Multi-event bin heart rate histogram for use with and implantable pacemaker

Event/rate data gathered by an implantable pacemaker is displayed in a histogram format as a function of heart rate and event type, with multiple events being included in the display of each rate bin of the histogram. Event types include a paced event, a sensed event, or a premature ventricular event (PVE). Two types of histograms are provided: (1) a heart rate histogram that shows the occurrence of each event type in each heart rate bin as a function of the percent of total events in all heart rate bins; and (2) a histogram that shows event type distribution by rate bin.

FIELD OF THE INVENTION 
The present invention relates to implantable medical devices and methods, 
and more particularly to an implantable pacemaker or pacemaker system 
wherein event/rate data associated with the operation of the pacemaker is 
gathered and displayed as a function of heart rate in a histogram having 
multi-event bins. Such multi-event bin heart rate histogram facilitates 
discernment of certain types of events that might otherwise go unnoticed 
in the event/rate data or conventional heart rate histogram. 
BACKGROUND OF THE INVENTION 
One of the most common types of implantable medical devices in use today is 
the implantable pacemaker. Modern pacemakers are small, battery-powered 
electronic devices that monitor the activity of the heart to determine 
when the heart is naturally beating, and provide stimulation pulses to the 
heart when the heart is not naturally beating, thereby maintaining a 
prescribed heart rhythm or rate. Advantageously, a pacemaker may be 
implanted in a patient, and coupled to the patient's heart via appropriate 
pacemaker leads that are also implanted. By implanting the pacemaker and 
leads, the pacemaker becomes an integral part of the patient, and the 
patient is able to maintain a substantially normal life style without the 
bother and worry that typically accompany the use of external 
(non-implanted), life-sustaining medical devices. 
Nearly all implantable pacemakers in use today, as well as similar 
implantable medical devices, can be configured by the attending physician 
in the physician's office. The process of configuring a pacemaker is 
commonly referred to as "programming". The programming process uses 
non-invasive telemetry to customize the operation of the pacemaker to fit 
the individual needs of the patient. Customization is achieved by 
adjusting a set of "pacemaker parameters" to values that cause the 
pacemaker to work in an optimum way for the particular patient within whom 
the device has been implanted. 
Disadvantageously, as the complexity of new implantable devices has evolved 
over the past several years, it has become increasingly difficult for the 
attending physician, or other medical personnel, to determine how the 
pacemaker should be programmed in order to provide the most effective 
therapy for a given patient. This difficulty is particularly manifest with 
recent-generation pacemakers that tend to be more automatic and autonomous 
than earlier-generation pacemakers, and that respond to input control 
signals from one or more sensors that attempt to assess the physiological 
needs of the patient. 
A significant factor that makes the optimum programming of 
recent-generation pacemakers more difficult is the variation in each of 
the sensor inputs from patient to patient. Such variation is caused by 
numerous factors, including the patient's physical structure, age, sex, 
the implant site, the particular disease or malady the patient has and its 
progression within the patient's heart or other body tissue, the patient's 
physical condition and associated activity level, the drugs being taken by 
the patient to treat his or her condition, etc. Thus, to appropriately 
program the pacemaker for a given patient, the physician must anticipate 
how the pacemaker will operate given all of these variables, and given all 
the environments and activities that the patient is expected to encounter. 
Programming a modern pacemaker may thus comprise an extremely formidable 
task, for which task there is a critical need for programming aids to 
assist the physician in anticipating the pacemaker response for each 
particular patient. 
An important aid known in the art to help properly program an implantable 
pacemaker, and to facilitate the physician's understanding of the 
pacemaker's programmed operation as its interacts with the patient's 
natural cardiac activity, is the sensing and recording of various 
pacemaker and cardiac events, including the rate of occurrence of such 
events (hereafter "event/rate data"). Once such event/rate data has been 
collected, it may be presented in a histogram format, as taught, e.g., in 
U.S. Pat. No. 4,513,743 (van Arragon et al.). The van Arragon '743 patent 
teaches various types of single-event histograms which display or show the 
distribution of a single event as a function of a specified class. The 
specified class may be, e.g., an atrial rate, with each class comprising a 
particular range of atrial rates, e.g., 0-50 ppm, 51-60 ppm, 61-70 ppm, 
etc. The van Arragon '743 patent further teaches that two such single 
event histograms may be shown in parallel, as shown in FIG. 3(d) of the 
'743 patent, or that a plurality of such single event histograms may be 
shown in series (time sequence), as shown in FIG. 3(e) of the '743 patent. 
It is further known to display the event/rate data in an event count table, 
as taught, e.g., in U.S. Pat. No. 5,309,919 (Snell et al.), incorporated 
herein by reference. The Snell '919 patent teaches gathering of such 
event/rate data over a significant period of time, e.g., several hours, 
days, or months, and then (when requested by a physician or other medical 
personnel) downloading the event/rate data to the pacemaker's programming 
device ("programmer") for further processing and display. In particular, 
the Snell '919 patent teaches that such event/rate data, after having been 
gathered and downloaded, may be displayed in the form of an event/rate 
table. An event/rate table of the type created and displayed in the Snell 
'919 patent is shown, for example, in FIG. 6. 
Unfortunately, the information conveyed in a conventional heart rate 
histogram, such as is taught in the van Arragon '743 patent, is somewhat 
incomplete because only a single event is displayed in each histogram, 
while other events are either not displayed, or must be displayed in a 
different histogram which is displayed separately, or in parallel, or in 
series with, other histograms. Such multiple single-event histogram 
displays, while potentially conveying a great deal of information, do not 
collectively convey such information in a format that is very easy for an 
attending physician (or other medical personnel) to readily comprehend, or 
that is easy to correlate with the other information. Further, while the 
data presented in an event/rate table, such as is developed in the Snell 
'919 patent, and is shown in FIG. 6 herein, is very complete, such data is 
not particularly easy to comprehend, visualize or correlate without 
careful analysis thereof. 
In view of the above, it is evident that what is needed are improved 
techniques and methods of presenting existing event/rate data in a way 
that makes such event/rate data much easier to quickly comprehend and 
correlate, thereby facilitating its use in evaluating the performance of 
the patient's pacemaker. Once the data/rate information is properly 
understood, it thereafter serves a more useful purpose in correctly 
guiding subsequent reprogramming of the pacemaker, as required, and in 
aiding the development of appropriate treatment therapy for the patient. 
