Source: https://patents.google.com/patent/EP0970721A2/en
Timestamp: 2018-07-18 09:50:45
Document Index: 619334217

Matched Legal Cases: ['art 16', 'art 16', 'art 16', 'art 16', 'art 16', 'art 16', 'art 16', 'art 16', 'art 16', 'art 16', 'art 16']

EP0970721A2 - Apparatus for monitoring atrioventricular intervals - Google Patents
Apparatus for monitoring atrioventricular intervals Download PDF
EP0970721A2
EP0970721A2 EP19990119901 EP99119901A EP0970721A2 EP 0970721 A2 EP0970721 A2 EP 0970721A2 EP 19990119901 EP19990119901 EP 19990119901 EP 99119901 A EP99119901 A EP 99119901A EP 0970721 A2 EP0970721 A2 EP 0970721A2
EP0970721A3 (en )
This invention relates to the field of implantable medical devices, and more particularly relates to cardiac pacemakers with variable pacing rate.
Pacemakers are also known which respond to other types of physiologically-based signals, such as signals from sensors for measuring the pressure inside the patient's ventricle or for measuring the level of the patient's physical activity. In recent years, pacemakers which measure the metabolic demand for oxygen and vary the pacing rate in response thereto have become widely available. Perhaps the most popularly employed method for measuring the need for oxygenated blood is to measure the physical activity of the patient by means of a piezoelectric transducer. A piezoelectric crystal for activity sensing is typically fixed to the pacemaker shield and generates an electrical signal in response to deflections of the pacemaker shield caused by patient activity. Piezoelectric, microphone-like sensors are widely used in rate-responsive pacemakers because they are relatively inexpensive, their manufactured yield is high, and they transduce the acoustic energy of patients' motion in a highly reliable manner. A pacemaker employing a piezoelectric activity sensor is disclosed in U.S. Patent No. 4,485,813 issued to Anderson et al. Although piezoelectric activity sensors are common, there are other methods of monitoring a patient's metabolic demand for oxygenated blood. For example, blood oxygen saturation may be measured directly, as disclosed in U.S. Patent No. 4,467,807 issued to Bornzin, U.S. Patent No. 4,807,629 issued to Baudino et al., and in U.S. Patent No. 4,750,495 issued to Brumwell et al. Alternatively, pacing rate can be varied as a function of a measured value representative of stroke volume, as described in U.S. Patent No. 4,867,160 to Schaldach. Other physiologic conditions that can be used as an indication of a patient's metabolic demand for oxygenated blood include: right ventricular blood pressure and the change of right ventricular blood pressure over time, venous blood temperature, respiration rate, minute ventilation, and various pre- and post-systolic time intervals. Such conditions can be measured, for example, by impedance or pressure sensing within the right ventricle of the heart.
In one prior art technique employing a piezoelectric, microphone-like sensor for transducing patient activity, the raw electrical signal output from the sensor is applied to an AC-coupled system which bandpass filters the signal prior to being applied to pacemaker rate-setting logic. This arrangement is disclosed in U.S. Patent No. 5,052,388 to Sivula et al. According to the Sivula et al. patent, peaks in the bandpass filtered sensor signal which exceed a predetermined threshold are interpreted by the rate-setting logic as an indication of patient activity of sufficient magnitude that an increase in the pacing rate may be warranted. The predetermined threshold, which may also be selectable by a physician from one of a plurality of programmable settings, is intended to screen out background "noise" in the sensor output signal indicative of low amplitude patient motion. Each occurrence of a peak in the bandpass-filtered sensor signal which exceeds the threshold level is known as a "sensor detect". A sum of sensor detects is computed over some period of time; for example, the number of sensor detects may be determined every two seconds. If, at the end of that period, the number of sensor detects exceeds some predetermined value, the rate-setting logic interprets this as an indication that the pacing rate should be incrementally increased.
Similarly other pacemakers, such as Medtronic, Inc.'s Activitrax II Models 8412-14, Medtronic, Inc.'s Legend Models 8416-18, Siemens, Elema AB's Sensolog 703, Cook Pacemaker Corp.'s Sensor Model Kelvin 500, Telectronics' Meta MV Model 1202, Cordis Pacing Systems' Prism CL Model 450A, Intermedics, Inc.'s Nova MR, and Vitatron Medical B.V.'s Diamond pacemakers have incorporated the programmability feature of various variables associated with their rate-responsiveness.
Cordis Pacing Systems' Prism CL Model 450A is a rate-responsive, single-chamber, multi-programmable ventricular pacemaker. The parameters programmable in the Model 450A include: pacing mode, rate-response (on or off), electrode polarity, lower and upper rate limits, output current, output pulse width, sensitivity, refractory period, and automatic calibration speed. In the Prism CL, a dynamic variable called the Rate Control Parameter (RCP) is first determined by an initialization process when rate-response is programmed 'on'. The Prism CL uses the RCP as a reference to control the pacing rate. The pacemaker determines what the appropriate rate should be by comparing the measured RCP to the target RCP. If the measured RCP is different to the target RCP, rate is increased or decreased until the two values are equal. The pacemaker continuously makes automatic adjustments to the target RCP to adjust rate response.
The initial RCP in the Prism CL is determined while the patient is at rest During initialization, the RCP is measured for approximately twenty paced cycles to establish the target RCP. If intrinsic activity is sensed during the initialization process, initialization is temporarily suspended and the rate is increased by 2.5 pulses per minute (PPM) until pacing resumes. Once initialization is completed and the target RCP has been established, rate response is automatically initiated and the calibration function is enabled. The pacemaker indicates the end of the initialization process by issuing an ECG signature in the succeeding cycle.
Intermedics, Inc.'s Nova MR is a unipolar (atrial or ventricular) pacemaker which senses variations in blood temperature and uses this information to vary the pacing rate. The following functions are programmable to determine the pacemaker's response to detected variations in blood temperature: rate response, onset detection sensitivity, and post-exercise rate decay.
Other examples of AV interval rate-adaptation have been shown In the prior art. In U.S. Patent No. 4,060,090 to Lin et al. entitled "Variable P-R Interval Pacemaker", for example, there is described a circuit for allowing the time between the detection of an atrial contraction and the provision of an electrical stimulus to cause a ventricular contraction to vary with the rate of sensed atrial contractions. In U.S. Patent No. 4,421,116 to Markowitz entitled "Heart Pacemaker With Separate A-V Intervals for Atrial Synchronous and Atrial-Ventricular Sequential Pacing Modes", there is described a pacemaker having separately definable AV intervals for atrial-synchronous and atrial-ventricular sequential pacing.
EP-A-0495424 discloses a rate-responsive pacemaker system for sensing and storing intracardiac signals for subsequent retrieval, analysis and display. The signals may be processed off-line and displayed with respect to time, allowing enhanced detection of particular physiologic phenomena not readily discerned in the real-time signals.
