Apparatus for selecting a sensing vector configuration in a medical device

The present disclosure relates generally to implantable medical devices, and more precisely to devices and methods for selecting sensing vectors in medical devices.

Implantable medical devices are available to prevent and treat cardiac arrhythmias by delivering anti-tachycardia pacing therapy and electroconvulsive therapy to perform cardioversion or defibrillation of the heart. Implantable cardioverter defibrillators or such devices, commonly known as "ICDs," sense the patient's cardiac rhythm to detect episodes of tachycardia or fibrillation and perform the rhythm in multiple beats. Classify according to zone.

As soon as the abnormal rhythm is detected, the ICD will deliver the appropriate therapy. Pathological forms of ventricular tachycardia can usually be terminated by anti-tachycardia pacing therapy. Anti-tachycardia pacing therapy is followed by high-energy shock therapy when needed. The termination of tachycardia by shock therapy is commonly referred to as the "cardio version." Ventricular fibrillation (VF) is a form of tachycardia that is a seriously life-threatening condition and is usually treated by immediate delivery of high-energy shock therapy. The termination of VF is commonly referred to as "defibrillation." Accurate in choosing the right therapy to effectively treat arrhythmias and in avoiding the delivery of unwanted cardioversion / defibrillation (CV / DF) shocks that can be distressing to the patient. Arrhythmia detection and arrhythmia differentiation are essential.

In past practice, ICD systems have employed intracardiac electrodes supported by intravenous leads to sense electrical signals in the heart and to deliver electrotherapy. Newly emerging ICD systems are adapted for subcutaneous or submuscular implantation and employ electrodes that are integrated onto the ICD housing and / or are supported on subcutaneous or submuscular leads. These systems, commonly referred to herein as "subcutaneous ICD" or "SubQ ICD" systems, do not rely on electrodes that are implanted in direct contact with the heart. SubQ ICD systems are less invasive and are therefore easier and faster to implant than ICD systems that employ intracardiac electrodes. However, the reliable detection of cardiac arrhythmias using a subcutaneous system poses a greater challenge. The amplitude of the R wave on the SubQ ECG signal may be about 1/10 to 1/100 of the amplitude of the R wave sensed in the ventricle. Furthermore, the signal quality of the subcutaneously sensed ECG signal is more likely to be influenced by myoelectric potential noise, environmental noise, patient posture, and patient activity than the intracardiac myocardial electrocardiogram (EGM) signal.

The ability of a subcutaneous ICD to detect tachyarrhythmias and eliminate noise depends on its ECG signaling characteristics. For higher amplitude R waves, higher frequency (higher through rate) R waves, higher R wave / T wave ratios, lower frequency signals around R waves (eg P and T waves), skeletal myoelectric potential ECG vectors with lower sensitivity and greater R-wave consistency between periods are preferred over ECG vectors without these attributes. Subcutaneous ICDs with a minimum of 2 ECG leads or vectors in a plane (using a minimum of 3 electrodes) use these physical vectors to generate a virtual ECG vector using a linear combination of the physical vector ECGs. can do. However, given the changing environment of the subcutaneous system, choosing the optimal vector can sometimes be a challenge. Thus, there is a need for systems and methods that advance reliable and accurate sensing arrhythmia detection using optimally available sensing vectors when sensing ECG signals via subcutaneous electrodes.

<p><patcit num="1"><text>U.S. Pat. No. 5,163,427</text></patcit><patcit num="2"><text>U.S. Pat. No. 5,188,105</text></patcit><patcit num="3"><text>U.S. Pat. No. 6,505,067</text></patcit><patcit num="4"><text>U.S. Pat. No. 6,236,882</text></patcit><patcit num="5"><text>U.S. Pat. No. 5,464,434</text></patcit><patcit num="6"><text>U.S. Pat. No. 5,593,431</text></patcit><patcit num="7"><text>U.S. Pat. No. 4,567,892</text></patcit><patcit num="8"><text>U.S. Pat. No. 5,176,137</text></patcit><patcit num="9"><text>U.S. Pat. No. 4,548,209</text></patcit><patcit num="10"><text>U.S. Pat. No. 5,127,404</text></patcit><patcit num="11"><text>U.S. Pat. No. 4,374,382</text></patcit><patcit num="12"><text>U.S. Pat. No. 4,556,063</text></patcit><patcit num="13"><text>U.S. Patent Application No. 14 / 250,040</text></patcit></p>

<p> An object of the present invention is to provide a system and a method for advancing highly reliable and accurate sensing arrhythmia detection using an optimally available sensing vector when sensing an ECG signal via a subcutaneous electrode.</p>

<p> The method for determining the sensing vector and the medical device detect the cardiac signal from multiple electrodes forming the plurality of sensing vectors, and the signal difference during the detection window in each of the plurality of sensing vectors. A step of determining, a step of ranking the sensing vectors of a plurality of sensing vectors according to the determined signal difference, and a step of ranking one or more of the plurality of sensing vectors according to the determined ranking. Includes selection steps and.</p>

<figref num="1">It is a conceptual diagram of a patient who is implanted with an extravascular cardiac fibrillation system as an example.</figref><figref num="2">FIG. 6 is a wiring diagram as an example of an electronic circuit mechanism in a sealed housing of a subcutaneous device according to an embodiment of the present invention.</figref><figref num="3">One embodiment is a graph representation of a cardiac signal sensed along a plurality of sensing vectors during selection of sensing vectors in a medical device.</figref><figref num="4">FIG. 5 is a flow diagram of a method for selecting one or more sensing vectors according to an exemplary embodiment.</figref><figref num="5">FIG. 5 is a flow diagram of a method for selecting one or more sensing vectors according to another exemplary embodiment.</figref><figref num="6">FIG. 5 is a flow diagram of a method for selecting one or more sensing vectors according to another exemplary embodiment.</figref>

FIG. 1 is a conceptual diagram of a patient 12 implanted with an extravascular cardiac fibrillation system 10 as an example. In the embodiment depicted in FIG. 1, the extravascular cardiac defibrillation system 10 is an implantable subcutaneous ICD system. On the other hand, the techniques of the present disclosure include other extravascular implantable cardiac fibrillation systems, such as cardiac fibrillation systems with leads that are implanted at least partially substernally or submuscularly. It can also be used with. In addition, the techniques of the present disclosure are like implantable pacing systems, implantable neurostimulation systems, drug delivery systems, or other systems in which leads, catheters or other components are implanted extravascularly within patient 12. It can also be used with other implantable systems. The present disclosure, however, is described in the context of an implantable extravascular cardiac fibrillation system for purposes of illustration.