SUMMARY OF THE INVENTION 
The present invention advantageously addresses the above and other needs by 
providing a heart rate histogram having multi-event bins that graphically 
conveys event/rate data gathered by an implantable pacemaker as a function 
of heart rate and event type. The multiple events included in each bin of 
the heart rate histogram include: a paced event, a sensed event, or a 
premature ventricular event (PVE). Heart rate bins define the various 
heart rate zones within which each of the listed events are classified, 
and the number of occurrences of each event type in each heart rate bin is 
graphically displayed as part of the histogram. Two types of multi-event 
bin histograms are provided: (1) a heart rate histogram that shows the 
different event types occurring in each heart rate bin as a percentage of 
the total events occurring in all of the heart rate bins; and (2) a 
histogram that shows the distribution of each event type within each rate 
bin. The event distribution may also be displayed as a percentage of the 
total time period that data was collected. Advantageously, each histogram 
type is a single histogram, yet each displays within each rate bin all of 
the event types, clearly marked, so that the multi-event/rate data is 
quickly conveyed and easily understood at a glance. The combination of the 
two histograms is particularly helpful in conveying, in an easy to 
understand and quick to comprehend format, all of the relevant data 
contained within the event/rate table. 
Thus, in accordance with one aspect of the invention, an implantable 
pacemaker senses and records event/rate data. At the appropriate time, 
such event/rate data is downloaded to an external programming device, 
where it is processed and displayed and/or printed by the programming 
device in a format that facilitates a physician's ability to quickly and 
comprehensively assess the performance of the implanted pacemaker over the 
relevant data-gathering time period, which data-gathering time period may 
be on the order of days, weeks, or months. 
More particularly, the present invention provides an external programmer, 
or equivalent data receiving and data processing device, that is 
configured to receive, process, and display (e.g., print) event/rate data 
gathered by the pacemaker as a heart rate histogram having multi-event 
bins. Such multi-event bin heart rate histogram is divided into a 
multiplicity of heart rate bins, or rate zones, each of which provides an 
indication of the number and/or distribution of multiple types of events 
occurring within each rate bin during the relevant data-gathering time 
period. 
In a first embodiment of the multi-event bin heart rate histogram of the 
present invention, multiple types of events are displayed in each heart 
rate bin as a function of the percent of total events that occurred during 
the total data-gathering time period. The events occurring within each 
rate bin are represented as a bar graph, with the different types of 
events being represented as separate identifiable segments or portions of 
the bar. The total length of the bar (including all segments) of a given 
rate bin is representative of the percent (or ratio) of the total events 
for that rate bin to the total events for all rate bins. 
In a second embodiment of the multi-event bin heart rate histogram of the 
present invention, each rate bin is divided into a display of 100% of the 
events in each bin, thereby allowing certain specific types of events that 
occur as part of the bin event data to be readily discerned, even though 
such specific types of events may have a relatively low rate of 
occurrence, and may thus be indiscernible (buried within the heart rate 
histogram data) in the first histogram embodiment described above. 
Thus, it is a feature of the invention to present or display event/rate 
data gathered by a pacemaker in an easy-to-understand graphical 
representation, and in particular, to present such data in a heart rate 
histogram that distinguishes the occurrence of multiple events within each 
heart rate bin of the histogram. 
It is a further feature of the invention, in accordance with one embodiment 
thereof, to display a heart rate histogram that shows the occurrence of 
the multiple event data in each rate bin of the histogram as a percent of 
the total events that have occurred in all of the rate bins over the total 
time that the event/rate data was gathered. 
It is an additional feature of the invention, in accordance with another 
embodiment thereof, to display the relative distribution of all of the 
event types in each rate bin. 
It is an additional feature of the invention to provide heart rate/event 
data of a pacemaker patient in a histogram format that enables an 
attending physician (or other medical personnel), with just a glance or 
two at the histogram, to quickly and correctly comprehend the performance 
of the pacemaker and its interaction with the patient, thereby guiding the 
physician (or other medical personnel) to the most effective pacemaker 
therapy for the patient as the pacemaker is programmed and reprogrammed.

DETAILED DESCRIPTION OF THE INVENTION 
The following description is of the best mode presently contemplated for 
carrying out the invention. This description is not to be taken in a 
limiting sense, but is made merely for the purpose of describing the 
general principles of the invention. The scope of the invention should be 
determined with reference to the claims. 
As indicated above, the present invention relates to a particular 
technique, method, or format, for presenting heart rate event data that is 
sensed and gathered by an implantable pacemaker over a substantial period 
of time, e.g., days or weeks or months. Once a sufficient amount of the 
heart rate event data has been gathered, it may then be downloaded to an 
external programmer where it is displayed in the heart rate histograms 
having multi-event rate bins that comprise the present invention. It is 
important to note that the present invention is not directed to the 
implantable pacemaker that senses and gathers the heart rate data, nor is 
it directed, per se, to the programmer used with such pacemaker. In fact, 
any conventional pacemaker that has the capability of gathering heart rate 
event data, and any conventional programmer that has the ability to 
receive and display such data, such as the pacemaker and programmer 
disclosed, e.g., in U.S. Pat. No. 5,309,919 (previously incorporated 
herein by reference), can be configured to practice the present invention. 
To better understand how a pacemaker and programmer may be configured to 
practice the present invention, it will first be helpful to review the 
main components, and basic operation, of a pacing system, i.e., the 
pacemaker and the programmer. Accordingly, the following overview of a 
pacemaker and programmer is presented. 
The Pacemaker 
The pacemaker side of a pacing system is shown in FIG. 1. As seen in FIG. 
1, an implantable pacemaker 16 may have a physiological sensor 26 
associated therewith. (Note, not all pacemakers need have a physiological 
sensor 26; but many do. Thus, although a sensor 26 is shown coupled to the 
pacemaker 16 in FIG. 1, it is to be understood that the present invention 
may be used with pacemakers that do not have a sensor 26 coupled thereto; 
or to pacemakers wherein such a sensor is inside of the pacemaker 16; or 
to pacemakers wherein such sensor 26, if present, has been programmed to 
an OFF or PASSIVE mode.) 
The pacemaker 16 is coupled to a heart 18 by way of pacing leads 30 and 31. 
