Method and apparatus for screening electrocardiographic (ECG) data

A time saving automatic screening system for detection, measurement, analysis and plotting of electrocardiographic (ECG) signals employing arrhythmia analysis programs on long term ambulatory (Holter) recordings to assess the ECG signals and categorize the recorded data as either artifact, ventricular ectopic, superventricular ectopic, unknown or normal and to calculate a level of confidence that the category as chosen is a correct assessment. A system is disclosed that thresholds the occurrences of each category as well as the level of confidence to determine if significant abnormalities have occurred in the recording process, the hearts arrhythmia, or the heartbeat morphology. The method and apparatus disclosed make it possible to identify and screen out entire long term (Holter) ECG recordings containing no significant abnormalities in the hearts arrhythmia or the beat morphology. Thus, the cost of Holter scanning is greatly reduced by reserving for manual scanning only those recordings that contain significant abnormalities in the hearts arrhythmia or the beat morphology.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the field of electrocardiography and, more 
specifically, to a method and apparatus for increasing the throughput and 
lowering the cost in the process of analyzing ambulatory recorded 
electrocardiographic (Holter ECG) data by automatically scanning patient 
recordings at high speed and automatically segregating recordings that 
contain no significant abnormalities from those that contain significant 
abnormalities. In the case where a Holter recording has significant 
abnormalities, the invention terminates the automatic analysis based on 
preset or variable parameters relative to heart arrhythmias, heart 
morphology, artifact and a level of confidence provided by special 
algorithms. The preset or variable parameters relative to heart 
arrhythmias and heart morphologies are based in part on an expanded Lown 
grade scale. If the high speed analysis indicates that the preset 
thresholds are exceeded, then the high speed scan is terminated and the 
recording is relegated to a manual confirm scan using conventional Holter 
analysis techniques. 
The process above can be represented by a medical term known as 
"Triage.TM.." Triage.TM. relates to the medical screening of three types 
of patients to determine their priority for treatment. In the case of the 
invention, the scanning of Holter tapes involves three operational modes 
which operate in sequence but in any sequential order. In this case, the 
three modes are the fully automatic, manual confirm and the new mode known 
as Triage.TM.. In the Triage.TM. mode where the high speed analysis of a 
Holter recording can continue automatically where no morphology limits are 
exceeded, or converts to a manual confirm mode when limits are exceeded, 
or is terminated early when the recording quality or morphology indicates 
special manual analysis will be required from the beginning. 
2. Description of the Prior Art 
In ambulatory monitoring, as normally practiced, the patient wears a device 
for measuring or sensing physiological or physical variables such as ECG, 
blood pressure, EEG, posture, etc. These sensed signals are recorded 
typically on magnetic tape or a solid-state memory. In the case of ECG 
signals recorded on tape, this is known as a Holter recorder. The 
recording sessions may last for twenty-four hours or more; thus, the 
analysis of these tapes is only practical at a higher speed than the 
recording time, typically 120 to 240 times faster. The signals after 
analysis on the playback apparatus are typically printed on a high speed 
laser printer which produces a numerical report with graphical charts and 
ECG presentations. 
Recent developments in high-speed, low-cost computers using Digital Signal 
Processing (DSP) techniques have made it possible to automatically scan 
recorded multichannel electrocardiographic data at speeds in the range of 
240 to 500 times or higher than the speed at which the data was actually 
recorded. However, it has remained necessary for most clinical reporting 
thereon to have skilled personnel scan a tape at high speed, beat by beat, 
using visual prospective or retrospective techniques to access and correct 
the computer analyzed data. Using these manual techniques, it is found 
that typically 30% of the recordings contain no significant abnormalities 
or artifact; thus, fully automatic analysis is practical with this type of 
ECG data. The separation of these tapes from the other 70% decreases the 
amount of skilled technician time in that 30% of the tapes may undergo 
fully automatic analysis. There still remains the need for scanning 
recorded ECG data interactively with the technician on a beat-by-beat 
basis using existing techniques. 
An early example of a system for recording and playing back ECG signals is 
found in Holter et al U.S. Pat. No. 3,215,136 issued on Nov. 2, 1965. A 
contemporary apparatus for playback and analysis of recorded tapes is 
described in Cherry and Anderson U.S. Pat. No. 4,006,737 issued Feb. 8, 
1977, for "Electrocardiographic Computer." A reissue application of the 
later patent was filed Apr. 24, 1978, which matured into U.S. Pat. No. Re. 
29,921 issuing on Feb. 22, 1979 and a divisional application, Ser. No. 
773618, filed Mar. 2, 1977, which matured into U.S. Pat. No. 4,123,785 
issuing on Oct. 31, 1978, both being directed to a recorder for cardiac 
signals. A much improved recorder is described in application Ser. No. 
