Methods and apparatus for manually suspending intrathoracic impedance fluid status measurements

The capability to suspend a patient alert relating to a monitored physiologic parameters addresses a need to selectively shut off a patient-alert signal or signals during the time a patient is being treated for an excursion in the parameter. Of course, in general a signal call attention to a patient's a potentially deleterious status or condition for which they should seek medical attention. Once a chronically-implanted monitoring device has detected or provided information about the parameter relative to a desired value, trend, or range and a clinician has been notified and intervened the alert signal is temporarily disabled for a predetermined period. That is, once the notification occurs and alert has served its purpose, the alert mechanism is selectively deactivated while the patient ostensibly begins to gradually correct the monitored physiologic parameter under a caregiver's direction and control. After which time, the alert will reactivate.

FIELD OF THE INVENTION

The present invention relates to improved methods and apparatus for monitoring the intra-thoracic fluid status of an individual and selectively permitting a reduction in notification(s) regarding the status during times when the status is being acutely adjusted.

This patent disclosure hereby incorporates the entire contents of non-provisional U.S. patent application Ser. No. 10/727,008 filed 3 Dec. 2003 and entitled, “Method and Apparatus for Detecting Change in Intrathoracic Electrical Impedance”, patent application, allowed Mar. 28, 2010 and U.S. Pat. No. 6,599,250 issued 29 Jul. 2003 to Webb and Bennett and entitled, “Heart Failure Monitor Quicklook Summary for Patient Management Systems.”

SUMMARY

The capability to suspend a patient alert comes addresses a need to selectively shut off a signal related to an undesirable trend, range, or value of a physiologic parameter of a patient. For instance, an audible patient-alert tone can be disabled during the time a patient is being treated for an excursion in the parameter (e.g., intra-thoracic fluid accumulation). Of course, in general an alert signaling regime notifies a patient, caregiver, and/or clinician attention of a potentially deleterious heart failure event such as an acute decompensation for which they should seek medical attention. In one embodiment, a chronically-implanted intra-thoracic fluid status monitoring device is interrogated by an external programming device and the patient evaluated and a caregiver then can optionally suspend the alert notification process for a predetermined period. Thus, according to the invention once the patient notification or alert has occurred, the alert mechanism is selectively deactivated while the patient ostensibly begins to gradually correct the excursion under a physician's direction and control. After a predetermined period of time the alert will reactivate.

The inventive user interface (UI) screens described herein, and their functionality, are designed to meet many of the following user requirements: clinicians must not be forced to schedule a special office visit to just turn on or off the alert and patients then do not need to be subjected to undesired, frequent (e.g., daily) alert tones.

Ultimately, suspension of the alert must be implemented in a way to preserve the feature's ability to detect a subsequent excursion in the patient's fluid status (trend or acute readings). Implementing alert suspension is designed so that it will not affect the storage or graphing of the fluid status and/or fluid status trend. The alert is thus suspended by programming a “suspend” parameter (e.g., via a programmable-field window launched from an external programmer for an implantable medical device). In one form of the invention, a parameter-launched selection menu with a response (i.e., yes/no) and a series of days (e.g., 2, 3, 5, 7, 9, 12, 14 days) selections. If a number of day selection is made, below the value selection field, a text message will show when the fluid status monitoring alert will resume (e.g., “resume alert on 30-January-05”).

In addition, optionally a feedback loop acknowledges that the alert was suspended by a notation added to the patient's report and/or the trends on a long-term tracking report. A similar notation can also appear in an events log so users can track the operation of the intra-thoracic fluid status. To maintain consistency, it is proposed that when an audible alert is suspended, a related, complementary wireless transmission of same can also be suspended.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

In the following detailed description, references are made to illustrative embodiments for improved physiologic monitoring of potentially deleterious and/or pathogenic patient conditions wherein following clinical intervention notification signaling schemes are temporarily suspended.

The present invention provides enhanced intra-thoracic impedance measurements for the detection of hemodynamic changes, in particular fluid retention. Three components of intra-thoracic impedance are used to determine fluid overload; namely, 1) daily thoracic impedance measurements, 2) thoracic reference impedance, and 3) fluid index threshold. When the daily thoracic impedance and reference impedance diverge the fluid index increases. Once the fluid index passes the user programmable threshold, if enabled, an audible alert sounds from the implantable device. The audible alert will sound daily as long as the fluid index is greater than the threshold. The capability to suspend the alert was designed to address the situation whereby a patient and/or clinician simply needs silence from the device alerts during, for example a recovery period or when under acute observation in a clinical setting. As it is currently designed, when enabled, the intra-thoracic impedance algorithm triggers an audible device alert when, for instance, a heart failure decomposition event is detected. After the patient has been seen, evaluated, and properly treated by a clinician, ideally the daily impedance should recover (i.e., increase) and rejoin the reference impedance. Because the speed at which the patient's daily impedance measurements change is typically more rapid than the response of the thoracic impedance reference, the alert can continue being activated for an extended period (e.g., on a daily basis for several days) during a recovery period.

