Patent Document:

u . s . patent application ser . no . 09 / 761 , 333 filed jan . 18 , 2001 assigned to the same assignee as this invention and entitled cardiac electrode catheter and method of manufacturing same now______ , incorporated herein by reference describes an endocardial lead having multiple electrodes that can be deployed in a heart chamber or coronary vasculature . the electrodes are electrically isolated so that they can function independently . different embodiments of this cardiac lead can be placed into the great cardiac vein , in the right atrium , and the right ventricle . in the right atrium or ventricle , the cardiac lead can be deployed so that electrodes positioned throughout the heart chamber , including the septal wall and the right ventricular outflow tract . in the great cardiac vein , multiple electrodes can be deployed along a significant length of the vasculature . the adapter of this invention allows the terminals of a proximal end of a multi - electrode cardiac lead to be connected to the connectors of any currently marketed pacemaker or other pulse generator conforming to the is - 1 standard . refer now to fig1 a for an overview of the cardiac pacing system of this invention , consisting of a lead 5 a , a pacemaker 20 with a header or is - 1 connector 15 and an adapter 10 . in fig1 a the distal end of the endocardial multi - electrode cardiac lead 5 a is implanted within the heart 25 as described above . the proximal end of the multi - electrode cardiac lead 5 a is coupled to the adapter 10 . the adapter 10 has circuitry that selects which electrodes of the lead 5 a are connected electrically to the pacemaker 20 . in fig1 b , the distal end of epicardial multi - electrode cardiac lead 5 b is placed on the exterior surface of the heart 25 . the proximal end of the epicardial multi - electrode cardiac lead 56 is coupled to adapter 10 as described above in fig1 a . further , as described in fig1 a , the adapter 10 has circuitry to select which of the electrodes of the multi - electrode cardiac lead 5 a are connected to pacemaker 20 . as shown in both fig1 a and 1 b , adapter 10 is connected to the is - 1 type connector 15 of the cardiac pacing pulse generator 20 through a multi - conducting wire 12 . the general structure of the adapter 10 of this invention is shown in fig2 . the adapter 10 includes an is - 1 compatible connector 30 that connects to the pacing pulse generator 20 . the adapter 10 also has a lead 5 ( numeral 5 is used to refer collectively to leads 5 a and 5 b ) through the terminals 45 of the multi - electrode cardiac leads . the multiplexer 35 contains a connection matrix ( discussed in detail below ) that makes the required connections between the is - 1 connector 30 and the lead connector 40 . the adapter 10 can be customized for each patient or for each pacemaker using an external programming device . for example , if it is determined that multi - site pacing from electrodes 2 , 9 , and 16 is needed within lead 5 ( shown in fig1 a ), the appropriate connections will be made by the multiplexer 35 . refer now to fig3 a the multiplexer 35 includes a bank of links 50 . the bank consists of link 51 a , . . . , 51 n each of which is connected between one lead terminal of the multi - lead connector 40 such as 41 and one of the contacts of the is - 1 connector 30 such as 42 . the links of bank 50 can be breakable or fusible links . [ 0054 ] fig3 b illustrates a typical breakable link 51 for the bank 50 . the link 51 is formed as a metal conductor 55 deposited on a substrate . alternatively , the link 51 could be formed without a substrate . the metal conductor 55 has a thinned region 52 . the external programmer is attached to the ends 54 and 56 of the metal conductor 55 through connections 30 and 40 . a current is forced through the metal conductor 55 until the current density in the thinned region 52 of the metal conductor 55 is sufficient to melt it and the link 51 is opened . this is a phenomenon well known in the art and not discussed further . if the links 50 of fig3 a are a breakable type , an external programmer is used to break all the links of bank 50 that are not required leaving only the required link closed . [ 0056 ] fig3 c illustrates a typical fusible link 51 ′. the link 51 ′ is formed of two metal conductors separated by a dielectric material 64 . the dielectric material may be air , a polymeric insulator , silicon dioxide , or other known insulator . metal conductors 62 are placed in close proximity to the separating dielectric material 64 and the ends of the two metal conductors 60 a and 60 b . the programmer is attached to the metal conductors 60 a and 60 b through connectors 30 , 40 . the programmer ( not shown ) applies a sufficiently high voltage between the metal conductors such that the separating dielectric material breaks down and a conducting plasma is