918,698 filed June 23, 1978, and issuing as U.S. Pat. No. 4,211,238, on 
July 8, 1980, for "Recorder for Ambulatory Monitoring of Electrical 
Signals," by Shu and Squires. A new method for marking and enhancing CRT 
screens showing abnormal ECG beats is described in Wong U.S. Pat. No. 
4,625,278 issued Nov. 25, 1986. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide an automatic analysis of 
Holter-type recording of ambulatory ECG at a high speed that identifies 
recordings that do not contain clinically significant abnormalities. It is 
also the object of this invention to provide an improved ECG system that 
is capable of improved detection and analysis of high fidelity, analog or 
digital ECG recordings from either magnetic or solid state media. Another 
object of this invention to provide a system that can scan recorded 
electrocardiographic data in either automatic, manual or a combination of 
automatic and manual modes. Additionally, it is the object of this 
invention to provide a novel means of automatically scanning, identifying 
and classifying a plurality of individual patient recordings in sequence 
by using a batch mode that employs an automatic handling means to 
sequentially scan individual patient ECG recordings without requiring 
operator assistance. 
Disclosed is a system that consists of a high-speed ECG analyzer which 
detects heart beats on one, two or three channels using digital techniques 
for feature vector extraction and noise estimation. Beats having similar 
feature vectors are grouped into clusters which are then classified to 
provide for rhythm determination. Confidence testing is performed on all 
beat and cluster classifications by determining the degree of difficulty 
in making the respective classifications. 
The Triage.TM. feature of this invention employs three separate operational 
modes. Typical operation uses an automatic mode having operator adjustable 
thresholds that are used to terminate a scan when exceeded based on a 
"Lown" grade criteria. Thresholds are provided for the occurrence of VE's, 
SVE's, Artifact and unknowns as well as thresholding limits for ST levels 
and confidence levels. Recordings that do not exceed any of the thresholds 
are determined to contain no clinically significant abnormalities and are 
segregated. The recordings that do exceed thresholds may be further 
analyzed by operator selection of either automatic, manual or Triage.TM. 
modes.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1a, the Triage.TM. system configuration employs a 
high-speed, Intel 80486-based, personal computer system 10 providing the 
speed and power required to execute advanced digital signal processing 
(DSP) analysis on ambulatory 24 hour multi-channel recordings 20. In the 
preferred embodiment the multichannel recording 20 is made using three 
channels X, Y and Z (80, 82,84) of ECG input from the patient 30. The 
computer system 10 includes a high resolution display 14 and a keyboard 12 
for operator input. 
Referring to FIG. 2, the Triage.TM. System analyzes up to three channels X, 
Y, Z (90, 92, 94) of analog Holter (ambulatory) ECG data to detect and 
identify significant abnormalities in the heart arrhythmia and in 
heartbeat morphology. In the preferred embodiment, three National 
Semiconductor ADC0820 high speed A/D convertors (102, 104, 106) are used 
to convert three channels of analog ECG data X, Y, and Z (90,92,94) into 
into three digital 8-bit bytes. The converted digital data is stored in 
either Ram Bank 1 (108), or Ram Bank 2 (110) in 8-bit bytes after being 
transmitted from the A/D converters to either of the rams along the 8-bit 
bus (96). Ram Bank 1 (108) and Ram Bank 2 (110) are configured in what is 
commonly known within the art as a ping-pong arrangement. In this 
arrangement one of the rams will be written to while the other is being 
read from. Thus, X, Y, and Z (90, 92, 94) analog ECG data can be converted 
from analog to digital and stored in one of the rams in three sequential 
writes of 8-bit bytes, while at the same time, a Direct Memory Access 
(DMA) transfer can read data out of the other ram. The DMA transfer is 
performed by DMA Controller (114) to read data out of the ram that is not 
being written to transfer the data to disc storage (116). The DMA transfer 
is initiated by the CPU (112) after receiving an interrupt request IRQ 
(118). The IRQ is generated when either Ram 1 Full (120) or Ram 2 Full 
(122) are active, which indicates that one of the rams has been written to 
full capacity and is ready to be read. Only one of the ram full signals 
may be active at any given time due to the fact that each ram has all of 
its memory locations written in 45 msec while either ram can be read in 7 
msec, therefore the faster reading time prevents the occurrence of the 
circumstance in which both rams are full. In the event that both ram full 
signals are active at any given time, an error 130 results and the system 
terminates operation. 
As seen in FIG. 3, an arrhythmia analysis and an analysis of the beat 
morphology and QRS detection are performed by the program modules seen on 
FIG. 3. Using one, two or three ECG leads, various ventricular and 
supraventricular arrhythmia are detected. Also detected are assessments of 
artifact, unknown events and confidence levels. The modules for this 
analysis perform beat detection 210, feature-vector extraction 220, noise 
estimation 225, measure euclidean distance 230, euclidean distance within 
3 standard deviations (3 std) 235, cluster creation 242, cluster 
classification 250, beat classification 260 and rhythm classification 270. 
