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Computer analysis of the electrocardiogram
EDITORIALS
Computer Analysis of the Electrocardiogram
CHARLES
A.
BERTRAND,
MD,
FACC
White Plains, New York
The comprehensive review by Caceresl in this issue of the Journal touches on all of the major contributions in the relatively new field of computer electrocardiography. He writes of $220 million worth of computer systems and $135 million of related terminals to be purchased by 1980 and of further annual expenditures in excess of $200 million. Thus, there is an obvious need not only to evaluate the current status of computer electrocardiography but also to obtain some idea of its future use. Several more or less independent procedures are needed to arrive at a computer-interpreted electrocardiogram. Initially the data are acquired by a three channel electrocardiograph that records the 12 lead electrocardiogram or three orthogonal (vector) leads, or both. Frequency modulation tape may be used for recording and storage. Since the computer deals with numbers only, an analog to digital converter is used to convert the electrocardiographic tracing or analog signal into a series of numbers or digits. Work in this area was originally done by Taback et aL2 and later extended by Stallman and Pipberger3 and Caceres et a1.4 Samples of the tracing are usually taken at intervals of 2 to 4 msec. The digitized values are read into the computer and are compared with the criteria of the analysis program. One computer program is used for wave recognition. A second is used to determine wave amplitudes and durations as well as various time intervals. Still another is used for rhythm analysis, as first developed by Bonner and Schwetman in 1968 but not available for routine use at that time.5 Actually, one structured multiphased program is used that identifies waves, performs the various measurements and analyzes rhythm and contour. Currently, most records are stored on tape or even disk, but improvements are needed, essentially for data compression or transformation into some yet to be perfected efficient storage medium. Although some comparison programs of serial tracings have been undertaken,6 more evaluation of such programs is needed and problems of storage and retrieval From the Division of Cardiology, St. Agnes and Lawrence Hospitals, Office of Consultant in Cardiology, International Business Machines, White Plains, N. Y. and the Department of Medicine, New York Medical College, New York, N. Y. Address for reprints: Charles A. Bertrand, MD, 170 Maple Ave., White Plains, N. Y.
394
September 1976
The American Journal of CARDIOLOGY
must be solved. The results of the last 16 years suggest that computer analysis of electrocardiograms is good for normal tracings and less good for tracings the computer labels abnormal. Without discussing sensitivity and specificity it is reasonable to state that, in our experience, when a computer interprets an electrocardiogram as normal it has a better than 95 percent probability of being correct, allowing for minor degrees of S-T segment deviation; this figure is in agreement with the data of Crevasse and Ariet.7 Since 1968, we have performed more than 100,000 multiphasic health testing examinations and in most subjects have recorded the electrocardiogram on tape for computer analysis. (Until July 1974 we used the Smith-Hyde vector-lead programs and since then have used the Bonner 12 lead program.g) In our experience, the computer tends to be accurate in interpreting normal tracings, but has at least a 1 in 3 chance of being partly or completely in error about tracings it labels abnormal. Yet its performance is better with some abnormal tracings. For example, when the computer interprets a left ventricular conduction disturbance or left bundle branch block, it is virtually always correct; in contrast, there is greater variability with a right ventricular conduction disturbance or right bundle branch block. Two major limitations to computer use are implied in these considerations: First, the computer’s low level of reliability in interpreting abnormal tracings limits its clinical usefulness since, in most hospitals, the majority of recorded electrocardiograms are abnormal. Second, the lack of a practical comparison program further limits routine clinical use. What then, is the present “place” of the computer in electrocardiographic interpretations? We may consider using computer analysis of the electrocardiogram in three areas: (1) screening programs, (2) the doctor’s office, and (3) in hospitals. (1) In screening programs, the computer probably functions at its highest level. Simply expressed, the computer may be used to sort out the normal from the abnormal. We recommend that the screening be followed with a sampling review procedure (at IBM, 10 percent of normal electrocardiograms and virtually all abnormal records are reviewed by cardiologists). We have found the computer to be very helpful and have arrived at a computer-assisted type of electrocardio-
Volume 36
EDITORIALS
