52 is preferably lodged in ~he right atrlu~. Th~ u~
of the Yentricular sense ~rnplifier 40 and the ou~u~ of the ventricul~r s~m~lus pulse gener~or 32 are onnec~ed b~ conductors Ihrough a second ~MT filtering ~eedthrou~h 54. ~e conduciors pais chroueh a conventional se~ond lead 56 which is inset~ intrave~iollgly or otherwi~ in the right Yentricle ~8 o~ ~he heart 50. Ihe second lead 56 has an electrically conductive p~cin~lser~ing tip ~0 or tip md ring at its dist~l end. The pacin~l~ensing tip 60 ;s eiecsricaILy connected to the conductors in second lead 5~. The pacin~lsensing tip 6d IS pceferably lo~ged cn the ~all of ~he ri~ght ~0 ventricle ~8.
lhe conductors cond~lct the s~i2nullLs p~ses gener~ted by the atriaJ and ~~en~;ricular sti~lulus pulse ~generators 30, 3~ to the pacing/sensing tips S~, 60. The paci~!sensing tips 52. ~a and corresponding conductors al~o conduct cardiac electrical signals sensed in t~e right ~triurn ~d ri~h~
ven~ricle to the atrial ana ven~ricular ~nplifiers, 38, ~0 re~pectively, The sense amplifiers ~g, ~0 ''5 enllaneelhe~ieC~riCai signais. Tn u~ preterred embod~ rxs ~f the inven~ion, the arnplifiers 38, 40 ha~ie an autornatic g3in cont~ol ~atNre, as described in U.S. Patent ~,903,699 1o Baker, er ~1. That applicatisn is a~si~ned to the same assignee ~s tl~ present inve~tion.
T~e imrl~nt~ble cardiac stim~ tor 10 also ha~ a defibrillator ci~cuit 62. If fibrillation ~s deteaed ~hrough the a~rial ~r ven~ricular sense amplifiers 38, 40, a high ener~y s~.ock can be delivere~ ~hrough defibrill3.tion lead 6~ and elect~ode S6. De~ection algorithms for de~ection of tachycardias and fibr .lation are described in Pless, et ~l., U.S. Patent 4,880,~05. Allh~ugh an endocardi..l ~lectrod~ and use of ~he conductive part of th~ can or case are ~uggested by the drawin~, pa~ch-type epicardial e~ectrodes ~or defibrillaliorl are al~o AMENDED SHEET
,. . .. . ..
..... ~ ,.. . .
63Pc~
known. Tne shock is, contro!led l~y a shc~ck driv~er circuit 68, which will be more particularly describ,ed herea~r A~l of the s~orementioned co~ponents are p~wered b~ a power sup~ly 70. The po~er sup,uly 70 may comprise elther s~andard or rechargeable battcries or b~th. which ;nay b dedicate,~ ~ the operation of different parts of the ~tirr~ r 10.
In the preferred embodiment of the inven~ion, it is considere~ d~sir,~ble to pro~uce multi-ph,~,ic shocks for defib"llatiorl through the shock driver 68. Circuitry partlcu~arly v, el,' adapced for producing such wave forms ir describe~ in detai~ in U.S. Paten~ ~c. 4.800,883 to W~nstrom.
Circu,~ry for the ~,hock driver 68 is sh~Jwn with greater particul,~-ity in PIG. 2. FIG. 2 illu~trates the ~hock drivcr 58 conr.eeted to the patie~'~, hear~ 50 through dle lead ~4 and el~ctrode 56 and througn the call 66;~ produce a ~iph~sic w~e forrn, a b,~k of four three-ter~ninal semiconduetor sw~ches 72, ~4~ ?~ sueh as ir~ulated g~te bipolar trans~tor (rGBri switches, rnay ~e empl.~ d. It wiil ~_ be unders~ood, however, tt~t the invention can ~e emplo~ed with mo~opl~sic ~ulse gener~tors and ~ith p-~lse generator~, incorporating rn~1~tirh~cic ~tim~ orl~ The switches 72, ?~ " 78 are c~ntrolled hy drivers 82, 84, 86, 8~ respectively. The drivers 82, 84, 86, 88 a~e c~n~rolLed by ~5 command puises from the miCrroproceggor L2 through control lines 80 ~nd 91, as will De snore particular~y dcscrlbed below. The energy to pr~duce bi~hasic defi~ri!1arng shocks is ~plied from high vol~age capacitor 92. High volt~ge capacitcr 92 is conn~te~ to swi~ches, 2 and 7~, and c~Lrrerlt therefrotn returns ~ ia switches 76 or 7~. The first leaà 64 is cnnnPrte~ beeween switche~ 72 and 76 wniie the second lead 66 i~ connected berween switches 74 and 78.
2n ~ amount o~ energy deliver~d to t}~e heart is de~endanl upon ~e voltage on the high voltage c~acitor. rhe voltage appearirlg OII the capaci~ot 9~ i5 controlled by voltage c~ntroller 9 which is coanected to ~ source of power s~lch as the battery or po~er supp1y 70 through line iO0.
The voltage controller 9~ ls controlled t~ro~lgh a line 1~4 from the microproc~ssor I2. This -~ configuIation is described in more detaii in Lhe ~i~trom patent rnen~ione~ above. In ~he '~ CO~fij~,'Ula;iOrl ~hUWl~ t~ pro~ucc a ~Lnidirectionai current pulse ~hrou~h the heart 50, the m~croprocessor 12 issues a c~lnrnand along lLne 8~) to drivers 82 and 88, closing ~v~tches 72 ar~d 7~.
Both be~or~ and ~er the comrnand, all ~witches are normally opened. To produce ~ opposite currerlt, the microprvcessor !2 issues a command on line 90, clo~ir4 cwitches 84 and ~6 and directing ~;he curren~ flow in the oppo6ite direction through the heart 50.