A discussion of the operation of each module follows. The operating 
sequence of the analysis is shown in FIG. 3. 
Input digitized data 202 is first tested by Beat Detection 210 for valid 
heartbeats. A more detailed diagram of the Beat Detection Module can be 
seen in FIG. 4 to which the following discussion relates. Initially, the 
ECG data is subjected to a matched filter 211 with an 8-16 Hz bandpass. 
ABS 212 calculates the absolute value of the filter output of the matched 
filter 211. The ABS 212 output is then used by Find Peaks 213 to find 
small peaks. A small peak is defined as a sample point that exceeds the 
previous sample point by 0.25 mV and is greater or equal to the following 
sample value. This process is repeated by Find Peaks 213 until all the 
peaks in an interval equal to the mean R to R interval of the previous 
peaks are found. The peaks found by Find Peaks 213 are then analyzed by 
P/T Exclusion 214 to find those peaks that are larger than all the 
neighboring peaks within a window of 200 to 300 mSec. These larger peaks 
are then used as candidates. From the candidates found by P/T Exclusion 
214, all those which exceed one half the average R wave amplitude are 
selected as QRS points by QRS Selection 215. The period of the selected 
QRS points is measured by QRS Period 216. If the duration of the period as 
found by QRS Period 216 is found to be longer than 11/2 times the mean R 
to R interval then it is determined that a beat has been missed and this 
will be indicated by QRS Test 217 . Upon an indication from QRS Test 217 
that a beat has been missed QRS Selection 215 will then select the peak 
within the mean R-R interval that has the highest amplitude. 
Referring again to FIG. 3, Feature vector extraction 220 analyzes the data 
determined to contain valid heartbeats by the Beat Detection 210 analysis 
to obtain a vector representation of the heartbeat. A plurality of feature 
vectors components are extracted to create a multi-dimensional feature 
vector that characterizes heart beat shape. The multi-dimensional feature 
vector is created by a modified version of the Karhunen Loeve Transform 
(KLT) to represent QRS Morphology. This mathematical transformation is 
applied to detected beats in each channel. The transform characterizes the 
beat in terms of significant principal components, creating a 
multi-dimensional feature vector that characterizes the shape of the 
detected beat. Each QRS complex has samples taken during a 200 millisecond 
period from a plurality of ECG leads. From these samples QRS pattern 
vectors are defined. 
The KLT is a principle component analysis and that can represent a signal 
or a waveform by using a finite number of coefficients. A principle 
component analysis requires that a specific signal or waveform type be 
modeled in order to create the principle components. An analogy can be 
made to a Fourier transform in that a Fourier transform can represent a 
waveform using a finite number of coefficients. However, the base 
functions of a Fourier Transform are sine functions. Whereas, the KLT 
creates principle components of a waveform by modeling the waveform to 
calculate eigenfunctions and using the eigenfunctions as the basis 
functions. 
It is well known that an arbitrary function f(t) can be represented by a 
series of orthogonal functions say G.sub.m (t) on an interval 0 to a thus, 
##EQU1## 
Here, the numbers a.sub.m are called the coefficients of this this 
expansion. 
Again making an analogy to a Fourier series expansion, the set of 
orthogonal functions G.sub.m (t) in a Fourier expansion would be sine 
functions, and the coefficients a.sub.m would be Fourier coefficients on 
the interval 0 to 2.pi.. The accuracy to which f(t) can be represented 
obviously depends on the number of coeficients a.sub.m that are used in 
the series. The accuracy to which f(t) can be represented for a given 
number of coeficients will depend on the set of orthogonal functions 
G.sub.m (t) that are used. 
The concept of the Karhunen-Loeve transform is also known as a principle 
component transform, is that a set of orthogonal functions is selected by 
examining the function to be represented. Thus, the set of derived 
functions will most accurately represent the original function for any 
given number of coefficients. 
In the preferred embodiment, the function to be represented is the ECG 
complex in an interval of 200 milliseconds as shown in FIG. 12b (722, 724, 
726, 728, 730, 734 and 736). The set of orthogonal functions used are the 
first five order eigenfunctions (702,704,706,708,710) as seen in FIG. 12a. 