Pacemaker manufacturers have attempted to alleviate the problem of pacemaker optimization by providing extensive diagnostic and monitoring capabilities in their pacemaker systems. For example, the above-described Vitatron Diamond pacemaker offers extensive diagnostic features. The Diamond can transmit event markers to its programmer so that the occurrence of paced and sensed cardiac events can be viewed on a monitor or printed on a strip chart. In addition, the Diamond can generate histograms showing P-wave amplitude, atrial rates, ventricular rate, premature ventricular contraction (PVC) coupling intervals, AV intervals versus atrial rate, VA intervals, atrial rates and PVC, PVC versus time of day, and SVT versus time of day. The Diamond can also function as a 24-hour Holter monitor, or as an activity sensor monitor. Several counters in the Diamond can be interrogated by the programmer to provide the clinician with information such as the percentage of atrial or ventricular paced events, the percentage of sensed evoked T-waves, the percentage of A-V synchronous beats, the number of PVCS, and the period of time during which the atrial rate was above the upper rate limit.
Similarly EP-A-0392032 discloses an implantable device with means for telemetering out data.
EP-A-0225839 discloses a pacemaker having storage means for storing operating parameters and values detected by the sensing electrodes. Stored data may be read out via an I/O unit and a telemetry unit.
Even with all of the diagnostic and measurement data available to the clinician, it is sometimes difficult to assimilate all of the information correctly to arrive at optimal pacemaker settings. Often, the interplay between various settings may not be apparent. A pacemaker's programmed upper rate must be higher than its programmed lower rate, the interaction between other programmable settings might not be so apparent. For example, in the above-referenced Sivula et al. patent, there is discussed the problem that a selected rate-response slope may not provide for sufficient incrementation to the base pacing rate at maximum sensor output to actually allow the pacemaker to ever reach the programmed upper rate. This defeats the physician's intent in selecting the upper rate, and substantially decreases the physician's ability to fine-tune the pacemaker to the patient's particular needs.
In order to reduce the burden on a clinician in programming a pacemaker, as well as to assist the clinician in making the most appropriate parameter selections, it has been proposed in the prior art that the pacemaker be capable of performing some parameter selection automatically. Described in "Rate Responsive Pacemaker and Method for Automatically Initializing the Same", there is described a pacemaker system capable of automatically initializing such parameters as sensitivity threshold, pacing pulse width, pacing pulse amplitude, activity threshold, and rate-response gain. While the teachings of "Rate Responsive Pacemaker and Method for Automatically Initializing the Same" represents an improvement over prior methods of parameter selection in an implantable pacemaker, the present inventors believe that there is room for further improvements to achieve even greater levels of optimization In pacemaker therapy. In particular, with regard to selectable rate-response settings as well as to the provision of a rate-adaptive AV delay which takes into account the inversely proportional relationship between heart rate and AV intervals, prior implementations (as exemplified by the above-described Vitatron Diamond) have depended on the clinician tailing the rate-response and AV adaptation in a relatively "blind", ad hoc way, usually in the office during a patient follow-up. In addition, the physician is typically limited to selecting from among a relatively few different adaptive AV settings. Moreover, rate-response setting selection and AV interval adjustment are typically done with little diagnostic or hemodynamic performance data to guide the clinician's choices for the patient at hand. Ideally, the tailoring to a patient would be driven by optimization of one or more hemodynamic parameters, such as ejection fraction, ventricular filling, or stroke volume. However, measurement of those parameters requires the presence of special sensors, which may not always be available.
The present invention, therefore, relates to an apparatus for determining a patient's profile for rate-adaptive sense and pace AV intervals and for generally assisting the physician in selecting appropriate available rate-response settings.
According to the invention, there is provided a rate-responsive pacemaker system, comprising an implantable pulse generator and an external programming unit, wherein said implantable pulse generator comprises:
a sensing means for detecting electrical cardiac signals;
a control circuit means for controlling the rate of delivery of pacing pulses by said implantable pulse generator in accordance with programmed rate response settings, said control circuit further comprising a means for inhibiting delivery of pacing pulses in the presence of normal electrical cardiac signals;
a memory unit for storing numeric data;
a timing circuit means coupled to said control circuit and to said memory unit to simultaneously compute and store in said memory unit data reflecting a patient's heart rate and the percentage of paced events over a given period of time and data reflecting AV interval durations of each one of a succession of cardiac cycles;
a first telemetry circuit coupled to said memory unit and to said control circuit, said first telemetry circuit responsive to an interrogate signal from said data stored in said memory unit to said external programming unit to transmit said atrial rate data and said AV interval data to said external programming unit;
wherein said external programming unit comprises:
a processing means for producing graphics and text data;
a display means for displaying said graphics and said text data; and
a second telemetry circuit means for sending said interrogate signal and to receive said data transmitted by said first telemetry transmitter circuit; characterised by
graphics circuitry means adapted to graph a sensor indicated activity rate versus time indicating the pacemaker activity rate in response to predetermined pacemaker parameter settings, on said display screen; said graphic circuitry means also adapted to simultaneously graph the actual heart rate of the patient over the same period of time and to provide simultaneously an indication of the percentage of paced events occurring over that time; and
input means associated with said display means via which said pacemaker parameter settings can be adjusted, wherein said processing means and graphic circuitry means show on said display means changes in the displayed rates and percentage due to changes in said pacemaker parameter settings.
The disclosed activity exercise test assists the clinician in selecting appropriate rate response parameters and AV rate-adaptation profiles through a defined protocol involving a pacemaker and a programmer. The test results are displayed in novel ways which allow the clinician to observe the impact of activity sensing on the pacing therapy. The clinician can also modify the activity sensor parameters and review the resulting impact. Such forecasting capability allows the clinician to select appropriate sensor parameters based upon information about both the sensor and any intrinsic response that may occur during the exercise. It is believed that the present invention enables a clinician to achieve a greater degree of optimization of a pacemaker's operation to the needs of a given patient
For patients with high-degree AV block, the clinician could program an AV delay rate-adaptation that mimics the adaptation profile of healthy hearts, and hope that the profile is appropriate for the patient at hand. However, for patients with sufficient intrinsic conduction at certain ranges of heart rate, it may be preferable to allow the intrinsic ventricular contraction to occur so that enhanced ejection fraction, increased myocardial efficiency, and longer pacemaker battery life can be achieved. The present invention relates to an apparatus for guiding, and/or automatically making, the selection of rate-adaptive AV parameters for patients with some intrinsic conduction.
During the patient exercise, the pacemaker temporarily sets the programmable AV duration values to be relatively long. (e.g., 250-mSec or so), with zero offset between paced and sensed AV; that is, the AV delay for atrial-sense-to-ventricular-pace (AS-to-VP) is the same as that for atrial-pace-to-ventricular-pace (AP-to-VP). The pacemaker records in its memory every AS-to-VS AV interval duration, if the patient has intrinsic atrial rate at rest, as well as every AP-to-VS AV interval duration. The AV interval duration values are accumulated in "bins" as a function of the atrial rate (counting sensed, paced, and refractory-sensed atrial events to determine atrial rate). The result is a distribution of the two types of AV conduction times in each rate bin.
Also recorded during the exercise test is data reflecting the A-A interval durations, percentage of paced events, and activity sensor detects during the exercise. In addition, the pacemaker records data regarding the percentage of paced events in relation to the total number of cardiac cycles, and this data is similarly accumulated in bins as a function of atrial rate.
