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Distinguishing sinus from paroxysmal tachycardia by rate of onset
ABSTRACTS
Distinguishing Sinus F r o m P a r o x y s m a l Tachycardia by R a t e of Onset J. Brown, E Gillette, T. Goh and R. Arzbaecher. Pritzker Institute of Medical Engineering, Illinois Institute of Technology, Chicago, IL It is commonly held that sinus tachycardias have a gradual increase in rate while pathological tachycardias exhibit sudden, paroxysmal increases in rate. The concept of using suddenness of onset as an identifying criterion is very appealing and has been incorporated into several arrhythmia detection algorithms Two such algorithms were tested using 17 sinus tachycardia records from children riding the Skyscreamer at Houston's Astroworld amusement park and 17 paroxysmal tachycardia records from electrophysiology studies. One algorithm was developed by us {ONSET} and the other by Intermedics (INTERTACH}. Both initially detect a tachycardia by detecting a sustained run of fast heart beats. ONSET averages the last four pre-tachycardia cycle lengths and compares each of the first four intervals in fhe tachycardia to that average. Paroxysmal tachycardia is diagnosed if a programmable number {1 to 4) of the first four tachycardia intervals is shorter by 25% or more than the pre-tachycardia average. INTERTACH compares the first tachycardia interval to the previous two cycle lengths. If the first tachycardia interval is shorter than either of the two preceding ones by a preset difference (100, 200 or 300 msec) then paroxysmal tachycardia is assumed. ONSET had a sensitivity and specificity of 88% {criterion: 4 intervals); sensitivity increased but specificity decreased as the criterion was lowered. INTERTACH had a sensitivity of 88% and a specificity of 79% (criterion: 100 ms); sensitivity decreased and specificity slightly increased as the criterion was increased. Neither algorithm is entirely adequate in separating sinus tachycardia from paroxysmal tachycardiv. Our conclusion is that, because of the overlap in onset rates between sinus and paroxysmal tachycardias, suddenness of onset will not be sufficiently accurate for distinguishing one from the other in most cases. This work was supported in part by USPHS Grant No. HL35554.
Serial Comparison in the Glasgow ECG Analysis Program. Peter W. Macfarlane, Marion Podolski. University Department of Medical Cardiology, Royal Infirmary, Glasgow, Scotland. Methods for comparison of serial electrocardiograms were introduced in our laboratory in the early 1970s based on the XYZ orthogonal lead ECG. The method has now been extended to incorporate the 12-1ead ECG but the basic concept of utilizing the minimum of data to store findings and undertake a comparison is still retained. The current ECG can be compared with up to 3 previous ECGs including the first and the two most recent in a series. 140 bytes of data are used for each ECG. For rhythm and conduction defects, statement codes are stored. Hence serial analysis is based on their comparison. On the other hand, for myocardial infarction a more complex use of the stored record is adopted. Individual bits and bytes of part of this record are used to describe the location, severity and age of an infarct and in addition, various amplitudes including those of the ST and T wave am stored. Thus, for myocardial infarction, serial comparison is based on a study of ST-T amplitude shift as well as changes in severity of findings. Similar concepts apply to ST-T changes in the absence of Q waves. The main diagnostic logic incorporates the serial comparison so that relevant statements are embodied in the ECG report and are not appended at the end of the interpretation. A statement
d. ELECTROCARDIOLOGY 19 (3), 1986
309
such as '~quential changes of inferior infarction" is typical of a comparison output. It is felt that this approach is the optimum method in terms of requiring limited storage yet providing ease of incorporation of comparisons into the program. The statements produced am similar to those of a cardiologist and the technique is rapid since it avoids repeating the analysis of previous ECGs. The basic concept outlined above has been incorporated into the MINGOCARE system available through Siemens-Elema.
