Source: https://patents.google.com/patent/US20020133206A1/en
Timestamp: 2018-07-20 03:18:05
Document Index: 507568962

Matched Legal Cases: ['art 115', 'art 115', 'art 115', 'art.\n3', 'art.\n9', 'art.\n33']

US20020133206A1 - Cardiac rhythm management system with defibrillation threshold prediction - Google Patents
US20020133206A1
US20020133206A1 US09808419 US80841901A US2002133206A1 US 20020133206 A1 US20020133206 A1 US 20020133206A1 US 09808419 US09808419 US 09808419 US 80841901 A US80841901 A US 80841901A US 2002133206 A1 US2002133206 A1 US 2002133206A1
US09808419
US6751502B2 (en )
[0011]FIG. 1 is a schematic/block diagram illustrating portions of the present cardiac rhythm management system and portions of an environment of use.
[0012]FIG. 2 is a flow chart illustrating a technique for estimating defibrillation thresholds such as using the system of FIG. 1.
[0013]FIG. 3 is a lookup table illustrating estimating defibrillation threshold voltages based on an indication of electric field near a defibrillation electrode and a distance therefrom.
[0014]FIG. 4 is a schematic/block diagram illustrating an alternative embodiment of portions of the present cardiac rhythm management system that determines a distance from the defibrillation electrode without requiring fluoroscopic or other imaging.
[0015]FIG. 5 is a flow chart, similar to that of FIG. 2, illustrating another method of operation such as using the system of FIG. 4.
[0016]FIG. 6 is a flow chart and accompanying graph illustrating one technique for estimating a distance from an electrode
[0017]FIG. 7 is a flow chart illustrating another embodiment providing an indicator of the predicted defibrillation threshold and/or selecting an appropriate cardiac rhythm management device for implant.
[0018]FIG. 8 is a flow chart illustrating another embodiment providing a defibrillation shock based on the predicted defibrillation threshold energy.
[0019]FIG. 9 is a flow chart illustrating another embodiment for recording acute or chronic computed defibrillation thresholds.
[0020]FIG. 10 is a flow chart illustrating another embodiment for modifying the delivery of a defibrillation shock or other therapy based on previously acquired defibrillation threshold data over a range of another patient characteristic.
[0023]FIG. 1 is a schematic/block diagram illustrating generally, by way of example, and not by way of limitation, one embodiment of portions of the present cardiac rhythm management system 100 and portions of an environment in which the present system 100 and associated techniques are used. System 100 includes, among other things, cardiac rhythm management device 105 and leadwire (“lead”) 110 for communicating signals between device 105 and a portion of a living organism, such as heart 115. Embodiments of device 105 include, but are not limited to, bradycardia and antitachycardia pacemakers, cardioverters, defibrillators, combination pacemaker/defibrillators, drug delivery devices, and any other implantable or external cardiac rhythm management apparatus capable of providing therapy to heart 115.
[0026]FIG. 1 also illustrates, in an exploded view block diagram form, portions of device 105. It is understood that device 105 is coupled to heart 115 via lead 110; the illustrated connection lines associated with the exploded view are illustrative only. In FIG. 1, test energy module 150 generates an energy from which a heart characteristic can be determined via response signal module 155. From these measurements, a defibrillation threshold is computed, for example, either by a defibrillation threshold estimation module in controller 160, which itself is in device 105, or in external programmer 170, which is communicatively coupled to a transmitter or receiver in device 105, such as transceiver 175. The defibrillation estimation module is implemented as a sequence of steps carried out on a microprocessor or other microsequencer, in analog, digital, or mixed-signal hardware, or in any suitable hardware and/or software configuration. In this example, SVC electrode 130 is electrically connected in common with housing electrode 140, at node 165, and also coupled to each of test energy module 150 and response signal module 155.
[0027]FIG. 2 is a flow chart illustrating generally, by way of example, but not by way of limitation, one embodiment of a technique for estimating defibrillation thresholds such as using the system 100 of FIG. 1. This technique is carried out as executable instructions, such as by controller 160, but it need not be carried out in the exact sequence illustrated in FIG. 2. At step 200, test energy module 150 applies a test energy by providing a drive current of predetermined magnitude (e.g., approximately 30 to 1000 microamperes, inclusive) between RV shock electrode 125 and housing electrode 140. In one example, this drive current is delivered in a continuous or pulsed/strobed 25 kHz waveform; in this example the 30 to 1000 microamperes current magnitudes are the zero-to-peak values of this test waveform. However, it is understood that the technique could use any other test energy that does not defibrillate the associated heart tissue and does not induce fibrillation, such as when the energy is delivered during a cardiac repolarization or by using a non-painful stimulus such as a pacing pulse (e.g., amplitude approximately between 0.1 Volt and 10 Volts, inclusive, duration approximately between 0.05 milliseconds and 10 milliseconds, inclusive). In one embodiment, the test energy typically has an energy less than 10 milliJoules, while typical defibrillation threshold energies are between 1 and 40 Joules. The test energy may be delivered from either a current source or a voltage source.
For ease of use, such as in an implantable device, the defibrillation threshold voltage is, in one embodiment, stored in a lookup table in a memory device. FIG. 3 illustrates generally, by way of example, but not by way of limitation, one embodiment of such a lookup table. In this embodiment, the defibrillation threshold voltage needed to obtain a 5 Volts/cm electric field at the left ventricular heart periphery is given as a function of: (1) the measured distance d2 less the known distance d1 ; and (2) the fractional tip voltage parameter. Thus, the lookup table in FIG. 3 represents solving the electric field distribution for a particular lead geometry and a range of various heart sizes, calibrating the resulting cubic-fitted electric field equations according to different measured values of electric field as indicated by the range of fractional tip voltage parameters, and obtaining the corresponding defibrillation threshold voltage by scaling the test voltage by the ratio of the “safe” value of electric field at the heart periphery to the extrapolated value of the electric field at the heart periphery as obtained from the calibrated electric field equation in response to the test voltage delivered from the defibrillation coil electrode 120. Thus, FIG. 3 indicates, for example, for a measured distance, (d2 −d1 ), of 3.4 cm and a fractional tip voltage parameter of 45.0, then the predicted defibrillation threshold voltage given by the table in FIG. 3 is 408 Volts.
[0037]FIG. 4 is a schematic/block diagram illustrating generally, by way of example, and not by way of limitation, another embodiment of portions of system 100 providing an alternate embodiment of determining the distance d2, such as described with respect to step 220 of FIG. 2, that does not require the use of fluoroscopic or other imaging. FIG. 4 includes an additional peripheral electrode 400 located at or close to the peripheral portion of the left ventricle (a distance d2 away from RV shock electrode 125) at which the predetermined electric field magnitude (e.g., 5 Volts/cm, as in the previous example) is desired during defibrillation. In one embodiment, this peripheral electrode 400 is introduced into the left ventricular periphery (e.g., coronary sinus and/or great cardiac vein) by an transvascular lead 405 through the right atrium and coronary sinus. In another embodiment, peripheral electrode 400 is a patch-type defibrillation electrode disposed on the exterior portion of the left ventricle. In either case, lead 405 may also include additional electrodes.
[0038]FIG. 5 is a flow chart, similar to that of FIG. 2, illustrating generally, by way of example and not by way of limitation, another method of operation such as using the embodiment illustrated in FIG. 4. This technique is carried out by executable instructions, such as on controller 160, but it need not be carried out in the exact sequence indicated in FIG. 5. At step 500, an additional voltage measurement V3 is taken between peripheral electrode 400 and housing electrode 140 in response to the current delivered by test energy module 150 at step 200. At step 505 the distance d2 from RV shock electrode 125 to the heart periphery electrode 400 is estimated without relying on fluoroscopic or other imaging techniques to make a measurement. Instead, the distance d2 is estimated using the measured voltage V3 obtained in step 500.
[0039]FIG. 6 is a flow chart and accompanying graph illustrating generally, by way of example, but not by way of limitation, one technique for estimating the distance d2, at step 505. In this technique, the electric field near RV shock electrode 125 is approximated, as a function of distance, as a decaying exponential, for distances measured radially outward from RV shock electrode 125. By using (V1+V2) and V2 as points on this exponential curve that are separated by the known distance d1, as illustrated in FIG. 6, a decay rate “R” (i.e., the argument of the decaying exponential function) is computed at step 600. Then, at step 605, the distance d2 is estimated using the previously determined decay rate R. Having determined the distance d2 without relying on fluoroscopic imaging techniques, the defibrillation threshold energy is estimated as previously described herein with respect to FIGS. 1-3, or by other suitable technique.
[0040]FIG. 7 is a flow chart illustrating generally, by way of example, but not by way of limitation, another embodiment of using system 100. This embodiment includes steps for estimating defibrillation threshold voltages for a particular defibrillation waveform delivered from a particular electrode configuration, such as described with respect to FIG. 5 (or FIG. 2). Then, at step 700, an indication of the defibrillation threshold energy is provided to the user. In one example, the defibrillation threshold energy estimated within device 105 is communicated by telemetry transceiver 175 to external programmer 170 for display, such as on a computer monitor, audible output, printed means, or using any other indicator. In another example, the defibrillation threshold energy is estimated by hardware included within external programmer 170, which is itself coupled to lead 110 with or without actually implanting a device 105. A resulting indication of the defibrillation threshold energy is displayed on programmer 170. Based on this indicated defibrillation threshold energy, the user selects an appropriate cardiac rhythm management device 105 for implantation. In this way, an implantable cardiac rhythm management device 105 having a larger battery capacity is selected for a patient exhibiting a larger defibrillation threshold voltage than for a patient exhibiting a lesser defibrillation threshold voltage. This selection of a cardiac rhythm management device 105 having appropriate energy capacity may also be based on other factors, including, by way of example, but not by way of limitation, the expected frequency of needed defibrillation episodes, the patient's need for other power-consuming features in the implantable cardiac rhythm management device. Thus, according to this technique of computing defibrillation thresholds for a particular electrode configuration, the user may advantageously determine the appropriate cardiac rhythm management device 105 before actually performing an implantation.
[0041]FIG. 8 is a flow chart illustrating generally, by way of example, but not by way of limitation, another embodiment of using system 100. This embodiment includes steps for estimating defibrillation threshold voltages for a particular defibrillation waveform and providing an indicator of the defibrillation threshold energy to the user, as described with respect to FIG. 7. Then, at step 800, a defibrillation shock having a magnitude based on the predicted defibrillation threshold energy (e.g., equal to the predicted defibrillation threshold energy) is delivered to a patient in fibrillation to test whether the applied defibrillation shock magnitude is sufficient to defibrillate the patient. If the defibrillation is successful, the user may again test efficacy using a lesser defibrillation shock; if the defibrillation is not successful, the user may again test efficacy using a greater defibrillation shock.
[0042]FIG. 9 is a flow chart illustrating generally, by way of example, but not by way of limitation, another embodiment of using system 100. This embodiment includes steps for estimating defibrillation threshold voltages for a particular defibrillation waveform (as described with respect to FIGS. 2 and 5). At step 900, the computed defibrillation threshold energy and corresponding time is stored in memory in controller 160. After a delay at step 905, the defibrillation threshold estimation steps are repeated and the resulting defibrillation threshold energy and time are again recorded and stored. The stored defibrillation threshold energy and corresponding time data is, in one embodiment, communicated to external programmer 170 by transceiver 175. In one embodiment, a relatively short delay (e.g., approximately between 1 hour and 1 day, inclusive) is used at step 905, during a period of time immediately following implantation of defibrillation lead 110. In this way, acute changes in defibrillation threshold are monitored and stored. In another embodiment, a longer delay (e.g., approximately between 1 day and 1 month, inclusive) is used at step 905. In this way, chronic changes in defibrillation threshold are monitored and stored. Such chronic changes in defibrillation threshold provide one indication of patient well-being and suitability for continued use of the cardiac rhythm management system 100.