The pacing lead 30 has an electrode 46 positioned in the right ventricle 
32 of the heart 18. The lead 30 is thus typically referred to as the 
ventricular lead, and the signals generated by the pacemaker for delivery 
to the heart through electrode 46 over lead 30, or the signals sensed 
through electrode 46 and the lead 30, are processed by circuits in what is 
known as the ventricular channel of the pacemaker 16. Similarly, the 
pacing lead 31 has an electrode 24 positioned in the right atrium 28 of 
the heart 18. The lead 31 is thus typically referred to as the atrial 
lead, and the signals generated by the pacemaker for delivery to the heart 
through the electrode 24 over lead 31, or the signals sensed through 
electrode 24 and the lead 31, are processed by circuits in what is known 
as the atrial channel of the pacemaker 16. 
That which is shown in FIG. 1 is a dual-chamber pacemaker. This means that 
sensing and/or pacing may occur in both chambers of the heart 18, i.e., in 
the atrium 28 and/or the ventricle 32. The present invention is useful 
with a dual-chamber pacemaker. However, the basic principles of the 
invention (sensing and displaying paced and sensed events, including 
sensed premature ventricular events) could be practiced using a single 
chamber pacemaker, where sensing and pacing occur in only one chamber, 
e.g., the ventricle, of the heart. It should also be understood that most 
pacemakers that provide a dual-chamber configuration, such as is 
illustrated in FIG. 1, may also be programmed to operate in a single 
chamber mode. 
Referring next to FIG. 2, a functional block diagram of the dual chamber 
pacemaker 16 is shown. Note that as shown in FIGS. 1 and 2, the atrial 
lead 31 and the ventricular lead 30 are unipolar leads. In unipolar 
operation, the tip electrode 24 or 46 provides one signal path, with the 
return signal path being provided through conductive body tissue and 
fluids to an exposed portion of the pacemaker case 64. It is to be 
understood, however, that either one or both of the leads 30 or 31 could 
be bipolar leads, having two electrodes, in which case the signal return 
path is provided through the other electrode (which other electrode is 
typically a ring electrode that is positioned only a few centimeters from 
the tip electrode). 
As shown in FIG. 2, the pacemaker 16 may be in telecommunicative contact 
with an external programmer 20 via a telemetry link 70. The programmer 20 
includes a telemetry receiver and monitor external to the patient's skin 
21. The pacemaker 16 includes a telemetry subsystem 40 for transmitting 
data and parameter values to the external telemetry transmitter and 
receiver of the external programmer 20, and for receiving data 
instructions and the like from the external programmer 20. Data 
instructions received from the external programmer 20 are decoded in 
decoder and encoder 60 and stored in memory 62. Likewise, data and 
parameter values to be sent to the external programmer 20 are encoded in 
the decoder and encoder circuit 60 prior to transmission. The manner of 
establishing and operating a telemetry link between an external programmer 
and implantable medical devices is known in the art. 
The data instructions stored in the memory 62 control the operation of the 
pacemaker. In particular, the stimulation pulses generated by the 
pacemaker are generated in pulse output circuits 44 as triggered by 
appropriate trigger signals obtained from a microprocessor control unit 
52. The microprocessor control unit 42 defines a plurality of operating 
states for the pacemaker 16 as a function of various timing signals, also 
generated by the microprocessor control unit 52, and/or various other 
signals or conditions sensed through the atrial, ventricular, or telemetry 
channels of the pacemaker 16. For example, at the conclusion of an 
appropriate timing interval, typically referred to as the atrial escape 
interval, control unit 52 changes to a particular state that causes an 
atrial stimulation pulse (A-pulse) to be generated by the pulse output 
circuits 44 and delivered to the atrium 28 through the electrode 24 via 
the atrial lead 31. In a similar manner, the control unit 52 changes to 
another particular state that causes a ventricular stimulation pulse 
(V-pulse) to be generated at the conclusion of another timing interval, 
typically referred to as the ventricular escape interval, which V-pulse is 
delivered to the ventricle 32 through the electrode 46 via the ventricular 
lead 30. 
When operating in a demand mode, stimulation pulses are provided as above 
described only in the absence of natural cardiac activity, i.e., only when 
the heart 18 is not beating (contracting) on its own. Natural cardiac 
activity is determined by monitoring the leads 30 and/or 31 for electrical 
activity indicative of muscle contraction. Atrial contraction is manifest 
by the presence of a P-wave sensed through the atrial tip electrode 24 and 
the atrial lead 31 through amplifier 48. Similarly, ventricular 
contraction is manifest by the presence of an R-wave sensed through the 
ventricular tip electrode 46 and the ventricular lead 30 through amplifier 
46. Thus, the occurrence of a P-wave, for example, causes the control unit 
52 to immediately assume a different state, which state restarts the 
atrial escape interval timer (which timer function is carried out by 
appropriate timer circuits that form part of the microprocessor control 
unit 52), and thus inhibits an A-pulse from being generated. In like 
manner, the occurrence of an R-wave causes the control unit 52 to assume 
yet another state, which state restarts the appropriate time intervals in 
the pacemaker timer circuits, and inhibits a V-pulse from being generated. 
The physiological sensor 26 (usually referred to as just the "sensor"), 
when used, senses an appropriate physiological parameter, such as physical 
activity, blood oxygen level, respiration rate, etc. The physiological 
parameter thus sensed provides some indication of how fast the heart 18 
should be beating. That is, in times of high physiological stress, such as 
a high physical activity level, the heart needs to beat at a much faster 
rate in order to provide an adequate blood supply to the patient's body. 
Contrariwise, in times of low physiological stress, such as a very low 
physical activity level (e.g., when the patient is sleeping), the heart 
may beat at a much slower rate. Thus, in a pacemaker programmed to operate 
using the physiological sensor 26, the state logic 42 receives a signal 53 
generated by the sensor 26 (generally referred to as the "sensor input 
signal", because it is the signal that is "input" to the pacemaker 16 from 
the sensor 26), processes the signal 53 in an appropriate manner, and uses 
the processed result to alter or adjust the basic time intervals of the 
pacemaker so that the pacemaker will provide stimulation pulses on demand 
at a faster or slower rate, as needed. A common type of sensor 26 is an 
activity sensor, realized using a piezoelectric element that is mounted 
inside of the case of the pacemaker, which senses the physical activity of 
the patient. 
A pacemaker 16 that is capable of adjusting the rate that stimulation 
pulses are provided on demand as a function of one or more sensed 
physiological parameters is known as a "rate-responsive pacemaker." The 
present invention has applicability to rate-responsive pacemakers, as well 
as non-rate-responsive pacemakers. 