The foregoing and other aspects of the present invention will be best appreciated with reference to the detailed description of a specific embodiment of the invention, which follows, when read in conjunction with the accompanying drawings, and is given by way of example only.
Figure 1 is an illustration showing the implantation of a pacemaker 10 in accordance with one embodiment of the present invention;
Figure 2 is a block diagram of the pacemaker of Figure 1;
Figure 3 is a block diagram of an external programming unit in accordance with the disclosed embodiment of the invention;
Figure 4 is a flow diagram illustrating the algorithm for determining the percentage of paced events during the exercise test in accordance with the disclosed embodiment of the invention;
Figure 5 is a flow diagram illustrating the algorithm for computing a bin value as a function of atrial rate in accordance with the disclosed embodiment of the invention;
Figure 6 is an illustration of a programmer display screen in accordance with the disclosed embodiment of the invention; and
Figure 7 is an illustration of another programmer display screen in accordance with the disclosed embodiment of the invention.
Figure 1 shows generally where a rate-responsive, dual chamber pacemaker 10 in accordance with one embodiment of the present invention may be implanted in a patient 11. It is to be understood that pacemaker 10 is contained within a hermetically-sealed, biologically inert outer shield or "can", in accordance with common practice in the art. One or more conventional pacemaker leads are electrically coupled to pacemaker 10 and extend into the patient's heart 16 via a vein 18. In Figures 1 and 2, two such leads, a ventricular lead 14 and an atrial lead 15, are shown. Located on the distal end of leads 14 and 15 are one or more exposed conductive electrodes for receiving electrical cardiac signals and/or for delivering electrical pacing stimuli to the heart 16. As would be appreciated by those of ordinary skill in the art, dual-chamber pacing can be accomplished with a variety of different lead configurations, including one in which only a single lead having multiple electrodes thereon is used. Thus, although separate atrial and ventricular leads are shown in the Figures, this is done for the purposes of illustration only, and it is to be understood that the present invention is not limited to this particular lead configuration.
Turning now to Figure 2, a block diagram of pacemaker 10 from Figure 1 is shown. Although the present invention will be described herein in conjunction with a pacemaker 10 having a microprocessor-based architecture, it will be understood that pacemaker 10 may be implemented in any logic based, custom integrated circuit architecture, if desired. The pacemaker shown in Figure 2 is substantially similar to that described in "Method and Apparatus for Implementing Activity Sensing in a Pulse Generator", and also described in "Method and Apparatus for Rate-Responsive Cardiac Pacing".
Although a particular implementation of a rate-responsive pacemaker is disclosed herein, it is to be understood that the present invention may be advantageously practiced in conjunction with many different types of rate-responsive pacemakers, such as the pacemaker described in "Method and Apparatus for Rate-Responsive Cardiac Pacing". Furthermore, although the present invention will be described herein in the context of a rate-responsive pacemaker utilizing a microphone-like piezoelectric sensor as described above, it is also to be understood that the present invention may be advantageously practiced in conjunction with pacemakers having other types of sensors (e.g., pressure, blood-oxygen, impedance, temperature, etc...) which provide an indication of a patient's metabolic demand for oxygenated blood.
In the illustrative embodiment shown in Figure 2, pacemaker 10 includes an activity sensor 20, which may be, for example, a piezoelectric element bonded to the inside of the pacemaker's shield. Such a pacemaker/activity sensor configuration is the subject of the above-referenced patent to Anderson et al. Piezoelectric sensor 20 provides a sensor output which varies as a function of a measured parameter that relates to the metabolic requirements of patient 11.
Pacemaker 10 of Figure 2 is programmable by means of an external programming unit (not shown in Figure 2). One such programmer suitable for the purposes of the present invention is the Medtronic Model 9760 programmer which is commercially available and is intended to be used with all Medtronic pacemakers. The 9760 programmer is a microprocessor-based device which provides a series of encoded signals to pacemaker 10 by means of a programming head which transmits radio-frequency (RF) encoded signals to pacemaker 10 according to the telemetry system laid out, for example, in U.S. Patent No. 5,127,404 to Wyborny et al. entitled "Improved Telemetry Format". It is to be understood, however, that the programming methodology disclosed in the above-referenced patent is identified herein for the purposes of illustration only, and that any programming methodology may be employed so long as the desired information can be conveyed between the pacemaker and the external programmer.
The external programmer should also preferably be capable of displaying both text and graphics, as will be hereinafter become apparent Also, programmer should be capable of interrogating the pacemaker's internal memory.
It is believed that one of skill in the art would be able to choose from any of a number of available pacemaker programmers and programming techniques to accomplish the tasks necessary for practicing the present invention. As noted above, however, the Medtronic Model 9760 programmer is presently preferred by the inventors. This programmer will be hereinafter described in greater detail with reference to Figure 3.
In addition, a programmer may include means for selection of acceleration and deceleration parameters which limit the rate of change of the pacing rate. Typically, these parameters are referred to in rate responsive pacemakers as acceleration and deceleration settings, respectively, or attack and decay settings, respectively. These may be expressed in terms of the time interval required for the pacemaker to change between the current pacing rate and 90% of the target pacing interval, assuming that the activity level corresponding to the desired target rate remains constant Appropriate selectable values for the acceleration time would be, for example, 0.25 minutes, 0.5 minutes, and 1 minute. Appropriate selectable values for the deceleration time would be, for example, 2.5 minutes, 5 minutes, and 10 minutes.
Pacemaker 10 is schematically shown in Figure 2 to be electrically coupled via pacing lead 14 and 15 to a patient's heart 16. Leads 14 and 15 include one or more intracardiac electrodes, designated as 17 and 18 in Figure 2, located near their distal ends of leads 14 and 15, respectively, and positioned within the right ventricular (RV) and right atrial (RA) chambers, respectively of heart 16. As previously noted, leads 14 and 15 can be of either the unipolar or bipolar type as is well known in the art; alternatively, a single, multiple-electrode lead may be used.
Electrodes 17 and 18 are coupled via suitable lead conductors through input capacitors 19 to input/output terminals of an input/output circuit 22. In the presently disclosed embodiment, activity sensor 20 is bonded to the inside of the pacemaker's outer protective shield, in accordance with common practice in the art. As shown in Figure 2, the output from activity sensor 20 is also coupled to input/output circuit 22.
It will be understood that each of the electrical components represented in Figure 2 is powered by an appropriate implantable battery power source 32, in accordance with common practice in the art. For the sake of clarity, the coupling of battery power to the various components of pacemaker 10 has not been shown in the Figures.
An antenna 23 is connected to input/output circuit 22 for purposes of uplink/downlink telemetry through an RF transmitter and receiver unit 33. Unit 33 may correspond to the telemetry and program logic employed in U.S. Patent No. 4,556,063 issued to Thompson et al. on December 3, 1985 and US. Patent No. 4,257,423 issued to McDonald et at on March 24, 1981. Telemetering analog and/or digital data between antenna 23 and an external device, such as the aforementioned external programmer (not shown in Figure 2), may be accomplished in the presently disclosed embodiment by means of all data first being digitally encoded and then pulse-position modulated on a damped RF carrier, as substantially described in the above-reference patent to Wyborny et al. The particular programming and telemetry scheme chosen is not believed to be important for the purposes of the present invention so long as it provides for entry and storage of values of operational parameters, and for the interrogation of pacemaker memory, as discussed herein.