graphic interpretation. lo Computer analysis is of value for sorting out normal tracings, giving precise time intervals and measurements and offering various diagnostic possibilities for the cardiologist’s consideration. I think, therefore, that computer analysis leads to both increased speed and increased accuracy in interpreting the electrocardiogram. (2) In the doctor’s office, there is a greater degree of variability. Ideally, a doctor who takes an electrocardiogram should be qualified to interpret it; if not, some other doctor or facility should be available for interpretation. Probably computer interpretation of the electrocardiogram has little practical application for the qualified physician who has a low to moderate volume of electrocardiograms to interpret. It may be more useful to the unqualified doctor, or for the doctor in a remote area where facilities for interpretation are not available. For example, telephone transmission of the electrocardiogram to a computer center may be utilized, with the interpretation relayed back to the attending physician. (3) Among hospitals, paradoxically, both the smallest and the largest institutions appear to be best suited for computer interpretation of electrocardiograms. The smallest hospitals are suitable because they may have no cardiologist available to interpret the tracings; in such a case, the electrocardiogram may be transmitted to a center by telephone line. Larger hospitals may have so large a volume of electrocardiograms that computer use is cost-justified. Intermediate-sized hospitals probably represent the exception because, presumably, they have qualified physicians available to interpret the electrocardiograms and the volume of tracings in most of these hospitals is probably insufficient to justify the cost of computers. For hospitals of all sizes, lack of a comparison program presents problems since not only are many electrocardiograms abnormal, but also in many hospitalized patients serial electrocardiograms are taken, thus further limiting the usefulness of computer interpretation. Furthermore, patients may be nervous or seriously ill, have tremors or postoperative bandages, or have other factors that could cause the recording of any electrocardiogram (and therefore input to the computer) to be suboptimal. Prospects for the future: Within 5 years I believe there will be a major development-considerable use
of the “stand-alone” unit, that is, a simple box containing a three channel electrocardiograph with an analog to digital converter to digitize the electrocardiographic signal and a dedicated minicomputer whose sole function will be to interpret the electrocardiogram. I can envision a 12 lead or a 3 orthogonal lead electrocardiogram with the interpretation printed on the tracing itself. This unit may be adequate for one tracing, but what about the complicated cases in which one tracing is abnormal and serial tracings are required? And what about physician review? Herein lies the major problem! Unless, and until, a practical, reliable comparison program is available and has been well tested and validated, the potential of computer interpretation of the electrocardiogram will be sharply limited. Instead of using “stand-alone units,” one may transmit the electrocardiographic signals directly to a computer center for processing or use a stand-alone unit with provision for transmitting to a computer center, thus allowing greater flexibility; but a comparison program will still be required. When the comparison and storage-retrieval problems have been resolved, we may then anticipate other problems, such as regionalization, possible use of Social Security numbers for identification, use of data banks and problems of program evaluation and selection (which program or programs to use and how to validate them). Other problems-those associated with use of the computer in exercise testing and rights of privacy of the patient-loom just over the horizon. Nonetheless, I believe that miniaturization will progress, a practical comparison program will be developed, extensive data banks will be established, and many other problems will be resolved, but the solutions will take years to accomplish. A competent cardiologist will always be needed to interpret the abnormal electrocardiogram. I doubt that the accuracy of the computer will ever be sufficiently great to permit its unaided use in interpreting a difficult arrhythmia. I can also envision problems related to time in comparison of electrocardiograms, problems of correlation with clinical events in a satisfactory manner. Hence we may anticipate the continued coexistence of cardiologists and computers in, I hope, a constructive way leading to greater speed and procession of electrocardiograms but, more importantly, ultimately to a higher quality of interpretation.
References 1. Caceres CA: Limitations of the computer in electrocardiographic interpretation. Am J Cardiol 38:362-376, 1976 2. Taback L, Marden E, Mason HL, et al: Digital recording of electrocardiographic data for analysis by a digital computer. IRE Trans Med Electronics 6:167-171, 1959 3. Stallman FW, Pipberger HV: Automatic recognition of electrocardiographic waves by digital computer. Circ Res 9: 1138-I 143, 1961 4. Caceres CA, Steinberg CA, Abraham S, et al: Computer extraction of electrocardiographic parameters. Circulation 25356-362, 1962 5. Bonner RE, Schwetman HD: Computer diagnosis of electrocardiograms. Ill. A computer program for arrhythmia diagnosis.
Comput Biomed Res I, 387-407. 1968 6. Pryor TA, Lindsay AE, England RW: Computer analysis of serial electrocardiograms. Comput Biomed Res 5709-714, 1972 7. Crevasse L, Arlet M: A new scalar electrocardiographic computer program. Clinical evaluation. JAMA 226:1089-1093, 1973 8. Smith RE, Hyde CM: A computer system for electrocardiographic analysis. Third Annual Rocky Mountain Bioengineering Symposium, Univ. Colorado, Boulder, May 2-3, 1966 9. Bonner RE, Crevasse L, Ferrer MI: A new computer program for analysis of scalar electrocardiograms. Comput Biomed Res 5: 629-653, 1972 10. Bertrand CA, Godbold EO, Duffy JC, et al: How the computer helps the cardiologist interpret ECG’s. Ind Med Surg 42:14-17, 1973
September 1976
The American Journal of CARDIOLOGY
Volume 38
395
Computer Analysis of the Electrocardiogram
CHARLES
A.
