Abstract:
In order to reduce bias associated with conventional ECG analysis, the present invention provides a method and apparatus to improve diagnosis of acute cardiac syndromes (ACS), such as acute myocardial infarction and acute cardiac ischemia (unstable angina), in specified groups of patients using ECG signals and automatic detection analysis. Specific criteria are developed and utilized based on a prespecified group selection for the particular patient. After identifying group membership for the particular patient, ECG data are acquired from a patient experiencing ACS symptoms. Known criteria typically used for assessing ACS are then modified for the particular group membership. Such criteria significantly reduce the bias found in a baseline group for which the known criteria were established. The invention is particularly useful in identifying an ACS, and the type of ACS, in females under the age of 60 where it has been found that the current critical ST threshold is too high to consistently identify an ACS in this subgroup.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to electrocardiograms (ECGs) and the use thereof, and more particularly to, a method and apparatus to detect acute cardiac syndromes that is specific with respect to gender, age, height, weight, and/or race. 
     ECG analysis is a well established method for studying the function of the heart and identifying disorders of the heart. ECG is an important tool in diagnosing patients presented to an emergency room with chest pain. One particular disorder that is studied using ECG is acute cardiac syndromes (ACS), which includes, but is not limited to, acute myocardial infarction (MI) and acute cardiac ischemia (ACI), the latter of which is commonly referred to as unstable angina. Acute ischemia includes the starvation of oxygen to a portion of the heart, commonly caused by a partial blockage of the coronary arteries providing oxygenated blood to the heart, and acute infarction is due to the complete blockage of oxygen to a portion of the heart. Ischemia, or unstable angina, can lead to or be a symptom of infarction. It is well known that time is critical in diagnosing these conditions in a patient experiencing chest pain. Delay in diagnosis and therapy can result in serious impairment of the heart&#39;s function, including sudden death. 
     An ECG is a graphic tracing of the variations in the electrical potential caused by the excitation of the heart muscle and is detected at the body surface by an ECG device. The typical ECG is a scale or representation that shows deflections resulting from cardiac activity as changes in the magnitude of voltage and polarity over time and includes a P-Wave, a QRS complex, a T-Wave, and a U-Wave. These waves are then analyzed using a set of rules and parameters to determine what is normal and what is not. Certain deviations are used to flag a possible ACS. 
     However, recent studies indicate a significant difference in these “typical” clinical profiles, presentations, and outcomes between men and women with ACS that were not attributable to differences in baseline characteristics. Studies have shown that younger women have a higher mortality than older women, and men of all ages, following myocardial infarction. However, to date, these studies have not conclusively shown direct evidence that the findings might be attributed to pathophysiological and/or anatomical differences between men and women. For example, electrocardiographic evidence of acute MI conventionally includes the presence of ST elevations of at least 100 μV in two anatomically contiguous leads (a higher threshold of 200 μV is used for precordial leads). Since the previous studies used conventional, clinical criteria to assess the presence of acute MI and thereby determine the course of care for the patients, it is believed that the differences in mortality rates may be attributed, at least partially, to sub-clinical differences in the ST elevation levels on the admission ECG. If present, the sub-clinical differences in ST levels between symptomatic male and female patients (e.g., those complaining of chest pain) may be revealed only through more accurate computerized measurements of the ST levels from signal averaged (median) data. It is believed that these differences may have been obscured by the fact that development of conventional criteria for ECG ACS evidence was carried out through manual ST measurements on a baseline group that was largely male dominated or undifferentiated by gender, age, height, weight and race. 
     There are a number of computerized ECG analysis systems in the marketplace. However, it is generally believed that they all rely on a baseline group of patients that provides criteria that may be biased against certain groups of patients. It would therefore be advantageous to optimize the performance of computerized ACS criteria to more accurately detect such acute cardiac syndromes as acute MI and ACI for a patient falling within one group that does not necessarily have the same characteristics of the baseline group. For example, it is proposed herein that female patients under the age of 60 should have a lower ST elevation threshold than the male dominated group used as the traditional baseline. Therefore, it would be advantageous to improve the sensitivity for detection of acute MI/ACI for female patients while maintaining high specificity and, thus, eliminate the bias in the current criteria used. 
     SUMMARY OF THE INVENTION 
     A method and apparatus is disclosed to improve detection of acute cardiac syndromes (ACS) in specified groups of patients using ECG analysis to eliminate bias introduced by the current criteria that solves the aforementioned problems. 