The reconstruction of the ECG complex shown in FIG. 12c (742, 744, 746, 
748, 750, 752,754, and 756) is accomplished using the eigenfunctions 
(702,704,706,708,710) of FIG. 12a. Assuming that the waveform is not 
unduly noisy, the five principal components (702,704,706,708,710) 
establish a comprehensive base from which virtually any ECG signal can be 
analyzed. The analysis is accomplished by correlating the components of an 
analyzed input signal with the comprehensive base that is generated from 
the five principal components that are used as basis functions, similar to 
the manner in which sine functions are used as basis functions for Fourier 
transforms. The comprehensive base is generated prior to running the 
arrhythmia analysis and is permanently stored in the system in the 
preferred embodiment. By having a comprehensive base built upon ECG basis 
functions, ECG analysis can be accomplished by correlating the components 
of an input waveform in real time. 
The KLT residual is the amount of energy in the original ECG which is not 
contained in the resultant KLT transformed values. The KLT residual is one 
of several indicators of noise level used by the Noise Estimation Module 
224. Noise is a major source of error in all arrhythmia analysis programs. 
The KLT's ability to separate noise is directly relational to the number 
of coefficients that are used. The larger the number of coefficients the 
better the noise separation. 
The measured Euclidean distance 230 takes the results of the feature vector 
extraction 220 and measures the squared euclidean distance between the 
beats feature vectors and the center of each cluster. 
In the preferred embodiment a beat is considered part of a cluster if the 
measured euclidean distance 230 is within three standard deviations. The 
measurement threshold used to approximate three standard deviations in the 
preferred embodiment is 2NF+4. Here, NF is the number of features which in 
the preferred embodiment is equal to 5. Three standard deviations is a 
measure that includes 98% of the features of beats within a cluster. 
Cluster Creation 240 is responsible for the generation of clusters in 
accordance with beat morphology and confidence levels. Cluster Creation 
240 is a means for creating clusters by grouping the heart beats having 
similar feature vectors. Beats of similar shape have similar feature 
vectors. As each new feature vector is created, it is compared with 
clusters of previously existing vectors. Clusters are compared by Measure 
euclidean distance 230 squaring the euclidean distance of the vector and 
measuring the distance between the recently created vector and each 
existing cluster. If the Euclidean distance of a vector is not within 
three standard deviations of an existing cluster, then this is so 
indicated by Standard Deviation 235 and Cluster Creation 240 creates a new 
cluster. If a vector's euclidean distance to any existing cluster is 
within three standard deviations of an existing cluster then the vector is 
placed within that cluster. 
Once created, a cluster is classified by the Cluster Classification 250 as 
Normal, VE, SVE or Unknown, depending on characteristics of the beats 
comprising the cluster. Beat Classification 260 then classifies and labels 
the beat. Generally the beat is classified the same as the matching 
cluster classification. One exception is a beat which matches a normal 
cluster is called an SVPB if it is premature by 20% or more, otherwise it 
is classified as normal. In the preferred embodiment the criteria used for 
determining beat type is the beat annotation label as shown in Table 1. 
TABLE 1 
______________________________________ 
Beat Types 
Label Beat Type Criteria 
______________________________________ 
o Normal Normal cluster not meeting SVPB 
prematurity criteria. 
V Ventricular Abnormal cluster that is premature, or 
Ectopic (VE) on time, or late compared to the 
current mean R-R interval. 
S Supraventricular 
Beat (SVPB) Normal cluster having beats 
Premature (SVPB) premature by 20% or more. 
Q QRS of unknown 
Beat does not fit criteria for normal 
type or abnormal or is too noisy to cluster. 
? Learning First 50 detected beats used to 
establish normal cluster and initial R-R 
interval. 
O Other Miscellaneous categories such as 
pacer, aberantly conducted SVE's, etc. 
May be labeled in post-analysis review. 
______________________________________ 
The Rhythm Classification 270 is the sequence and interval of the 
heartbeats and it is used to detect and label various arrhythmia episodes. 
In the preferred embodiment of the invention, the sequence and interval 
criteria used to describe the arrhythmia episodes are described in Table 2 
below. 
TABLE 2 
______________________________________ 
Arrhythmia Episodes 
Arrhythmia Criteria 
______________________________________ 
Ventricular Bigeminy* 
Ventricular extrasystoles occurring 
alternately with other beats 
beat sequence VxVxV 
Ventricular Ventricular extrasystoles occurring 
Trigeminy* alternately with other beats 
Beat sequence VxxVxxV 
Ventricular Couplet 
Two ventricular beats with a heart rate 
of greater than 95 bpm 
Beat sequence xVVx. 
Ventricular Triplet 
A sequence of three ventricular beats 
with a heart rate greater than 95 bpm 
Beat sequence xVVVx. 
Ventricular A rapid succession of four or more 
Tachycardia ventricular eptopic beats occurring 
consecutively in which there is a three 
beat average rate of 95 bpm or greater. 
Idioventricular 
An arrhythmia of three or more 
Rhythm (IVR) sequential ventricular ectopics with a 
three beat average heart rate of less 
than 50 bpm. 
