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Bi-ventricular ventricular capture management in cardiac resyncronization therapy delivery devicesRelated Patent Categories: Surgery: Light, Thermal, And Electrical Application, Light, Thermal, And Electrical Application, Electrical Therapeutic Systems, Heart Rate Regulating (e.g., Pacing)Bi-ventricular ventricular capture management in cardiac resyncronization therapy delivery devices description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060155338, Bi-ventricular ventricular capture management in cardiac resyncronization therapy delivery devices. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATIONS [0001] This non-provisional U.S. patent application claims the benefit of prior U.S. provisional patent application Ser. No. 60/637,633 of common title, filed 20 Dec. 2004 and also relates to a co-pending provisional U.S. patent application by Sheth et al.; namely Ser. No. 60/637,620 (Atty. Dkt. P-10798.00) filed 20 Dec. 2004, and entitled, "AUTOMATIC LV/RV CAPTURE VERIFICATION AND DIAGNOSTICS;" a co-pending provisional U.S. patent application by Sheldon et al.; namely Ser. No. 60/637,571 (Atty. Dkt. P-20777.00) filed 20 Dec. 2004, and entitled, "METHOD OF CONTINUOUS CAPTURE VERIFICATIONS IN CARDIAC RESYNCHRONIZATION DEVICES," and a co-pending provisional U.S. patent application by Kleckner et al., namely Ser. No. 60/637,532 (Atty. Dkt. No. P-21289.00) filed 20 Dec. 2004 and entitled "LV THRESHOLD MEASUREMENT AND CAPTURE MANAGEMENT," the entire contents of each, including all exhibits thereof, are hereby incorporated by reference herein. FIELD OF THE INVENTION [0002] The invention pertains to cardiac pacing systems and relates to apparatus and methods for triggering automatic verification of pacing capture of ventricular chambers and for managing pacing therapy delivery to ensure continued pacing capture. In particular, the invention relates to verification of pacing capture for both ventricular chambers during bi-ventricular pacing, including various forms of cardiac resynchronization therapy (CRT) delivery, such uni-ventricular, fusion-type CRT delivery. BACKGROUND OF THE INVENTION [0003] Cardiac resynchronization cardiac pacing devices operate by either delivering pacing stimulus to both ventricles or to one ventricle with the desired result of a more or less simultaneous mechanical contraction and ejection of blood from the ventricles. However, due to a number of factors for a variety of patients such cardiac pacing systems may not always effectively delivery CRT. For example, varying capture thresholds, pacing lead and/or electrode migration or dislodgement, time required for appropriate signal processing, confounding conduction delays or conduction blockages, diverse electrode placement locations, and the like. [0004] In either form of CRT delivery, whether fusion-based or the more traditional bi-ventricular stimulation, confirming that pacing stimulus captures each paced ventricle is a very important clinical issue so that the desired benefits of the CRT are in fact delivered to a patient. [0005] Assuming that the reader is familiar with bi-ventricular pacing, the following should provide additional insight into the importance of capture detection in a fusion-based bi-ventricular pacing engine. One premise underlying fusion-based pacing is the notion that a fusion-based evoked left ventricular (LV) depolarization enhances stroke volume in hearts where the right ventricle (RV) depolarizes first. This is commonly due to intact atrio-ventricular (AV) conduction to the RV of a preceding intrinsic or evoked atrial depolarization wave front, and wherein the AV conducted depolarization of the LV is unduly delayed. The fusion depolarization of the LV is attained by timing the delivery of the LV pace (LVp) pulse to follow the intrinsic depolarization of the RV but to precede the intrinsic depolarization of the LV. Specifically, an RV pace (RVp) pulse is not delivered due to the inhibition of the RVp event upon the sensing of RV depolarization (RVs), allowing natural propagation of the wave front and depolarization of the intraventricular septum, while an LVp pulse is delivered in fusion with the RV depolarization. For supporting mode switches to alternate pacing modalities, fusion-based CRT delivery engines typically include at least one electrode in each ventricle which allows such engines to be used in conjunction with the present invention, as will be apparent upon review of the following written description and drawings of the invention. [0006] Left ventricular capture in particular is a clinical issue with present-generation (and foreseeable) CRT systems, due to acknowledged difficulty of maintaining stable lead situation in the cardiac venous anatomy. Since CRT delivery becomes ineffective (possibly even deleterious) if LV capture is lost, diagnosis of dislodgment and maintenance of capture are high priorities. [0007] Cardiac Resynchronization Therapy (CRT) devices have been shown to improve quality of life (QOL), exercise capacity and New York Heart Association (NYHA) heart failure class. The NYHA rating varies from Class I to Class IV, as follows: Class I: patients with no limitation of activities; they suffer no symptoms from ordinary activities. Class II: patients with slight, mild limitation of activity; they are comfortable with rest or with mild exertion. Class III: patients with marked limitation of activity; they are comfortable only at rest. Class IV: patients who should be at complete rest, confined to bed or chair; any physical activity brings on discomfort and symptoms occur at rest. [0008] Currently approved CRT devices incorporate bi-ventricular pacing technology with simultaneous pacing in the right ventricle (RV) and the left ventricle (LV). Since the devices are implanted essentially only to provide continuous bi-ventricular pacing therapy, it is imperative that each pacing pulse stimulus delivered to the two LV and RV provide an evoked response (i.e., each stimulus delivered to a ventricle "captures" the ventricle). Thus, if electrodes disposed in electrical communication with a ventricle rapidly sense depolarization wavefronts a control sequence for the pacing engine will inhibit ventricular pacing. For example, such a situation occurs during rapidly conducted atrial fibrillation (AF). When bi-ventricular pacing is inhibited the patient's symptoms of heart failure return, and can sometimes even worsen as compared to their pre-implant status. Similarly, if one of the pacing sites loses capture (e.g., the LV) the subsequent RV-only pacing will prevent the patient from receiving the intended benefit of CRT delivery. To that end the inventors have addressed a need in the art regarding capture verification in heart failure devices, such as bi-ventricular CRT devices that indicates when capture is occurring in both the LV and the RV. [0009] Presently, the only somewhat similar diagnostic available in CRT devices is percent-ventricular pacing (%Vpacing), which indicates the percentage of time bi-ventricular pacing therapy is being delivered; however, a limitation of the %Vpacing metric is that bi-ventricular pacing may be "occurring" close to 100% of the time but the LV chamber may not be captured at all. Currently, cardiac device specialists assess LV capture acutely during office visits by looking at the morphology of an electrogram (EGM) or by temporarily setting pacing to RV-only and LV-only pacing. Current state of the art pacemakers (e.g., the Kappa.RTM. brand family of pacemakers provided by Medtronic, Inc.) incorporate ventricular capture management algorithms. However, such algorithms require specific circuitry and sensing capabilities to be able to perform this function that are not currently available in the CRT products. Also, the feasibility of this technology for LV capture management has yet to be established. The present invention advantageously contributes to both capture verification and management. [0010] Previously others addressed issues related to capture management; for example, Ventricular Capture Management (VCM) has been successfully implemented in the Kappa.RTM. 700 dual-chamber pacemaker sold by Medtronic, Inc. by measuring evoked responses on the bipolar pair of electrodes in the right ventricle (RV). In this device the pacing output energy is monitored and automatically adjusted as required by the patient. This pacing threshold search (PTS) measures the rheobase and chronaxie of the current pacing threshold. The following can be used to determine rheobase and chronaxie: 1--determine the rheobase, which is the minimum Stimulus Strength that will produce a response (his is the voltage to which the Strength-Duration curve asymptotes). Step 2--calculate 2.times.rheobase and step 3--determine chronaxie, which is the Stimulus Duration that yields a response when the Stimulus Strength is set to exactly 2.times.rheobase. [0011] Then, a pulse width and amplitude safety margin is calculated and the output of the device is set to that new value. The PTS is conducted on a programmable periodic basis, commonly set up to measure the thresholds once a day (typically at night). [0012] Currently in the bi-ventricular pacing CRT devices like the InSync.RTM. family of implantable pulse generators, including ICDs), no capture verification or threshold management scheme exists. Instead, pacing thresholds are manually measured at the right ventricular and the left ventricular pacing sites. The site with the highest pacing threshold requirement dictates the programmed output of the device to assure proper capture at both ventricular sites for devices with a single ventricular pacing stimulus energy output. [0013] A need therefore exists in the art to effectively chronically deliver ventricular pacing therapies (including CRT) to patients who might not otherwise receive the full benefit of such therapies. SUMMARY [0014] Among other contributions to the art, the present invention addresses the issues identified above of not providing adequate metrics (or diagnostics) to a physician regarding LV (and therefore bi-ventricular) capture. The invention addresses this significant need where capture management functionality is not available in a CRT device. According to the invention, the bi-ventricular capture management as described here measures and monitors pacing thresholds at each of pacing sites being used in CRT delivery while the patient is ambulatory. The ability to obtain the LV and RV thresholds and modulate these outputs helps assure greater likelihood of bi-ventricular capture. Such dual site capture is critical in order for a patient to benefit from CRT. Bi-ventricular capture verification and capture management is also an important element to enable remote follow-up (e.g., via a patient management network or the like) and to provide a triage tool for understanding whether worsening heart failure is due to a device pacing-capture problem versus a manifestation of worsening heart failure. The clinically important aspect of managing pacing capture thresholds in these patients is that an HF decompensation event that might have been related to bi-ventricular capture problems are eliminated due to the dynamic nature of the (left-sided) pacing stimulus output energy. In the event that the capture detection and management scheme detects a situation of failed LV capture (e.g., left side lead dislodgement), a clinician or physician can be notified via a network such as the Medtronic CareLink.RTM. network alert system utilizing e-mail, fax, phone calls, paging networks and the like. [0015] Currently no bi-ventricular capture management scheme has been implemented in any pacing therapy delivery device, such as an IPG. As stated hereinabove, the advantages are both from a clinician ease-of-use perspective, for example a clinically significant aspect of assuring CRT is being effectively delivered as planned, and a timesaving triage tool which would help identify left-lead issues that comprise a significant issue for patients who are scheduled to receive chronic CRT delivery. [0016] Thus, at least on exemplary algorithm is described for rapid incorporation into next-generation CRT devices that actively performs LV capture verification and threshold test(s) on a daily (or other) basis with automatic retry and wireless communication of testing results, trends and the like (including any testing anomalies). The results of the test(s) can be stored and/or provided to the user, a clinician, or other entity. The results of the tests can be provided remotely or via a programming head at a next programmer-based session, as is known in the art. The data regarding LV capture can be used, for example, to record or demonstrate whether an intended CRT delivery is occurring and the amount of time or percentage that a patient in fact received CRT. If LV capture verification is NOT confirmed, in addition to the stored diagnostic metrics, a patient alert can be triggered to warn the patient (and/or a clinician) that the device is not functioning as intended and the patient should consider consulting a physician. [0017] In one form of the invention, such a patent alert can be triggered on a remote patient management network (e.g., the Medtronic Medtronic CareLink.RTM. remote monitoring service for patients with Medtronic cardiac devices) to notify third parties of the lack of CRT delivery. This test and the resultant diagnostic metric values (e.g., percentage of actual CRT delivery in temporal terms, by the number of cardiac cycles with and without CRT delivery, or by time of day and the like) simply and accurately depicts actual CRT delivery. The values also provide assurance to the physician, patient and/or care-giver that the device is not only pacing in both ventricular chambers, but capturing, thereby providing maximal therapeutic benefit to the patient. The values also help in the early identification of a situation where, for some reason a pacing lead is not capturing in the associated ventricle thereby minimizing patient discomfort and restoration of the desired therapeutic regime. Also, a test according to the invention can be applied to verify RV capture and for in-office, easy-to-use acute confirmation of capture verification of the LV and RV. [0018] Multiple approaches can be used for measuring the pacing threshold at the left and right ventricular sites. [0019] For example, evoked response measurement at each site: this involves measuring the pacing threshold using the evoked response approach previously used in the Kappa devices of Medtronic, Inc. The capture management feature provides automatic monitoring of ventricular pacing thresholds and automatic adjustment of amplitude and pulse width to maintain capture. When capture management is programmed to monitor only, the pacemaker periodically causes paces to be delivered (affecting pacemaker timing temporarily if necessary). The pacemaker then monitors the paces by changing first amplitude and then pulse width to find two points that lie on the strength duration curve that define the boundary between settings that capture and those that do not. How often the pacemaker performs this pacing threshold search is determined by the programmable Capture Test Frequency parameter. This parameter determines how often the pacing threshold search will be initiated and provides for retry if the test is delayed. When Capture Management is programmed to Adaptive, the pacemaker responds to monitoring by adapting ventricular amplitude and pulse width using the following programmable parameters: [0020] Amplitude Margin and Pulse Width Margin--the pacemaker determined threshold multiplied by a selected safety factor. Continue reading about Bi-ventricular ventricular capture management in cardiac resyncronization therapy delivery devices... 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