BERTRAND,
MD,
FACC
White Plains, New York
The comprehensive review by Caceresl in this issue of the Journal touches on all of the major contributions in the relatively new field of computer electrocardiography. He writes of $220 million worth of computer systems and $135 million of related terminals to be purchased by 1980 and of further annual expenditures in excess of $200 million. Thus, there is an obvious need not only to evaluate the current status of computer electrocardiography but also to obtain some idea of its future use. Several more or less independent procedures are needed to arrive at a computer-interpreted electrocardiogram. Initially the data are acquired by a three channel electrocardiograph that records the 12 lead electrocardiogram or three orthogonal (vector) leads, or both. Frequency modulation tape may be used for recording and storage. Since the computer deals with numbers only, an analog to digital converter is used to convert the electrocardiographic tracing or analog signal into a series of numbers or digits. Work in this area was originally done by Taback et aL2 and later extended by Stallman and Pipberger3 and Caceres et a1.4 Samples of the tracing are usually taken at intervals of 2 to 4 msec. The digitized values are read into the computer and are compared with the criteria of the analysis program. One computer program is used for wave recognition. A second is used to determine wave amplitudes and durations as well as various time intervals. Still another is used for rhythm analysis, as first developed by Bonner and Schwetman in 1968 but not available for routine use at that time.5 Actually, one structured multiphased program is used that identifies waves, performs the various measurements and analyzes rhythm and contour. Currently, most records are stored on tape or even disk, but improvements are needed, essentially for data compression or transformation into some yet to be perfected efficient storage medium. Although some comparison programs of serial tracings have been undertaken,6 more evaluation of such programs is needed and problems of storage and retrieval From the Division of Cardiology, St. Agnes and Lawrence Hospitals, Office of Consultant in Cardiology, International Business Machines, White Plains, N. Y. and the Department of Medicine, New York Medical College, New York, N. Y. Address for reprints: Charles A. Bertrand, MD, 170 Maple Ave., White Plains, N. Y.
394
September 1976
The American Journal of CARDIOLOGY
must be solved. The results of the last 16 years suggest that computer analysis of electrocardiograms is good for normal tracings and less good for tracings the computer labels abnormal. Without discussing sensitivity and specificity it is reasonable to state that, in our experience, when a computer interprets an electrocardiogram as normal it has a better than 95 percent probability of being correct, allowing for minor degrees of S-T segment deviation; this figure is in agreement with the data of Crevasse and Ariet.7 Since 1968, we have performed more than 100,000 multiphasic health testing examinations and in most subjects have recorded the electrocardiogram on tape for computer analysis. (Until July 1974 we used the Smith-Hyde vector-lead programs and since then have used the Bonner 12 lead program.g) In our experience, the computer tends to be accurate in interpreting normal tracings, but has at least a 1 in 3 chance of being partly or completely in error about tracings it labels abnormal. Yet its performance is better with some abnormal tracings. For example, when the computer interprets a left ventricular conduction disturbance or left bundle branch block, it is virtually always correct; in contrast, there is greater variability with a right ventricular conduction disturbance or right bundle branch block. Two major limitations to computer use are implied in these considerations: First, the computer’s low level of reliability in interpreting abnormal tracings limits its clinical usefulness since, in most hospitals, the majority of recorded electrocardiograms are abnormal. Second, the lack of a practical comparison program further limits routine clinical use. What then, is the present “place” of the computer in electrocardiographic interpretations? We may consider using computer analysis of the electrocardiogram in three areas: (1) screening programs, (2) the doctor’s office, and (3) in hospitals. (1) In screening programs, the computer probably functions at its highest level. Simply expressed, the computer may be used to sort out the normal from the abnormal. We recommend that the screening be followed with a sampling review procedure (at IBM, 10 percent of normal electrocardiograms and virtually all abnormal records are reviewed by cardiologists). We have found the computer to be very helpful and have arrived at a computer-assisted type of electrocardio-
Volume 36
EDITORIALS