The extravascular cardiac defibrillation system 10 includes an implantable cardioverter defibrillator (ICD) 14 connected to at least one implantable cardioverter-defibrillator lead 16. ICD14 in FIG. 1 is subcutaneously implanted on the left side of patient 12. The defibrillation lead 16 connected to the ICD 14 extends inward from the ICD 14 towards the patient 12's sternum 28 and xiphoid process 24. Near the xiphoid process 24, the defibrillation lead 16 bends or turns and extends subcutaneously upwards, substantially parallel to the sternum 28. In the embodiment depicted in FIG. 1, the defibrillation lead 16 is implanted with the lead 16 offset outward to the left side of the sternum 28 (eg, towards the left side of patient 12). There is.

The defibrillation lead 16 has a therapy vector between the defibrillation electrode 18 and the second electrode (eg, the housing of the ICD14 or the electrode located on the can 25 or the second lead) that is substantially the heart 26. It is placed along the sternum 28 across the ventricles of the heart. The therapy vector, in one embodiment, is viewed as a line extending from a point on the defibrillation electrode 18 to a point on the housing or can 25 of the ICD14. In another embodiment, the defibrillation lead 16 is sternum such that the therapy vector between the defibrillation electrode 18 and the housing or can 25 (or other electrode) of the ICD 14 substantially crosses the atrium of the heart 26. It may be installed along 28. In this case, the extravascular ICD system 10 is used to provide atrial therapy, such as therapy to treat atrial fibrillation.

The embodiment depicted in FIG. 1 is an example configuration of an extravascular ICD system 10 and should not be considered to limit the techniques described herein. For example, the defibrillation lead 16 is depicted in the embodiment of FIG. 1 as being offset outward from the midline of the sternum 28, but the lead 16 is offset to the right of the sternum 28 or the sternum 28. It may be planted so as to be more centrally located. In addition, the defibrillation lead 16 is not substantially parallel to the sternum 28, but instead is offset at an angle from the sternum 28 (eg, the sternum 28 at either the proximal or distal end). It may be implanted so that it can be angled outward from. As another embodiment, the distal end of the defibrillation lead 16 may be positioned near the second or third rib of patient 12. On the other hand, the distal end of the defibrillation lead 16 may be positioned further up or down, depending on the location of the ICD 14, the locations of the electrodes 18, 20, and 22, or other factors. Good.

ICD14 is depicted as being implanted near the mid-axillary line of patient 12, while ICD14 is also depicted at other subcutaneous locations in patient 12, eg, further posterior to the posterior axillary line on the trunk. It may be implanted further anterior to the anterior axillary line on the trunk, within the pectoral muscle area, or elsewhere in patient 12. In the case of ICD14 being implanted in the pectoralis major, the lead 16 would follow a different path, for example across the upper thoracic area and downward along the sternum 28. When the ICD14 is implanted in the thoracic muscle region, the extravasation ICD system includes a second lead containing a defibrillation electrode that extends along the patient's left side and defibrillates the second lead. The moving electrode is positioned along the left side of the patient to act as the anode or cathode of the therapy vector of such an ICD system.

The ICD14 includes a housing or can 25 that forms a sealing seal to protect the components within the ICD14. The housing 25 of the ICD14 can be formed of a conductive material such as titanium or other biocompatible conductive material or a combination of a conductive material and a non-conductive material. In some cases, the housing 25 of the ICD 14 is used in combination with one of the electrodes 18, 20, or 22 to deliver therapy to the heart 26 or to sense the electrical activity of the heart 26 (housing electrode). Or it is called a can electrode). The ICD14 may further include a connector assembly (sometimes also referred to as a connector block or header) that includes an electrical feedthrough, through which the electrical connection is within the defibrillation lead 16. It is made between the conductor and the electronic components contained within the housing. The housing contains one or more of the processor, memory, transmitter, receiver, sensor, sensing circuit mechanism, therapy circuit mechanism, and other suitable components (often referred to here as modules). The components may be enclosed.

The defibrillation lead 16 has a lead body having a proximal end including a connector configured to connect to the ICD 14 and a distal end containing one or more electrodes 18, 20, and 22. Includes. The lead body of the defibrillation lead 16 can be formed from non-conductive materials, including silicones, polyurethanes, fluoropolymers, mixtures thereof, and other suitable materials, and one or more conductors. It can be molded to form one or more lumens extending therein. However, the technique is not limited to such construction. Although the defibrillation lead 16 is depicted as containing three electrodes 18, 20, and 22, the defibrillation lead 16 may contain more or fewer electrodes.

The defibrillation lead 16 is an elongated electrical conductor (not depicted) that extends within the lead body from the connector on the proximal end side of the defibrillation lead 16 to electrodes 18, 20, and 22. ) Is included. In other words, each of one or more elongated electrical conductors housed within the lead body of the defibrillation lead 16 can engage the electrodes 18, 20, or 22, respectively. When the connectors at the proximal end of the defibrillation lead 16 are connected to the ICD14, each conductor connects to a connector assembly containing a feedthrough associated with a circuit mechanism such as the therapy module or sensing module of the ICD14. Will be electrically connected via. The electrical conductor transmits therapy from the therapy module within ICD14 to one or more of electrodes 18, 20, and 22, and sensed electricity from one or more of electrodes 18, 20, and 22. The signal is transmitted to the sensing module in ICD14.

The ICD14 can sense the electrical activity of the heart 26 via one or more sensing vectors that include a combination of electrodes 20 and 22 with the housing or can 25 of the ICD14. For example, the ICD14 is sensed using the sensing vector between the electrode 20 and the conductive housing or can 25 of the ICD14, which obtains the sensed electrical signal using the sensing vector between the electrodes 20 and 22. Obtaining an electrical signal, using the sensing vector between the electrode 22 and the conductive housing of the ICD14 or the can 25 to obtain the sensing electrical signal, or using a combination thereof to obtain the sensing electrical signal. Can be done. In some cases, the ICD14 is like a sensing vector between the defibrillation electrode 18 and one of the electrodes 20 or 22 or between the defibrillation electrode 18 and the housing or can 25 of the ICD14. A sensing vector containing a defibrillation electrode 18 is used to sense the electrical signal of the heart.