The EhlI fiiter according to ~he in~entton will now be descr~bed. A prior art EMI ~Iter 90 i~ illussra~ ,;n FIG. 3. Such a filter 90 migkt be comprised ~f discrcte con~ponents, or incorporated into a set of discoid~l capacitors. Such di~c~ capacitors m~gh~ be mounted in a feedthrvugh such as feedthrough 54. or adJacen~ the feedthrough, as described jTl St.~pher~,on et al. U.S. PateM
AMEN~D SHEEt . ..... , , , ".. ,, ,, ,, ,, ~, .. .
CA 022~3476 1998-11-03 W O 97/41923 PCTrUS97/07572 5,333,095. Fundamentally, an EMI filter 90 comprises a lead 92 which would pass through a desired case such as the can 66 to provide an electrical connection through the can 66. The lead 92 might, for example, be connected to the ventricular sense circuit 40 and the ventricular stimulus generator 32 within the can at pin l and to the tip electrode 60 outside of the can. A first capacitor 94 is connected from the lead 92 to the can 66 to provide a high frequency path for EMl. Multiple leads and capacitors could be provided in a single configuration or at a single feedthrough. For example, as shown in FIG. 3, an additional lead 96 could be provided within an associated capacitor g8 connected from the additional lead 96 to the can 66. Pin 2 of lead 96 might be connected, for example, to the shock driver 68 within the can and to the endocardial electrode 70 outside of the can.
In an implantable cardioverter defibrillator, charging noise is generated during the process of charging the high voltage capacitors in the defibrillator 62 prior to shock delivery. Charging noise may be present as an electric field coupling from the can or by induction of eddy currents. This sometimes occurs when a "hot can" electrode has been introduced into the shock delivery pathway, that is, when the can 66 is used as one of the electrodes. The prior art connection of the C 1 and C2 capacitors 94, 98 respectively, directly to the can 66 can cause an inappropriate sensing during the charging cycle and premature termination of a can-delivered shock. Even if two or more defibrillation electrodes remote from the can are used, charging noise can still prevent a sensing circuit from detecting the electrical condition of the heart, if continuous confirmation of the life-threatening condition is attempted. These situations are avoided by the configuration of the invention illustrated in FIG. 4.
FIG. 4 illustrates an EMI filter 100 according to the invention. The EMI filter 100 comprises at least one lead 102, configured to pass through the can 66. As before, this lead 102 might be connected within the can at pin 1 to the ventricular sense circuit 40 and the ventricular stimulus generator 32. Outside the can 66 the lead 102 might be cormected to the ventricular tip electrode 60. A shunt capacitor 104 is provided similar to the capacitor 94 described above.
However, instead of being connected to the can 66, this capacitor is connected directly to the internal system ground 106. A C3 capacitor 108 is connected between the common contact of the Cl capacitor 104 and of the system ground 106 and the can 66. In the preferred embodiment, the capacitance of the C I capacitor and the C3 capacitor are approximately equal. Charging noise is generally within the frequency range of 100 kHz to 200 kHz. Consequently, the Cl capacitor is chosen to easily pass freql~Pn~ies higher than 100 kHz. These frequencies are passed directly to the system ground since it passes tllrough but a single capacitor. This adequately (limini.~hes the effect of charging noise on the circuit and prevents improper sensing. On the other hand, external EMI
generally consists of frequencies in excess of 1 MHZ. These frequencies are passed easily through .., .. ~ ~ .. . ..
.. , . . . , . .. ~ ~
CA 022~3476 1998-11-03 W O 97/41923 PCTrUS97/07572 the capacitor C1 and C3 in series and are diverted to the can. External EMI entering either from the tip electrode 60 or the endocardial defibrillation electrode 70 needs to be ~tteml:~ted before it can be demodulated by the rectifying properties of semi-conductor junctions. This is done by .~hllnting the EMI currents back to the can which acts as a Faraday Cage for the device. The C3 capacitor 108 S provides a low impedance path from the ground reference to the can. Multiple leads may be provided through the can, either electrically a~j~rent, or both electrically and physically adjacent one another. For example, an additional lead 110 could be provided to connect to the endocardial defibrillation electrode 70 and through pin 2 to the shock driver 68. A C2 capacitor 112 is connected from the lead 10 to the system ground 106 and to the C3 capacitor 108.
0 The EMI filter 100 of the invention may be provided as separate components connected to a standard feedthrough. However, the preferred embodiment is to construct a feedthrough and EMI
filter as a common feedthrough structure 114 as illustrated in perspective view in FIG. 4. The feedthrough structure 114 comprises the leads 102 and 110 described above and a system ground connection 116 for connection to the system ground 106. The leads 102, 110 and 116 are embedded in a feedthrough 118 having a metal ferule 120 for connection to the can 66 which houses a capacitor structure 122. The capacitor structure 122 may be constructed in a variety of ways, as will IIOW be explained.
One embodiment is shown in FIG. 6, which represents a plane through section of the feedthrough system 114 of FIG. 4. As seen in FIG. 6, the metal ferrule 120 of the feedthrough 118 has a circumferential groove 124 for receiving the can 66. A hermetic seal 126 plugs one end of the feedthrough 118 around the leads 102 and 110. Such hermetic seals are known in the art, and are described, for example, in U.S. Patents 3,920,888 and 4,678,868. The capacitor assembly 122 comprises chip capacitors employed for the capacitors 104, 112 and 108. The shunt capacitor 108 is connected by a jumper 128 to the metal ferrule 120. Alternatively, the jumper 128 could be connected directly to the can 66.