As shown in FIG. 2, the preferred control unit 52 comprises a 
microprocessor that is controlled by an appropriate programmed set of 
instructions in the memory 62. Using a microprocessor in this fashion to 
control a pacemaker is known in the art, as described, e.g., in U.S. Pat. 
Nos. 5,309,919 (previously incorporated herein by reference). Reference is 
also made to U.S. Pat. Nos. 4,940,052; 5,431,691; 5,456,692; and U.S. 
patent application Ser. No. 08/365,278, filed Dec. 28, 1994; all of which 
patents and application are assigned to the same assignee as the present 
application, and all of which are incorporated herein by reference. The 
'919, and '692 patents, as well as the 08/365,278 patent application, are 
particularly relevant for teaching the best mode of implementing a 
microprocessor-controlled pacemaker, which microprocessor-controlled 
pacemaker senses, stores and downloads heart rate event data in accordance 
with the present invention. 
The External Programmer 
It is noted that FIGS. 1 and 2, as described above, relate primarily to the 
pacemaker side of a pacing system 16. However, as noted above, the 
external programmer side of a pacing system also plays a key part of the 
invention. It is the external programmer 20 wherein the heart rate/event 
data is received, processed and displayed (either as an image on a display 
screen or printed) as a multi-event bin heart rate histogram of the 
present invention. Hence, a brief overview of the external programmer 20 
used with the present invention will next be presented. Such brief 
overview will be made in connection with FIGS. 3 and 4. FIG. 3 shows a 
block diagram of an external programmer 20 usable as part of the present 
invention, while FIG. 4 shows a perspective view of the external 
programmer of FIG. 3. A more complete description of an external 
programmer 20 suitable for use with the present invention may be found, 
e.g., in U.S. Pat. Nos. 4,791,936 and 4,809,697, which patents are also 
incorporated herein by reference. 
The programmer 20 comprises a sophisticated, microprocessor-based 
programming system that can be used to non-invasively interrogate and 
program a programmable, implantable pacemaker 16 of the type described 
above in connection with FIGS. 1 and 2. Because the programmer 20 is 
itself a microprocessor-based programming system, controlled by program 
code that may be loaded or inserted therein, any suitable programmer 
adapted to request and receive heart rate event data from an implantable 
pacemaker may be configured, or programmed, to prepare the multi-event bin 
heart rate histograms of the present invention. It is to be understood, 
therefore, that the description of the programmer that follows is only 
exemplary and not limiting. 
Turning to FIG. 3, a simplified block diagram of the programmer 20 is 
shown. The programmable pacemaker 16, presumably implanted within living 
tissue, is in electrical contact with the heart 18 via at least one 
pacemaker lead 30. (It is noted that while the pacemaker 16 in FIG. 3 is 
presumed to be implanted in a patient, it need not be implanted for the 
programmer to function. For example, for training purposes, it is quite 
common to use a programmer 20 with a non-implanted pacemaker that is 
coupled to a heart simulator.) As described above in connection with FIGS. 
1 and 2, the pacemaker 16 is a self-contained unit capable of both sensing 
natural cardiac activity (P-waves and/or R-waves) and providing 
stimulation pulses (A-pulses and/or V-pulses) to invoke paced cardiac 
activity. The operating characteristics of the pacemaker 16 can be 
non-invasively programmed by way of command signals received over 
telemetry link 70, which command signals are received from a telemetry 
head 74 connected to the programmer processing circuits 76 by way of a 
connection cable 77. The command signals are generated within the 
programmer processing circuits 76 as a function of operating commands 
received by way of a touch sensitive screen 78. That is, a programmer 
operator selects a desired command by touching a designated area on the 
touch screen 78, which designated area is defined by a particular pattern 
displayed on a display screen 80. Advantageously, the touch screen 78 
overlays the display screen 80 so that all one need do to make a command 
selection is to touch the screen at the area indicated on the display for 
the desired command. 
The pacemaker 16 is also capable of sending operating data and measured 
data over the telemetry link 70 to the telemetry head 74. Such measured 
data includes heart rate/event data as described more fully below, which 
heart rate/event data is determined by monitoring particular changes in 
state of the microprocessor control unit 52. The telemetry head 74 
preliminarily processes such data and forwards it on to the programmer 
processing and memory circuits 76. Data received at the programmer 
circuits 76 may be displayed on the display screen 80, printed on a 
printer 82, and/or stored within the memory elements of the programmer 
circuits 76 for subsequent retrieval and display. Alternatively or 
conjunctively, rate/event data received at the programmer circuits 76 may 
be transmitted over an appropriate data channel 84 to a desired external 
device, such as a modem, an X-Y plotter, a tape or disk drive, a personal 
computer, or other peripheral device. 
Operation of the programmer processing and memory circuits is controlled by 
way of a program cartridge 86 that is detachably connected to the 
processing and memory circuits 76. Removable program cartridge 86 thus 
advantageously allows the operating characteristics of the programmer 
device to be easily upgraded to include new features and to properly 
interface with new pacemakers, as new features and new pacemakers are 
developed. Such upgrading can occur at minimal cost because all that is 
required is a new program cartridge 86, rather than a whole new 
analyzer-programming system 20, as has been required in the past. The 
present invention, relating to a the creation and display of a heart rate 
histogram with multi-event bins is facilitated through the use of a such 
new program in a new program cartridge 86. 
FIG. 4 illustrates a housing 90 within which the programmer system 
components are housed. In accordance with one embodiment, all of the 
circuits of the programmer processing circuits and memory 76, including 
the printer 82, the display screen 80, the touch screen 78, and the 
program cartridge 86, are housed within the housing 90. The telemetry head 
74 is coupled to the housing 90 by way of cable 77. A CRT screen 92, over 
which touchscreen 78 is laid, provides a readily visible and accessible 
means for viewing displays and selecting commands. Similarly, the printer 
82 provides a paper copy 94 of that which is displayed on the screen of 
the CRT 92, or other desired information, as selected by the various 
commands available through touching the touchscreen. The telemetry head 
module 74 is attached to cable 77 which plugs into a connector 96 located 
on the bottom front side of the housing 90. A power cord 98 similarly 
plugs into socket 99 at the rear of the housing and allows the programmer 
20 to be powered from any suitable electrical outlet providing 110 VAC at 
60 Hz or other available primary power. The power cord 98 may be stored on 
the bottom of the housing 90 for ease of transportation and storage. 
Similarly, the telemetry head 74, when detached, can be stored in a 
removable front cover (not shown) when not in use. 