The ICD can analyze the sensed electrical signals to detect tachycardia such as ventricular tachycardia or ventricular fibrillation and generate electrotherapy in response to the detection of tachycardia to the heart 26. Can be delivered. For example, the ICD 14 can deliver one or more defibrillation shocks via a therapy vector that includes a defibrillation electrode 18 of the defibrillation lead 16 and a housing or can 25. The defibrillation electrode 18 may be, for example, an elongated coil electrode or another type of electrode. In some cases, ICD14 may be given one or more pacing therapies, such as anti-tachycardia pacing (ATP) or post-shock pacing, prior to or after delivery of defibrillation shock. It may be delivered. In these cases, ICD14 generates and delivers pacing pulses via a therapy vector that includes one or both of electrodes 20 and 22 and / or housing or can 25. Electrodes 20 and 22 may include ring electrodes, hemispherical electrodes, coil electrodes, spiral electrodes, split electrodes, directional electrodes, or other types of electrodes, or a combination thereof. The electrode 20 and the electrode 22 may be of the same type or different types of electrodes, but in the embodiment of FIG. 1, both the electrode 20 and the electrode 22 are drawn as ring electrodes.

The defibrillation lead 16 may further include an attachment form 29 at or near the distal end of the lead 16. The attachment form 29 may be a loop, link, or other attachment form. For example, the attachment form 29 may be a loop formed by sutures. As another embodiment, the attachment feature 29 may be a metal, coated metal, or polymer loop, link, or ring. The attachment feature 29 may be formed in any of a number of shapes having uniform or varying thicknesses and varying dimensions. The attachment feature 29 may be integrated into the reed or may be added by the user prior to implantation. The attachment form 29 may be useful to assist in implanting the lead 16 and / or to secure the lead 16 to the desired implantation site. In some cases, the defibrillation lead 16 may include a anchoring mechanism in addition to or in place of the adherent feature. The defibrillation lead 16 is depicted with the attachment form 29, but in other embodiments the lead 16 may not include the attachment form 29.

The lead 16 may further include a connector, such as a DF4 connector, a bifurcated connector (eg, a DF-1 / IS-1 connector), or other type of connector, at the proximal end of the lead 16. The connector at the proximal end of the lead 16 may include a terminal pin that connects to a port in the connector assembly of the ICD14. In some cases, the lead 16 may include an attachment feature at the proximal end of the lead 16 that can be connected to an implantation tool that assists in implanting the lead 16. The attachment form at the proximal end of the lead may be separated from the connector and integrated into the lead or added by the user prior to implantation.

The defibrillation lead 16 further has a suture sleeve or other anchoring mechanism (not shown) configured to anchor the lead 16 near the xiphoid process or lower sternum location close to the electrode 22. May be included. The anchoring mechanism (eg, suture sleeve or other mechanism) may be integrated into the lead or may be added by the user prior to implantation.

The examples depicted in FIG. 1 are illustrative in nature and should not be considered limiting the techniques described in this disclosure. For example, the extravascular cardiac fibrillation system 10 may contain more than one lead. In one embodiment, the extravascular cardiac defibrillation system 10 may include a pacing lead in addition to the defibrillation lead 16.

In the embodiment depicted in FIG. 1, the defibrillation lead 16 is implanted subcutaneously, eg, between the skin and the ribs or sternum. In other cases, defibrillation leads 16 (and / or voluntary pacing leads) may be implanted at other extravascular sites. In one embodiment, the defibrillation lead 16 may be implanted at least partially below the sternum. In such a configuration, at least a portion of the defibrillation lead 16 may be located in the mediastinum just below or behind the sternum, or more precisely in the anterior mediastinum. The anterior mediastinum is bordered laterally by the pleura, posteriorly by the pericardium, and anteriorly by the sternum 28. The defibrillation lead 16 is implanted, at least in part, in another extrapericardial location, i.e., within the region around the outer surface of the heart 26, but without direct contact with the outer surface of the heart 26. You may be. These other extrapericardial locations are within the mediastinum, but offset from the sternum 28, within the superior mediastinum, within the mediastinum, within the posterior mediastinum, below the xiphoid process or within the xiphoid process area, and the apex. It can include the vicinity, or other places that are not in direct contact with the heart 26 and are not subcutaneous. In yet another embodiment, the reed may be implanted in the pericardium or epicardial location outside the heart 26.

FIG. 2 is a wiring diagram as an example of an electronic circuit mechanism in a sealed housing of a subcutaneous device according to an embodiment of the present invention. As depicted in FIG. 2, the subcutaneous device 14 is a power supply unit that supplies power to the circuit mechanism of the subcutaneous device 14 and a pacing output capacitor that supplies pacing energy by a method well known in the art. Includes a low voltage battery 153 connected to (not shown). The low voltage battery 153 may be, for example, one or two conventional LiCFs._XCell, LiMnO₂Cell or Lil₂It can be formed in cells. The subcutaneous device 14 further comprises one or two conventional LiSVO cells or LiMnO.₂It includes a high voltage battery 112, which may be formed of cells. According to an embodiment of the present invention, FIG. 2 shows both a low voltage battery and a high voltage battery, but the device 14 uses a single battery for both high voltage use and low voltage use. It is possible that you are doing it.

Further referring to FIG. 2, the functions of the subcutaneous device 14 are controlled using software, firmware, and hardware, which collaboratively monitor the ECG signal, and the cardio version-defibrillation shock. Alternatively, determine if pacing is required and deliver the prescribed cardioversion-defibrillation therapy and pacing therapy. Subcutaneous device 14 is US Pat. No. 5,163,427 to Keimel, "A device for delivering single and multiple cardioversions and defibrillation pulses" and US Pat. No. 4,037, to Keimel, which was transferred to the transferee of the present application. Devices and Methods for Treating Tachyarrhythmias, Nos. 5,188,105, Monophasic, Simultaneous Biphasic, and Sequential Biphasic Cardioversions-Circuit for Selective Defibrillation Shock Delivery A mechanism, typically to the ICD IPG housing electrode 28 connected to the common output 123 of the high voltage output circuit 140 and to the HVI output 113 of the high voltage output circuit 140 located subcutaneously behind. A connected cardiover version-a defibrillation electrode 24 and a circuit mechanism that employs it may be incorporated.