FIG. 1is a schematic diagram of an implantable medical device according to an embodiment of the present invention. In the heuristic drawing ofFIG. 1, a section of a body11is shown with a cut-away area12to allow for illustration of an implantable medical device according to an embodiment of the present invention. As illustrated inFIG. 1, an exemplary embodiment of an implantable medical device10includes two electrodes15aand15bon the surface of a shell14of device10. Power is provided to the circuitry internal to the shell14by a power supply18, which drives a stimulation circuit16, sending electrons through various pathways in the body (such pathways are heuristically illustrated as being primarily in the area surrounded by dotted line13) between electrodes15aand15b. An impedance measurement device17determines the impedance of the circuit pathway13.

According to an embodiment of the present invention, because of the possible poor signal characteristics that may be found using the same electrodes for generating the impedance test pulse signal and taking the measurement from the same electrodes, impedance measurements are made in a uniform part (or relatively noiseless area) of the field. One way to do this is using one electrode, electrically isolated from the large surface indifferent electrode (like the can or housing of a pacemaker, device10, or other implant) to deliver the test pulse, and a second electrically isolated electrode to measure the voltage difference in the tissue between the indifferent electrode and this second electrode. Another embodiment can use two completely independent electrodes in the field to measure the impedance, thus having a quadric-polar system. In various configurations of this invention additional electrodes can be imagined for flexibility where needed or to use electrodes on leads locatable in specific places within the field created by the test, or excite pulse.

FIG. 2is a schematic diagram of exemplary electrode configurations in an implantable medical device according to an embodiment of the present invention. This acceptable variety of configuration to achieve different impedance measurement signal values is illustrated, for example, inFIG. 2wherein an implantable medical device has electrodes denoted e1, e2, eg and em and either electrodes e1or e2can be used for developing the test pulses. The value being measured (voltage or impedance of the tissue between these electrode pairs) is taken between another electrically isolated measuring electrode em and the indifferent or ground electrode eg; between em and e1; or between em and e2. Or, of course, the measurement could be taken between the two test pulse delivery electrodes e1, and eg; or between e2and eg in another embodiment.

As will be described with reference to various figures below, substantial variation can be used for each of the elements described with reference toFIGS. 1-3, and still be within the scope of this invention. For example, according to an embodiment of the present invention, the excitation pulse is delivered between electrodes e3and eg and the value measured is taken between electrodes e2and eg. In a exemplary quadrapolar arrangement, the excitation pulse is delivered between electrodes em and e3and the value measured is taken between electrodes e1and e2.

FIG. 3is a schematic diagram of an implantable medical device in which the present invention may usefully be practiced according to an embodiment of the present invention. As illustrated inFIG. 3, an implantable medical device100according to an embodiment of the present invention includes a ventricular lead105having an elongated insulative lead body116carrying three mutually insulated conductors. Located adjacent the distal end of the lead105are a ring electrode124, an extendable helix electrode126, mounted retractably within an insulative electrode head128, and an elongated coil electrode120. Each of the electrodes120,124and126is coupled to one of the three conductors within the lead body116. Electrodes124and126are employed for cardiac pacing and for sensing ventricular depolarizations, and electrode120is employed for cardioversion and/or defibrillation and for sensing depolarizations, as described below. At the proximal end of the lead105is a bifurcated connector114, which carries three electrical connectors, each coupled to one of the coiled conductors.

An atrial/SVC lead107includes an elongated insulative lead body115, also carrying three mutually insulated conductors. Located adjacent the J-shaped distal end of the lead107are a ring electrode121and an extendible helix electrode117, mounted retractably within an insulative electrode head119. Each of the electrodes117and121is coupled to one of the conductors within the lead body115. Electrodes117and121are employed for atrial pacing and for sensing atrial depolarizations. An elongated coil electrode123is provided, proximal to electrode121and coupled to the third conductor within the lead body115. At the proximal end of the lead107is a bifurcated connector113, which carries three electrical connectors, each coupled to one of the coiled conductors.