Gathering the Heart Rate/Event Data 
With the above overview in mind of both the pacemaker 16 and the external 
programmer 20 of a representative pacing system, reference is next made to 
FIG. 5 where there is shown a more detailed functional block diagram of 
the pacemaker 16 that highlights the key elements used to gather the heart 
rate/event data used with the present invention. Shown in FIG. 5 is the 
microprocessor control unit 52, which microprocessor unit controls the 
various states and operation of the pacemaker. Also shown in FIG. 5 are 
the pacemaker timer circuits 50, referred to as the pacemaker timer block. 
Such timer circuits 50 are actually realized within the microprocessor 
control unit 52, but are shown separately as the timer block 50 to 
highlight the separate timing function performed with such circuit. The 
pacemaker inputs, i.e., signals sensed by the pacemaker that are not 
programmed, include an atrial sensor 102 and a ventricular sensor 104 that 
sense P-waves and R-waves, respectively. The pacemaker inputs may also 
include the sensor input signal 53 obtained from the physiological sensor 
26, when used. 
In addition to the above-described pacemaker inputs, there are several 
pacemaker parameters that are input to the pacemaker microprocessor 
control unit 52 in order to control the operation of the pacemaker in a 
desired fashion. Such parameters are normally programmed into the memory 
62 of the pacemaker 16 using the appropriate telemetry link 70. Such 
parameters include, e.g., the programmed rate at the which the stimulation 
pulses are to be generated by the pacemaker, the particular mode of 
operation of the pacemaker, and the like. 
The pacemaker outputs, i.e., signals generated by the microprocessor 
control unit 52 in response to the pacemaker inputs and/or pacemaker 
parameters include an atrial output 106 and a ventricular output 108. The 
atrial output 106 provides an A-pulse for delivery to the atrium at an 
appropriate time, e.g., on demand as needed to maintain a programmed or 
sensor-indicated heart rate. The ventricular output 108 similarly provides 
a V-pulse for delivery to the ventricle at an appropriate time, e.g., on 
demand as needed to maintain a programmed or sensor-indicated heart rate. 
The pacemaker timer circuits 50 include at least five separate timers. A 
rate timer 110 measures the overall pacing cycle duration. An AV Delay 
Timer 112 defines the time period between an A-pulse or natural atrial 
contraction and a V-pulse. A Max Track Timer 114 defines the time period 
of the maximum rate at which the pacemaker is allowed to provide 
ventricular stimulation pulses in response to natural atrial contractions, 
i.e., it defines the maximum tracking rate (MTR). An Atrial Refractory 
Timer 116 defines the atrial refractory period (i.e., that time period 
during which the atrial channel is refractory). Similarly, a Ventricular 
Refractory Timer 118 defines the ventricular refractory period, or that 
time during which the ventricular channel is refractory. 
Typically, there are some eighteen states associated with the operation of 
the pacemaker 16 when configured for operation in a dual-chamber mode. 
Three of the eighteen defined states relate directly to cardiac activity 
that occurs in the atrium. These three atrial states are: (1) atrial pulse 
(A-pulse); (2) sensed P-wave; and (3) sensed P-wave during the Maximum 
tracking interval. Similarly, two of the eighteen defined states relate to 
cardiac activity that occurs in the ventricle. These two ventricle states 
are: (1) ventricular stimulation pulse (V-pulse); and (2) sensed R-wave. 
Advantageously, the changing of the state of the microprocessor control 
unit 52 from one state to another state signals the occurrence of a 
particular event. Selected state changes associated with the 
microprocessor control unit 52 may thus be considered as "pacing events". 
In accordance with the present invention, such "pacing events are recorded 
as a function of the type of event that occurred, and as a function of the 
rate of occurrence of such event. 
There are multiple pacing event types that are recorded for use by the 
present invention; the set of applicable events depends on the pacing 
mode. For dual-chamber modes wherein pacing and sensing occur in both 
chambers of the heart, e.g., a DDD or DDDR mode, these events are: (1) a 
P-wave followed by a V-pulse (referred to as a "PV" event); (2) a P-wave 
followed by an R-wave (referred to as a "PR" event); (3) an A-pulse 
followed by a V-pulse (referred to as an "AV" event); (4) an A-pulse 
followed by an R-wave (referred to as an "AR" event); and (5) a premature 
ventricular event (referred to as a "PVE"). A premature ventricular event, 
or PVE, is defined as an R-wave that occurs without an appropriate 
intervening atrial event. 
For a VDD mode (wherein pacing only occurs in the ventricle, but sensing 
occurs in both the atrium and ventricle), the pacing event types that are 
recorded for use by the invention include: (1) a PV event; (2) a PR event; 
(3) a V-pulse (also referred to as a "V" event), and (4) a "PVE". 
If only single chamber pacing is employed (wherein pacing and sensing occur 
in just one chamber of the heart), then the pacing events that are 
counted, and their respective rates, are simply "sensed events" and "paced 
events". 
Because the pacing events defined above are reflected in prescribed state 
changes of the microprocessor control unit 52, the occurrence of such 
events may be readily determined by simply monitoring the microprocessor 
control unit 52 for the prescribed state changes. In particular, in 
accordance with the present invention, the occurrence of any of the 
above-defined five pacing events are counted in appropriate pacemaker 
event counters as a function of rate of occurrence, as shown in FIG. 5. 
Thus, for example, an AV event table 120 is maintained that keeps track of 
(i.e., counts) each AV event that occurs. The AV events are tracked in a 
"table", as opposed to a "counter" because such events are tracked as a 
function of rate, as well as occurrence. That is, each occurrence of an AV 
event is logged into the AV event table 120 in an appropriate cell 
corresponding to the particular frequency or rate of occurrence of the AV 
event. Thus, the AV event table 120 may be considered as an array of AV 
event counters, with each counter in the array being assigned a particular 
rate range, as explained more fully below in connection with FIG. 6. 
In a similar manner, an AR event table 122 is maintained to keep track of 
each AR event that occurs. Likewise, other tables are maintained to keep 
track of each PVE (table 124), each PV event (table 126), each PR event 
(table 128), and other events. 
The event tables 120-132 are maintained in the memory 62 of the pacemaker 
16. As taught in U.S. Pat. No. 5,309,919, the count data stored in such 
tables may be organized into an event count table 140 as illustrated in 
FIG. 6. As seen in FIG. 6, the event count table 140 defines a plurality 
of rates, expressed as a function of pulses per minute (ppm), along the 
left side of the event count table. The pacing events being tracked are 
listed along the top side of the event count table 140. Each column of the 
event count table 140 shown in FIG. 6 thus corresponds to one of the 
"event tables" of FIG. 5, and reference numerals have been added at the 
top of each column in FIG. 6 to show this correspondence. 