Cardioversion-Defibrillation shock energy and capacitor charging voltage is at least one cardioversion in contact with the heart-ICD with defibrillation electrodes and cardioversion in contact with skin-Most AEDs with defibrillation electrodes Can be intermediate to the voltage supplied by. The typical maximum voltage required for an ICD using most biphasic waveforms is approximately 750 volt, with an associated maximum energy of approximately 40 joules. The typical maximum voltage required for an AED is approximately 2000-5000 Volts and the associated maximum energy is approximately 200-360 joules, depending on the model and waveform used. The subcutaneous device 14 of the present invention uses a maximum voltage in the range of about 300 to about 1500 volts and is associated with an energy of about 25 to 150 joules or more. The total high voltage capacitance can range from about 50 to about 300 microfarads. Such cardioversion-defibrillation shocks occur only during malignant tachyarrhythmias, eg, through the processing of the Farfield cardiac ECG, where ventricular fibrillation employs the detection algorithms described below. Delivered only when detected.

In FIG. 2, the sensing amplifier 190, in combination with the pacer / device timing circuit 178, traverses a particular ECG sensing vector defined by a selected pair of subcutaneous electrodes 18, 20, 22 and a can or housing 25 of the device 14. The Farfield ECG sensed signal expressed in the above, or optionally, a virtual signal (ie, a mathematical combination of two vectors) is processed. For example, the device may be adapted to generate the virtual vector signal described in US Pat. No. 6,505,067 to Lee et al., "Systems and Methods for Deriving Virtual ECG or EGM Signals." , Both patents are used here as references in their entirety. In addition, vector selection may be selected by the patient's physician and programmed by the programmer via telemetry links.

The selection of sensing electrode pairs is made in a manner that provides the most reliable sensing of the ECG signal of interest through the switch matrix / MUX191, and the ECG signal of interest is at risk of ventricular fibrillation leading to sudden death. For a convinced patient, it is an R wave. The Farfield ECG signal is passed to the input of the sensing amplifier 190 through the switch matrix / MUX191, which, in combination with the pacer / device timing circuit 178, evaluates the perceived EGM. Asystole, or asystole, is typically determined by a replenishment contraction interval timer in the pacer timing circuit 178 and / or control circuit 144. If the interval between successive R waves exceeds the replenishment contraction interval, a pace trigger signal is applied to the pacing pulse generator 192 to generate the pacing stimulus. Defibrillation pacing is usually provided temporarily to maintain cardiac output after delivery of cardioversion-defibrillation shock, slowly slowing the heart as it recovers to normal function. Can be beaten. Sensing of subcutaneous farfield signals in the presence of noise is by using the appropriate denial and expandable adaptation period described in US Pat. No. 6,236,882, "Noise Removal for Monitoring ECGs" to Lee et al. It may be supported, and the patent is used here as a reference in its entirety.

The detection of malignant tachyarrhythmia is determined in the control circuit 144 as a function of the interval between the pacer / device timing circuit 178 and the sensing amplifier circuit 190 to the timing and the R wave sensing event signal output to the control circuit 144. To. It should be noted that the present invention utilizes not only interval-based signal analysis methods, but also auxiliary sensors and morphological processing methods and equipment as described herein below.

Auxiliary sensors such as tissue color, tissue oxygenation, respiration, patient activity, and the like can be used to help determine whether to apply or withhold defibrillation therapy. This is described in its entirety in US Pat. No. 5,464,434, "Medical Intervention Device Responsive to Sudden Hemodynamic Changes," to Alt, which is incorporated herein by reference in its entirety. To do. The sensor processing block 194 provides sensor data to the microprocessor 142 via the data bus 146. Specifically, patient activity and / or posture is described in US Pat. No. 5,593,431 to Sheldon, "Medical Services and Methods Adopting Multiple DC Accelerometers for Patient Activity and Posture Sensing." It can be determined by the equipment and methods described in, and the patent is hereby incorporated by reference in its entirety. Patient respiration can be determined by the equipment and methods described in US Pat. No. 4,567,892, "Implantable Cardiac Pacemaker" to Plicchi et al., Which patent is hereby incorporated by reference in its entirety. Patient tissue oxygenation or tissue color can be determined by the sensor devices and methods described in US Pat. No. 5,176,137 to Erickson et al., Which patent is hereby incorporated by reference in its entirety. To do. The '137 patented oxygen sensor may be located in the subcutaneous device pocket or instead located on the lead 18 to allow oxygenation or color sensing of the tissue in contact or near contact. You may be.

Specific steps in the performance of the detection algorithm criteria are programmed into the microprocessor, RAM and ROM, associated circuit mechanisms, and RAM via the prior art telemetry interface (not shown). It is performed collaboratively within a microcontroller 142 that includes a stored detection criterion that may be acceptable. Data and commands are exchanged between the microcomputer 142 and the timing and control circuit 144, the pacer timing / amplifier circuit 178, and the high voltage output circuit 140 via the bidirectional data / control bus 146. The pacer timing / amplifier circuit 178 and control circuit 144 are clocked at a slower clock speed. The microcomputer 142 is normally in a sleep state, but an interrupt generated by each R wave sensing event, an interrupt generated when a downlink telemetry programming instruction is received, or an interrupt generated as soon as a cardiac pacing pulse is delivered. Awakened by, operated by a fast clock, to perform any necessary mathematical calculation, to perform tachycardia and fibrillation detection procedures, and to be monitored and controlled by a timer in the pacer / device timing circuit mechanism 178. Update the time interval to be done.

When malignant tachycardia is detected, the high voltage capacitors 156, 158, 160, and 162 are charged to voltage levels pre-programmed by the high voltage charging circuit 164. It is generally considered inefficient to maintain a constant charge on the high voltage output capacitors 156, 158, 160, 162. Instead, charging is initiated by the control circuit 144 issuing a high voltage charging command HVCHG delivered over line 145 to the high voltage charging circuit 164, charging from the bidirectional control / data bus 166 and HV output circuit 140. It is controlled by using the feedback signal VCAP of. The high voltage output capacitors 156, 158, 160, and 162 may be constructed of film, aluminum electrolysis, or wet tantalum.

The negative terminal of the high voltage battery 112 is directly connected to the system ground. Since the switch circuit 114 is normally open, the positive terminal of the high voltage battery 112 is disconnected from the positive power input of the high voltage charging circuit 164. The high voltage charging command HVCHG is further conducted through the conductor 149 to the control input of the switch circuit 114, which in response closes and closes the positive high voltage battery voltage EXT B + to the positive of the high voltage charging circuit 164. Connect to the power input. The switch circuit 114 may be, for example, a field effect transistor (FET) whose source-drain path interrupts the EXT B + conductor 118 and whose gate is receiving the HVCHG signal on the conductor 145. The high voltage charging circuit 164 is thereby ready to begin the stage of charging the high voltage output capacitors 156, 158, 160, and 162 with the charging current from the high voltage battery 112.