Digital controller/timer circuit 31 is coupled to sensing circuitry including a sense amplifier circuit 38 and a sensitivity control circuit 39. In particular digital controller/timer circuit 31 receives an A-EVENT (atrial event) signal on line 40, and a V-EVENT (ventricular event) signal on line 41. Sense amplifier circuit 38 is coupled to leads 14 and 15, in order to receive the V-SENSE (ventricular sense) and A-SENSE (atrial sense) signals from heart 16. Sense amplifier circuit 38 asserts the A-EVENT signal on line 40 when an atrial event (i.e., a paced or intrinsic atrial event) is detected, and asserts the V-EVENT signal on line 41 when a ventricular event (paced or intrinsic) is detected. Sense amplifier circuit 38 includes one or more sense amplifiers corresponding, for example, to that disclosed in U.S. Patent No. 4,379,459 issued to Stein on April 12, 1983.
A V-EGM (ventricular electrocardiogram) amplifier 42 is coupled to lead 14 to receive the V-SENSE signal from heart 16. Similarly, an A-EGM (atrial electrocardiogram) amplifier 43 is coupled to lead 15 to receive the A-SENSE signal from heart 16. The electrogram signals developed by V-EGM amplifier 42 and A-EGM amplifier 43 are used on those occasions when the implanted device is being interrogated by an external programmer, to transmit by uplink telemetry a representation of the analog electrogram of the patient's electrical heart activity, such as described in U.S. Patent No. 4,556,063, issued to Thompson et al.
Digital controller and timer circuit 31 is coupled to an output amplifier circuit 44 via two lines 45 and 46, designated V-TRIG (ventricular trigger) and A-TRIG (atrial trigger), respectively. Circuit 31 asserts the V-TRIG signal on line 45 in order to initiate the delivery of a ventricular stimulating pulse to heart 16 via pace/sense lead 14. Likewise, circuit 31 asserts the A-TRIG signal on line 46 to initiate delivery of an atrial stimulating pulse to heart 16 via pace/sense lead 15. Output amplifier circuit 44 provides a ventricular pacing pulse (V-PACE) to the right ventricle of heart 16 in response to the V-TRIG signal developed by digital controller/timer circuit 31 each time the ventricular escape interval times out, or an externally transmitted pacing command has been received, or in response to other stored commands as is well known in the pacing art. Similarly, output amplifier circuit 44 provides an atrial pacing pulse (A-PACE) to the right atrium of heart 16 in response to the A-TRIG signal developed by digital controller/timer circuit 31. Output amplifier circuit 44 includes one or more output amplifiers which may correspond generally to that disclosed in U.S. Patent No. 4,476,868 issued to Thompson on October 16, 1984.
As would be appreciated by those of ordinary skill in the art, input/output circuitry will include decoupling circuitry for temporarily decoupling sense amplifier circuit 38, V-EGM amplifier 42 and A-EGM amplifier 43 from leads 14 and 15 when stimulating pulses are being delivered by output amplifier circuit 44. For the sake of clarity, such decoupling circuitry is not depicted in Figure 2.
While specific embodiments of sense amplifier circuitry, output amplifier circuitry, and EGM amplifier circuitry have been identified herein, this is done for the purposes of illustration only. It is believed by the inventor that the specific embodiments of such circuits are not critical to the present invention so long as they provide means for generating a stimulating pulse and provide digital controller/timer circuit 31 with signals indicative of natural and/or stimulated contractions of the heart it is also believed that those of ordinary skill in the art could chose from among the various well-known implementations of such circuits in practicing the present invention.
Digital controller/timer circuit 31 is coupled to an activity circuit 47 for receiving, processing, and amplifying activity signals received from activity sensor 20. A suitable implementation of activity circuit 47 is described in detail in the above-referenced Sivula et al. It is believed that the particular implementation of activity circuit 47 is not critical to an understanding of the present invention, and that various activity circuits are well-known to those of ordinary skill in the pacing art.
A generalized block diagram of programmer 11 in accordance with the presently disclosed embodiment of the invention is provided in Figure 3. As shown in Figure 3, programmer 11 is a personal-computer type microprocessor-based device incorporating, a central processing unit 50, which may be, for example, an Intel 80386 microprocessor or the like.
Graphics circuit 53, in turn, is coupled to a graphics display screen 55, which in the case of the Medtronic Model 9760 programmer is a cathode ray tube (CRT) screen 55 having a resolution of 720 x 348 pixels. In the presently preferred embodiment of the invention, screen 55 is of the well-known "touch sensitive" type, such that a user of programmer 11 may interact therewith through the use of a stylus 56, also coupled to graphics circuit 53, which is used to point to various locations on screen 55. Various touch-screen assemblies are known and commercially available.
With continued reference to Figure 3, programmer 11 further comprises an interface module 57 which includes digital circuitry 58, non-isolated analog circuitry 59, and isolated analog circuitry 60. Digital circuitry 58 enables interface module 57 to communicate with interface controller module 54.
As previously noted, pacemaker 10 is provided with EGM amplifiers 42 and 43 which produce ventricular and atrial EGM signals. These EGM signals may be digitized by ADC 36 and up-link telemetered to programmer 11. The telemetered EGM signals are received in programming head 61 and provided to non-isolated analog circuitry 59. Non-isolated analog circuitry 59, in turn, converts the digitized EGM signals to analog EGM signals (as with a digital-to-analog converter, for example) and presents these signals on output lines designated in Figure 3 as A EGM OUT and V EGM OUT. These output lines may then be applied to a strip-chart recorder, CRT, or the like, for viewing by the physician. As these signals are ultimately derived from the intracardiac electrodes, they often provide different information that may not be available in conventional surface ECG signals derived from skin electrodes.
Pacemaker 10 may also be capable of generating so-called marker codes indicative of different cardiac events that it detects. A pacemaker with marker-channel capability is described, for example, in Markowitz entitled "Marker Channel Telemetry System for a Medical Device". The markers provided by pacemaker 10 may be received by programming head 61 and presented on the MARKER CHANNEL output line from non-isolated analog circuitry 59.
In order to ensure proper positioning of programming head 61 over implanted device 10, circuitry is commonly provided for providing feedback to the user that programming head 61 is in satisfactory communication with and is receiving sufficiently strong RF signals from pacemaker 10. This feedback may be provided, for example, by means of a head position indicator, designated as 61 in Figure 3. Head position indicator 62 may be, for example, a light-emitting diode (LED) or the like that is lighted to indicate a stable telemetry channel.
Programmer 11 is also provided with a strip-chart printer or the like, designated in 63 in Figure 3, which may be used, for example, to provide a hard-copy print-out of the A EGM or V EGM signals transmitted from pacemaker 10.