The other information shown in FIG. 6 along with the event count table 140 
represents additional pacing information that could be made available 
through the programmer 20 to a cardiologist, or other medical personnel, 
who is monitoring the status and operation of the pacemaker 16. All of 
this information together is referred to as an "Event Histogram", as seen 
by the title at the top of FIG. 6. (Note, FIG. 6 conveys essentially the 
same information as is presented in FIG. 19 of U.S. Pat. No. 5,309,919.) 
Included in the Event Histogram data is an indication of how long of a 
time period has elapsed to gather the data shown in the Event Count Table 
140. As shown in FIG. 6 at 160, for example, immediately below the title 
"Event Histogram", the elapsed sampling time for the data shown in FIG. 6 
was 86 days (d), zero hours (h), 38 minutes (m), and 50 seconds (s), and 
the sampling was done on an every event basis. Next, at 162 of FIG. 6, the 
programmed parameters of the pacemaker are listed. Such parameters include 
the pacing mode, whether the sensor in "ON" or "OFF", the base pacing 
rate, the maximum tracking rate, the maximum sensor rate, the AV delay, 
and whether the rate responsive AV delay is ON or OFF. Then the Event 
Counts Table 140 is presented, as described above. Based on the data in 
the Events Count Table, a calculation is then made, with the results 
printed at 164, as to how much pacing occurred in the atrium, how much 
occurred in the ventricle, and how much time was spent pacing at the 
maximum tracking rate of the pacemaker. Also, a bar-graph display 166 is 
included that shows the percent of total time during which there occurred 
PV events, PR events, AV events, AR events, or PVE events. For the 
particular data included in the Event Histogram shown in FIG. 6, it is 
seen that the vast majority of events (81%) were AR events, and most of 
the rest of the events (18%) were PR events. Such information is helpful 
to the cardiologist, or other medical personnel, as they evaluate the 
performance of the pacemaker 16 for the particular patient within whom it 
has been implanted. 
Heart Rate Histogram with Multi-Event Bins 
While the information included in the Event Histogram printout of the type 
shown in FIG. 6 is extremely useful to medical personnel as they evaluate 
the performance of a pacemaker implanted in a given patient, such 
information falls short in providing such personnel with a quick, 
easy-to-understand overview of exactly what types of events are happening 
at which heart rates. To overcome this difficulty, the present invention 
improves the manner in which the heart rate event data included in the 
event count table 140 is graphically presented. 
More particularly, the present invention creates two different types of 
multi-event bin heart rate histograms as shown in FIGS. 7 and 8. Such 
multi-event bin heart rate histograms, once the need for such histograms 
has been identified and specified, as presented herein, may be compiled 
from the data in the event count table 140 using conventional programming 
techniques known to those of skill in the art. There are two types of 
heart rate histograms shown in each of FIGS. 7 and 8. Each type of heart 
rate histogram thus shown in FIGS. 7 and 8 is a multi-event bin histogram. 
This means that multi-event data is included, or graphically depicted, 
within each bin of each histogram. More particularly, each bin of each 
histogram shows whether the events that occurred at the rate of that 
particular bin included a "paced" event (which includes AV or AR events 
for the histograms shown in FIG. 7; and includes V events for the 
histograms shown in FIG. 8), a "sensed" event (which includes PV or PR 
events for both FIGS. 7 and 8), or a premature ventricular event ("PVE"). 
Referring first to FIG. 7, which shows the multi-event bin heart rate 
histograms of the present invention as obtained from a DDDR pacing mode, a 
first type of multi-event bin heart rate histogram is shown at 170 in FIG. 
7. As seen in FIG. 7, the multi-event bin heart rate histogram 170 
comprises a two-dimensional graphical chart 171 of the heart rate event 
data. The chart 171 includes a multiplicity of heart rate zones (or bins), 
e.g., nine rate bins, arranged in order of increasing heart rate along a 
first axis, e.g., along the horizontal axis. Thus, as seen in FIG. 7, from 
left to right, there is a first rate bin 172 for the 45-59 ppm rate zone, 
a second rate bin 174 for the 60-66 ppm rate zone, a third rate bin 176 
for the 67-74 ppm rate zone, a fourth rate bin 178 for the 75-85 ppm rate 
zone, a fifth rate bin 180 for the 86-99 ppm rate zone, a sixth rate bin 
182 for the 100-120 ppm rate zone, a seventh rate bin 184 for the 121-150 
ppm rate zone, an eighth rate bin 186 for the 151-200 ppm rate zone, and a 
ninth rate bin 188 for the &gt;200 ppm rate zone. 
The chart 171 also includes a graphical representation of the number of 
heart rate events that occur within each heart rate zone, or bin. While 
many different types of graphic representations could be used for this 
purpose, that used in FIG. 7 is simply a vertical display bar for each bin 
that extends upwards by an amount indicative of the relative number of 
events, or event counts, that have occurred within the bin. Thus, for 
example, for the particular heart rate event data shown in FIG. 7, most 
(75%) of the events have occurred in the second rate bin 174, and thus the 
vertical bar for rate bin 174 extends up much higher than any of the other 
bars for the other rate bins. A significant number of events (17%) also 
occurred in the third rate bin 176, and thus the vertical bar for rate bin 
176 extends up almost one quarter of the height of the second bin 174 
(because 17% is roughly 23%--almost 1/4--of 75%). It is noted that while 
FIG. 7 shows the chart 171 with the display bars being vertical bars, and 
the rate bins distributed along the horizontal axis, there is no reason 
why the display bars could not be made horizontal bars, with the 
distribution of rate bins (or zones) occurring along the vertical axis. 