Any other known lead configurations may also be utilized other the lead configuration ofFIG. 3. For example, coil electrode123could be located on ventricular lead105and positioned within the atrium or SVC by ventricular lead105rather than by atrial lead107.

A coronary sinus/coronary vein lead109includes an elongated insulative lead body106, carrying three conductors, one of which is coupled to an elongated coiled defibrillation electrode108. Electrode108, illustrated in broken outline, is located within the coronary sinus and great vein of the heart. Located adjacent the distal end of lead109is a ring electrode125and a tip electrode127. Each of electrodes125-127is coupled to one of the remaining two of the three conductors located within lead body106. At the proximal end of the lead109is a connector plug104that carries an electrical connector, coupled to the coiled conductors.

The implantable medical device100includes a hermetically sealed enclosure111containing the electronic circuitry (FIG. 4) used for generating cardiac pacing pulses for delivering cardioversion and defibrillation shocks and for monitoring the patient's heart rhythm. Implantable medical device110is shown with the lead connector assemblies104,113and114inserted into the connector block112, which serves as a receptacle and electrical connector for receiving the connectors104,113and114and interconnecting the leads to the circuitry within enclosure111.

Insulation of the outward facing portion of the housing111of the implantable medical device110may be provided or a portion130of the outward facing portion may instead be left uninsulated, or some other division between insulated and uninsulated portions may be employed. The uninsulated portion130of the housing111optionally serves as a subcutaneous defibrillation electrode, used to defibrillate either the atria or ventricles, and as a sensing electrode for sensing depolarizations of the heart. Other lead configurations and electrode locations may of course be substituted for the lead set illustrated. For example, atrial defibrillation and sensing electrodes might be added to either the coronary sinus lead or the right ventricular lead instead of being located on a separate atrial lead, allowing for a two lead system.

FIG. 4is a functional block diagram of an exemplary implantable medical device of the type illustrated inFIG. 3, in which the present invention may usefully be practiced. The device is provided with a lead system including electrodes, which may be as illustrated inFIG. 3. Alternate lead systems may of course be substituted such as pericardial, epicardial, subcutaneous arrays, pairs and single electrodes as is well understood by those of skill in the art. If the electrode configuration ofFIG. 3is employed, the correspondence to the illustrated electrodes is as follows. Electrode311corresponds to an electrode formed along the uninsulated portion130of the housing of the implantable medical device110. Electrode320corresponds to electrode120and is a defibrillation electrode located in the right ventricle. Electrode310corresponds to electrode108and is a defibrillation electrode located in the coronary sinus. Electrode318corresponds to electrode123and is a defibrillation electrode located in the superior vena cava. Electrodes324and326correspond to electrodes124and126, and are used for sensing and pacing in the ventricle. Electrodes317and321correspond to electrodes117and121and are used for pacing and sensing in the atrium.

Electrodes310,311,318and320are coupled to high voltage output circuit234. Electrodes324and326are coupled to an R-wave amplifier, which preferably takes the form of an automatic gain controlled amplifier providing an adjustable sensing threshold as a function of the measured R-wave amplitude, included in a sense amplifier circuit200. A signal is generated on R-out line202whenever the signal sensed between electrodes324and326exceeds the present sensing threshold.

Electrodes317and321are coupled to a P-wave amplifier, which preferably also takes the form of an automatic gain controlled amplifier providing an adjustable sensing threshold as a function of the measured P-wave amplitude, included in sense amplifier circuit200. A signal is generated on P-out line206whenever the signal sensed between electrodes317and321exceeds the present sensing threshold. Numerous prior art sense amplifiers employed in implantable cardiac pacemakers, defibrillators and monitors may be usefully be employed in conjunction with the present invention.

Switch matrix208is used to select which of the available electrodes are coupled to wide band amplifier210for use in digital signal analysis. Selection of electrodes is controlled by the microprocessor224via data/address bus218, which selections may be varied as desired. Signals from the electrodes selected for coupling to bandpass amplifier210are provided to multiplexer220, and thereafter converted to multi-bit digital signals by A/D converter222, for storage in random access memory226under control of direct memory access circuit228. Microprocessor224may employ digital signal analysis techniques to characterize the digitized signals stored in random access memory226to recognize and classify the patient's heart rhythm employing any of the numerous signal processing methodologies known to the art.