An alternative construction comprised of discoidal capacitors is illustrated in through section in FIG. 7. As in the embodiment of FIG. 6, the leads 102, 110 and 116 and the metal ferrule 120 and hermetic plug 126 are substantially as described above, and perform the same functions. Instead of the chip capacitors, however, the capacitors 104, 108 and 112 are comprised of discoidal capacitors. In particular, the ground line 116 which is intended to be connected to system ground 106 is connected to an annular ring conductor 130. Plates on the outside of this ring 130 interleave with plates connected to the ferrule 120, thus forming the shunt capacitor 108 which connects to the can through the ferrule 120. On the inside of the annular conductor 130, additional plates h1terleave with plates connected to the lines 102 and 110 to form capacitors 104 and 112 respectively CA 022~3476 l998-ll-03 W O97/41923 PCTrUS97/07572 A third embodiment is illustrated in through section in FIG. 8. As in FIGS. 6 and 7, like numerals indicate like parts. In this embodiment, however, the capacitors 104, 108 and 112 are formed as individual stacked discoidal capacitors formed adjacent their respective leads 102, 116 and 110.
Each of the embodiments of FIGS. 6, 7 and 8 are shown with the capacitor structure 102 contained within the ferrule 120 of the feedthrough 118. However, the invention could also be implemented using discoidal capacitors attached around the ferrule, as shown, for example, in Stephenson et al. U.S. Patent 5,333,095.
Technical Field The present invention is directed towards an implantable biomedical device such as a cardiac cardioverter-defibrillator, incorporating an output regulating circuit for controlling energy applied to the heart and a sensing circuit for d~t~cting electrical conditions in the heart, and particularly to filters for suppressing electro-magnetic hlle~relence (EMI) and the effects of defibrillation shocks.
B~rk~ground Art The basic implantable cardioverter/defibrillator system consists of at least one electrode attached to the heart and connected by a flexible lead to a shock or pulse generator. This generator is a c~ billalion of a power source and the microelectronics required for the system to perform its intended function. An implantable cardioverterldefibrillator may also include a p~cem~ker to treat bradycardia. Many cardioverter/defibrillators in current use incorporate circuits and antennae to communicate non-invasively with external instruments called programmers. Implantable cardioverters/ defibrillators have the capability of correcting dangerous arrhythmias and fibrillation by applying selected slim~ tion patterns or high energy shocks. High energy shocks are used primariJy to correct life-thre:ltening fibrillations by e~.senti~lly stopping the heart and allowing an apl.lol)~iate rhythm to re-establish itself.
To achieve reversion to an organized rhythm, it is generally believed that the heart should receive an effective amount of electrical energy, equal to or exceeding a threshold energy. The threshold energy may vary from patient to patient. Consequently, a physician will customarily perform certain tests when implanting a defibrillator and will select an energy level for defibrillating shocks. Implantable defibrillators are configured to deliver electrical energy by controlling the voltage on or applied from output capacitors.
Implantable medical devices such as p:lrem~k~rs, defibrillators, and other implantable pulse generators generally comprise one or more electrical leads in electrical communication with the pulse generator which emanate from the housing and typically terminate at a distal location within the patient. The leads transmit electrical signals to and from the device and, as such, are fabricated having a conductor made from a metal alloy to enable good conductivity. Because of their conductive properties, these leads effectively act as an antenna and thus tend to conduct unwanted electromagnetic interference (EMI) signals. These EMI signals may be transmitted to the medical _, .. . . . ... . . . . .. .
CA 022~3476 1998-11-03 device and interfere with normal operations. Sources of EMI signals are prevalent and include, for example, radio and TV transmitters, cellular telephones, medical electrosurgical equipment, microwave devices, welding equipment, security and surveillance systems, and other sources of radio frequency illt~lrele~lce (RFI). In implantable cardioverter/defibrillators, charging and delivery of a defibrillating shock can cause EMI which adversely affects the sensing circuits or the operation of the device.
Two basic a~-oaclles are employed to reduce the effects of u~ nted EMI on implantable medical device operations. In the first approach, the medical device is enclosed in a metallic housing or shield which may be conductively connected to a ground reference of the device. In the second approach, a filtering circuit attenuates potential EMI before it reaches the circuitry of the medical device. The two approaches may be used separately or combined.
Presently, multilayer ceramic type capacitors and, in particular, discoidal capacitors are recognized as an effective alternative for filtering EMI. In a typical construction, these discoidal capacitors form part of a feedthrough filter assembly, which admits patient connections through the hermetic barrier of the device. The feedthrough assembly includes a metallic ferrule connected to the capacitor and a terminal pin hermetically supported from and extending through the ferrule. The metallic ferrule is connected to and hermetically sealed with the medical device. Typically, the discoidal capacitor has two separate electrode plate sets which are embedded within a dielectric substrate. One set of the electrode plates is electrically coupled to the terminal pin. This pin is electrically connf cted at one end to the medical device circuitry and at another end to the lead used to transmit the desired electrical signals to and from the patient. The other set of electrode plates is electrically coupled to a cylindrically shaped ferrule which, in turn, is welded to the housing of the medical device. Generally, the ferrule consists of a conductive material and may have an in.c~ ting material disposed along an inner portion of the outer conductive surface. This insulating material is used to support the terminal pin and rn~int~in it in nonconductive relation with the housing of the medical device.
During signal tr~n.cmis.cion, the discoidal capacitor permits passage of relatively low frequency signals along the lead, through the terminal pin, and to the medical device. Higher frequencies, representative of the spectrum of unwanted EMI, however, are shunted to the housing of the medical device by the capacitor and not permitted to pass into the medical device. As a consequence, interfering signals which could otherwise adversely affect the performance of the device are filtered as they enter the medical device.