graphic interpretation. lo Computer analysis is of value for sorting out normal tracings, giving precise time intervals and measurements and offering various diagnostic possibilities for the cardiologist’s consideration. I think, therefore, that computer analysis leads to both increased speed and increased accuracy in interpreting the electrocardiogram. (2) In the doctor’s office, there is a greater degree of variability. Ideally, a doctor who takes an electrocardiogram should be qualified to interpret it; if not, some other doctor or facility should be available for interpretation. Probably computer interpretation of the electrocardiogram has little practical application for the qualified physician who has a low to moderate volume of electrocardiograms to interpret. It may be more useful to the unqualified doctor, or for the doctor in a remote area where facilities for interpretation are not available. For example, telephone transmission of the electrocardiogram to a computer center may be utilized, with the interpretation relayed back to the attending physician. (3) Among hospitals, paradoxically, both the smallest and the largest institutions appear to be best suited for computer interpretation of electrocardiograms. The smallest hospitals are suitable because they may have no cardiologist available to interpret the tracings; in such a case, the electrocardiogram may be transmitted to a center by telephone line. Larger hospitals may have so large a volume of electrocardiograms that computer use is cost-justified. Intermediate-sized hospitals probably represent the exception because, presumably, they have qualified physicians available to interpret the electrocardiograms and the volume of tracings in most of these hospitals is probably insufficient to justify the cost of computers. For hospitals of all sizes, lack of a comparison program presents problems since not only are many electrocardiograms abnormal, but also in many hospitalized patients serial electrocardiograms are taken, thus further limiting the usefulness of computer interpretation. Furthermore, patients may be nervous or seriously ill, have tremors or postoperative bandages, or have other factors that could cause the recording of any electrocardiogram (and therefore input to the computer) to be suboptimal. Prospects for the future: Within 5 years I believe there will be a major development-considerable use
of the “stand-alone” unit, that is, a simple box containing a three channel electrocardiograph with an analog to digital converter to digitize the electrocardiographic signal and a dedicated minicomputer whose sole function will be to interpret the electrocardiogram. I can envision a 12 lead or a 3 orthogonal lead electrocardiogram with the interpretation printed on the tracing itself. This unit may be adequate for one tracing, but what about the complicated cases in which one tracing is abnormal and serial tracings are required? And what about physician review? Herein lies the major problem! Unless, and until, a practical, reliable comparison program is available and has been well tested and validated, the potential of computer interpretation of the electrocardiogram will be sharply limited. Instead of using “stand-alone units,” one may transmit the electrocardiographic signals directly to a computer center for processing or use a stand-alone unit with provision for transmitting to a computer center, thus allowing greater flexibility; but a comparison program will still be required. When the comparison and storage-retrieval problems have been resolved, we may then anticipate other problems, such as regionalization, possible use of Social Security numbers for identification, use of data banks and problems of program evaluation and selection (which program or programs to use and how to validate them). Other problems-those associated with use of the computer in exercise testing and rights of privacy of the patient-loom just over the horizon. Nonetheless, I believe that miniaturization will progress, a practical comparison program will be developed, extensive data banks will be established, and many other problems will be resolved, but the solutions will take years to accomplish. A competent cardiologist will always be needed to interpret the abnormal electrocardiogram. I doubt that the accuracy of the computer will ever be sufficiently great to permit its unaided use in interpreting a difficult arrhythmia. I can also envision problems related to time in comparison of electrocardiograms, problems of correlation with clinical events in a satisfactory manner. Hence we may anticipate the continued coexistence of cardiologists and computers in, I hope, a constructive way leading to greater speed and procession of electrocardiograms but, more importantly, ultimately to a higher quality of interpretation.
References 1. Caceres CA: Limitations of the computer in electrocardiographic interpretation. Am J Cardiol 38:362-376, 1976 2. Taback L, Marden E, Mason HL, et al: Digital recording of electrocardiographic data for analysis by a digital computer. IRE Trans Med Electronics 6:167-171, 1959 3. Stallman FW, Pipberger HV: Automatic recognition of electrocardiographic waves by digital computer. Circ Res 9: 1138-I 143, 1961 4. Caceres CA, Steinberg CA, Abraham S, et al: Computer extraction of electrocardiographic parameters. Circulation 25356-362, 1962 5. Bonner RE, Schwetman HD: Computer diagnosis of electrocardiograms. Ill. A computer program for arrhythmia diagnosis.
Comput Biomed Res I, 387-407. 1968 6. Pryor TA, Lindsay AE, England RW: Computer analysis of serial electrocardiograms. Comput Biomed Res 5709-714, 1972 7. Crevasse L, Arlet M: A new scalar electrocardiographic computer program. Clinical evaluation. JAMA 226:1089-1093, 1973 8. Smith RE, Hyde CM: A computer system for electrocardiographic analysis. Third Annual Rocky Mountain Bioengineering Symposium, Univ. Colorado, Boulder, May 2-3, 1966 9. Bonner RE, Crevasse L, Ferrer MI: A new computer program for analysis of scalar electrocardiograms. Comput Biomed Res 5: 629-653, 1972 10. Bertrand CA, Godbold EO, Duffy JC, et al: How the computer helps the cardiologist interpret ECG’s. Ind Med Surg 42:14-17, 1973
September 1976
The American Journal of CARDIOLOGY
Volume 38
395