Bradycardia A slowness of the heart beat, here 
defined as three beat average heart rate 
that is less than 45 bpm with the three 
intervals between beats constituting the 
bradycardia and the previous beat being 
greater than 1500 mS. 
SV Tachycardia 
A 3-beat average heart rate less than 
80 bpm with all three beats being at 
least 20% premature. 
Pause Where the interval between two 
consecutive R waves is greater than 2 
seconds. 
2 R-R The interval between two consecutive R 
waves is twice the previous interval 
plus or minus 25%, or twice the 
following interval plus or minus 25%. 
Atrial Fib or 
A complex computation based on 
Flutter prematurity produces a number for each 
beat. These numbers are averaged over 64 
beats (excluding VE's). Atrial 
fibrillation is declared if the average 
is greater than 100 bpm and heart rate 
is greater than seventy (70). 
SVE Single Beat sequence "xSx." 
______________________________________ 
LEGEND 
V = ventricular ectopic 
S = supraventricular ectopic 
x = any other type beat 
*Taken in a literal sense, bigeminy and trigeminy would define groupings 
of two and three pairs respectively. However, after repeated use these 
terms have come to signify the occurrence of two, three and four beats. I 
is in this sense that these terms are used herein. 
Referring to FIG. 5, the Arrhythmia analyzed data is categorized by 
category type 310 as being either VE 350, SVE 400, artifact 450, unknown 
500, or normal 550. Once the arrhythmia analyzed data's proper category is 
determined processing then branches to the appropriate routine. Confidence 
testing 600 is performed on all type categories after processing for that 
particular category has been completed. After confidence testing is 
performed, a decision is made whether to analyze more data 602. This 
decision can be based on a variety of factors, one of them being the 
completion of testing. In the preferred embodiment a completion of testing 
would generally occur at about 20 hours into a 24 hour test. A decision 
that testing is complete would yield a negative answer to analyze more 
data 602, while if more testing still had to be done would yield a 
positive answer to analyze more data 602. 
Referring to FIG. 6, data assessed to be in the VE category causes the VE 
accumulator 355 to be incremented. The VE accumulator 355 actually 
consists of two accumulators, one to count the occurrences of VE's during 
the last hour and another to count the occurrences of total VE's. Once VE 
accumulator 355 counts the occurrence of a VE, the Triage.TM. threshold 
timer 360 is checked to determine whether thresholding will take place. In 
the preferred embodiment the Triage.TM. timer is preset to 10 minutes of 
patient time although various presets may possibly be used. In the event 
that the Triage.TM. timer has not elapsed, processing returns to retrieve 
more arrhythmia analyzed data. However, when the Triage.TM. timer has 
elapsed the VE grade as determined by the arrhythmia analyzer is compared 
with the preset grade threshold 365. The VE grade may be set to any of the 
values in Table 3. A decision is then made based on whether the grade has 
been exceeded 370. If the VE grade has been exceeded then the prompt 
termination 396 box is executed. When prompt termination 396 is activated 
the operator has three choices: (1) return to Triage.TM.; (2) enter 
confirm mode; and (3) terminate the program. 
TABLE 3 
______________________________________ 
(1) no VE activity 
(2) between one and 30 VE events within the 
span of sixty minutes 
(3) more than 30 VE events in the span of 
sixty minutes 
(4) a VE pair (two consecutive beats being 
classified as VE) occuring 
(5) an intraventricular run of more than 
three VE's occuring with a heart rate of 
less than 95 beats per minute 
(6) a VE triplet (three consecutive beats 
classified as VE with a heart rate of 
more than 95 beats per minute occuring 
(7) a VT run of 4 or more VE's 
______________________________________ 
In the event that the VE grade selected from Table 3 is not exceeded, 
compare VE hourly 375 checks the VE occurrences within the last hour as 
compared to the preset threshold to see if the hourly occurrence threshold 
has been exceeded. CNT/HR Threshold Exceeded 380 prompts termination 396 
from the operator in the event the VE hourly threshold is exceeded, as 
discussed above. Compare VE total 385 checks the total numbers of VE 
occurrences against the threshold for the total number of occurrences if 
the threshold for hourly occurrences has not been exceeded. Total 
threshold exceeded 390 will route system analysis to prompt termination 
396 if the comparison of total VE 385 occurrences exceeds the preset 
threshold and return operation to retrieve more arrhythmia analyzed data 
if the threshold has not been exceeded. 
Referring to FIG. 7, data that the arrhythmia analyzer has assessed to be 
of the SVE category is used to increment the SVE Accumulator 405 which 
will accumulate both occurrences of SVE's during the last hour and 
occurrences of total SVE's in the same manner as discussed for VE's above. 