Discoidal capacitors, as well as other multilayer ceramic capacitors, are formed of multiple layers of alternating ceramic and metallic materials. Generally, the multilayer ceramics are available CA 022~3476 1998-11-03 W O 97/41923 PCTrUS97/07572 in several different dielectrics and the choice of material depends on the desired capacitance volume efficiency and the operating temperature range. Ceramic capacitors of this nature, however, primarily serve to filter EMI and not protect against voltage transients and surges. For further information regarding discoidal and multilayer capacitors, reference should be made to U.S. Pat. No.
5,333,095 by Stevenson et al., issued July 26, 1994, entitled "Feedthrough Filter Capacitor Assembly for Human Implant", and Ivan G. Sarda and William H. Payne, "Ceramic EMI Filters -A Review," Ceramic Bulletin, Vol. 67, No. 4 (1988), pp. 737-746.
Implantable defibrillators usually produce high voltage, high energy shocks by charging large capacitors. It takes a certain amount of time, depending on the condition of the batteries and other factors, to charge these high voltage capacitors. During this interval, it is possible that the heart may spontaneously revert to a normal sinus rhythm. Since a defibrillation shock is both painful and potentially dangerous, it is desirable to avoid delivering unnecessary shocks. To do this, implantable defibrillators are programmed to continue to monitor the electrical condition of the heart during a capacitor charging interval. If normal sinus rhythm is detecte-l, charging is interrupted and a shock is not delivered. This is soml~times referred to as "continuous collfi.,llalion," m~ning that the existence of a life-threatening tachycardia or fibrillation is constantly detected. It has been observed, however, that the process of charging the high voltage capacitors can be so electrically noisy that the heart's electrical signal cannot be reliably detected. This noise appears as internally-generated EMI, tran.cmirted from high voltage leads or electrodes to a sensing circuit. It is desirable, therefore, to reduce or eliminate this noise so that the sensing circuit can more readily detect the heart's electrical slgnals.
Certain implantable cardioverter/defibrillators have been developed which deliver shocks between an electrode mounted on a lead, preferably an endocardial lead, and a conductive part of the hermetically sealed case or can C.~ i..i.,g the pulse generator. This is sometimes referred to as a "hot can" and is analogous to so-called unipolar operation of a pacemaker, wherein a stin nl~ting pulse is delivered between an electrode and a pacemaker can. The m~gnitude of a shock is, of course, substantially greater than a pacing pulse and presents additional difficulties. In particular, in a "hot can" implantable cardioverter/defibrillator with EMI filters, a shock waveform may be prematurely terminated by a feedback effect. This appears to be attributable to the use of at least two EMI Su~ g capacitor filters, between each pace/sense electrode, which may also be a high voltage or shock electrode, and the can.
This phenomenon can be avoided by removing the EMI su~plessillg capacitor filters or by substantially reducing their capacitance. This, however, renders the device more susceptible to externally generated electromagnetic interference.
... .... .. . .
CA 022~3476 1998-ll-03 It is an object of the invention, therefore, to provide an implantable cardioverterldefibrillator in which the design of EMI suppressing filters is not influenced by the programmed selection of shock delivery path.
It is a further object of the invention to provide an EMI filter configuration for an implantable cardioverter/defibrillator which prevents premature termination of shock delivery.
It is another object of the invention to provide an implantable defibrillator which has continuous confirmation, but which is not susceptible to charging noise.
Disclosure of the Invention The present invention is addressed to an implantable defibrillator, which may include cardioversion and pa~.em~ker capabilities, which has EMI filters which are not susceptible to defibrillation shocks and which reduce or elirninate the effects of charging noise on sensing circuits used for continuous confirmation. A first filter capacitor is provided between a sense electrode, which may include pacing capabilities, and a ground reference within a hermetically sealed can containing a pulse/shock generator. A second filter capacitor is provided between a pacing/sensing reference electrode, which may also be a high voltage or shock electrode, and the ground reference.
In addition, there is a third filter capacitor between the ground reference and the can. Preferably, the connections of the first, second and third filter capacitors are physically as well as electrically adjacent to each other. In the preferred embodiment, the filter capacitors are housed in the can and in or adjacent to a feedthrough assembly which passes through the can. Most preferably, the filter capacitors are discoidal capacitors mounted in or adjacent to the feedthrough.
Bri~f Pescription of Drawings FIG. 1 is a block diagram of an implantable pac.em~ker/defibrillator.
FIG. 2 is a block diagram of an output circuit for use in the defibrillator of FIG. 1.
PIG. 3 is a schematic diagram of a prior art EMI filter circuit.
FIG. 4 is a scl~m~tic diagram of an EMI filter circuit according to the invention.
FIG. 5 is a perspective view of a combined hermetic feedthrough and filter circuit according to the invention.
FIG. 6 is a through section plan view of a first embodiment of the feedthrough and filter circuit of FIG. 5.
FIG. 7 is a through section plan view of a second embodiment of the feedthrough and filter circuit of FIG. 5.
FIG. 8 is a through section plan view of a third embodiment of the feedthrough and filter circuit of FIG. 5.
Best Mode for Carryin~ Out the Invention . ., . _ _ , .
~M 363 ~T
FIG I is a block diagrarn illustrating a rate adaptive pacern~rldefibrillator 10 according t~ the invention. A micropr~cessor 12 preferably provides p.lcent~er control ~n~ ccmp\lta~ion~l facilities. It will be appreciated that other form~ of circ~litry, such as analog or discrele digital circui~ry c~n bc used in place ~f rnicroprocessor 12. Ho~ever, a microprocessor is preferred for its miniature size and its tlexibility, ~oth of which are of critical importance in the imri~f~ble systen~s in which it is envisioned the invention will find use. A particulally energy efficient microproc~sscr ~hich i9 designed 6pecifically for use with imr~ t~le medical device~ i~ fuily describdd i;l Gor~on, ~r ~1., U.S. Pa~ent N~. 4,404,g72, which i5 also assi~ned to the assignee.
l'he micmprocessor 12 has ~nput~output ports conr~ec~ed in ~ conventional rnanner via bidirectinrlal bu~ 1~ t~ a n~ernory 15, an .~-V interva] timer 18, ~nd a p2~ing interval ~m~er 20. I~
~- addition. ~he A-V interval t~mer 18 and pacing inter-~a~ timer 20 each has an output connected individually to a COr~eSpQlldiIlg input pQrtofthe mlcroprocess~r 12 by lines 22 and ~4 respecti~ely.