High voltage output capacitors 156, 158, 160, and 162 are charged to very high voltages, such as 300-1500V, and discharged through the body and heart between the electrode pairs of subcutaneous cardioversion-defibrillation electrodes 113 and 123. It may be. The details of the voltage charging circuit mechanism are also not considered definitive with respect to the practice of the present invention, but one high voltage charging circuit that is believed to be suitable for the purposes of the invention is disclosed. The high voltage capacitors 156, 158, 160, and 162 are described in detail in, for example, US Pat. No. 4,548,209 "Energy Converter for Implantable Cardioverters" to Wielders et al. It can be charged by the high voltage charging circuit 164 and the high frequency high voltage transformer 168 described. Proper charging polarity is maintained by diodes 170, 172, 174, and 176 that interconnect the output windings of the high voltage transformer 168 with the capacitors 156, 158, 160, and 162. As pointed out above, the state of capacitor charging is monitored by a circuit mechanism within the high voltage output circuit 140, which provides the timing and control circuit 144 with VCAP, which is a feedback signal indicating the voltage. To do. The timing and control circuit 144 terminates the high voltage charging command HVCHG when the VCAP signal matches the programmed capacitor output voltage, i.e. cardioversion-defibrillation peak shock voltage.

The control circuit 144 then expresses NPULSE1 and NPULSE2, respectively, which are the first and second control signals applied to the high voltage output circuit 140 to trigger the delivery of the shock for cardioversion or defibrillation. In particular, the NPULSE1 signal triggers the discharge of the first capacitor bank with capacitors 156 and 158. The NPULSE2 signal triggers the discharge of the first capacitor bank and the second capacitor bank with capacitors 160 and 162. Selection between multiple output pulse regimes is feasible by simply modifying the number and chronological order of assertions for the NPULSE1 and NPULSE2 signals. The NPULSE1 signal and the NPULSE2 signal can be provided sequentially, simultaneously or individually. In this way, the control circuit mechanism 144 has a pair of cardioversion-defibrillation electrodes that connect a high-energy cardioversion-defibrillation shock to the HV-1 and COMMON outputs, as shown in FIG. It serves to control the operation of the high voltage output stage 140 delivered between 18 and 25.

Thus, the subcutaneous device 14 monitors the patient's heart condition and requires cardioversion-in response to the detection of defibrillation tachyarrhythmia, cardioversion-cardioversion through defibrillation electrodes 18 and 25- Initiate delivery of defibrillation shock. The high HVCHG signal connects the high voltage battery 112 to the high voltage charging circuit 164 through the switch circuit 114 to initiate charging of the output capacitors 156, 158, 160, and 162. Charging continues until the programmed charging voltage is reflected by the VCAP signal, at which point the control and timing circuit 144 sets the HVCHG signal low to terminate charging and open the switch circuit 114. The subcutaneous device 14 can also be programmed to attempt to deliver a cardioversion shock to the heart in the manner described above in time with the detected R wave, or described above. Cardioversion shocks to the heart in the manner in which it is used can also be programmed or made to deliver without attempting to synchronize delivery to the detected R wave. Detection of Tachyarrhythmias and Cardioversion-Episode data associated with the delivery of defibrillation shocks is uploaded to external programmers well known in the art to facilitate the diagnosis of the patient's cardiac condition. It can be stored in RAM in preparation for link telemetry transmission. Patients accepting device 14 for prophylactic reasons should report each such episode to their physician for further assessment of the patient's condition and assessment of the need for more advanced ICD implantation. Will be instructed by.

The subcutaneous device 14 preferably includes a telemetry circuit (not shown) so that the device is programmed by an external programmer 20 via a two-way telemetry link (not shown). Is possible. Uplink telemetry allows device status and diagnostic / event data to be sent to an external programmer 20 for review by the patient's physician. Downlink telemetry allows external programmers to program device functions and optimize detection and therapy for specific patients under the control of a physician. Programmers and telemetry systems suitable for use in the practice of the present invention have been well known for many years. So that the programmer can send control commands and operating parameter values that should be received by the implanted device, and that the implanted device can communicate diagnostic and operational data to the programmer. Known programmers typically communicate with the implanted device partner via a bidirectional radio frequency telemetry link. Programmers believed to be suitable for the purposes of practicing the present invention include programmers of Model 9790 and CareLink® commercially available from Medtronic, Inc., Minneapolis, Minnesota. ..

Various telemetry systems have been developed to provide the required communication channels between the external programming unit and the implanted device and are well known in the art. A telemetry system believed to be suitable for the purposes of practicing the present invention is, for example, entitled "Telemetry Format for Implanted Medical Devices" to the following US patent, Wyborny et al. US Pat. No. 5,127,404, US Pat. No. 4,374,382 entitled "Markowitz Markowitz," Markowitz, "Telemetry for Medical Devices," Thompson et al., "Telemetry for Medical Devices." It is disclosed in US Pat. No. 4,556,063, entitled "System." Wibonnie et al. '404, Markovitz's '382, and Thompson et al. '063 have been assigned to the assignees of the present invention, each of which is incorporated herein by reference in its entirety.

According to certain embodiments of the present invention, in order to automatically select a suitable ECG vector set, it is necessary to have an index of merit on which to rate the quality of the signal. "Quality" is defined as the ability of the signal to provide accurate heart rate estimation and accurate morphological waveform separation between the patient's normal sinus rhythm and the patient's ventricular tachyarrhythmia.

Appropriate indicators are R-wave amplitude, R-wave peak amplitude vs. R-wave waveform amplitude (ie signal-to-noise ratio), low slope content, relative high-to-low frequency power, average frequency estimation, probability density. It may include a function, or any combination of these metrics.