In the presently disclosed embodiment of the invention, there are a number of counters, registers, and timers implemented in the digital controller/timer circuit 31 of pacemaker 10. These registers and counters are used for measuring certain time intervals necessary for carrying out the pacing/rate-response algorithm and other functions of pacemaker 10. The use of counters, registers, and timers for this purpose is well-known in the art, and is also described in the above-references of Stein and Wahlstrand et al. One counter in circuit 31 is called the PACE COUNTER, and is used to store a numeric value corresponding to the number of pacing stimuli delivered by the device. As would be appreciated by those of ordinary skill in the art, for dual-chamber pacemakers, two count values could be maintained, an APACE COUNTER reflecting the number of atrial stimulating pulses delivered and a VPACE COUNTER reflecting the number of ventricular stimulating pulses delivered. Another counter is called the TOTAL EVENT COUNTER, and is used to store a numeric value corresponding to the number of cardiac events which occur. Still another counter relevant to the presently disclosed embodiment of the invention is an ACTIVITY COUNTER, which is used to count the number of sensor detects. Therefore, if it is desired, for example, to count the number of ventricular pacing pulses delivered during a given interval, circuit 31 will reset the VPACE COUNTER at the beginning of the interval of interest, and then cause the value of the VPACE COUNTER to be incremented by one each time the V-TRIG signal is asserted. Similarly, if it is desired to count the number of cardiac cycles (e.g., A-A intervals) occurring during a given time interval, circuit 31 will reset the TOTAL EVENT COUNTER at the beginning of the interval of interest, and then cause the value of the TOTAL EVENT COUNTER to be incremented by one each time the A-EVENT signal is asserted by sense amplifier circuitry 38, and each time ATRIG is asserted by digital circuit 31. (Of course, the number of cardiac cycles could also be determined by counting the number of V-V intervals, in which case the TOTAL EVENT COUNTER would be incremented by one each time the V-EVENT signal is asserted.)
One of the timers implemented in circuit 31 is called the INTERVAL TIMER and is used to measure the duration of cardiac cycles (i.e., A-A intervals or V-V intervals). Another timer, called the AV TIMER, is used to measure the duration of A-V intervals (i.e., the interval between an atrial paced or sensed event and a ventricular paced or sensed event). As would be appreciated by those of ordinary skill in the art, the INTERVAL TIMER, AV TIMER, and other timers to be described in greater detail below, are, in actuality, counters which receive a clock signal at an increment or decrement input thereto, such that the counter value is incremented or decremented by one each clock cycle. The real-time duration of an interval measured by such counters can then be determined based upon the counter value at the end of the interval in question and the frequency of the clock signal applied to the counter. In the presently disclosed embodiment of the invention, it will be assumed that the timers in circuit 31 are clocked by a 128-Hz clock signal, which of course can be readily derived from the system clock signal from crystal oscillator circuit 34.
As pacemaker 10 may be a dual-chamber pacemaker having both atrial and ventricular sensing capabilities, a cardiac cycle may be defined in terms of either an A-A interval (i.e., the interval from one atrial event, paced or sensed, to the next), or a V-V interval (i.e., the interval from one ventricular event, paced or sensed, to the next). Naturally, if pacemaker 10 were a single-chamber pacemaker having sensing capabilities in only one chamber, a cardiac cycle would of necessity be defined in terms of successive events in the sensed chamber. For the purposes of the following description, the term "cardiac cycle" will be used to indicate an A-A interval, although it is to be understood that a cardiac cycle could also be defined in terms of V-V intervals.
In accordance with the presently disclosed embodiment of the invention, pacemaker 10 performs a number of operations at the end of each cardiac cycle. At the end of each cardiac cycle, circuit 31 will cause the value held in the INTERVAL TIMER to be stored in memory 29. Microcomputer circuit 24 maintains an area of successive memory locations in RAM/ROM unit 29 for storing successive INTERVAL TIMER values, so that information regarding the length of a plurality of recent cardiac cycles can be subsequently retrieved. The INTERVAL TIMER is reset following each cardiac cycle, so that the value of the INTERVAL TIMER at the end of a cardiac cycle reflects the duration of that cardiac cycle. Also, at the end of each cardiac cycle, circuit 31 increments the value of the PACE COUNTER by one if an atrial stimulating pulse was delivered during the cycle. (Again, it is to be understood that cardiac cycles could also be defined in terms of V-V intervals, in which case the PACE COUNTER would be incremented if a ventricular stimulating pulse was delivered during the cycle. It is also contemplated that separate counters and timers could be maintained for both the atrium and the ventricle; however, the consumption of memory and processing capability may mandate that only one chamber or the other could be monitored.)
For the purposes of implementing the rate-response algorithm described in the above-references to Stein and to Wahstrand et al., pacemaker 10 also performs a number of operations at the end of each two-second interval.
Generally speaking, two sets of data are gathered by pacemaker 10 during the activity test One set consists of data collected at the end of each cardiac cycle during the test, and another set consists of data collected at the end of each two-second interval during the test
Turning now to Figure 4, there is shown a flow chart depicting the steps involved in the computation of the PERCENT PACED value at the end of each two-second interval of the exercise test. Block 100 in Figure 4 indicates that the bin computation is performed only at the end of each two-second interval, as previously described. At the end of the two-second interval, microcomputer 24 determines whether the PACE COUNTER value is equal zero, (i.e., no paced events during the last two-second interval), as indicated by decision block 106 in Figure 4. If so, PERCENT PACED is assigned a value of zero, in block 108. If some paced events did occur during the two-second interval, flow proceeds to block 110, where the PACE COUNTER value is multiplied by eight, and then to block 112, where the PERCENT PACED value is initialized to zero. Next, in block 114, it is determined whether the PACE COUNTER value is greater than or equal to zero. If the PACE COUNTER value is greater than or equal to zero, the current PACE COUNTER value is assigned a value corresponding to the PACE COUNTER value minus the TOTAL EVENT COUNTER value, in block 116, and the PERCENT PACED VALUE is incremented by one, in block 118.
When the PACE COUNTER value becomes less than zero in block 114, flow proceeds to decision block 120, where a determination is made whether the PERCENT PACED value is greater than three. If so, PERCENT PACED is decremented by one, in block 122, and then flow proceeds to block 124. If the PERCENT PACED value was less than or equal to three in block 120, a determination is made in block 124 whether the PERCENT PACED value is greater than or equal to five. If so, PERCENT PACED is decremented by one, in block 126. However, if the PERCENT PACED value was less than five in block 124, flow proceeds to block 128. Flow also proceeds to block 128 from block 126. The PACE COUNTER value is reset to zero in block 128, and then the TOTAL EVENT COUNTER is reset in block 130. Then, the PERCENT PACED algorithm terminates, until the end of the next two-second interval.
The algorithm just described with reference to Figure 4 may alternatively be expressed in the form of a pseudo-code subroutine, as follows:
PERCENT PACED DISPLAYED PERCENTAGE RANGE (DPR)
0 DPR = 0
1 0 < DPR < 12.5
2 125 ≤ DPR < 25
3 25 ≤ DPR < 50
4 50 ≤ DPR < 75
5 75 ≤ DPR < 87.5
6 87.5 ≤ DPR < 100
7 DPR = 100
In Figure 5, there is shown a flow diagram illustrating the algorithm performed by pacemaker 10 for converting an INTERVAL TIMER value into a bin number corresponding to a range of heart rates. It is to be understood that the computations described with reference to Figure 5 are based on an assumed clock rate of 128-Hz, and that the INTERVAL TIMER maintained in digital controller/timer circuit 31 is decremented by one on each clock cycle, starting with an initial value of 256. Of course, if a different clock rate were used, certain numeric values in the bin calculation algorithm would have to be changed.