Memory 1~ preferably in~;ludes ~oth ~OM arld RAI~!~. The microproce~sor 12 m~y also 1 j contain ~ itionsl RG~f and RAhI as aescribed ~n the G~r~o~, e~ al. ~r.s. Pa~ent ~o. 4,404,~, 2.
~he paeema~er op rating rout~ne is stored in ROM The RA-~ stores v~rious prognrr~ le parameters and l/~riables.
The A ~' and pac~ng inte~al timers 18 2nd ~0 may be ex~ernal to the rnicroproces~or I,, as illustrate-l, or int~rnal thereto. as described in the Gordon, et al. U.S. Patcnt No. 4,~ 72. The Jl~) hmess l~ 20 are suitable con~er~tional up or down counter~ of tlle type that are i~i~ially loaded with a count value and count up to or down from the value and output a roll~ver bit upon co~pleting ~.e pro~rarrlnled coun~. The initial count value is loaded ~Ilto the timers 18, 20 on bus 14 and ~e respective rol~ ver bi~s are ~utput to t~e n~icroprocessor 12 on lines 22, 24.
The micro,~roces~or 12 preferably also has an input/output port cc)nrlecte~ to a telemetry ~5 lr.te.face 26 by IjLA~e f~O. ~hC de,~brill&tor, -w-hen impl~n~u, is ~us abie io receiYe pacing, arrhy~nmia t~r~py, and rate controL parameters fr~m an ~xterIIal program~er and send data to an exterDal receiver if desired. Many suitable telemetry s!~stems are known to those skilled in the arl. One ~u~h syst m and encoding arrangernent is d~cribed i~.4r7nstrong a~d Co,~, U.S. Patent No. 5,3S3,91' whi~ is al~o as~igned to the a~signee.
The ll,icr.~ uees~or output ports are &onn~t~d to inputs of an atrial sti~ulu~ pulse generator 30 and a ventricle stirn~lus pul~e generator 32 b~ ~ontrol lines 34 an~l 36 rcspectiYely. The microprocessor I2 ~ansmi~ pul e para~neter data, such as arnplitude and width, as well ~s enable/disable and puise initiatioxl codes to the g~ ators 30, 32 on the respec~iVe control lines. The microproce~sor 12 also has input ports co~n~ct~d to outputs of an atr~al ~ensc amplifier 38 and a ~Ç~ 3 S~
o K~ L. ~ t. ~ , r~J ~ J ~ J ~C~.~ . f~ I ~J
~ -36~CT -6-venIricular sense a!r.pli~ier 40 by lin~s 42 and 44 respe~tively. Tbe ~tIial and ven~ricular scnse amplifiers 3&. 10 detect elec~rical conditions irl the hea~t ~ncluding ~brill~tion and occurrences of P-waYes ar~ R-waves. The atrial sense an~p'ifier 38 output~ a sigrlal on liIle 42 co the microproc~ssor 1~ whe~ ic de~ec~s a P-wave. This sign~l is latched to the microproces~or 12 input port by a S conventional la~ch (r.ot ~houn) ~he ~entr.cular sense arnpl~fier 40 outputs a ~ignal on llne 44 to the microprocessor 12 when it det~cts an R-wave. Thi~ signal ~s also latched tQ the microproce~sor 12 IrlpUt port by a conventional latch (not shown).
~he ~r~put of the atrial sense arnplifier 38 and the ourput of the atrial stirnulus pulse get~erat~r 30 are cormected ~ conductors through a first ~MT filter,ng feedthJorl,~h 4b, and through a con~entional first lead 48 to a paticnt's heart ~0. Lead ~8 i~ inserted mto ~he pahent's heart 50 intra~e~ously or in ~.ny other suitabl~ 2~anner. The lead 4~ has an el~ctric,ali~ conduc~i~e t~ pacing/sensing ~ip C2 or tip and ritlg at its dis~a' ~nd which is electric~lly colm~cted to the conductors in lead 48. 'rhe paeingJsensing tip 52 is preferably lodged in ~he right atrlu~. Th~ u~
of the Yentricular sense ~rnplifier 40 and the ou~u~ of the ventricul~r s~m~lus pulse gener~or 32 are onnec~ed b~ conductors Ihrough a second ~MT filtering ~eedthrou~h 54. ~e conduciors pais chroueh a conventional se~ond lead 56 which is inset~ intrave~iollgly or otherwi~ in the right Yentricle ~8 o~ ~he heart 50. Ihe second lead 56 has an electrically conductive p~cin~lser~ing tip ~0 or tip md ring at its dist~l end. The pacin~l~ensing tip 60 ;s eiecsricaILy connected to the conductors in second lead 5~. The pacin~lsensing tip 6d IS pceferably lo~ged cn the ~all of ~he ri~ght ~0 ventricle ~8.
lhe conductors cond~lct the s~i2nullLs p~ses gener~ted by the atriaJ and ~~en~;ricular sti~lulus pulse ~generators 30, 3~ to the pacing/sensing tips S~, 60. The paci~!sensing tips 52. ~a and corresponding conductors al~o conduct cardiac electrical signals sensed in t~e right ~triurn ~d ri~h~
ven~ricle to the atrial ana ven~ricular ~nplifiers, 38, ~0 re~pectively, The sense amplifiers ~g, ~0 ''5 enllaneelhe~ieC~riCai signais. Tn u~ preterred embod~ rxs ~f the inven~ion, the arnplifiers 38, 40 ha~ie an autornatic g3in cont~ol ~atNre, as described in U.S. Patent ~,903,699 1o Baker, er ~1. That applicatisn is a~si~ned to the same assignee ~s tl~ present inve~tion.