[0043]FIG. 10 is a graph of transthoracic impedance (Z) versus time. FIG. 10 illustrates another aspect of the present system 100 in which a patient characteristic, such as breathing (also referred to as respiration or ventilation) is monitored. One technique for monitoring breathing is by measuring transthoracic impedance, as described in Hartley et al. U.S. Pat. No. 6,076,015 entitled “RATE ADAPTIVE CARDIAC RHYTHM MANAGEMENT DEVICE USING TRANSTHORACIC IMPEDANCE,” assigned to Cardiac Pacemakers, Inc., which is incorporated herein by reference in its entirety. As illustrated in FIG. 10, defibrillation thresholds are repeatedly computed, according to the techniques described herein, at several different times during the patient's breathing cycle of inhaling and exhaling. An indication of the portion of the breathing cycle that corresponds to the lowest computed defibrillation threshold is recorded. In one example, this is implemented by recording a transthoracic impedance corresponding to the lowest defibrillation threshold. In another embodiment, this is implemented by recording a time delay from a fiducial point of the thoracic impedance waveform (e.g., maxima, minima, “zero”-crossing, etc.). Then, at some later time when the patient is in fibrillation, a defibrillation shock is delivered by system 100 synchronized to (among other things) the portion of the respiration cycle that was found to correspond to the lowest defibrillation threshold energy. In a broader sense, because the defibrillation threshold estimation techniques disclosed herein do not require an actual defibrillation energy or fibrillation-inducing energy, such defibrillation threshold estimation can be carried out repeatedly for evaluation over a range of any other patient characteristics (e.g., posture, etc.) besides breathing. Variations in the defibrillation threshold energy may then be used to synchronize delivery of the defibrillation shock to that particular patient characteristic, or to otherwise modify therapy delivery.
2. The method of claim 1, in which delivering the test energy to the heart includes delivering a continuous or pulsed carrier signal to the heart.
3. The method of claim 2, in which the carrier signal frequency is greater than or equal to 1 kiloHertz.
4. The method of claim 3, in which the carrier signal frequency is less than or equal to 100 kiloHertz.
6. The method of claim 5, in which at least one of the third and fourth electrodes is electrically in common with one of the first and second electrodes.
7. The method of claim 6, in which at least one of the third and fourth electrodes is the same electrode as one of the first and second electrodes.
8. The method of claim 1, in which the heart characteristic includes an electric field associated with a voltage drop across first and second locations in the heart.
9. The method of claim 1, in which estimating the defibrillation threshold includes comparing the heart characteristic to a desired value.
10. The method of claim 9, further including selecting the desired value of the heart characteristic to ensure a desired value of electric field associated with the portion of the heart to be defibrillated.
11. The method of claim 1, further including selecting a cardiac rhythm management device for implantation based on the estimated defibrillation threshold and an energy capability of the cardiac rhythm management device.
12. The method of claim 1, further including providing a user with the estimated defibrillation threshold.
13. The method of claim 1, further including delivering a test defibrillation pulse based on the estimated defibrillation threshold.
14. The method of claim 13, further including delivering a series of test defibrillation pulses in which an energy of the first test defibrillation pulse in the series is based on the estimated defibrillation threshold.
15. The method of claim 1, further including repeating the aforementioned steps over a period of time that is long enough to detect changes in acute defibrillation thresholds.
16. The method of claim 1, further including repeating the aforementioned steps over a period of time that is long enough to detect changes in chronic defibrillation thresholds.
repeating the steps of delivering, detecting, and estimating during a time period that includes the different patient characteristic.
18. The method of claim 17, in which sensing the different patient characteristic includes sensing a portion of a respiration cycle, and the step of repeating includes repeating the steps of delivering, detecting, and estimating during a different portion of the respiration cycle.
19. The method of claim 18, further including synchronizing delivery of therapy to a portion of the respiration characteristic that corresponds to a lower estimated defibrillation threshold over the respiration cycle than another defibrillation threshold over a different portion of the respiration cycle.