The automatic vector selection may be performed at the time of implantation, regularly (daily, weekly, monthly), or both. At the time of implantation, automatic vector selection may be initiated as part of an automated device turn-on procedure that performs activities such as measuring lead impedance and battery voltage. The device turn-on procedure may be initiated by the implant physician (eg by pressing the programmer button) or instead, it will be initiated automatically as soon as there is automatic detection of the device / lead implant. You may be. The device of the subcutaneous device 14 is sewn in place and prior to closing the incision, the turn-on procedure also uses automatic vector selection confirmation criteria, and the quality of the ECG vector is for the current patient and for the device and lead position. , May be to determine if it is appropriate. Such an ECG quality label should allow the implant physician to steer the device to a new location or direction to improve the quality of the ECG signal as needed. In addition, a suitable singular or plural ECG vector may be selected at the time of implantation as part of the device turn-on procedure. A suitable vector may be a vector having an index that maximizes rating estimation and detection accuracy. Moreover, as long as there is a deductive set of vectors preferred by the physician and they exceed a minimum threshold, or they are negligible than some other more desirable vectors. As long as it is not bad, a vector suitable for deduction may be selected. Certain vectors may be considered nearly identical and they will not be tested unless the deductively selected vector index falls below a predetermined threshold.

Instrument Metrics Depending on power consumption and power requirements, ECG signal quality metrics may be measured as often as desired based on a range of vectors (or a subset instead). Data may be collected, for example, on a minute, hourly, daily, weekly, or monthly basis. More frequent (eg, minutely) measurements are averaged over time and used, for example, based on the susceptibility of the vector to transient noise, motion noise, or EMI. You may choose a vector.

Instead, the subcutaneous device 14 has a patient activity indicator / sensor (piezoresistive, accelerometer, impedance, or similar) with minimal or no automatic vector measurements during medium or high patient activity periods. It may be delayed for automatic vector measurements during the activity period. One typical scenario is that the ECG vector was determined to be sleeping (using an internal clock (eg, 2 am)) once daily or once weekly, or (axis 2 or 3). It may include testing / assessing while inferred to be asleep by determining the patient's position and lack of activity (via accelerometer). In another possible scenario, the step of testing / evaluating the ECG vector may be performed once daily or once weekly while the patient is known to be doing gymnastics.

Even with infrequent, automatic, and regular measurements, the noise in the signal (eg, muscle, exercise, EMI, etc.) is still measured and vector-selective measurements are taken until the noise subsides. It is desirable to postpone it.

The subcutaneous device 14 may optionally have an indication of the patient's posture (via a 2-axis or 3-axis accelerometer). This sensor can be used to ensure that ECG quality differences are not simply the result of attitude / position changes. Sensors may be used to collect data in multiple postures so that ECG quality can be averaged over these postures, or otherwise combined, or instead a preferred posture. May be selected for.

In one embodiment, vector quality metric calculations are performed by a clinician using the programmer either at the time of implantation or during subsequent visits, or a remote link with the device and programmer. It is designed to be carried out remotely via. According to another embodiment, the vector quality metric calculation is automatically performed by the device a predetermined number of times, such as multiple times daily, once daily, once weekly, or monthly, for each available sensing vector. It is supposed to be carried out. In addition, those values may be averaged for each vector over the course of, for example, a week. The averaging may consist of moving averages or iterative averaging, depending on time weighting and memory considerations.

FIG. 3 is a graphical representation of the cardiac signals sensed along a plurality of sensing vectors during selection of sensing vectors in a medical device according to one embodiment. As depicted in Figure 3, during the vector selection process, the device references cardiac signals for each available sensing vector, eg, here as a reference in its entirety, US Patent Application No. 14 / 250,040. Sensing using sensing techniques known in the art, such as No., ranking the available sensing vectors based on the results of the sensed signal, and ranking the resulting sensing vectors 102-106. Determine one or more desirable sensing vectors based on. For example, according to one embodiment as depicted in FIG. 3, the device has a horizontal sensing vector 102 extending between the housing or can 25 and electrode 22, and an oblique extending between the housing or can 25 and electrode 20. The ECG signal 100 is sensed from each of the available sensing vectors 104, including the sensing vector 104, and the vertical sensing vector 106 extending between the electrodes 20 and 22. For each sensing vector 102-106, the device determines that the sensed R wave 108 is occurring when the sensed signal exceeds the time-dependent autonomously controlled sensing threshold 110.

When the R wave 108 is sensed, the device senses the vector quality metric detection window 112 to determine the vector quality metric associated with the sense vector 102-106, and the sensed R wave for each of the sense vectors 102-106. Set based on 108. According to one embodiment, the device associates a quality metric detection window 112 starting at a starting point 114 located at a predetermined distance 116 from the R wave 108 with a QRS signal associated with the R wave 108 being sensed for analysis of signal 100. The detection window width 118 is set so that the T wave of the signal 100 can be performed within the expected range of the signal 100. For example, the device has a quality metric detection window 112 with a width of approximately 200 ms and is positioned between the R wave 108 where the starting point 114 of the quality metric detection window 112 is sensed and approximately 150-180 ms. The width 118 is set to extend 200 ms from the detection window start point 114 to the detection window end point 120, that is, from the detected R wave 108 to the end point 120 at a distance of approximately 350-380 ms. Once the quality metric detection window 112 is set, the device is sensed, i.e. the minimum signal difference 122 between the perceived signal 100 and the perceived threshold 110 in the quality metric detection window 112, as described below. Determine the minimum distance that extends between the signal 100 and the sensing threshold 110.

FIG. 4 is a flow diagram of a method for selecting one or more sensing vectors according to an exemplary embodiment. For each cardiac signal 100 obtained from each sensing vector 102-106, as depicted in FIGS. 3 and 4, the device obtains the perceived R wave 108 of the cardiac signal 100, blocks 200, and Set the quality metric detection window 112 based on the perceived R wave 108 for the sensing vector 102-106, block 202. Once the quality metric detection window 112 has been positioned, the device determines the minimum signal difference 122 between the perceived cardiac signal 100 and the sensing threshold 110 within the quality metric detection window 112 for each of the sensing vectors. 204. The determined minimum signal difference 122 is stored and the device determines if the minimum signal difference 122 has been determined for a predetermined threshold number of cardiac cycles for each of the sensing vectors 102-106, block 206. If the minimum signal difference is not fixed for a predetermined threshold number of cardiac cycles for each sensing vector 102-106, ie No in block 206, the device picks up the next R wave 108 for each sensing vector 102-106. Enter, the process is repeated for the next sensed cardiac cycle for each of the sense vectors 102-106. According to one embodiment, the minimum signal difference 122 is determined for, for example, 15 cardiac cycles.

If the minimum signal difference 122 has been determined for all of the predetermined threshold number of cardiac cycles, i.e. yes in block 206, the device has determined the vector selection metric for each vector 102-106, 15 for that vector. Determined based on the minimum signal difference 122 of, block 208. For example, according to one embodiment, the device determines the median of 15 minimum signal differences 122 for each sensing vector and the determined center of the minimum signal difference 122 associated with the vector selection metric for that sensing vector. Set equal to the value. Once the vector selection metrics have been determined for each of the sensing vectors 102-106 in block 208, the device ranks those vector selection metrics for sensing vectors 102-106, block 210. For example, the device ranks the determined vector selection metrics from top to bottom, so that in the embodiment of FIG. 3, the oblique sensing vector 104 has a median minimum signal difference for that vector. The horizontal sensing vector 102 is ranked second because it was 0.84 millivolts, and the horizontal sensing vector 102 is ranked second because the median minimum signal difference for that vector is 0.82 millivolts. Since the median minimum signal difference for the sensing vector is 0.55 millivolts, it will be ranked third.

Once the sensing vectors have been ranked in block 210, the device selects the sensing vector (s) to be utilized during subsequent sensing and arrhythmia detection by the device, block 212. Depending on the amount of time programmed to occur between updates of the sensing vectors 102-106, i.e. hours, days, weeks, or months as an example, the device will then select the vector scheduled. Waiting for confirmation, block 214, at which point the vector selection process is repeated.

FIG. 5 is a flow diagram of a method for selecting one or more sensing vectors according to another exemplary embodiment. As depicted in FIGS. 3 and 5, according to another embodiment, for each heart signal 100 obtained from each sensing vector 102-106, the device is a heart, as described above. Block 302, which obtains the R wave 108 of signal 100 and sets the quality metric detection window 112 based on the detected R wave 108 for block 300 and the sensing vector 102-106. Once the quality metric detection window 112 is positioned, the device determines the minimum signal difference 122 between the perceived cardiac signal 100 and the sensing threshold 110 in the quality metric detection window 112 for each of the sensing vectors 102-106. , Block 304. The determined minimum signal difference 122 is stored and the device determines if the minimum signal difference 122 has been determined for a predetermined threshold number of cardiac cycles, or 15 cardiac cycles as an example, for each sensing vector 102-106. Block 306.

If the minimum signal difference 122 is not fixed for a predetermined threshold number of cardiac cycles for each sensing vector 102-106, ie No in block 306, the device determines if the default timer has expired, block. 308. If the timer has not expired, ie no in block 308, the device gets the next R wave 108 for each sensing vector 102-106 and the next sensed for each sensing vector 102-106. The process is repeated for the cardiac cycle. According to one embodiment, the timer at block 308 is set to, for example, 40 seconds.

In some cases, the device may not have been able to obtain the required number of minimum signal differences 122 for one or more of the sensing vectors, and if the timer expires, i.e. block. If Yes at 308, the device determines if the required minimum signal difference has been obtained for at least two of the sensing vectors 102-106, block 314. If the required number of minimum signal differences was not obtained for at least two of the sensing vectors, i.e. only for one of the sensing vectors 102-106, or not for any of them, i.e. no in block 314. In the case of, the device determines that it is impossible to make a sensing vector selection, and the amount of time programmed to occur between updates of blocks 310, and sensing vectors 102-106, i.e. the number of hours, as an example. Depending on the number of days, weeks, or months, the device waits for the next scheduled vector selection confirmation, block 312, at which point the vector selection process is repeated.

If the required minimum signal difference has been obtained for at least two of the sensing vectors 102-106, ie yes in block 314, the device will detect those two sensing vectors in block 320 and subsequent sensing and device arrhythmia. Select as to be utilized during detection. As described above, the device depends on the amount of time programmed to occur between updates of the sensing vectors 102-106, i.e., hours, days, weeks, or months, as an example. Waits for the next scheduled vector selection confirmation, block 312, at which point the vector selection process is repeated.

If the minimum signal difference 122 has been determined for a predetermined number of cardiac cycles for each sensing vector 102-106, i.e. yes in block 306, the device sets the vector selection metric for each vector 102-106 to that vector. Determined based on the determined minimum signal difference 122 of 15 for block 316. For example, according to one embodiment, the device determines the median of 15 minimum signal differences 122 for each sensing vector and the minimum signal difference 122 associated with the vector selection metric for that sensing vector. Set equal to the median. Once the vector selection metrics have been determined for each of the sensing vectors 102-106 in block 316, the device ranks those vector selection metrics for the sensing vectors 102-106, block 318. For example, the device ranks the determined vector selection metrics from top to bottom, so that in the embodiment of FIG. 3, the oblique sensing vector 104 has a median minimum signal difference of 0.84 for that vector. The horizontal sensing vector 102 is ranked second because it was millivolts, and the vertical sensing vector 106 is ranked second because the median minimum signal difference for that vector is 0.82 millivolts. Since the median minimum signal difference for the sensing vector is 0.55 millivolts, it will be ranked third.

Once the sensing vectors have been ranked in block 318, the device selects the sensing vector (s) to be utilized during subsequent sensing and arrhythmia detection by the device, block 320. According to another embodiment, the ranking result may be displayed on a programmer or the like to allow the user to select the sensing vector (s). Depending on the amount of time programmed to occur between updates of the sensing vectors 102-106, i.e. hours, days, weeks, or months as an example, the device will select the next scheduled vector. Wait for confirmation, block 312, at which point the vector selection process is repeated. In addition, according to another embodiment, the user can manually initiate the vector selection process, which causes the device to wait for the user input to be received, at which point the next appointment is made. The vector selection process is repeated.

FIG. 6 is a flow diagram of a method for selecting one or more sensing vectors according to another exemplary embodiment. As described above, in some cases the device may not be able to obtain the required number of minimum signal differences 122 for one or more of the sensing vectors. In addition, the minimum signal difference 122 for one or more of the cardiac cycles in one or more of the sensing vectors 102-106 is the quality metric detection window 112 for one or more ECG signals in the cardiac cycle. There may be cases where it is equal to zero if it is greater than or equal to the sensing threshold throughout. Examples of such zero minimum signal differences include either T-wave oversensing, frequent ventricular extrasystoles, high beat sensing (greater than 150 beats per minute), or noise generation at the sensing vector. It may be reflected.