T~e imrl~nt~ble cardiac stim~ tor 10 also ha~ a defibrillator ci~cuit 62. If fibrillation ~s deteaed ~hrough the a~rial ~r ven~ricular sense amplifiers 38, 40, a high ener~y s~.ock can be delivere~ ~hrough defibrill3.tion lead 6~ and elect~ode S6. De~ection algorithms for de~ection of tachycardias and fibr .lation are described in Pless, et ~l., U.S. Patent 4,880,~05. Allh~ugh an endocardi..l ~lectrod~ and use of ~he conductive part of th~ can or case are ~uggested by the drawin~, pa~ch-type epicardial e~ectrodes ~or defibrillaliorl are al~o AMENDED SHEET
,. . .. . ..
..... ~ ,.. . .
63Pc~
known. Tne shock is, contro!led l~y a shc~ck driv~er circuit 68, which will be more particularly describ,ed herea~r A~l of the s~orementioned co~ponents are p~wered b~ a power sup~ly 70. The po~er sup,uly 70 may comprise elther s~andard or rechargeable battcries or b~th. which ;nay b dedicate,~ ~ the operation of different parts of the ~tirr~ r 10.
In the preferred embodiment of the inven~ion, it is considere~ d~sir,~ble to pro~uce multi-ph,~,ic shocks for defib"llatiorl through the shock driver 68. Circuitry partlcu~arly v, el,' adapced for producing such wave forms ir describe~ in detai~ in U.S. Paten~ ~c. 4.800,883 to W~nstrom.
Circu,~ry for the ~,hock driver 68 is sh~Jwn with greater particul,~-ity in PIG. 2. FIG. 2 illu~trates the ~hock drivcr 58 conr.eeted to the patie~'~, hear~ 50 through dle lead ~4 and el~ctrode 56 and througn the call 66;~ produce a ~iph~sic w~e forrn, a b,~k of four three-ter~ninal semiconduetor sw~ches 72, ~4~ ?~ sueh as ir~ulated g~te bipolar trans~tor (rGBri switches, rnay ~e empl.~ d. It wiil ~_ be unders~ood, however, tt~t the invention can ~e emplo~ed with mo~opl~sic ~ulse gener~tors and ~ith p-~lse generator~, incorporating rn~1~tirh~cic ~tim~ orl~ The switches 72, ?~ " 78 are c~ntrolled hy drivers 82, 84, 86, 8~ respectively. The drivers 82, 84, 86, 88 a~e c~n~rolLed by ~5 command puises from the miCrroproceggor L2 through control lines 80 ~nd 91, as will De snore particular~y dcscrlbed below. The energy to pr~duce bi~hasic defi~ri!1arng shocks is ~plied from high vol~age capacitor 92. High volt~ge capacitcr 92 is conn~te~ to swi~ches, 2 and 7~, and c~Lrrerlt therefrotn returns ~ ia switches 76 or 7~. The first leaà 64 is cnnnPrte~ beeween switche~ 72 and 76 wniie the second lead 66 i~ connected berween switches 74 and 78.
2n ~ amount o~ energy deliver~d to t}~e heart is de~endanl upon ~e voltage on the high voltage c~acitor. rhe voltage appearirlg OII the capaci~ot 9~ i5 controlled by voltage c~ntroller 9 which is coanected to ~ source of power s~lch as the battery or po~er supp1y 70 through line iO0.
The voltage controller 9~ ls controlled t~ro~lgh a line 1~4 from the microproc~ssor I2. This -~ configuIation is described in more detaii in Lhe ~i~trom patent rnen~ione~ above. In ~he '~ CO~fij~,'Ula;iOrl ~hUWl~ t~ pro~ucc a ~Lnidirectionai current pulse ~hrou~h the heart 50, the m~croprocessor 12 issues a c~lnrnand along lLne 8~) to drivers 82 and 88, closing ~v~tches 72 ar~d 7~.
Both be~or~ and ~er the comrnand, all ~witches are normally opened. To produce ~ opposite currerlt, the microprvcessor !2 issues a command on line 90, clo~ir4 cwitches 84 and ~6 and directing ~;he curren~ flow in the oppo6ite direction through the heart 50.
The EhlI fiiter according to ~he in~entton will now be descr~bed. A prior art EMI ~Iter 90 i~ illussra~ ,;n FIG. 3. Such a filter 90 migkt be comprised ~f discrcte con~ponents, or incorporated into a set of discoid~l capacitors. Such di~c~ capacitors m~gh~ be mounted in a feedthrvugh such as feedthrough 54. or adJacen~ the feedthrough, as described jTl St.~pher~,on et al. U.S. PateM
AMEN~D SHEEt . ..... , , , ".. ,, ,, ,, ,, ~, .. .
CA 022~3476 1998-11-03 W O 97/41923 PCTrUS97/07572 5,333,095. Fundamentally, an EMI filter 90 comprises a lead 92 which would pass through a desired case such as the can 66 to provide an electrical connection through the can 66. The lead 92 might, for example, be connected to the ventricular sense circuit 40 and the ventricular stimulus generator 32 within the can at pin l and to the tip electrode 60 outside of the can. A first capacitor 94 is connected from the lead 92 to the can 66 to provide a high frequency path for EMl. Multiple leads and capacitors could be provided in a single configuration or at a single feedthrough. For example, as shown in FIG. 3, an additional lead 96 could be provided within an associated capacitor g8 connected from the additional lead 96 to the can 66. Pin 2 of lead 96 might be connected, for example, to the shock driver 68 within the can and to the endocardial electrode 70 outside of the can.