20. The method of claim 17, further including synchronizing delivery of therapy to a portion of the patient characteristic that corresponds to a lower estimated defibrillation threshold than another defibrillation threshold over a different portion of the patient characteristic.
21. A method of determining a defibrillation threshold energy, the method including:
22. The method of claim 21, in which measuring the distance, d2, includes fluoroscopically determining d2.
23. The method of claim 22, in which fluoroscopically determining d2 includes assessing d2 based on a known fluoroscopically viewable distance.
24. The method of claim 23, in which fluoroscopically determining d2 includes assessing d2 based on a known fluoroscopically viewable distance d1 between the first and second electrodes.
25. The method of claim 21, in which measuring the distance, d2, includes:
26. A method of determining a defibrillation threshold energy, the method including:
27. The method of claim 26, in which measuring the distance, d2, includes fluoroscopically determining d2.
28. The method of claim 27, in which fluoroscopically determining d2 includes assessing d2 using a known fluoroscopically viewable distance.
29. The method of claim 28, in which fluoroscopically determining d2 includes assessing d2 using the known fluoroscopically viewable distance d1.
30. The method of claim 26, in which measuring the distance, d2, includes:
estimating an exponential decay rate, R, using V1, V2, and the known distance d1 ; and
32. The system of claim 31, in which the first and second electrodes are configured for association with a right ventricle of the heart.
33. The system of claim 32, in which the first electrode includes a macroscopic surface area that is approximately between 1 mm2 and 20 mm2, inclusive.
34. The system of claim 31, in which the first electrode is selected from a group consisting of a tip electrode and a ring electrode.
35. The system of claim 31, in which the second electrode includes a shock electrode.
36. The system of claim 31, in which the second electrode includes a coil electrode.
37. The system of claim 31, in which the test energy module includes a test current source.
38. The system of claim 37, in which the test current source includes a carrier signal.
39. The system of claim 38, in which the carrier signal has a frequency that is approximately between 1 kHz and 100 kHz, inclusive.
40. The system of claim 38, in which the carrier signal is continuous.
41. The system of claim 38, in which the carrier signal is pulsed.
42. The system of claim 38, in which the response signal module includes a demodulater for demodulating a detected response to a portion of the carrier signal.
43. The system of claim 31, in which the controller includes executable instructions determining an electric field near the second electrode based on voltages measured at the first and second electrodes and a known distance between the first and second electrodes.
44. The system of claim 43, in which the controller includes executable instructions determining an electric field near the distal portion of the heart tissue based on the electric field near the second electrode and a distance between the second electrode and the distal portion of the heart tissue.
45. The system of claim 44, in which the controller includes executable instructions for determining the defibrillation threshold energy based on scaling the voltage measured at the second electrode by a ratio of the desired electric field at the distal portion of the heart tissue to the previously determined electric field near the distal portion of the heart tissue.
47. A system including:
means, coupled to the response signal module, for performing the function of estimating the defibrillation threshold energy.
a defibrillation threshold energy estimation module, coupled to the response signal module, and estimating a defibrillation threshold energy based on: (a) a predetermined desired defibrillation electric field at portion of the heart tissue to be defibrillated that is distal to the second RV electrode;
(b) a distance from the second electrode to the distal portion of the heart tissue; (c) an indication of the electric field near the second electrode obtained by measuring the response signal at the first and second electrodes and by using the predetermined separation between the first and second electrodes.
49. The system of claim 48, in which the housing electrode and the SVC electrode are electrically connected in common.
US09808419 2001-03-14 2001-03-14 Cardiac rhythm management system with defibrillation threshold prediction Active 2021-04-23 US6751502B2 (en)
US10744991 Continuation US6859664B2 (en) 2001-03-14 2003-12-23 Cardiac rhythm management system with defibrillation threshold prediction
US20020133206A1 true true US20020133206A1 (en) 2002-09-19
US6751502B2 US6751502B2 (en) 2004-06-15
DE69315930D1 (en) * 1992-09-16 1998-02-05 Pacesetter Ab An implantable cardiac defibrillation
US7643877B2 (en) 2010-01-05 grant