Telemetry circuit330receives downlink telemetry from and sends uplink telemetry to the patient activator by means of antenna332. Data to be uplinked to the activator and control signals for the telemetry circuit are provided by microprocessor224via address/data bus218. Received telemetry is provided to microprocessor224via multiplexer220. The atrial and ventricular sense amp circuits of sense amplifier circuit200produce atrial and ventricular EGM signals which also may be digitized and uplink telemetered to an associated programmer on receipt of a suitable interrogation command. The device may also be capable of generating so-called marker codes indicative of different cardiac events that it detects. The particular telemetry system employed is not critical to practicing the invention, and any of the numerous types of telemetry systems known for use in implantable devices may be used. In particular, the prior telemetry systems as disclosed in U.S. Pat. No. 5,292,343 issued to Blanchette et al., U.S. Pat. No. 5,314,450, issued to Thompson, U.S. Pat. No. 5,354,319, issued to Wyborny et al. U.S. Pat. No. 5,383,909, issued to Keimel, U.S. Pat. No. 5,168,871, issued to Grevious, U.S. Pat. No. 5,107,833 issued to Barsness or U.S. Pat. No. 5,324,315, issued to Grevious, all incorporated herein by reference in their entireties, are suitable for use in conjunction with the present invention. However, the telemetry systems disclosed in the various other patents cited herein which are directed to programmable implanted devices, or similar systems may also be substituted. The telemetry circuit330is of course also employed for communication to and from an external programmer, as is conventional in implantable anti-arrhythmia devices.

A patient notification circuit331enables the patient to be notified in the event that it is determined that a significant change in impedance has occurred, as will be in detail described below.

The remainder of the circuitry is dedicated to the provision of cardiac pacing, cardioversion and defibrillation therapies, and, for purposes of the present invention may correspond to circuitry known in the prior art. An exemplary apparatus is disclosed for accomplishing pacing, cardioversion and defibrillation functions as follows. The pacer timing/control circuitry212includes programmable digital counters which control the basic time intervals associated with DDD, WI, DVI, VDD, AAI, DDI, DDDR, WIR, DVIR, VDDR, MIR, DDIR and other modes of single and dual chamber pacing well known to the art. Circuitry212also controls escape intervals associated with anti-tachyarrhythmia pacing in both the atrium and the ventricle, employing, any anti-tachyarrhythmia pacing therapies known to the art.

Intervals defined by pacing circuitry212include atrial and ventricular pacing escape intervals, the refractory periods during which sensed P-waves and R-waves are ineffective to restart timing of the escape intervals and the pulse widths of the pacing pulses. The durations of these intervals are determined by microprocessor224, in response to stored data in memory226and are communicated to the pacing circuitry212via address/data bus218. Pacer circuitry212also determines the amplitude of the cardiac pacing pulses under control of microprocessor224.

During pacing, the escape interval counters within pacer timing/control circuitry212are reset upon sensing of R-waves and P-waves as indicated by signals on lines202and206, and in accordance with the selected mode of pacing on time-out trigger generation of pacing pulses by pacer output circuits214and216, which are coupled to electrodes317,321,324and326. The escape interval counters are also reset on generation of pacing pulses, and thereby control the basic timing of cardiac pacing functions, including anti-tachyarrhythmia pacing.

The durations of the intervals defined by the escape interval timers are determined by microprocessor224, via data/address bus218. The value of the count present in the escape interval counters when reset by sensed R-waves and P-waves may be used to measure the durations of R-R intervals, P-P intervals, PR intervals and R-P intervals, which measurements are stored in memory226and are used in conjunction with tachyarrhythmia detection functions.

Microprocessor224operates as an interrupt driven device, and is responsive to interrupts from pacer timing/control circuitry212corresponding to the occurrences of sensed P-waves and R-waves and corresponding to the generation of cardiac pacing pulses. These interrupts are provided via data/address bus218. Any necessary mathematical calculations to be performed by microprocessor224and any updating of the values or intervals controlled by pacer timing/control circuitry212take place following such interrupts. Microprocessor224includes associated ROM in which the stored program controlling its operation as described below resides. A portion of the memory226may be configured as a plurality of recirculating buffers, capable of holding series of measured intervals, which may be analyzed in response to the occurrence of a pace or sense interrupt to determine whether the patient's heart is presently exhibiting atrial or ventricular tachyarrhythmia.

Arrhythmia detection may include any of the numerous available prior art tachyarrhythmia detection algorithms. One preferred embodiment may employ all or a subset of the rule-based detection methods described in U.S. Pat. No. 5,545,186 issued to Olson et al. or in U.S. Pat. No. 5,755,736 issued to Gillberg et al., both incorporated herein by reference in their entireties. However, any of the various arrhythmia detection methodologies known to the art might also usefully be employed in alternative embodiments of the invention.