In an implantable cardioverter defibrillator, charging noise is generated during the process of charging the high voltage capacitors in the defibrillator 62 prior to shock delivery. Charging noise may be present as an electric field coupling from the can or by induction of eddy currents. This sometimes occurs when a "hot can" electrode has been introduced into the shock delivery pathway, that is, when the can 66 is used as one of the electrodes. The prior art connection of the C 1 and C2 capacitors 94, 98 respectively, directly to the can 66 can cause an inappropriate sensing during the charging cycle and premature termination of a can-delivered shock. Even if two or more defibrillation electrodes remote from the can are used, charging noise can still prevent a sensing circuit from detecting the electrical condition of the heart, if continuous confirmation of the life-threatening condition is attempted. These situations are avoided by the configuration of the invention illustrated in FIG. 4.
FIG. 4 illustrates an EMI filter 100 according to the invention. The EMI filter 100 comprises at least one lead 102, configured to pass through the can 66. As before, this lead 102 might be connected within the can at pin 1 to the ventricular sense circuit 40 and the ventricular stimulus generator 32. Outside the can 66 the lead 102 might be cormected to the ventricular tip electrode 60. A shunt capacitor 104 is provided similar to the capacitor 94 described above.
However, instead of being connected to the can 66, this capacitor is connected directly to the internal system ground 106. A C3 capacitor 108 is connected between the common contact of the Cl capacitor 104 and of the system ground 106 and the can 66. In the preferred embodiment, the capacitance of the C I capacitor and the C3 capacitor are approximately equal. Charging noise is generally within the frequency range of 100 kHz to 200 kHz. Consequently, the Cl capacitor is chosen to easily pass freql~Pn~ies higher than 100 kHz. These frequencies are passed directly to the system ground since it passes tllrough but a single capacitor. This adequately (limini.~hes the effect of charging noise on the circuit and prevents improper sensing. On the other hand, external EMI
generally consists of frequencies in excess of 1 MHZ. These frequencies are passed easily through .., .. ~ ~ .. . ..
.. , . . . , . .. ~ ~
CA 022~3476 1998-11-03 W O 97/41923 PCTrUS97/07572 the capacitor C1 and C3 in series and are diverted to the can. External EMI entering either from the tip electrode 60 or the endocardial defibrillation electrode 70 needs to be ~tteml:~ted before it can be demodulated by the rectifying properties of semi-conductor junctions. This is done by .~hllnting the EMI currents back to the can which acts as a Faraday Cage for the device. The C3 capacitor 108 S provides a low impedance path from the ground reference to the can. Multiple leads may be provided through the can, either electrically a~j~rent, or both electrically and physically adjacent one another. For example, an additional lead 110 could be provided to connect to the endocardial defibrillation electrode 70 and through pin 2 to the shock driver 68. A C2 capacitor 112 is connected from the lead 10 to the system ground 106 and to the C3 capacitor 108.
0 The EMI filter 100 of the invention may be provided as separate components connected to a standard feedthrough. However, the preferred embodiment is to construct a feedthrough and EMI
filter as a common feedthrough structure 114 as illustrated in perspective view in FIG. 4. The feedthrough structure 114 comprises the leads 102 and 110 described above and a system ground connection 116 for connection to the system ground 106. The leads 102, 110 and 116 are embedded in a feedthrough 118 having a metal ferule 120 for connection to the can 66 which houses a capacitor structure 122. The capacitor structure 122 may be constructed in a variety of ways, as will IIOW be explained.
One embodiment is shown in FIG. 6, which represents a plane through section of the feedthrough system 114 of FIG. 4. As seen in FIG. 6, the metal ferrule 120 of the feedthrough 118 has a circumferential groove 124 for receiving the can 66. A hermetic seal 126 plugs one end of the feedthrough 118 around the leads 102 and 110. Such hermetic seals are known in the art, and are described, for example, in U.S. Patents 3,920,888 and 4,678,868. The capacitor assembly 122 comprises chip capacitors employed for the capacitors 104, 112 and 108. The shunt capacitor 108 is connected by a jumper 128 to the metal ferrule 120. Alternatively, the jumper 128 could be connected directly to the can 66.
An alternative construction comprised of discoidal capacitors is illustrated in through section in FIG. 7. As in the embodiment of FIG. 6, the leads 102, 110 and 116 and the metal ferrule 120 and hermetic plug 126 are substantially as described above, and perform the same functions. Instead of the chip capacitors, however, the capacitors 104, 108 and 112 are comprised of discoidal capacitors. In particular, the ground line 116 which is intended to be connected to system ground 106 is connected to an annular ring conductor 130. Plates on the outside of this ring 130 interleave with plates connected to the ferrule 120, thus forming the shunt capacitor 108 which connects to the can through the ferrule 120. On the inside of the annular conductor 130, additional plates h1terleave with plates connected to the lines 102 and 110 to form capacitors 104 and 112 respectively CA 022~3476 l998-ll-03 W O97/41923 PCTrUS97/07572 A third embodiment is illustrated in through section in FIG. 8. As in FIGS. 6 and 7, like numerals indicate like parts. In this embodiment, however, the capacitors 104, 108 and 112 are formed as individual stacked discoidal capacitors formed adjacent their respective leads 102, 116 and 110.