formed . the heat of the plasma melts the metal conductors 62 and they fuse to form a bridge ( not shown ) to the metal conductors 60 a and 60 b . the metal conductors 62 generally are formed of a metal having a low melting point to allow the formation of the bridge at a relatively low temperature . the lower temperature should be much less than the melting point of the metal conductors 60 a and 60 b thus allowing fusing of the link with no degradation of the metal conductors 60 a and 60 b . again , this process is well known and will not be described in more detail . for this embodiment , only the required links are fused . the external programmer 65 , as shown in fig4 has a power source 67 that provides the programming voltage ( vprog ) and the programming current ( iprog ). when a link 51 a , . . . , 51 n of fig3 a is to be broken or fused , the external programmer 65 is connected to one terminal of the lead connector 40 and to one contact of the is - 1 connector 30 . if the link 51 of fig3 a is to be opened , the programming current iprog is set to the level that allows the thinned region 52 of fig3 b to melt . alternately , if the link 51 ′ of fig3 b is to be fused , the voltage vprog is set such that the separating dielectric 64 of fig3 c breaks down causing a plasma which melts the metal conductors 62 of fig3 c to bridge the metal conductors 60 a and 60 b as described . the programmer 65 steps through each of the links of bank 50 and opens or closes them as required . importantly , once a link is opened or closed , it remains in that state and the process cannot be reversed . refer now to fig5 for discussion of a second embodiment of the adapter of this invention . in the second embodiment , the multiplexer is formed of a bank 65 of electronic switches . each switch 66 a , . . . , 66 n of bank 65 has a first switch terminal a connected to one of the contacts of the is - 1 connector 30 and a second switch terminal b connected to one lead terminal 45 of the lead connector 40 . further , each switch 66 a - n has a control terminal c connected to the control circuit 70 . the control circuit 70 provides a control signal to selectively open or close switches 66 a - n as required . a program input circuit 80 is connected to the control circuit 70 the program input circuit 80 and receives an encoded programming signal . the program - input circuit 80 decodes the encoded programming signal to define the control signal to the respective switches . the program - input circuit 80 senses the control signal to the control circuit 70 . the control circuit 70 then routes the control signal to the control terminal c of the desired switches 66 a , . . . , 66 n . in a preferred implementation of the second embodiment of the adapter of this invention , the program input 80 is connected to a radio frequency ( rf ) receiver 85 . the rf receiver 85 is connected to a receiving antenna 90 . the receiving antenna 90 receives a radio transmission from the transmitting antenna 95 . the transmitting antenna 95 is connected to the rf transmitter 100 , which is connected to the program controller 105 . upon selection of the desired group of electrodes of the multi - electrodes cardiac lead , the program controller 105 creates the encoded program signal . the program controller 105 transfers the encoded program signal to the rf transmitter , where it modulates the rf transmission . the rf transmission modulated with the encoded program signal is transferred to the transmitting antenna 95 for transmission to the receiving antenna and then to the rf receiver 85 . the rf receiver 85 then demodulates the rf transmission to extract the encoded program signal . the encoded program signal is then transferred to the program input circuit 85 . the methods and techniques for programming cardiac pacing systems is well known in the art and are not discussed further . a power source 75 is connected to provide voltage to the control circuit 70 , the multiplexer 35 , the program input circuit 80 and the rf receiver 85 . the power source could be a battery included within the adapter . in an alternate implementation of the second embodiment of the adapter of this invention , the power source 75 has a power conversion unit connected through the is - 1 connector 30 to the pulse generator 20 . the power conversion circuit captures a portion of the energy present in the stimulation signal provided by the pulse generator 20 and converts the energy to a voltage to power the circuit incorporated in the adapter 10 . the power conversion circuit shown in fig6 has a capacitor c 1 , which is charged during the active period of the pulse . the capacitor c 1 is connected to act as a voltage source to power the multiplexer circuit 35 . a diode d 1 is connected between the capacitor c 1 and the contact of the is - 1 connector 30 to prevent the charge present on the capacitor c 1 from being transferred back to the contacts of the is - 1 connector 20 when the pulse is not active . the power conversion circuit 75 , additionally , has a rechargeable battery vb 1 which acts as a voltage source if the pacing signal does not provide sufficient energy to keep the capacitor c 1 charged adequately to power the multiplexer circuit 35 . the diode d 2 is connected between the capacitor c 1 and the battery vb 1 to prevent the charge present on the capacitor c 1 from trying to charge the battery vb 1 . capacitor c 1 can be connected through appropriate diodes to a plurality stimulation wire from pulse generator 20 . as described above , multi - focal pacing or optimal site pacing can be achieved by having one electrode or group of electrodes of the multi - electrode cardiac lead designated for transmission of the stimulation signal and another electrodes or group electrodes of the multi - electrode cardiac lead to provide sense points for sensing the heart activity . this requires that different sets of electrodes of the multi - electrode cardiac lead be connected through the adapter to the stimulation pulse generator during the period that the stimulation signal is active than when stimulation signal is inactive and the pacemaker is sensing the heart activity . [ 0067 ] fig7 illustrates a third embodiment of the adapter of this invention where a pacing set of electrodes is coupled to the pulse generator during the time the pacing signal is active and a sensing set of electrodes is coupled to the pulse generator during the time that the pacing signal is inactive . the adapter 100 of this embodiment has two multiplexers , a pacing multiplexer 110 and a sensing multiplexer 125 . the pacing multiplexer 110 and the sensing multiplexer 125 are formed of electronic switches 111 a - n and 126 a - n , respectively . each switch 111 a - n and 126 a - n has a first switch terminal a connected to one of the contacts of the is - 1 connector 30 and a second switch terminal b connected to one of the lead terminals of the lead connector 40 . a control terminal c controls the opening and closing of each switch upon receipt of a control signal . the control terminals c of the switches 111 a - n of the pacing multiplexer 110 are connected to the pacing control circuit 115 . the pacing control circuit 115 is connected to the program input circuit 80 to receive a programming signal designating , which of the switches 111 a - n are closed to connect the pacing set of electrodes through the adapter 100 to pulse generator 20 to receive the pacing signal . the pacing control circuit 115 transfers the appropriate control signals to the control terminals c to close the designated switches 111 a - n connected to the pacing electrodes during the period when the pacing signal is active . the control terminals c of the switches 126 a - n of the sensing multiplexer 125 are connected to the sensing control circuit 120 . the sensing control terminals of the switches 126 a - n of the sensing multiplexer 125 are connected to the sensing control circuit 120 . the sensing control circuit 120 is connected to the program input circuit 80 to receive a programming signal designating , which of the switches 126 a - n are to be closed to connect the sensing set of electrodes through the adapter 100 of this invention to the pacemaker generator 20 to provide the sense points for the pacemaker generator 20 to sense the heart activity . the sensing control circuit 120 transfers the appropriate control signals to the control terminals c of the sensing multiplexer 125 . to close the designated switches 111 a - n connected to the sensing electrodes during the period when the pacing signal is inactive and the pulse generator 20 is sensing the heart activity . the pacing control circuit 115 and the sensing control circuit 120 are connected to the contacts of the is - 1 connector 30 . the pacing control circuit 115 and the sensing control circuit 120 examine the is - 1 connector 30 for the presence of the pacing signal . at the beginning of the pacing signal , the pacing control circuit 115 sends a close signal to the respective control terminals c of the pacing multiplexer 110 to cause closure of the selected switches such that the selected pacing electrodes of the lead 5 receive the pacing signal . moreover at the beginning of the pacing signal , the sensing control circuit 120 sends an open signal to open to the control terminals to cause all the switches of the sensing multiplexer 125 to prevent the pacing pulse from being coupled to the sensing electrodes of the multi - electrode cardiac lead and to avoid frying the sense arcuitry within the pacing electrode . after the pacing signal has terminated , control circuit 115 sends an open signal to the control terminals to cause all the switches of the pacing multiplexer 110 to be opened . at this same time