Thus, according to one embodiment, for each heart signal 100 obtained from each sensing vector 102-106, as shown in FIGS. 3 and 6, the device is a heart, as described above. Block 402, which obtains the perceived R-wave 108 of signal 100 and sets the quality metric detection window 112 based on the perceived R-wave 108 for block 400, and the sensing vector 102-106. Once the quality metric detection window 112 is positioned, the device determines the minimum signal difference 122 between the perceived cardiac signal 100 and the sensing threshold 110 in the quality metric detection window 112 for each of the sensing vectors 102-106. , Block 404. In addition, the device determines for each sensing vector 102-106 whether a zero minimum signal difference has occurred during the detection window 112, block 416. If there is a zero minimum signal difference in the detection window 112, ie yes in block 416, the R wave associated with that vector is discarded and block 418, the timer expires as described below. A judgment is made as to whether or not it was.

If no zero minimum signal difference has occurred in the detection window 112, ie no in block 416, has the device established a minimum signal difference 122 for a predetermined threshold number of cardiac cycles, ie 15 cardiac cycles as an example? Determine if, block 406. If the minimum signal difference 122 is not determined for a predetermined threshold number of cardiac cycles for each sensing vector 102-106, ie No in block 406, the device determines if the default timer has expired, block 408. .. If the timer has not expired, ie no in block 408, the device gets the next R wave 108 for each sensing vector 102-106 and the next perceived cardiac cycle for each sensing vector 102-106. The process is repeated for. According to one embodiment, the timer at block 408 is set to, for example, 40 seconds.

If the timer has expired, i.e. yes in block 408, the device determines if the required number of minimum signal differences has been obtained for at least two of the sensing vectors 102-106, block 414. If the required number of minimum signal differences was not obtained for at least two of the sensing vectors, i.e. only for one of the sensing vectors 102-106, or not for any of them, i.e. no at block 414. In the case of, the device determines that it is impossible to make a sensing vector selection, and the amount of time programmed to occur between updates of blocks 410, and sensing vectors 102-106, i.e. the number of hours, as an example. Depending on the number of days, weeks, or months, the device waits for the next scheduled vector selection confirmation, block 412, at which point the vector selection process is repeated.

If the required minimum signal difference has been obtained for at least two of the sensing vectors 102-106, ie yes in block 414, the device will detect those two sensing vectors in block 320 and subsequent sensing and device arrhythmia. Select as to be utilized during detection. As described above, the device depends on the amount of time programmed to occur between updates of the sensing vectors 102-106, i.e., hours, days, weeks, or months, as an example. Waits for the next scheduled vector selection confirmation, block 412, at which point the vector selection process is repeated.

If the minimum signal difference 122 has been determined for the threshold number of cardiac cycles for each sensing vector 102-106, i.e. yes in block 406, the device will provide a vector selection metric for each vector 102-106 for that vector. Determined based on the confirmed 15 minimum signal differences 122 of, block 420. For example, according to one embodiment, the device determines the median of 15 minimum signal differences 122 for each sensing vector and the minimum signal difference 122 associated with the vector selection metric for that sensing vector. Set equal to the median. Once the vector selection metrics have been determined for each of the sensing vectors 102-106 in block 420, the device ranks those vector selection metrics for sensing vectors 102-106, block 422. For example, the device ranks the determined vector selection metrics from top to bottom, so that in the embodiment of FIG. 3, the oblique sensing vector 104 has a median minimum signal difference of 0.84 for that vector. The horizontal sensing vector 102 is ranked second because it was millivolts, and the vertical sensing vector 106 is ranked second because the median minimum signal difference for that vector is 0.82 millivolts. Since the median minimum signal difference for the sensing vector is 0.55 millivolts, it will be ranked third.

In addition to the three sensing vectors 102-16 described above, an optional virtual signal (ie, a mathematical combination of the two vectors) can be used in addition to the aforementioned sensing vectors, resulting in more than three. It is understood that the sensing vector of the above may be used, or the virtual signal may be used instead of the sensing vector described above. For example, the device may be adapted to generate the virtual vector signal described in US Pat. No. 6,505,067 to Lee et al., "Systems and Methods for Deriving Virtual ECG or EGM Signals," both patents. Is used here as a reference in its entirety. In addition, vector selection may be selected by the patient's physician and programmed by the programmer via telemetry links.

In addition, although the use of minimum signal differences is described, the device can also utilize other selection criteria for vector ranking. For example, according to one embodiment, the device determines the maximum signal amplitude in the detection window for each R wave for each vector and determines the difference between the maximum amplitude and the sensing threshold for each of the maximum amplitudes. The median maximum amplitude difference for each sensing vector over 15 cardiac cycles may be determined. The device then selects the vector with the largest median maximum amplitude difference as the (s) sensing vector to be utilized during subsequent sensing and arrhythmia detection by the device.

As described above, the methods and devices for verifying the differentiation of cardiac events have been presented with reference to specific embodiments in the above description. It is understood that various modifications to the referenced embodiments may be made without departing from the scope of the present disclosure set forth in the accompanying claims.

10 Extravascular cardiac defibrillator system 12 Patient 14 Implantable cardioverter defibrillator (ICD) 16 Implantable cardiac defibrillator lead 18 Defibrillator electrodes 20, 22 Electrodes 24 Sword-shaped protrusions 25 Housing or can 26 Heart 28 Chestbone 29 Adhesive body 100 ECG signal (heart signal) 102 Horizontal sensing vector 104 Diagonal sensing vector 106 Vertical sensing vector 108 R wave 110 Sensing threshold 112 High voltage battery (Fig. 2) 112 Quality metric detection window (Fig. 3) ) 114 Switch Circuit (Figure 2) 114 Window Start Point (Figure 3) 116 Default Distance from R Wave 118 Positive High Voltage Battery Voltage EXT B + Conductor (Figure 2) 118 Window Width (Figure 3) 120 Window End Point 122 Minimum Signal difference 140 High voltage output circuit 142 Microprocessor (Microcomputer) 144 Timing and Control Circuit 145 Line (Conductor) 146 Bidirectional Data / Control Bus (Data Bus) 149 Conductor 153 Low Voltage Battery 156, 158, 160, 162 High Voltage Output Condenser 164 High Voltage Charging Circuit 166 Bidirectional Control / Data Bus 168 High Frequency High Voltage Transformer 170, 172, 174, 176 Diode 178 Pacer / Device Timing Circuit 190 Sensing Amplifier 191 Switch Matrix / MUX 192 Pacing Pulse Generator 194 Sensor Processing Block