Each of the embodiments of FIGS. 6, 7 and 8 are shown with the capacitor structure 102 contained within the ferrule 120 of the feedthrough 118. However, the invention could also be implemented using discoidal capacitors attached around the ferrule, as shown, for example, in Stephenson et al. U.S. Patent 5,333,095.
Claims (10)
1. An implantable defibrillator [10] comprising an hermitically sealed can [66];
circuit means [12, 30, 40] for detecting the condition of the heart of a patient;
means [62,68] responsive to said circuit means for producing a defibrillation shock;
a battery [70] electrically connected to said circuit means and to said means for producing a defibrillation shock, said battery connected to an internal system ground [106];
means [48,56] for providing an electrical connection to a first electrode [52,60]; and a first EMI filter [46,54] connecting said circuit means and said means for providing an electrical connection to said first electrode, characterized in that said first EMI filter comprises an electrical conductor [102, 110] connecting said circuit means and said means for providing an electrical connection to said first electrode;
means [104,112] connected to said electrical conductor for conducting EMI having a first predetermined frequency range to said internal system ground [106]; and means [104,112,108] connected to said electrical conductor for conducting EMI having a second predetermined frequency range to said can.
circuit means [12, 30, 40] for detecting the condition of the heart of a patient;
means [62,68] responsive to said circuit means for producing a defibrillation shock;
a battery [70] electrically connected to said circuit means and to said means for producing a defibrillation shock, said battery connected to an internal system ground [106];
means [48,56] for providing an electrical connection to a first electrode [52,60]; and a first EMI filter [46,54] connecting said circuit means and said means for providing an electrical connection to said first electrode, characterized in that said first EMI filter comprises an electrical conductor [102, 110] connecting said circuit means and said means for providing an electrical connection to said first electrode;
means [104,112] connected to said electrical conductor for conducting EMI having a first predetermined frequency range to said internal system ground [106]; and means [104,112,108] connected to said electrical conductor for conducting EMI having a second predetermined frequency range to said can.
2. The implantable defibrillator according to claim 1 further comprising means [48,56] for providing an electrical connection to a second electrode; and a second EMI filter [46,54] connecting said circuit means and said means for providing an electrical connection to said second electrode, said second EMI filter comprising an electrical conductor [102,110] connecting said circuit means and said means for providing an electrical connection to said second electrode;
means [104,112] connected to said electrical conductor for conducting EMI havinga third predetermined frequency range to said electrical ground producing means;and means [104,112,108] connected to said electrical conductor for conducting EMI
having a fourth predetermined frequency range to said can.
means [104,112] connected to said electrical conductor for conducting EMI havinga third predetermined frequency range to said electrical ground producing means;and means [104,112,108] connected to said electrical conductor for conducting EMI
having a fourth predetermined frequency range to said can.
3. The implantable defibrillator according to claim 2 wherein said second predetermined frequency range is substantially equal to said fourth predetermined frequency range.
4. The implantable defibrillator according to claim 2 further comprising means [64] for providing an electrical connection to a first defibrillation electrode [70]; and wherein said second EMI filter [100] further connects said shock producing means [68] and said means [64] for providing an electrical connection to said first defibrillation electrode.
5. The implantable defibrillator according to claim 4 further comprising means for connecting said means [68] for producing a defibrillation shock to a second defibrillation electrode [66] and wherein at least a portion of said can [66] is said second defibrillation electrode.
6. The implantable defibrillator according to any of claims 1 through 5 wherein said means [104,112] for conducting EMI having a first predetermined frequency range comprises a first capacitor [104,112] connecting said electrical conductor to said internal system ground [106]; and said means [104,112,108] for conducting EMI having a second predetermined frequency range comprises a second capacitor [108] connecting said internal system ground [106] and said first capacitor [104,112] to said can [66].
7. The implantable defibrillator according to any of claims 2, 3, 4, 5, or 6 wherein said means [104,112] for conducting EMI having a third predetermined frequency range comprises a third capacitor [104,112] connecting said second electrical conductor to said internal system ground [106]; and wherein said means [104,112,108] for conducting EMI having a fourth predetermined frequency range comprises said second capacitor [108] connecting said internal system ground []
and said third capacitor [104,112] to said can [66].
and said third capacitor [104,112] to said can [66].
8. The implantable defibrillator according to any of the foregoing claims wherein at least one of said means for conducting EMI is a chip capacitor [Fig. 5].
9. The implantable defibrillator according to any on the foregoing claims wherein at least one of said means for conducting EMI is a discoidal capacitor [Fig. 7 and Fig. 8].
10. The implantable defibrillator according to any of the foregoing claims further comprising an hermetically sealed feedthrough [114] and wherein said EMI filter [100] is mounted adjacent said feedthrough [114].
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US64278096A | 1996-05-03 | 1996-05-03 | |
| US08/642780 | 1996-05-03 | ||
| PCT/US1997/007572 WO1997041923A1 (en) | 1996-05-03 | 1997-05-02 | Implantable cardiac cardioverter/defibrillator with emi suppression filter with independent ground |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2253476A1 true CA2253476A1 (en) | 1997-11-13 |
Family
ID=24577989
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002253476A Abandoned CA2253476A1 (en) | 1996-05-03 | 1997-05-02 | Implantable cardiac cardioverter/defibrillator with emi suppression filter with independent ground |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US5817130A (en) |
| EP (1) | EP0915722A1 (en) |
| JP (1) | JP2000510011A (en) |
| CA (1) | CA2253476A1 (en) |
| WO (1) | WO1997041923A1 (en) |
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Also Published As
| Publication number | Publication date |
|---|---|
| JP2000510011A (en) | 2000-08-08 |
| US5817130A (en) | 1998-10-06 |
| WO1997041923A1 (en) | 1997-11-13 |
| EP0915722A1 (en) | 1999-05-19 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |