Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
1999-11-03
2001-11-13
Evanisko, George R. (Department: 3762)
Surgery
Diagnostic testing
Cardiovascular
C607S059000
Reexamination Certificate
active
06317626
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to implantable medical devices and more particularly to implantable medical devices intended for use in monitoring a patient's heart rhythm.
Implantable pacemakers and cardioverters monitor the heart's rhythm in order to detect arrhythmias and deliver appropriate therapies to terminate detected arrhythmias. In conjunction with this function, the ability of the device is to store information with regard to monitored heart rhythms has dramatically increased over the past two years. Examples of implantable pacemakers and defibrillators and associated devices which have the capability of storing information related to monitor heart rhythms include U.S. Pat. No. 4,223,678, issued to Langer et al., U.S. Pat. No. 4,295,474 issued to Fischell, U.S. Pat. No. 4,625,730 issued to Fountain et al., U.S. Pat. No. 5,732,708 issued to Nau et al., U.S. Pat. No. 5,669,391 issued to Williams, U.S. Pat. No. 5,522,850 issued to Yomtov et al., U.S. Pat. No. 5,312,446 issued to Holschbach et al. and U.S. Pat. No. 5,776,168 issued to Gunderson, all incorporated herein by reference in their entireties. In addition, there have recently been developed subcutaneously implantable monitoring devices, which do not deliver any anti-arrhythmia therapies to the heart but simply store information regarding a patient's heart rhythms for later uplink to an external device. Such devices are disclosed in U.S. Pat. No. 5,331,966 issued to Bennett et al., U.S. Pat. No. 5,135,004 issued to Adams and U.S. Pat. No. 5,113,869 issued to Nappholz et al., all also incorporated herein by reference in their entireties.
In conjunction with implantable monitoring devices of the types discussed above, storage of information regarding episodes of arrhythmias is typically accomplished in response to either detection of an arrhythmia meeting pre-defined criteria, as described in the above-cited Langer, Yomtov and Nappholz patents, among others, or in response to a trigger signal received from the patient, typically provided by means of an external controller or activator, as disclosed in the above cited Bennett et al. patent. The above cited Fountain et al patent discloses a device having the capability of storing information related to episodes of arrhythmias in response to either a patient trigger or detection of an arrhythmia episode by the implanted device. U.S. Pat. No. 5,931,857 issued to Prieve et al. in particular discloses an implantable defibrillator, which confirms a patient's diagnosis of a need for therapy and in response, delivers the therapy. In the commercially marketed version of the device described in this patent, either confirmation of the patient's diagnosis of arrhythmia or detection of arrhythmia by the device may trigger storage of an associated electrogram.
While devices of the types discussed above are extremely valuable in monitoring the condition of a patient, automatic triggers for electrogram storage are subject to noise, particularly in the context of subcutaneous monitors, and as a result may record electrograms in response to events that are not actually arrhythmias. The use of manual triggers to trigger arrhythmia storage can result in inappropriate storage of electrogram data due to misperception by the patient, or alternatively can result in late initiation of electrogram storage due to a delay between onset of the arrhythmia and the point at which the patient perceives the symptoms of the arrhythmia. In this case in particular, late triggering may have result in the device failing to record the events that are associated with the onset of the arrhythmia, which are often of the most interest.
SUMMARY OF THE INVENTION
The present invention is directed toward an implantable device having enhanced capabilities for monitoring arrhythmia episodes over extended periods of time. The information collected by the implantable device is stored and telemetered to an associated external device such as a device programmer for display and analysis. In particular, the present invention provides an implantable monitor, which allows for a corroboration between the detection of the arrhythmias by the device and the occurrence of patient's symptoms. The invention provides the benefit of reducing the number of inappropriately stored electrocardiograms not actually indicative of arrhythmias and enables the device to record the onset of the arrhythmia, even in cases where the is a substantial delay between the onset of the arrhythmia and the onset of the patient's perceptible symptoms. The invention provides for the permanent storage of electrogram records associated in time with an electrogram storage trigger signal from the patient or a device generated internal electrogram storage trigger signal, in response to a confirming trigger signal thereafter of the other type, within a defined confirmation period.
In one embodiment, the implanted device may employ a looping memory as is described in the Langer patent cited above, wherein electrogram signals are continuously recorded in memory and overwritten, such that at any point in time, the electrogram signals corresponding to a proceeding period of time are stored, which time period may be for example, 10 or 20 seconds, up to a period of several minutes. The electrogram signals in the looping memory prior to and following the device and/or patient generated trigger signals may be permanently stored in an electrogram storage memory for later transmission to an external programmer or monitor. Transfer of the electrogram signals stored in the looping memory to the electrogram storage memory occurs in response to expiration of a defined record duration period, which may be timed from the trigger signal which initiated the confirmation period. In preferred embodiments, the electrogram signals present in the looping memory on expiration of the record duration period include signals occurring during a time interval initiated at a point preceding the trigger signal that initiated the confirmation period and extending for a defined period thereafter. In response to detection, during the confirmation period, of a confirming trigger signal of a type other than the trigger signal which initiated the confirmation period, the contents of the looping memory, previously or subsequently transferred to the electrogram storage memory are flagged as permanent and are not written over by subsequent electrogram records. The permanently stored electrogram records are available for later uplink to an external device.
The confirmation periods following patient trigger signals and internal trigger signals may be the same, or more preferably the confirmation periods following internal trigger signals may be substantially greater to allow for the fact that an arrhythmia may persist for minutes or hours prior to onset of the patient's symptoms. For example, the confirmation period following patient trigger signals will generally be in the range of up to a few minutes, while the confirmation period following device generated internal trigger signal may extend for up to a period of several hours. In some preferred embodiments, permanent storage of electrogram signals in response to a patient signal within the confirmation period following an internal trigger signal may also be pre-conditioned on a failure of the device to detect termination of the arrhythmia which caused the internal trigger signal.
REFERENCES:
patent: 4223678 (1980-09-01), Langer et al.
patent: 4295474 (1981-10-01), Fischell
patent: 4374382 (1983-02-01), Markowitz
patent: 4428378 (1984-01-01), Anderson et al.
patent: 4535774 (1985-08-01), Olson
patent: 4625730 (1986-12-01), Fountain et al.
patent: 5107833 (1992-04-01), Barsness
patent: 5113869 (1992-05-01), Nappholz et al.
patent: 5117824 (1992-06-01), Keimel et al.
patent: 5135004 (1992-08-01), Adams et al.
patent: 5168871 (1992-12-01), Grevious
patent: 5176137 (1993-01-01), Erickson et al.
patent: 5179947 (1993-01-01), Meyerson et al.
patent: 5184615 (1993-02-01), Napphol
Evanisko George R.
Medtronic Inc.
Wolde-Michael Girma
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