     The invention includes the development and implementation of a computerized ACS criteria based analysis system to optimize performance for specified groups of patients. To develop the new criteria, a database of patient records is examined in which the patient records confirm the existence of ACS or the absence of ACS. That is, to ensure a bias neutral study, the presence or absence of ACS must be confirmed by a non-ECG diagnosis. For gender-based criteria, the database of admission ECGs divided into female and male groups. The difference of at least one ECG parameter is examined between the groups. In this example, the ECG parameter tested is the ST segment measurement of the ECG waveform. Either a fuzzy logic or a neural network can be used for pattern recognition in addition to classical pattern recognition methods such as linear discriminant function analysis and thresholding. After the differences are examined, a significance is assigned to the difference. Based on the significance assigned, the ECG-based automatic detection of ACS can be optimized for the specified subgroup. 
     In accordance with one aspect of the invention, a method of developing automatic detection of ACS using ECG signals includes examining a difference of at least one ECG parameter from patients in a baseline group that includes patients having ACS and those not having ACS, with patients in a second group that includes patients, also, having ACS and those not having ACS. After determining a significance of the differences examined, the method includes optimizing performance of ECG-based automatic detection of ACS for the second group of patients based on the significance determined. In a preferred embodiment, the ECG parameter is ST elevation. Since it has been found herein that female patients have a lower critical ST elevation than the baseline, male dominated group, the invention includes lowering the threshold level of the ST elevation parameter in the ECG analysis. 
     In accordance with another aspect of the invention, an ECG analysis program is disclosed which, when executed, causes a processor to acquire ECG data from a patient, determine whether the patient is in one of a prespecified group, and if so, applies analysis criteria specific for the prespecified group to identify if the patient has an ACS. If the patient is not in a prespecified group, the program applies known analysis criteria to the ECG data. The group is specified based on gender, age, race, weight, height, or a combination thereof. The analysis includes modifying various parameters based on the specific group selected. 
     In accordance with another aspect of the invention, a method and apparatus, that includes an ECG device, is disclosed. The method is a criterion based, group membership-specific ACS detection method. The method includes specifying a group membership designated as having differing ECG data as compared to a baseline group, acquiring ECG data from a patient experiencing ACS symptoms, and then analyzing the ECG data based on group membership. The steps of the method are programmed into a processing unit of an ECG device having a plurality of lead wires to acquire the ECG data from the patient. 
     In a preferred embodiment, the specified group is females under the age of 60 and the ECG data includes lowering the ST segment, checking ST depression level in reciprocal leads and T wave thresholds so as to more accurately identify acute anterior myocardial infarction (MI) and acute inferior MI in younger females. This gender and age specific ACS criteria improve the sensitivity while maintaining high specificity and overall accuracy of acute ACS detection for female patients, especially those under the age of 60. 
     Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings illustrate one preferred embodiment presently contemplated for carrying out the invention. 
     In the drawings: 
     FIG. 1 is a block diagram of an electrocardiogram device connected to an information management system incorporating the present invention. 
     FIG. 2 is a timeline of one cardiac cycle of an ECG signal depicting the various wave components of interest to ECG analysis. 
     FIG. 3 is a high level flow chart depicting an algorithm and the method implemented in the apparatus of FIG.  1 . 
     FIG. 4 is a low level flow chart showing a specific embodiment of the invention. 
     FIG. 5 is a low level flow chart showing a specific embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, an electrocardiogram device  10 , in accordance with the present invention, is shown optionally connected to an information management system  12  through a communications link  14 . A commonly used device for acquiring an ECG is a 12-lead electrocardiograph, such as the GE Marquette&#39;s MAC-5000 and a commonly used ECG analysis program is 12-lead ECG analysis program, such as GE-Marquette&#39;s 12SL™. The ECG device  10  and the information management system  12  receives power  16  from an external source. Among other things, the information management system  12  includes a central processing unit  18  connected to a memory unit, or database,  20  via a data link  22 . The memory unit  20  may be RAM, ROM, a mass storage unit, a floppy disk, or any other computer readable storage medium, or a combination thereof. The CPU  18  processes data and is connected to an output, such as printer  24  and/or display  26 . Alternatively, the electrocardiogram  10  can be connected directly to a printer  24  or display  26  through communications link  14  if the optional information management system  12  is not utilized, or the printer  24  and/or display  26  can be constructed integrally with the ECG device  10 . The software program of the present invention may reside in either the ECG device  10 , the information management system  12 , or another device associated to receive signals from the ECG device  10 . 
     The ECG device  10  is connected to a plurality of patient lead wires  28 , each having an electrode  30  to receive ECG signals from a patient  32  in a known manner. The ECG device  10  has a signal conditioner  34  that receives the ECG signals and filters noise, sets thresholds, segregating signals, and provides the appropriate number of ECG signals for the number of leads  28  to an A/D converter  36  which converts the analog signals to digital signals for processing by a microcontroller  38 , or any other type of processing unit. Microcontroller  38  is connected to a memory unit  40 , similar to memory unit  20 , or any other computer readable storage medium. In a preferred embodiment, memory unit  40  is a combination of ROM and RAM, wherein the ROM is used for static data, such as computer programs, and the RAM is used for dynamic data, such as the ECG signals received from patient  32 . 