Determination of ECG Sampling Rates Based on Measurement Accuracy Chr. Zywietz, Biosignal Processing, Medical School Hannover, Germany. Since the beg4n~ng of digital processing the sampling rate of ECGs has been subject to discussion. Sampling rates from 200Hz up to 10,000Hz have been reported; most common are sampling frequencie~ of 250 and 500Hz. For theoreticaland practicalreasons the determination of the upper frequency content of ECGs, and from this determination of sampling rates, is somewhat arbitrary. W e have developed a straightforward approach: the reconstruction error for analytically given elementary wave forms, such as triangle,parabolic arc,and approximate bell shaped cos2cot functions has been investigated after digitization. The difference between the original function and its digitalrepresentation has been calculated at various sampling rates and at systematically shifted sampling phases. Linear, Fourier and 3rd order spline interpolation were applied for wave form reconstruction. The major result is a nomogram which allows the determination of the sampling rate dependent on wave duration and on acceptable reconstruction (or measurement} error. Given a wave of duration T [ms], and an acceptable measurement error PE [%] of the peak amplitude the sampling interval S [ms] can be estimated by PE 0.833 For a wave duration of 20ms and an acceptable PE error of 10% one obtains for S < 2.44 ms. TOkeep the error below 10% of the waves peak amplitude sampling intervals should be smaller than ~-~ of the duration of the {minimum} wave to be measured. It can be concluded that for measurement of small Q-waves as well as of pediatric ECGs sampling rates should be at least 500 samples/sec.
New Electrocardiographic Criteria for Tricyclic Antidepressant Cardiotoxicity: Bayes' Theorem Applied to Clinical Electrocardiography. J. T. Niemann, M. M. Laks, H. A. Bessen, R. J. Rothsteln Harbor-UCLA Medical Center, Torrance, California. The tricyclicantidepressants (TCA) alter cardiac automaticity and conduction and are clinicallyrelevant because they are the third most c o m m o n cause of drug-related death. To determine if T C A cardiotoxicity is characterized by distinctive and potentially diagnostic E C G changes, 25 patients suspected of T C A overdose were studied. In 11 patients, TCA" toxicologic assays were positive {+TCA, Group I);in the remaining 14, toxicologic assays were negative {-TCA, Group 2). O n admission, Group I had a significantly greater heart rate {117+-23/rain vs 100--.22, p<0.05), Q R S duration {103--_15 msec vs 87--.10, p<0.005), and corrected Q T interval (449_*38 msec vs 418--.36 msec, p<0.05) than Group 2. These + T C A patients also had a more rightward terminal 40 msec frontal plane Q R S Vector {195_.51" vs 54 _ 64; p<0.001). A terminal Q R S Vector of 130-270" had a positive and negative predictive value of 1.0 in discriminating between Group I and Group II patients on admission. Normalization of the terminal Q R S Vector occurred
Distinguishing Sinus F r o m P a r o x y s m a l Tachycardia by R a t e of Onset J. Brown, E Gillette, T. Goh and R. Arzbaecher. Pritzker Institute of Medical Engineering, Illinois Institute of Technology, Chicago, IL It is commonly held that sinus tachycardias have a gradual increase in rate while pathological tachycardias exhibit sudden, paroxysmal increases in rate. The concept of using suddenness of onset as an identifying criterion is very appealing and has been incorporated into several arrhythmia detection algorithms Two such algorithms were tested using 17 sinus tachycardia records from children riding the Skyscreamer at Houston's Astroworld amusement park and 17 paroxysmal tachycardia records from electrophysiology studies. One algorithm was developed by us {ONSET} and the other by Intermedics (INTERTACH}. Both initially detect a tachycardia by detecting a sustained run of fast heart beats. ONSET averages the last four pre-tachycardia cycle lengths and compares each of the first four intervals in fhe tachycardia to that average. Paroxysmal tachycardia is diagnosed if a programmable number {1 to 4) of the first four tachycardia intervals is shorter by 25% or more than the pre-tachycardia average. INTERTACH compares the first tachycardia interval to the previous two cycle lengths. If the first tachycardia interval is shorter than either of the two preceding ones by a preset difference (100, 200 or 300 msec) then paroxysmal tachycardia is assumed. ONSET had a sensitivity and specificity of 88% {criterion: 4 intervals); sensitivity increased but specificity decreased as the criterion was lowered. INTERTACH had a sensitivity of 88% and a specificity of 79% (criterion: 100 ms); sensitivity decreased and specificity slightly increased as the criterion was increased. Neither algorithm is entirely adequate in separating sinus tachycardia from paroxysmal tachycardiv. Our conclusion is that, because of the overlap in onset rates between sinus and paroxysmal tachycardias, suddenness of onset will not be sufficiently accurate for distinguishing one from the other in most cases. This work was supported in part by USPHS Grant No. HL35554.