Once SVE accumulator 405 counts the occurrence of a SVE the Triage.TM. 
threshold timer 410 is checked to determine whether thresholding will take 
place. In the preferred embodiment the Triage.TM. timer is preset to 10 
minutes although many presets can be used. If the Triage.TM. timer has not 
run, processing returns to retrieve more arrhythmia analyzed. However, if 
the Triage.TM. timer has elapsed then Triage.TM. thresholding will take 
place. Once thresholding begins, the SVE grade as determined by the 
arrhythmia analyzer is compared with the preset threshold 415. The SVE 
grade may be set to any of the values in Table 4. Grade exceeded 420 then 
makes a decision based on the result of compare SVE grade to threshold 
415. If the SVE grade has been exceeded then the prompt termination 396 
box is executed. When prompt termination 396 is activated the operator has 
three choices: (1) return to Triage.TM.; (2) enter confirm mode; and (3) 
terminate the program. 
TABLE 4 
______________________________________ 
(1) no SVE activity 
(2) 1 to 30 SVE's in a sixty minute span 
(3) more than 30 SVE's occuring within an 
hour 
(4) a SVE pair 
(5) TBD 
(6) SVT run of three to five 
(7) SVT run of more than five 
(8) pause 
______________________________________ 
If the SVE grade as selected from Table 4 is not exceeded, then analysis 
proceeds in a fashion similar to that of VE occurrences. Compare SVE 
hourly 425 compares the SVE occurrences within the last hour against the 
preset threshold. If the hourly occurrence threshold has been exceeded 
then CNT/HR Exceeded 430 prompts termination 396 from the operator as 
discussed above. Alternatively, if the threshold for hourly occurrences is 
not exceeded compare SVE total 435 checks the total numbers of SVE 
occurrences against the threshold for total occurrences. Total threshold 
exceeded 440 will route system analysis to prompt termination 396 if the 
total number of SVE occurrences exceeds the threshold and return operation 
to retrieve more arrhythmia analyzed data if the threshold has not been 
exceeded. 
As shown in FIG. 5, once data is classified as artifact by the arrhythmia 
analyzer the system then begins a determination of whether an artifact 
minute should be accumulated. Referring to FIG. 8 artifact 450 calculates 
the cumulative number of artifact minutes by calculating the number of 
beats per minute during the last minute 460. If the bpm in the last minute 
is less than 30 465 then the artifact accumulator 470 is incremented prior 
to checking time to threshold 475. If the threshold timer has expended 
then compare to threshold 480 checks the present value of the accumulator 
against the preset value for the Triage.TM. threshold for artifact. If the 
threshold is exceeded 485 then the system prompts termination 396 from the 
operator. 
As shown in FIG. 5 data that has been categorized as unknown by the 
arrhythmia analysis is routed to the analysis for unknown data. Referring 
to FIG. 9, store feature vectors 502 retains the morphology of the unknown 
beat. The occurrence of the unknown is then used to increment the unknown 
accumulator 510. Operation then checks to see if its time to threshold 520 
and if not returns to retrieve more arrhythmia analyzed data. If time to 
threshold 520 is true then the unknown accumulator is compared to the 
Triage.TM. threshold 530. If the threshold is exceeded then the system 
prompts termination 396, otherwise operation returns to retrieve more 
arrhythmia analyzed data. 
Referring to FIG. 5, data that has been given the category type 310 of 
normal will be directed by type normal 550 to have the ST index 
calculated. As seen in FIG. 10, the ST Indexing 550 tracks the occurrences 
of ST episodes. An ST episode occurs when the ST level experiences a 0.1 
millivolt depression, which if witnessed on an ECG graph would be 
depressed one millimeter. There is operator adjustable hysteresis used in 
the calculation of the end point of the ST episode. Thus, the duration of 
an ST episode is determined both by the particular ECG recording and by 
the operator preset hysteresis. The ST index is defined as the amplitude 
of the depression multiplied by the length of the episode. All beats 
determined to be normal by the arrhythmia analyzer have their ST Level 
measured and stored 555. Time to average 560 a decides either to take the 
average of the ST Level over the last minute or to return processing to 
retrieve more arrhythmia analyzed data. If one minute has not past since 
the last ST level averaging time to average 560 returns processing to the 
arrhythmia analyzer to retrieve more data. If one minute has past since 
the last ST level averaging time to average routes processing to average 
ST level 565. Average ST Level 565 takes the sum of the ST levels computed 
by measure and store the ST level 555 over the last minute and averages 
the ST level over that minute. Once the ST level has been averaged ST 
level depressed 570 checks the averaged level against 0.1 millivolt. If 
the averaged ST level does not show at least a 0.1 millivolt depression 
then ST level depressed 570 directs the system to interrogate the 
Triage.TM. timer 599 in order to decide if the ST index should be compared 
to the Triage.TM. threshold. If ST level depressed 570 . finds a 0.1 
millivolt depression in the one minute averaged ST level, then begin ST 
episode 575 declares that an ST episode has begun by the detection of an 
ST depression. Processing will the test ST level on a one minute basis 580 
to check the ST level for a level that is considered normal. In the 
preferred embodiment a hysteresis of 0.05 millivolt is used in conjunction 
with a normal level to verify the return of ST level to normal. Once the 
ST level has returned to a normal level episode end 585 routes system 
operation to calculate the ST index 590. The ST index is defined as the 
absolute value of the ST depression multiplied by the duration of the 
episode. Accumulate ST index 595 sums all the ST indexes after the ST 
index is accumulated. Once the ST index has been accumulated the 
Triage.TM. timer 599 is then interrogated. If the Triage.TM. timer has not 
been expended the system then returns to retrieve more arrhythmia analyzed 
data. If the Triage.TM. timer has been expended, then the accumulated ST 
index is compared to a Triage.TM. threshold value 596. ST index threshold 
597 routes the systems operation to prompt termination 396 if the 
Triage.TM. ST index threshold 596 is exceeded. Prompt termination 396 
then prompts the operator as discussed above. If the Triage.TM. ST index 
threshold 597 has not been exceeded then threshold exceeded will return 
program operation to retrieve more arrhythmia analyzed data. 