     A power supply  42  is provided to supply isolated power  44  to the signal conditioner  34 , the A/D converter  36 , and any internal printer or display and provides an isolation barrier  46  to isolate the lead wires  28  from un-isolated power  48  and line voltage  16 . Such electrical isolation is typically provided by a medical grade isolation transformer. 
     FIG. 2 shows one cardiac cycle of a typical ECG signal  50 . The major components of the ECG signal  50  include the P-Wave  52 , the QRS segment  54 , and the T-Wave  56 . Of particular interest in the present invention, is the ST segment  55  and the T-Wave  56 . As is known, an elevated or depressed ST segment is an indication of acute myocardial infarction (MI), or acute cardiac ischemia (ACI), commonly known as unstable angina, both generically referred herein as acute cardiac syndromes (ACS). Another indication of ACS in the ECG signal  50  is an abnormal T-wave  56 , such as an inverted T-Wave, a biphasic T-Wave, a hyperacute T-Wave, or a flat T-Wave. These ECG parameters are utilized herein in accordance with the present invention. 
     The present invention includes a method of developing automatic detection of ACS based on a particular patient type using these ECG signals. The method includes building a database of patients in which some have ACS and others do not, by retrospectively examining stored ECG databases from various medical facilities. The patient records selected are those in which the patients have a confirmed diagnosis of the presence or absence of an ACS using non-ECG diagnostic techniques. Using this database, the method next includes examining a difference of at least one ECG parameter for patients in a baseline group against patients in a second group that also includes patients having confirmed ACS and those not having ACS. In a preferred embodiment, a database is used to examine the difference of ST segment and T wave measurements between male and female ACS patients using statistical and pattern recognition methods. 
     As previously mentioned, the present invention is based on the fact that the conventional criteria for ECG ACS examination were carried out through ST measurements on a largely male dominated patient population or a population undifferentiated by gender, age, height, weight and/or race. By segregating the records of the second group, females in this case, from the baseline male-dominated group, and comparing the difference of ST segment and T wave measurements, a significance can be assigned to the ST segment and T wave differences. Since it was found that the difference in ST elevations was more significant for women under the age of 60, the technique is also preferably age limited. The technique next includes optimizing performance of ECG-based automatic detection of ACS for the second group of patients based upon the significance determined. 
     In a typical automatic detection routine for ACS, the ECG waveforms from the multi-lead electrocardiogram are provided to the microcontroller to first detect the ECG features, such as the P-waves, the QRS complexes, and the T-waves. This routine then generates a representative medium cardiac cycle for each lead, and then, generates lead by lead measurements of the ECG features. Cardiac rhythm analysis is then performed, as well as morphology analysis of the ECG features. The measurements and interpretation statements are then provided to the medical care provider. The present invention modifies the morphology analysis of the ECG features. 
     FIG. 3 is a high level flow chart of a preferred implementation of the present invention. After verifying an ECG parameter threshold difference between the two groups  60 , which in the preferred embodiment is gender- and age-based, a new threshold is set for females under 60 years of age at 62. If the ECG parameter measurement is not greater than the new threshold level  64 ,  66 , there is no ACS condition in this particular patient and the algorithm exits this subroutine at  68 . In a preferred embodiment, the ECG parameters at issue are the ST elevation and T wave voltage. If the ST elevation is greater than the new threshold  64 ,  70  the reciprocal leads and the T-Wave are checked at  72  and if certain criteria for those parameters are met  74 ,  76 , the system outputs an ACS alert  80 . However, if the ST elevation is greater than the threshold  64 ,  70 , but the specified criteria are not met  74 ,  82 , the healthcare provider is advised to check for other possible causes  84 . 
     FIGS. 4 and 5 show specific embodiments of the present invention. FIG. 4 is a subroutine to determine acute inferior MI, whereas FIG. 5 shows a subroutine demonstrating the criteria to determine acute anterior MI. One skilled in the art will readily recognize that the implementation demonstrated in FIGS. 4 and 5 can be extended to the posterior and lateral diagnostic positions, as well as to other acute ischemia diagnoses. 
     Referring now to FIG. 4, a specific embodiment of the present invention is shown in detail. After the standard ECG analysis is implemented  100 , the patient&#39;s gender and age are checked at  102 . If the patient is not female or under the age of 60  104  the standard, known criteria are applied at  106  to continue the ECG analysis. However, if the patient is female and under the age of 60 at  102 ,  108 , the ST segment threshold is decreased by 20% at  110 . The known criteria are then modified accordingly and applied at  112 , and if the modified criteria call for an acute inferior myocardial infarction (MI) directly  114 ,  116  the system immediately provides an acute inferior MI output at  118 . If however, after applying the modified criteria  112 , there is no indication of acute inferior MI or it is inconclusive  114 ,  120  a new set of criteria  122  is applied. 