the sensing control circuit 120 sends a close signal to the appropriate control terminals of the sensing multiplexer 120 to cause closure of the switches connected to the sensing electrodes of the leads to connect the selected sensing electrodes to the is - 1 connector 30 . [ 0072 ] fig8 illustrates an implementation of the pacing control circuit 115 and the sensing control 120 in the form of a control circuit 130 . the control circuit 130 has a program decoder 135 that is connected to the program input 80 to receive the programming signal . the program decoder sends the control signal 140 to the logic circuit 145 pulse . the program decoder enables each of the switches ( or gates ) of the controller . the pacing controller closes the enabled switches on a pacing pulse . the sensing controller opens the enabled switches on a pacing pulse all electronic embodiments should have a back - up fail - safe mechanism in the switch controller that assures that during a failure the adapter 10 , 100 leaves the proper pacing and sensing group of electrodes of the multi - electrode cardiac lead connected to the is - 1 connector 30 . the group of electrodes that are connected would be programmed from the programming device , eliminating the possibility that the adapter would route pacing signals to an ineffective pair of electrodes . the switches 111 a - n and 126 a - n of the mul 1 tiplexer 65 of fig5 the pacing multiplexer 110 of fig7 and the sensing multiplexer 120 of fig7 may be implemented as solid state relays that are field effect transistors fet &# 39 ; s configured as pass - gates or transmission gates as is known in the art . refer now to fig9 for a description of the steps of the method to select the group of electrodes of the cardiac lead for connection to the is - 1 connector of a pacing pulse generator . as can be seen from the above description , the adapter ( 10 , 100 ) can be provided in a number of different configurations . in the simplest configuration ( fig3 b , 3 c , 4 ) the links of the adapter are set or “ burned in ” during the implantation procedure . for the other embodiments , ( fig5 ) the links of the multiplexer can be closed and opened at will . finally in th embodiments of fig7 and 8 the adapter is dynamic in the sense that it opens and closes the links of the matrix as the patient &# 39 ; s heart is being stimulated . after a multi - electrode load 5 is implanted , its electrodes must be designated for the appropriate functions . the physician can inspect the lead and its electrodes through x - ray or other imaging means and designate the electrodes on his own . alternatively , an automated procedure may be used to identify and designate the electrodes as follows . the lead 5 is implanted ( step 200 ) into the heart . the lead 5 contains any number of independent electrodes . in the preferred embodiment the multi - electrode cardiac lead may have up to 128 electrodes or even 256 electrodes . each electrode on the lead is theoretically capable of sensing the heart &# 39 ; s electrical activity and delivering an electrical pulse to the heart . the delivery of therapy can be for optimized for bradycardia pacing and for multi - site stimulation for congestive heart failure . the endocardial cardiac lead 5 a is placed in one or more chambers of the heart and the epicardial cardiac 5 b is placed on the exterior surface of the heart , thus allowing complete sensing and stimulating control of the entire chamber . alternately , electrodes are placed along the ventricular septum and up into the right ventricular outflow tract . electrodes may be placed along one wall of the heart chamber or in the atrium and continue into the ventricle . the electrodes are spaced appropriately on the lead for the intended application . upon proper implantation ( step 200 ) of the cardiac lead in the heart , each electrode is tested ( step 205 ) to determine which of the electrodes are positional for optimal sensing of the heart activity . single site sensing only attempts to determine whether a cardiac event occurred or not . this is determined by observing the cellular electrical activity that initiates the cardiac contraction . this is the same signal that is observed on a surface electrocardiogram ( ecg ), except at a more localized level . the surface ecg is a summation of the electrical activity of all of the cells of the heart . depending on how the electrode is placed , the signal seen by a pacemaker can range between less than 1 mv to greater than 10 mv . obviously , it is desirable to find the location with the largest signal . thus , during an implant , a location with a good amplitude sensing signal is determined . referring the fig1 , an electrode of a cardiac lead is tested as follows . in step 230 one of the electrodes is selected . the magnitude of the intrinsic electrical activity served through the selected ?? is