All arrhythmia analyzed data has confidence levels formed. As shown in FIG. 
5 the confidence testing 600 is not a decision but a function that is 
performed on all data. Two confidence levels are assessed in the preferred 
embodiment. The first for each beat to determine whether it belongs to a 
particular cluster. The second confidence level is used in a determination 
that the present selection of clusters is a valid cluster selection. There 
are several factors used in determining the confidence level. Referring to 
FIG. 11, measure artifact 602 determines the amount of artifact contained 
within each beat. The artifact is used in the measure of confidence. Next 
measure distance 604 places a confidence level on euclidean distances to 
the nearest VE clusters and to the nearest normal clusters. These 
confidence levels for each analyzed beat are then immediately stored. 
Cluster timer expended 606 then checks the time period since the last 
cluster confidence level determination. In the preferred embodiment, the 
cluster timer expended is preset to 10 minutes, although different presets 
can be used in various embodiments. If the cluster timer expended 606 
interrogation shows that the preset time has not past, then operation 
proceeds back to retrieve more arrhythmia analyzed data. Once an 
interrogation of cluster timer expended 606 shows that the preset period 
has lapsed then calculate cluster members 608 sums the number of beats 
associated with each cluster. Confidence levels are then assigned based 
upon the number of cluster members 610. Calculate cluster distance 612 
determines the euclidean distance between the various clusters. The 
calculated distance is then used by the distance confidence level 614 to 
assign another confidence level to the clusters. All the above confidence 
levels are scaled and summed together as each is calculated. The 
accumulated confidence level is then compared to the Triage.TM. confidence 
threshold 616. If the result of the comparison shows the threshold 
exceeded then the operator is prompted for termination 396 as discussed 
above. If the confidence threshold is not exceeded then the next piece of 
arrhythmia analyzed data is input and analysis continues. 
Referring to FIG. 13, predetermined thresholding values are preset by 
adjusting any of a plurality of graphical slider switches. The 
presentation of the graphical slider switches comes at the request of the 
operator and has the appearance of a group of slider switches that may be 
adjusted by the operator using the mouse or cursor keys to move the 
switches to the desired value. In the preferred embodiment the present 
accumulation of each category is displayed on the slider switch display 
along with the present Triage.TM. threshold. As analysis progresses the 
present accumulations are incremented for each occurrence of a respective 
category. If any of the threshold values are exceeded, analysis will stop, 
and the operator will be prompted for action as discussed above. The user 
may view the data and decide whether to terminate analysis, reset the 
thresholds and continue, or to change to a confirm mode analysis. A 
confirm mode is where the user is asked to validate or change what the 
analyzer would call a cluster when a new cluster is created. 
As seen on FIG. 13, graphical slider switches (802, 804, 806, 808, 810, 
812, 814, 816, 820, 822, 824, 826, 828) control the Triage.TM. thresholds 
by allowing for operator adjustment via computer keyboard or mouse input. 
Each of the thresholding switches is adjusted by the operator moving the 
bar on the slider switch. The slider switches for thresholding the 
occurrence of VE's per hour 804 and SVE's per hour 810 can be 
independently preset to anywhere between 0 to 200 occurrences per hour by 
moving the VE per hour slider bar 834 or the SVE per hour slider bar 840. 