In the event that an atrial or ventricular tachyarrhythmia is detected, and an anti-tachyarrhythmia pacing regimen is desired, timing intervals for controlling generation of anti-tachyarrhythmia pacing therapies are loaded from microprocessor224into the pacer timing and control circuitry212, to control the operation of the escape interval counters therein and to define refractory periods during which detection of R-waves and P-waves is ineffective to restart the escape interval counters.

In the event that generation of a cardioversion or defibrillation pulse is required, microprocessor224employs the escape interval counter to control timing of such cardioversion and defibrillation pulses, as well as associated refractory periods. In response to the detection of atrial or ventricular fibrillation or tachyarrhythmia requiring a cardioversion pulse, microprocessor224activates cardioversion/defibrillation control circuitry230, which initiates charging of the high voltage capacitors246,248via charging circuit236, under control of high voltage charging control line240. The voltage on the high voltage capacitors is monitored via VCAP line244, which is passed through multiplexer220and in response to reaching a predetermined value set by microprocessor224, results in generation of a logic signal, terminating charging. Thereafter, timing of the delivery of the defibrillation or cardioversion pulse is controlled by pacer timing/control circuitry212. Following delivery of the fibrillation or tachycardia therapy the microprocessor then returns the device to cardiac pacing and awaits the next successive interrupt due to pacing or the occurrence of a sensed atrial or ventricular depolarization. In the illustrated device, delivery of the cardioversion or defibrillation pulses is accomplished by output circuit234, under control of control circuitry230via control bus238. Output circuit234determines whether a monophasic or biphasic pulse is delivered, whether the housing311serves as cathode or anode and which electrodes are involved in delivery of the pulse.

A measurement circuit203, similar to measurement circuit37and excitation circuit34described above in reference toFIG. 4, is utilized in the delivery of excitation pulses and to measure the resulting impedances between a vector formed by any pair of electrodes selected from among electrodes310,311,317,318,320,321,324and326through connections made in switch matrix208. Measurement circuit203, which is coupled to data/address bus218, can be separate from or may be included within sense amplification circuit200, as shown.

According to the present invention, once impedance measurement is initiated by microprocessor224, an excitation pulse is generated by output circuit234and applied across an excitation path corresponding to a vector formed by selected electrodes, described above. The excitation pulse may be in the form of either a current pulse or a voltage pulse, and, in either case, may consist of one or more phases of differing polarity, or may correspond to a monophasic, constant voltage pulse for simplicity of implementation. In an embodiment of the present invention, for example, the excitation pulse has an amplitude of approximately 1 volt and a pulse width of approximately 90 microseconds, although any desired amplitude and pulse width may be utilized.

Measurement circuit203measures the voltage appearing across a measurement path corresponding to selected measurement electrodes, with the timing of the measurement by measurement circuit203being time by timing and control circuit212so as to be synchronized with delivery of the excitation pulse. Using the current delivered across the excitation path and the voltage measured across the measure path, microprocessor224then calculates the apparent intra-thoracic impedance using Ohm's Law. The process is repeated, so that multiple excitation pulses are delivered over a multiple number of days to generate multiple impedance measurements.

FIG. 5depicts a graphical user interface (GUI)500having an overlay menu501,501′ in an embodiment of the invention relating to the OptiVol® intra-thoracic fluid status trend feature of Medtronic, Inc. While a large variety of different GUI500can be utilized in practicing the present invention, a nominal GUI500can include, by illustration and without limitation some of the following. The overlay501′ of GUI500is dedicated to a single type of monitored physiologic parameter (as depicted intra-thoracic impedance reflecting possible fluid accumulation within a portion of the heart, lungs and/or pulmonary bed). A baseline reference value can be manipulated via a user-selectable button508as a threshold value504on GUI overlay501′ for ease of reference. The urgency of the notification signal(s) can be adjusted via button502and the notification signal(s) can be suspended as indicated by programmable and adjustable field506. Once a suspension period has been programmed an optional text message510can be configured to display, for example, the date when the notification will again become active. Of course, a similar function can be achieved with a counter (incremental or decremental) in lieu of or in addition to the depicted example.

In accordance with an aspect of the present invention, methods and apparatus are provided for improving notification signaling following a possibly deleterious excursion in a monitored physiologic parameter of a patient.

In addition, it will be understood that specifically described structures, functions and operations set forth in the above-referenced patents can be practiced in conjunction with the present invention, but they are not essential to its practice. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described without actually departing from the spirit and scope of the present invention.