     The new set of criteria  122  includes three distinct conditions  124 ,  126 , and  128 , and if any of the conditions provides a positive result  130 ,  132 ,  134 , the ECG device outputs an acute inferior MI warning at  118 . More specifically, if the ST measurement from at least two inferior leads is greater than a first ST threshold and the ST measurement from at least two reciprocal leads is less than a second ST threshold  124 ,  130 , the acute inferior MI alert is output at  118 . If not  124 ,  136 , the next set of criteria is checked at  126 . That is, if the ST measurement from at least one inferior lead is greater than the first ST threshold and the ST measurement from at least two reciprocal leads is less than the second ST threshold and at least two chest leads, or “V leads”, indicate an inverted T-wave  126 ,  132 , the acute inferior MI warning is produced at  118 . If neither of the first two criteria are met  136 ,  138 , the third set of criteria is checked  128 . The third set of criteria  128  requires the ST measurement from all three inferior leads to be greater than the first ST threshold to produce the acute inferior MI warning  134 ,  118 . If none of the criteria are met  136 ,  138 , and  140  only then is a negative inferior MI result created and displayed  142 . 
     Referring now to FIG. 5, an algorithm is depicted showing the present invention applied to acute anterior myocardial infarction (MI) analysis. After this subroutine is called from the standard ECG analysis  150 , the patient&#39;s gender and age are checked at  152 . If the patient is not female, or is female and over the age of sixty,  152 ,  154 , the known criteria for acute anterior MI are applied at  156 . However, if the patient is female and under the age of 60 at  152 ,  158 , the ST threshold is decreased by 20% at  160  and the known criteria are modified and applied at  162 . If the modified criteria indicate the presence of acute anterior MI  164 ,  166 , the ECG device displays an acute anterior MI warning  168 . However, if after applying the modified criteria  162 , there is no indication of an acute anterior MI  164 ,  170 , or is inconclusive, the analysis a new set of criteria is applied  172 . The new set of criteria  172  includes at least three separate sets of criteria  174 ,  176 , and  178 . If any of these criteria are met  180 ,  182 , or  184 , the acute anterior MI warning is generated at  168 . More particularly, the first set of criteria  174  includes checking if the ST measurement from at least two anterior leads is greater than the first ST threshold and if the ST measurement from at least one reciprocal lead is less than a second ST threshold  174 ,  180 , the acute anterior MI warning is output at  168 . If the first set of criteria is negative  174 ,  186 , then the second set of criteria is checked at  176 . The second set of criteria will be satisfied if the ST measurement from one interior lead is greater than the first threshold and the ST measurement from at least two reciprocal leads is less than the second ST threshold and at least one chest lead indicates an inverted T-wave  176 ,  182 , which will then result in the acute anterior MI output  168 . If the first two criteria are negative  186 ,  188 , the third set of criteria is executed at  178 . These criteria will set a warning for an acute anterior MI  184 ,  168  if the ST measurement from at least one anterior lead is greater than the first ST threshold and the ST measurement from at least two reciprocal leads is less than the second ST threshold. If none of the new criteria  172  are satisfied  186 ,  188 , and  190 , the ECG device indicates that the condition is negative for acute anterior MI  192 . 
     Accordingly, the present invention includes a criterion based, gender acute cardiac syndrome detection method that includes acquiring patient specific data including specifying a group membership designated as having differing ECG data as compared to a baseline group and acquiring ECG data from a patient experiencing ACS symptoms. The criterion based method next includes analyzing the ECG data based on the group membership. In a preferred embodiment, the baseline group is male dominated and the second group includes females under the age of 60. However, one skilled in the art will recognize that other groups may similarly be affected and of the application of such other group is well within the scope of the present invention. For example, although the preferred embodiment is gender and age specific, other groups may include race specific, gender only specific, age only specific, weight only specific, height only specific or any combination thereof. 
     The invention also includes an ECG analysis program residing in computer readable memory  20 ,  40  capable of causing a processor  18 ,  38 , when executed, to acquire ECG data from a patient and accept an input to determine whether the patient is in a prespecified group. If the patient is in a prespecified group, the program applies analysis criteria specific for the prespecified group to identify an ACS. If the patient is not in one of the prespecified groups, the known analysis criteria are applied. Threshold parameters are modified and a set of known criteria can be modified accordingly. Additionally, new sets of criteria can also be applied. 
     The aforementioned process and program can be implemented in an ECG device having a plurality of patient lead wires to acquire ECG data from a patient. The ECG device includes a processing unit connected to the plurality of patient lead wires to receive the ECG data and process the ECG data. The processing unit is also programmed to acquire patient specific data and ECG data from the patient. The ECG data is then analyzed as previously set forth. 
     The present invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.