Most importantly for purposes of the present invention, as also evident 
from FIG. 7, the multi-event bin chart 171 further includes an indication 
of which events in each heart rate zone or bin are sensed events, which 
are paced events, and which are premature events. Such indication is made 
by segmenting the display bars of each rate bin into first, second and 
third portions. A first portion, shown, e.g., as a black or filled portion 
of the display bar, has a segment length that represents the number of 
paced events (e.g., AV or AR events) that have occurred within the 
corresponding heart rate bin. A second portion, shown, e.g., as a white or 
non-filled portion of the display bar, has a segment length that 
represents the number of sensed events that have occurred within the 
corresponding heart rate bin. A third portion, shown, e.g., as a gray or 
partially-filled portion of the display bar, has a segment length that 
represents the number of premature events, or PVE's, that have occurred 
within the corresponding heart rate bin. (For the data included in the 
chart 171 of FIG. 7, the number of premature events that have occurred is 
so few that such a gray or partially-filled portion is not readily 
discernable.) In this manner, each rate bin of the heart rate histogram 
thus displays the relative occurrence of multiple events that have 
occurred at the rate zone corresponding to that bin. In other words, the 
bins of the histogram comprise multi-event bins where the relative 
occurrence of multiple events, e.g., paced, sensed, or PVE events, at that 
rate can be quickly and easily seen with just a glance at the histogram. 
It is to be emphasized that while only three types of events are depicted 
in the heart rate histogram 170 shown in FIG. 7, such is only exemplary. 
Any number of event types could be displayed as separate segments of the 
respective display bars. For purposes of the present invention, however, 
the three events displayed--paced events, sensed events, and PVE's--have 
been found to be sufficient for readily conveying to the medical personnel 
all of the information needed to make a quick and accurate assessment of 
the pacemaker's performance. 
Note that the multi-event bin histogram 170 in FIG. 7 also includes an 
indication of the total sampling time during which the heart rate event 
data was gathered by the implantable pacemaker. For the data shown in FIG. 
7, this sampling time is "97 d 4 h 22 m 15 s", or 97 days, 4 hours, 22 
minutes and 15 seconds. 
The type of multi-event bin heart rate histogram shown at 170 in FIG. 7 
depicts the events as a percent of total time, or total events. The total 
length of all of the display bars used in each rate bin thus represents 
100% of all the heart rate events that have occurred. Thus, where 75% of 
the events occurred at the rate defined by the second rate bin 174, the 
display bar for rate bin 174 is the longest (or highest) of all of the 
display bars. Similarly, where 17% of the events occurred at the rate 
defined by the third rate bin 176, the display bar for rate bin 176 is 
just a little less than 1/4 as long (or high) as the display bar for rate 
bin 174. Likewise, where 6% of the events occurred at the rate defined by 
the fourth rate bin 178, the display bar for rate bin 178 is about 1/3 the 
length (or height) as the display bar for rate bin 176. 
The percent-of-total-time format used for the multi-event bin heart rate 
histogram 170 of FIG. 7 necessarily limits the amount of useful 
information that can be gleaned from those rate bins wherein the number of 
occurrences is low, e.g., less than 1 or 2%. The display bars for rate 
bins 182, 184 and 186, for example, where the events that occurred were 
less than 1%, do not convey any meaningful information relative to the 
distribution of events within these rate zones (or bins). Further, because 
the number of PVE events in each of the rate bins is few, if any, it is 
impossible to discern how many PVE's occurred in any given rate bin. 
To overcome the above deficiencies, the present invention provides a second 
type of multi-event bin heart rate histogram as is shown at 190 in FIG. 7. 
This second type of histogram 190 shows the distribution of events within 
each bin, or rate zone, regardless of the number of events that occurred 
within such bin. As seen in FIG. 7, each display bar for each heart rate 
bin of the histogram 190 is of the same length. The length of the display 
bar represents 100% of the number of heart rate events that have occurred 
within the respective heart rate bin. The multiple events that occur 
within each heart rate bin, or zone, are then displayed by segmenting the 
display bar into however many multiple event types are being displayed. 
Thus, where three types of events are of interest--paced events, sensed 
events, and PVE's--the fixed-length display bar of each rate bin is 
divided into three segments. The segments are uniquely identified in the 
same manner as used for the histogram 170, i.e., sensed events are shown 
by a non-filled or white segment, paced events are shown by a 
completely-filled or black segment, and PVE's are shown by a 
partially-filled (or dotted, or cross-hatched) segment. The segment that 
corresponds to sensed events has a segment length corresponding to the 
number of sensed events that have occurred within that heart rate zone as 
compared with all of the heart rate events that have occurred in that 
corresponding heart rate zone. For example, 72% of the events that 
occurred in the seventh rate bin 192 (corresponding to the rate range of 
100-120 ppm) of histogram 190 in FIG. 7 were sensed events (PV or PR 
events), while less than 1% were paced events, and 28% were PVE's. (This 
quantitative percentage data is obtained from the "Event Distribution By 
Rate Bin (percent)" table 194 which appears immediately below the 
histogram 190 in FIG. 7.) Thus, the event bar of bin 192 is segmented into 
three portions. A first portion, corresponding to sensed events, has a 
length that is approximately 72% of the total length of the display bar. 
Similarly, a second portion, corresponding to paced events, has a length 
that is approximately 1% of the total length of the display bar; while a 
third portion, corresponding to PVE's, has a length that is approximately 
28% of the total length of the display bar. The display bars for the other 
rate bins are segmented in a similar manner, with each segment length of 
each rate bin representing the percentage of occurrences of the particular 
event of interest (sensed, paced, or PVE) within that rate bin relative to 
100% of the events that occurred in that particular rate bin. 
By using a heart rate histogram 190 as thus described, it is thus possible 
for medical personnel to quickly see at just a glance the distribution of 
events that occur within each rate bin, even though the total events 
within the rate bin may be a very small percentage of the total events 
that have occurred in all of the heart rate bins. For example, as seen in 
the histogram 170, the number of events that occurred in the rate bin 182 
corresponding to 100-120 ppm was less than 1% of the total events included 
in the sample size. Nonetheless, the histogram 190 breaks this 
less-than-1% data down and shows roughly that 75% of these events were 
sensed events, less than 1% were paced events, and 28% were PVE's. Such 
information, showing the distribution of events within each heart rate 
bin, represents extremely valuable information for the medical personnel 
who are monitoring the performance of the pacemaker for a given patient. 
The histogram 190 advantageously conveys this distribution event data 
quickly and qualitatively, while the event distribution table 194 below 
the histogram 190 (FIG. 7) presents the same information quantitatively. 
Referring next to FIG. 8, two additional heart rate histograms 200 and 220 
are illustrated to depict the event/rate data in a multi-event bin rate 
histogram format for event/rate data obtained while pacing in the VDD 
mode. The total sampling time over which the VDD event/rate data was 
obtained was 69 days, 7 hours, 26 minutes and 12 seconds, as indicated 
just below the title of the histogram 200. The histograms 200 and 220 of 
FIG. 8 are formatted the same as the histograms 170 and 190 described 
above in connection with FIG. 7, except that only eight rate bins are 
used, rather than the nine rate bins of FIG. 7. 