As previously noted, the bin-computation algorithm depicted in Figure 5 is performed by pacemaker 10 at the end of each cardiac cycle, based upon the A-A interval of that cycle, and at the end of each two-second interval. In the case of the computations performed at the end of each two-second interval, the bin computation is based upon the duration of the last cardiac cycle in that interval.
The algorithm depicted in Figure 5 begins at block 131, where the current INTERVAL TIMER value is decremented by one. Next, flow proceeds to decision block 132, where a determination is made (by microcomputer circuit 24) whether the INTERVAL TIMER value for the last cardiac cycle in the latest two-second interval is greater than 159 (recall that the INTERVAL TIMER value reflects the number of cycles of the 128-Hz clock in the cardiac cycle). If the INTERVAL TIMER value is greater than 159, the BIN value is set to 31 in block 134, and this BIN value is stored (as indicated by block 136 in Figure 5) in the remaining five bits of the byte containing the three-bit PERCENT PACED value previously described with reference to Figure 4.
If the INTERVAL TIMER value was found to be less than or equal to 63 in block 150, flow proceeds to decision block 156. From block 156, if the INTERVAL TIMER value is found to be greater than 48, BIN is assigned an initial value, in block 158, corresponding to the INTERVAL TIMER value shifted right by one binary place. (i.e., the INTERVAL TIMER value divided by two). Then, fifteen is subtracted from this initial BIN value, in block 160, to obtain a final BIN value which is stored in memory (block 136).
The bin-computation algorithm just described with reference to Figure 5 can alternatively be expressed in the form of a pseudo-code subroutine, as follows:
INTERVAL TIMER = INTERVAL TIMER -1
IF (INTERVAL TIMER > 159) THEN
ELSE IF (INTERVAL TIMER > 127) THEN
BIN = INTERVAL TIMER VALUE SHIFTED RIGHT 4 PLACES
ELSE IF (INTERVAL TIMER > 95) THEN
BIN = INTERVAL TIMER VALUE SHIFTED RIGHT 3 PLACES
ELSE IF (INTERVAL > TIMER > 63) THEN
BIN = INTERVAL TIMER VALUE SHIFTED RIGHT 2 PLACES
BIN = INTERVAL TIMER VALUE SHIFTED RIGHT 1 PLACE
BIN = INTERVAL TIMER VALUE -39
ELSE BIN = I
In the following Table 2, there is set forth the correspondence between the BIN values calculated according to the algorithm depicted in Figure 5, the displayed rate range (DR) for each BIN, the range of INTERVAL TIMER values (IT) corresponding to each BIN, and the range of real-time heart rates (HR) corresponding to each BIN. Again, it is to be understood that the INTERVAL TIMER values are based on a 128-Hz clock.
COMPUTED BIN VALUE DISPLAYED RATE RANGE (DR) (beats per minute) INTERVAL TIMER RANGE (IT) HEART RATE RANGE (HR) (beats per minute)
31 0 < DR < 50 161 ≤ IT ≤ 255 30.00 ≤ HR ≤ 47.70
30 51 < DR < 55 145 ≤ IT ≤ 160 48.00 ≤ HR ≤ 52.97
29 56 < DR < 60 129 ≤ IT ≤ 144 53.33 ≤ HR ≤ 59.53
28 61 < DR < 65 121 ≤ IT ≤ 128 60.00 ≤ HR ≤ 63.47
27 66 < DR < 70 113 ≤ IT ≤ 120 64.00 ≤ HR ≤ 67.96
26 71 < DR < 75 105 ≤ IT ≤ 112 68.57 ≤ HR ≤ 73.14
25 76 < DR < 80 97 ≤ IT ≤ 104 73.84 ≤ HR ≤ 79.17
24 81 < DR < 85 93 ≤ IT ≤ 96 80.00 ≤ HR ≤ 82.58
23 86 < DR < 90 89 ≤ IT ≤ 92 83.48 ≤ HR ≤ 86.29
22 91 < DR < 95 85 ≤ IT ≤ 88 87.27 ≤ HR ≤ 90.35
21 96 < DR < 100 81 ≤ IT ≤ 84 91.43 ≤ HR ≤ 94.81
20 101 < DR < 105 77 ≤ IT ≤ 80 96.00 ≤ HR ≤ 99.74
19 106 < DR < 110 73 ≤ IT ≤ 76 101.05 ≤ HR ≤ 105.21
18 111 < DR < 115 69 ≤ IT ≤ 72 106.67 ≤ HR ≤ 111.30
17 116 < DR < 120 65 ≤ IT ≤ 68 112.94 ≤ HR ≤ 118.15
16 121 < DR < 125 63 ≤ IT ≤ 64 120.00 ≤ HR ≤ 121.90
15 126 < DR < 130 61 ≤ IT ≤ 62 123.87 ≤ HR ≤ 125.90
14 131 < DR < 135 59 ≤ IT ≤ 60 128.00 ≤ HR ≤ 130.17
13 136 < DR < 140 57 ≤ IT ≤ 58 132.41 ≤ HR ≤ 134.74
12 141 < DR < 145 55 ≤ IT ≤ 56 137.14 ≤ HR ≤ 139.64
11 146 < DR < 150 53 ≤ IT ≤ 54 142.22 ≤ HR ≤ 144.91
10 151 < DR < 55 51 ≤ IT ≤ 52 147.69 ≤ HR ≤ 150.59
9 156 < DR < 160 49 ≤ IT ≤ 50 153.60 ≤ HR ≤ 156.73
8 161 < DR < 165 IT = 48 HR = 160.00
7 DR = 166 IT = 47 HR = 163.40
6 DR = 170 IT = 46 HR = 166.96
5 171 < DR < 175 IT = 45 HR = 170.67
4 DR = 176 IT = 44 HR = 174.54
3 DR = 180 IT = 43 HR = 178.60
2 181 < DR < 185 IT = 42 HR = 182.86
1 186 < DR < 190 0 ≤ IT ≤ 41 187.32 ≤ HR ≤ URL
As noted above, the activity test in accordance with the presently disclosed embodiment of the invention involves a brief period of patient exercise, preferably on the order of five minutes or so, during which time pacemaker 10 stores data in RAM 29 after each cardiac cycle (A-A interval) and after each two-second interval. The first byte stored after each two-second interval contains the BIN and PERCENT PACED values obtained as just described, while the second byte contains the sensor detects count for the two-second interval. These bytes are stored as successive two-byte pairs in a reserved portion of RAM 29, so that they may be subsequently retrieved through interrogation by programmer 11 in the order of storage.
It is contemplated that a special case maybe defined wherein the two bytes stored following a two second interval are both zero bytes. This special case could be used to indicate that a reed switch closure occurred while the exercise test was in progress.