The present value for the VE per hour threshold 864 is displayed to the 
left of the VE per hour slider switch 804, while the present threshold for 
SVE's per hour 870 is shown to the left of the SVE per hour slider switch 
810. In a similar manner the slider switch for thresholding the occurrence 
of total VE's 802 and total SVE's 808 can each be independently preset 
from anywhere from 0 to 2000 occurrences by adjusting the total VE slider 
bar 832 and the total SVE slider bar 838 respectively. The present 
threshold for total VE's 862 and the present threshold for total SVE's 868 
are displayed to the left of their respective slider switch. The 
thresholds for VE and SVE grade are controlled by the VE grade slider 
switch 806 and the SVE grade slider switch 808 being preset by the VE 
grade slider bar 836 and the SVE grade slider bar 842 respectively Again, 
the present value of the presets shown to the left of the slider switches. 
Proceeding in a similar fashion, the ST index slider switch 814 is preset 
by the ST index slider bar 844 which is displayed by the present ST index 
threshold display 874. The occurrence of unknown beats is thresholded by 
presetting the total unknown slider switch 816 and the unknown per hour 
slider switch 820 with respective slider bars 846, 820. The selected 
preset is displayed to the left of the slider switches by the total 
unknown threshold display 876 and unknowns per hour threshold display 880. 
Artifact is thresholded by presetting the artifact total minute slider 
switch 822 and the artifact per hour slider switch 824 by adjusting the 
artifact total minute slider bar 852 and the artifact per minute slider 
bar 854 to yield the display of the present threshold setting for artifact 
total minutes 882 and the display for the threshold preset for artifact 
per hour 884. The confidence level index is thresholded by adjusting the 
confidence index slider switch 826 to a scaled value of anywhere between 0 
and 100 by adjusting the confidence slider bar 856 to the desired preset 
value which is then displayed by the confidence threshold display 886. 
Finally, the running time of the test can also be thresholded by adjusting 
the percent complete slider switch 828 to the desired value by adjusting 
the confidence slider bar 858. The percentage at which the system will 
automatically stop operation is then displayed on the percent complete 
threshold 888. Thus, it is possible for the operator to determine the 
levels at which the system will automatically decide that the recording 
contains no significant abnormalities and may therefore be excluded from 
the requirement of manual analysis. 
As seen in FIG. 1b, a second embodiment of the invention uses an automatic 
feeder 40 to operate in a batch mode. The automatic feeder 40 as used in 
the preferred second embodiment is a modified version of cassette 
loader/feeders that are well known to the art, will load a plurality of 
patient ECG recordings 50 into the Triage.TM. system 10 to be scanned. 
Each of the patient recordings are first labeled with a bar code to 
identify the patient, any patient medication, the patient's doctor and the 
date the recording was made. Each of the patient recordings identification 
code is then entered into the scanner by the keyboard means 12. The 
patient recordings, which in the preferred embodiment would be tape 
cassettes, are loaded into the drawer 42 on the automatic feeder 40. The 
recordings are then sequentially tested by the Triage.TM. scanning method 
and apparatus to identify those recordings containing no significant 
abnormalities. As in the previous embodiment, the operator presets the 
thresholds used to identify significant abnormalities. Here batch refers 
to a mode of operation in which several ECG records are to be analyzed 
sequentially without an operator intervention. Multiple records of patient 
ECG data are loaded into a scanner that has the means to scan each of the 
records sequentially. Depending on the mode that the operator chooses, the 
operator may or may not be allowed to interact with the test while in 
progress and view the results when a threshold has been exceeded. Via 
operator selection tests may be run as shown in the preferred embodiment 
of the invention. Here, the operator must select either automatic, confirm 
or Triage.TM. modes of operation when prompted for termination after a 
threshold has been exceeded. Alternatively, operation in the batch mode 
may be selected to allow the tests to continue running if threshold is 
exceeded. Here, the operator may only view a report on the results of all 
the tests made on the recordings prior deciding which recordings contain 
no significant abnormalities. Thus, by batch mode loading of patient ECG 
recordings, it is possible to provide a unique Triage.TM. analysis to a 
plurality of ECG recordings that is fully automated. It is possible to 
eliminate as many as 30% of a plurality of recordings employing automatic 
recording feeders and using automated Triage.TM. thresholding techniques. 
A third embodiment of this invention would use digitally recorded ECG data 
in place of the analog recorded ECG data as disclosed in the preferred 
embodiment. Here digital recorded ECG data can be digitally recorded on 
tape or using means for solid state recording with the computer system 10. 
It is obvious to those skilled in the art that the above mentioned 
embodiments can be modified without departing from the spirit and scope of 
the invention. The embodiments as described herein are not, therefore, to 
be considered as illustrating all possible variations of the invention, 
and all changes that are embraced by the claims of the invention are 
therefore considered equivalent to the embodiments of the invention as 
disclosed and claimed herein.