For example, referring to the multi-event bin rate histogram 200 of FIG. 8, 
it is seen that the events are depicted as a percent of total time, or 
total events as vertical, segmented, display bars, with each bar 
corresponding to a rate bin. For the format used in FIG. 8, eight rate 
bins are used. A first rate bin 202 corresponds to the 45-60 ppm rate 
zone, a second rate bin 204 corresponds to the 61-67 ppm rate zone, a 
third rate bin 206 corresponds to the 68-75 ppm rate zone, a fourth rate 
bin 208 corresponds to the 76-85 ppm rate zone, a fifth rate bin 210 
corresponds to the 86-100 ppm rate zone, a sixth rate bin 212 corresponds 
to the 100-120 ppm rate zone, a seventh rate bin 214 corresponds to the 
121-149 ppm rate zone, and an eighth rate bin 216 corresponds to the &gt;149 
ppm rate zone. 
The multi-event bin rate histograms 200 and 220 of FIG. 8 (corresponding to 
a VDD mode of operation of the pacemaker) further differ from the 
histograms 170 and 190 of FIG. 7 (which correspond to a DDDR mode of 
operation) in that sensed events in FIG. 8 (comprising either PV or PR 
events) are depicted using a black or filled segment of the display bar, 
and paced events (comprising a "V" event) are depicted as a white or 
non-filled segment of the display bar. Such representation in FIG. 8 of 
which segments represent paced events and which represent sensed events is 
reversed from that used in FIG. 7 to highlight that the multi-event bin 
rate histograms thus displayed correspond to a different mode of operation 
of the pacemaker. 
Other than the number of rate bins and the reversal of the representation 
of paced and sensed events, the multi-event bin rate histograms of FIGS. 7 
and 8 are the same, and the description above of the histograms 170 and 
190, and the table 194, in connection with FIG. 7 applies equally well to 
the histograms 200 and 220, and the table 221, of FIG. 8. It is to be 
emphasized that the present invention is not limited to the particular 
formats used for the multi-event bin rate histograms shown in FIGS. 7 and 
8, but applies to any type of multi-event bin rate histogram of the 
general type shown in FIGS. 7 and 8, regardless of the number of rate bins 
employed, the range of ppm assigned to each rate bin, or the type of 
graphical marking (black, white, gray, colored, cross-hatched, dotted, 
etc.) used to mark one type of event segment from another within each rate 
bin. 
A flowchart showing the method used by the present invention to create a 
multi-event bin heart rate histogram is shown in FIG. 9. It is noted that 
the flowchart shown in FIG. 9 is a simplified flowchart in that it depicts 
only the main method steps used to create a multi-event bin heart rate 
histogram (MEBHRH) in accordance with the present invention. As is known 
by those of skill in the art, particularly those who write the operating 
code and programs for implanted pacemakers and programmers, there are many 
additional details and steps related to the operation of a pacing system 
which are not shown in FIG. 9, but which do not relate directly to the 
present invention. Hence, such details are not included in FIG. 9. 
As seen in FIG. 9, if a decision is made to create the MEBHRH (YES branch 
of block 230), then the rate/event data is retrieved from the pacemaker 
(block 234). If a decision is made not to create the MEBHRH (NO branch of 
block 230), and if the pacemaker is to continue its pacing operation in 
accordance with its programmed mode (YES branch of block 232), then such 
programmed pacing continues until a decision is made to either stop pacing 
(NO branch of block 232, which could include changing the programmed mode 
of operation) or to create the MEBHRH (YES branch on block 230). Such 
programmed pacing would include, e.g., continuing to gather and store the 
event histogram data as described in U.S. Pat. No. 5,309,919. 
Once the event/rate data has been retrieved, it is sorted as a function of 
event type and event rate (block 236). If such sorted data is not to be 
displayed in a MEBHRH (NO branch of block 238), then such sorted data may 
be stored for later use (block 240). If, however, the sorted event/rate 
data is to be displayed in a MEBHRH (YES branch of block 238), then 
multiple heart rate bins are defined and arranged in order to increasing 
heart rate along a first axis of the MEBHRH display (block 242). For 
example, as shown in FIG. 7, nine heart rate bins may be displayed, or as 
shown in FIG. 8, eight heart rate bins may be displayed. 
Next, a graphical representation of the number of heart rate events that 
occur within each heart rate bin is created (block 244). For example, such 
graphical representation may be a vertical bar of variable length as shown 
for the "Percent of Total Time" histograms 170 (FIG. 7) or 200 (FIG. 8); 
or may be a vertical bar of fixed length as shown for the "Event 
Distribution By Rate Bin" histograms 190 (FIG. 7) or 220 (FIG. 8). 
Finally, the graphical representation created (in block 244) is segmented 
by event type (block 246) in order to indicate each type of heart rate 
event that has occurred within each heart rate bin. For example, if three 
event types are to be shown within each heart rate bin, the vertical bars 
shown in FIGS. 7 or 8 are segmented with white (or non-filled) portions, 
black (or filled) portions, and/or gray (dotted, cross-hatched, etc.) 
portions, with each portion thus marked presenting a graphical indication 
of the relative number of that particular event type that has occurred 
within that rate bin. 
As described above, it is thus seen that the present invention displays 
event/rate data gathered by an implantable pacemaker in an 
easy-to-understand graphical representation. More particularly, the 
invention provides two types of heart rate histograms having multiple 
event bins. In a first, the number of occurrences of multiple events in 
each heart rate zone, or bin, is displayed as a function of the total 
number of occurrences at all rates. In a second, the distribution of the 
number of occurrences of multiple events in each heart rate zone, or bin, 
is conveyed regardless of the total number of occurrences within that bin. 
Through use of the multi-event bin heart rate histogram(s) of the present 
invention, the heart rate/event data is presented in a way that enables an 
attending physician (or other medical personnel), with just a glance or 
two at the histogram(s), to quickly and easily comprehend the performance 
of the pacemaker and its interaction with the patient. In turn, such 
information thereafter serves to guide the attending medical personnel to 
the most effective pacemaker therapy for the patient as the pacemaker is 
monitored, programmed and/or reprogrammed. 
While the invention herein disclosed has been described by means of 
specific embodiments and applications thereof, numerous modifications and 
variations could be made thereto by those skilled in the art without 
departing from the scope of the invention set forth in the claims.