It should be noted that the rate-response algorithm described in the above-references of Stein and Wahlstrand et al. applications use the same two-second sensor detects data that is stored during the activity test in accordance with the presently disclosed embodiment of the invention. Thus, when the sensor detects data accumulated during the exercise test is provided to external programmer 11, programmer 11 is able to independently execute the same rate-response algorithm that is performed internally by pacemaker 10, using the same rate-response parameter settings that are programmed into pacemaker 10. In addition, however, programmer 11 can perform the rate-response computations on the data using different rate-response parameter settings, so that the clinician may determine what the pacemaker's rate-response would have been with the different settings, given the same activity levels of the patient during the activity test. This allows the clinician to experiment with different rate-response settings to determine if a different combination of rate-response settings might have resulted in better rate-response in pacemaker 10 to the patient's activity.
Turning now to Figure 6, there is shown a reproduction of a display of the activity-test data by programmer 11. As previously noted, it is believed that the details of implementation of a pacemaker programmer capable of displaying graphics such as shown in Figure 6 are not essential to an understanding of the present invention, and that those of ordinary skill in the art would be readily able to select from among various well-known and commercially-available programmers which would be suitable for the purposes of practicing the present invention. In the presently preferred embodiment of the invention, programmer 11 is the Medtronic 9760.
The activity exercise test in accordance with the presently disclosed embodiment of the invention is accomplished through a number of instructional screens displayed on programmer screen 55. The pacemaker is programmed such that the available data memory will be divided into a plurality of areas. One area collects the heart rate (i.e., bin number) percent paced, and sensor detects data at two-second intervals, as previously described. Another area collects the bin number, AV interval, and AS-to-VS/AP-to-VS data after each cardiac cycle, as previously described.
After the patient has exercised and the data is interrogated (i.e., retrieved from pacemaker 10 and stored in programmer memory), the heart rate and percent paced data is displayed in the trend format depicted in Figure 6. The sensor detects data is recalculated using the same algorithms used by pacemaker 10 itself, and displayed as the projected activity rate. Initially, pacemaker 10 will preferably calculate the projected activity rate according to the parameters actually programmed into pacemaker 10. However, in accordance with one aspect of the present invention, the physician may change the rate-response settings and cause the projected activity rate to be recalculated using the changed settings. Thus, the physician can observe the effects that the hypothetical settings have on the actual patient exercise data. If the physician determines that the hypothetical settings are preferable to the currently programmed settings, there is the opportunity for the new settings to be programmed into pacemaker 10 from the screen shown in Figure 6.
In the programmer screen depicted in Figure 6, a parameter control area designated generally as 180 displays the pacemaker parameter settings, including the Activity Threshold Setting, Acceleration, Deceleration, Lower Rate, Upper Activity Rate, and Rate Response Setting. As previously noted, the values initially displayed in parameter area 180 are those currently programmed into pacemaker 10; the currently programmed values are determined through interrogation of pacemaker 10 upon initiation of the activity exercise test in accordance with the presently disclosed embodiment of the invention. Also in parameter area 180 are a plurality of parameter control "buttons" 182, 184, 186, 188, 190, 192, 194, 196, 198, and 200. As previously noted, programmer 11 preferably has a touch-sensitive screen such that the various buttons displayed thereon can be actuated by means of stylus 56 or the like. Thus, for example, if the physician desires to increase the rate-response Acceleration setting, this is accomplished by touching programmer screen 55 at the area of button 194; decreasing the Lower Rate setting is accomplished by touching screen 55 in the area of button 192, and so on.
Also displayed in parameter area 180 is the Max(imum) Achieved Rate, which reflects the maximum pacing rate that was attained by pacemaker 10 during the exercise test with the settings displayed in parameter area 180. A parameter called Desired Rate is controllable by means of buttons 182 and 184. Desired Rate is selected by the physician based upon his or her assessment of what pacing rate should be attained by pacemaker 10 given the exercise actually performed by the patient during the test. Changing the Desired Rate using buttons 182 and 184 has the effect of changing the Rate Response setting, which is also displayed in parameter area 180 but which is not itself directly adjustable on the screen of Figure 6.
On the left-hand side of the programmer screen depicted in Figure 6 is a data display area 202. Data display area 202 includes a graph of rate (in pulses per minute, along the vertical axis) versus time (in minutes, along the horizontal axis). A horizontal line 204 (UAR) represents the Upper Activity Rate setting displayed in parameter area 180. A horizontal line 206 (DR) represents the Desired Rate setting displayed in parameter area 180. A horizontal line 208 (LR) represents the Lower Rate Setting displayed in parameter area 180.
A dashed line 210 in data display area 202 represents the computed activity rate of pacemaker 10 given the activity performed by the patient during the test and the parameter settings displayed in parameter area 180. The activity rate represented by line 210 is computed according to the same algorithm used by pacemaker 10. Thus if the parameters displayed in parameter area 180 are the same as those actually programmed into pacemaker 10, the activity rate represented by line 210 will reflect the actual pacing rate of pacemaker 10 during the patient's exercise. However after the test, the physician can adjust the settings in parameter area 180 and the activity rate represented by line 210 will be recomputed using the same algorithm but with the adjusted settings. This allows the physician to observe the effects of different settings before actually programming such settings into pacemaker 10.
Also displayed in data display area 202 are a plurality of boxes, such as those designated by reference numerals 212, 214, 216, and 218 in Figure 6. Each of the boxes represents a bin value. In the presently preferred embodiment, each box is seven pixels wide. Therefore, if the exercise test is performed for two minutes or less, each box represents a single two-second interval. If the exercise test is performed for two to four minutes, each box represents an avenge of two two-second samples. Similarly, if the test is performed for four to six minutes, each box represents an average of three two-second interval values. For the projected activity sensor rate data, if the test is performed for two minutes or less, the projected sensor rate data is plotted in the center of each box. If the test is performed for two to four minutes, every other projected sensor rate data is plotted at the center of each box, and if the test is performed for four to six minutes, every third projected sensor rate data is plotted at the center of each box. The height and vertical position of each box represents a range of rates, i.e., the displayed rate range for a bin, as set forth in Table 2 above.
For example, the box designated 212 in Figure 6 represents a bin value of 28, which according to Table 2 corresponds to a rate range of between 60.47 and 64.00 beats per minute (BPM). Thus, box 212 indicates that during the two-second time interval corresponding to box 212, the patient's heart rate was in the range between 60.47 and 64.00 BPM. Likewise, box 214 is at a vertical position corresponding to a bin value of 24, indicating that during the two-second time interval corresponding to the horizontal position of box 214, the patient's heart rate was in the range between 80.84 and 83.48 BPM.
As shown in Figure 6, boxes such as 212, 214 and 216 are different shades. A legend designated as 220 in data display area 202 identifies the meaning of the different shades of the boxes. In particular, a white box, such as box 212, indicates that during the two-second interval corresponding to that box, the percentage of paced events was between zero and ten percent. A gray box, such as boxes 214 and 218, indicates that during the two-second time interval corresponding to such a box the percentage of paced events was between 11% and 89%. Finally, a black box, such as box 216 in Figure 6, indicates that during the two-second interval corresponding to that box, the percentage of paced events was between 90% and 100%.
In the particular case illustrated in the data display area in Figure 6, therefore, it can be seen that as the patient's heart rate increased, an increasing percentage of paced events occurred. This behavior is typical of one form of a common condition called chronotropic incompetence.