measured ( step 235 ). to be considered for inclusion for sensing , the electrode must provide a sensing signal greater than a minimum signal level . the measured magnitude of the intrinsic electrical activity as sensed by the electrode is compared ( step 240 ) to the minimum acceptable signal level . if the measured signal is not greater than the minimum acceptable signal level , a test if the chosen electrode is the last electrode being tested ( step 245 ) is performed . if it is not the last electrode being tested , a new electrode is selected ( step 230 ). if the measured magnitude of the intrinsic electrical activity as sensed by the chosen electrode is greater than minimum acceptable signal level , an electrode identifier with the measured level is logged ( step 250 ). the measured magnitude of the intrinsic electrical activity as sensed by the chosen electrode is compared ( step 255 ) to the magnitude as sensed by a previously identified electrode having the maximum measured . if the measured magnitude of the current electrode is not greater than the measured magnitude of the previously identified electrode , the electrode is tested ( step 245 ) for being the last electrode . if the electrode is the last electrode , the sensing testing ends ( step 265 ). if it is not the last electrode , the next electrode is selected ( step 230 ) and tested . if the measured magnitude of the current electrode is greater than the measured magnitude of the previously identified electrode , the electrode is identified ( step 260 ) as the electrode with the largest magnitude . the electrode is tested ( step 245 ) for being the last electrode . if the electrode is the last electrode , the sensing testing ends ( step 265 ). if it is not the last electrode , the next electrode is selected ( step 230 ) and tested . referring back to fig9 each lead is then tested 210 to determine which lead or set of leads are optimally connected for providing the pacing signal to the heart . using what is referred to in the art as “ sweet - spot pacing ”, or single - site optimization , pacing is accomplished through only one electrode , but only that electrode that optimizes a desired parameter is chosen . one parameter that could be optimized is the amount of the cardiac contraction caused by the pacing pulse to a particular electrode . a measure of a good cardiac contraction is the amount of time the entire contraction takes i . e ., the qrs width . a wider qrs indicates a slower spread of the wavefront across the heart and is usually typical of a poorly synchronized heartbeat . by pacing through each electrode and measuring the width of the qrs complex , we can find the best site from which to pace the heart . other methods , including invasive procedures , could be used to measures of cardiac output to select the optimum site . another optimization parameter can be the stimulation threshold , or the provisional amount of energy required to cause the heart to contract from a stimulating pulse ( capture ). this greatly affects the length of battery life and much time is spent during a pacemaker implant attempting to find the location with the lowest threshold . the threshold is determined by lowering the pacing energy while pacing until the pulses no longer capture the heart . the lowest value that captures the heart and augmented by a safety margin is the threshold . using the cardiac lead , the threshold of each electrode can be found and pacing is done using the electrode with the lowest threshold . as shown in fig1 , the testing ( step 210 ) for pacing begins by selecting ( step 270 ) which parameter is suitable for selecting a cardiac pacing leads . this step may be performed automatically or the parameter may be set by the physician . next , an electrode of the cardiac lead is chosen ( step 275 ) for testing . the initial selection ( step 275 ) of the electrode may be random . the electrode most likely to provide the best pacing such as one electrode near the tip of the cardiac lead , or a first terminal location on the connector . as is apparent , any initial choice ( step 275 ) of the electrode is in keeping with the intent of this invention . further , any pattern of selection of choosing ( step 275 ) subsequent electrodes is also in keeping with the intent of this invention . the pacing signal is applied ( step 280 ) through the respective electrode to the heart . the stimulation level required to stimulate the heart is recorded and compared ( step 285 ) to a maximum stimulation level allowed . if the stimulation level of the pacing signal is greater than the maximum stimulation level allowed ,. the electrode is to be ignored . the electrode is tested ( step 290 ) to determine if it is the last electrode in the cardiac lead to be evaluated . if it is not the last electrode in the multi - electrode cardiac lead to be evaluated , the next