Serial Comparison in the Glasgow ECG Analysis Program. Peter W. Macfarlane, Marion Podolski. University Department of Medical Cardiology, Royal Infirmary, Glasgow, Scotland. Methods for comparison of serial electrocardiograms were introduced in our laboratory in the early 1970s based on the XYZ orthogonal lead ECG. The method has now been extended to incorporate the 12-1ead ECG but the basic concept of utilizing the minimum of data to store findings and undertake a comparison is still retained. The current ECG can be compared with up to 3 previous ECGs including the first and the two most recent in a series. 140 bytes of data are used for each ECG. For rhythm and conduction defects, statement codes are stored. Hence serial analysis is based on their comparison. On the other hand, for myocardial infarction a more complex use of the stored record is adopted. Individual bits and bytes of part of this record are used to describe the location, severity and age of an infarct and in addition, various amplitudes including those of the ST and T wave am stored. Thus, for myocardial infarction, serial comparison is based on a study of ST-T amplitude shift as well as changes in severity of findings. Similar concepts apply to ST-T changes in the absence of Q waves. The main diagnostic logic incorporates the serial comparison so that relevant statements are embodied in the ECG report and are not appended at the end of the interpretation. A statement
d. ELECTROCARDIOLOGY 19 (3), 1986
309
such as '~quential changes of inferior infarction" is typical of a comparison output. It is felt that this approach is the optimum method in terms of requiring limited storage yet providing ease of incorporation of comparisons into the program. The statements produced am similar to those of a cardiologist and the technique is rapid since it avoids repeating the analysis of previous ECGs. The basic concept outlined above has been incorporated into the MINGOCARE system available through Siemens-Elema.
Determination of ECG Sampling Rates Based on Measurement Accuracy Chr. Zywietz, Biosignal Processing, Medical School Hannover, Germany. Since the beg4n~ng of digital processing the sampling rate of ECGs has been subject to discussion. Sampling rates from 200Hz up to 10,000Hz have been reported; most common are sampling frequencie~ of 250 and 500Hz. For theoreticaland practicalreasons the determination of the upper frequency content of ECGs, and from this determination of sampling rates, is somewhat arbitrary. W e have developed a straightforward approach: the reconstruction error for analytically given elementary wave forms, such as triangle,parabolic arc,and approximate bell shaped cos2cot functions has been investigated after digitization. The difference between the original function and its digitalrepresentation has been calculated at various sampling rates and at systematically shifted sampling phases. Linear, Fourier and 3rd order spline interpolation were applied for wave form reconstruction. The major result is a nomogram which allows the determination of the sampling rate dependent on wave duration and on acceptable reconstruction (or measurement} error. Given a wave of duration T [ms], and an acceptable measurement error PE [%] of the peak amplitude the sampling interval S [ms] can be estimated by PE 0.833 For a wave duration of 20ms and an acceptable PE error of 10% one obtains for S < 2.44 ms. TOkeep the error below 10% of the waves peak amplitude sampling intervals should be smaller than ~-~ of the duration of the {minimum} wave to be measured. It can be concluded that for measurement of small Q-waves as well as of pediatric ECGs sampling rates should be at least 500 samples/sec.
New Electrocardiographic Criteria for Tricyclic Antidepressant Cardiotoxicity: Bayes' Theorem Applied to Clinical Electrocardiography. J. T. Niemann, M. M. Laks, H. A. Bessen, R. J. Rothsteln Harbor-UCLA Medical Center, Torrance, California. The tricyclicantidepressants (TCA) alter cardiac automaticity and conduction and are clinicallyrelevant because they are the third most c o m m o n cause of drug-related death. To determine if T C A cardiotoxicity is characterized by distinctive and potentially diagnostic E C G changes, 25 patients suspected of T C A overdose were studied. In 11 patients, TCA" toxicologic assays were positive {+TCA, Group I);in the remaining 14, toxicologic assays were negative {-TCA, Group 2). O n admission, Group I had a significantly greater heart rate {117+-23/rain vs 100--.22, p<0.05), Q R S duration {103--_15 msec vs 87--.10, p<0.005), and corrected Q T interval (449_*38 msec vs 418--.36 msec, p<0.05) than Group 2. These + T C A patients also had a more rightward terminal 40 msec frontal plane Q R S Vector {195_.51" vs 54 _ 64; p<0.001). A terminal Q R S Vector of 130-270" had a positive and negative predictive value of 1.0 in discriminating between Group I and Group II patients on admission. Normalization of the terminal Q R S Vector occurred