In Figure 6, only three different shades of boxes, representing three percent paced ranges, are used. This is due mainly to the limited resolution of display screen 55. Recall from Table 1, however, that seven ranges of percent paced data are developed by the percent paced algorithm of Figure 4. Therefore, it is contemplated by the inventors that if higher resolution were available on the programmer's screen, as many as seven different shades of boxes could be displayed, giving the physician an even better indication of percentage of paced events throughout the course of the patient's exercise.
As would be appreciated by those of ordinary skill in the art, the display depicted in Figure 6 presents a considerable amount of information regarding the operation of and interaction between the patient's heart and pacemaker, including the percentage of paced events, the patient's actual heart rate, and the pacemaker's pacing rate. The information is presented in an advantageous way that is believed to be readily understandable and effective in showing the effects of different parameter settings on the operation of both the pacemaker and the patient
Turning now to Figure 7, there is shown another programmer screen that is used to display the AV interval data collected at the end of each cardiac cycle during the patient's exercise. The screen of Figure 7 is used to display the bin and AV data obtained at the end of each cardiac cycle, as previously described.
As set forth in the legend in the screen of Figure 7, several parameters are plotted therein. A first line, designated with reference numeral 250, shows that the AP-to-VP interval is temporarily programmed to a high level, e.g., 200-mSec, during the exercise test. Similarly, as shown by the line designated with reference numeral 252, the AS-to-VP interval is temporarily programmed to a high value during the exercise test. A line designated with reference numeral 254 indicates the programmed AP-to-VP interval profile (i.e., the AP-to-VP profile programmed before initiating the exercise test), and a line designated with reference numeral 258 indicates the programmed AS-to-VP profile (i.e., the AS-to-VP profile programmed prior to initiating the exercise test). Finally, a line representing the AV profile of a typical healthy heart is indicated with reference numeral 256.
As shown in Figure 7, the AV data collected during the activity exercise test in accordance with the presently disclosed embodiment of the invention is presented in two groups, one reflecting the AV interval durations for AP-to-VS cardiac cycles, the other reflecting the AV interval durations for AS-to-VS cardiac cycles. The data, after being communicated from pacemaker 10 to the external programmer, is sorted according to bin number and according to whether it represents AP-to-VS or AS-to-VS data. AP-to-VS data is displayed, for example, with solid data points such as the one designated by reference numeral 240, so as to be distinguished from AS-to-VS data, which is displayed, for example, with hollow data points like the one designated with reference numeral 242 in Figure 7.
Each data point in Figure 7 corresponds to one of the 32 bins identified in Table 2 above. The range of AV interval durations associated with each data point indicates the maximum and minimum AV interval durations for that bin; the data point itself represents the mean of all AV interval durations in the bin. Thus, for example, data point 244 and the range associated therewith is associated with bin 22, and reflects the fact that during the patient's exercise test, the cardiac cycles in the range of durations corresponding to bin 22 had a mean AS-to-VS AV interval duration of approximately 120-mSec, and had AV interval durations ranging from a maximum of approximately 130-mSec to a minimum of approximately 115-mSec.
Figure 7 also indicates that, in accordance with the presently disclosed embodiment of the invention, the programmed AS-to-VP and AS-to-VS AV interval durations were set at a high level, specifically, 200-mSec.
From the foregoing detailed description of a particular embodiment of the invention, it should be apparent that a method and apparatus for achieving optimal rate-responsive pacemaker therapy has been disclosed. Although a specific embodiment of the invention has been described herein in some detail, it is to be understood that this description has been provided for the purposes of illustration only, and is not intended to be limiting with respect to the scope of the invention. It is contemplated that numerous alternative implementations, and various alterations, substitutions and modifications may be made to the embodiment described herein may be made without departing from the scope of the present invention as defined in the appended claims.
A rate-responsive pacemaker system, comprising an implantable pulse generator (10) and an external programming unit (Fig.3), wherein said implantable pulse generator comprises:
a sensing means (20) for detecting electrical cardiac signals;
a control circuit means (22) for controlling the rate of delivery of pacing pulses by said implantable pulse generator in accordance with programmed rate response settings, said control circuit further comprising a means for inhibiting delivery of pacing pulses in the presence of normal electrical cardiac signals;
a memory unit (29) for storing numeric data;
a timing circuit means (31) coupled to said control circuit (22) and to said memory unit (29) to simultaneously compute and store in said memory unit (29) data reflecting a patient's heart rate and the percentage of paced events over a given period of time and data reflecting AV interval durations of each one of a succession of cardiac cycles;
a first telemetry circuit (33) coupled to said memory unit (29) and to said control circuit (22), said first telemetry circuit responsive to an interrogate signal from said said data stored in said memory unit to said external programming unit to transmit said atrial rate data and said AV interval data to said external programming unit;
wherein said external programing unit comprises:
a processing means (50) for producing graphics and text data;
a display means (55) for displaying said graphics and said text data; and
a second telemetry circuit means (57) for sending said interrogate signal and to receive said data transmitted by said first telemetry transmitter circuit;
graphics circuitry means adapted to graph a sensor indicated activity rate versus time indicating the pacemaker activity rate in response to predetermined pacemaker parameter settings, on said display screen (55); said graphic circuitry means also adapted to simultaneously graph the actual heart rate of the patient over the same period of time and to provide simultaneously an indication of the percentage of paced events occuring over that time; and
input means associated with said display means via which said pacemaker parameter settings can be adjusted, wherein said processing means (50) and graphic circuitry means (53) show on said display means (55) changes in the displayed rates and percentage due to changes in said pacemaker parameter settings.
A pacemaker system in accordance with claim 1 further comprising a sensor means (20) coupled to said implantable pulse generator, for producing an output signal reflecting a patient's metabolic demand for oxygenated blood.
A pacemaker system in accordance with claim 1 or 2, wherein the available memory of said memory unit is divided into a plurality of areas and wherein the patient's heart rate is stored in one area, the percentage of paced events is stored in another area and the sensor indicated activity rate is stored in another area.
A pacemaker system as claimed in claim 3, wherein the display means display a plurality of pacemaker parameter settings and a plurality of parameter control buttons and a data display area on which said graph is displayed.
A pacemaker system as claimed in claim 5, wherein said graphics circuitry operates to dIsplay on said data display area, a graph of heart rate versus time, and to simultaneously display an upper activity rate and a lower rate setting and a desired rate setting, in accordance with the parameters indicated in the parameter control area at that time, and wherein said graphics circuitry also simultaneously displays in said data display area the computed activity rate of the pacemaker in accordance with activity performed by the patient and the parameter settings currently displayed in the parameter control area, wherein the computed activity rate is computed according to the algorithm used by the pacemaker.
A pacemaker system as claimed in claim 5, wherein the graphics circuitry also simultaneously displays on said data display area a plurality of boxes, the height and vertical position of each box representing a range of heart rates for the patient, and wherein the degree of shading of each box is indictive of the percentage of paced events at that time.
EP0970721A2 true true EP0970721A2 (en) 2000-01-12
EP0970721A3 true EP0970721A3 (en) 2000-11-22
WO2011014311A1 (en) * 2009-07-29 2011-02-03 Medtronic, Inc. Algorithm to modulate atrial-ventricular delay and rate response based on autonomic function