electrode is selected ( step 275 ) for testing . if it is the last electrode to be evaluated , the pacing testing ends ( step 310 ). if the stimulation level of the pacing signal is less that the maximum stimulation level allowed , the electrode identification and the stimulation level is logged ( step 295 ) and compared ( step 300 ) to the stimulation level of the previously identified electrode as having the minimum stimulation level . if the currently tested electrode has a stimulation level greater than the stimulation level of the previously electrode identified as having the minimum stimulation level , the electrode is tested ( step 290 ) if it is the last electrode in the multi - electrode cardiac lead to be evaluated . if it is not the last electrode in the multi - electrode cardiac lead to be evaluated , the next electrode is selected ( step 275 ) for testing . if it is the last electrode to be evaluated , the pacing testing ends ( step 310 ). if the currently tested electrode has a stimulation level less than the stimulation level of the previously electrode identified as having the minimum stimulation level , the currently tested electrode is identified ( step 305 ) as the electrode having the minimum stimulation level . the electrode is tested ( step 290 ) if it is the last electrode in the multi - electrode cardiac lead to be evaluated . if it is not the last electrode in the multi - electrode cardiac lead to be evaluated , the next electrode is selected ( step 275 ) for testing . if it is the last electrode to be evaluated , the pacing testing ends ( step 310 ). once the sensing electrodes and pacing electrodes are determined , the correct combination of sensing electrodes and pacing electrodes are selected ( step 215 ) to be connected to the pacemaker . if the configurations of fig3 - 5 are used , then a compromise between the pacing threshold and the sensing signal must be made in choosing which of the electrodes are to be connected to the pacemaker . the optimization criteria for sensing is simply the site with the combination of the largest sense signal and the lowest stimulation threshold . the ability to activate the pacing electrode only during pacing and to activate the same electrode during sensing as described for fig7 above eliminates the need for this compromise and can both decrease the implant time and improve the efficacy and reliability of the therapy . returning to fig9 after the sensing and pacing electrodes have been designated , the proximal end of lead 5 is inserted into the lead connector 40 of the adapter 10 . the desired group of electrodes that provide optimum sensing and pacing are programmed ( step 220 ) within the multiplexer as described above . in other words , the multiplexer is programmed to connect the sense and pace electrodes of lead 5 to the corresponding terminals of the pacemaker 20 . the adapter 10 , 100 is connected to the is - 1 connector 15 of the pacemaker 20 . the functioning of the pacemaker and the programming ( step 220 ) of the multiplexer of the adapter is verified ( step 225 ) for proper operation . the verification may be as simple as observation of the operation of the pacemaker using normal ecg criteria . alternately , in a pacemaker system having the ability to communicate the status of the connections , the address of the adapter with a coding of the electrodes connected and not connected for comparison to the logging of the sense signal magnitude and the stimulation level logging . this comparison allows for verification and diagnostics of the performance of the pacemaker . in the procedure set forth in fig9 the adapter is connected to the lead 5 only after the designation of the electrode . the adapter can be connected to the lead right after the implantation , and an external programmer can be connected to the adapter using a standard s1 connector . in this way the programmer can use the adapter to step through the electrodes of lead 5 for scanning , pacing , etc . for example , as shown in fig1 a , cable 12 can be temporarily connected to an external programmer 77 as shown . the programmer performs the function as described in fig9 - 11 to designate the electrodes , or to provide guidance to a physician regarding the designation of the electrodes . the programmer also sets the links of the adapter based either on the results of the automatic designation , or as requested by the physician . while this invention has been particularly shown and described with reference to the preferred embodiments thereof , particularly implantable pacemakers , it will be understood by those skilled in the art that various changes in form and details such as use with other cardiac devices such as an implantable cardioverter / defibrillator or icd may be made without departing from the spirit and scope of the invention .

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