Methodology of ECG interpretation in the AVA program.

The AVA program combines a thirty-year history with an approach that remains innovative; namely: multivariate statistical analysis on orthogonal ECG leads. Its diagnostic reference base includes only diagnoses independently verified by non-ECG criteria. The diagnostic module assesses probabilities of nine alternative disease categories, based on QRS-T parameters; or four other categories in case of conduction defects. Probabilities of left or right atrial overload are also computed. The program also recognizes wall injury, T-wave abnormalities, electrolyte disturbances, myocardial ischemia, and makes differential diagnoses between strain and digitalis effects. An arrhythmia classification module can generate any of 40 rhythm statements. Signal recognition is based on the spatial velocity function. The program has been translated to a microcomputer version.

Optimal lead subsets for reconstruction of QRS and ST-T in 35-lead precordial maps.

Precordial maps have been used for some 15 years to estimate the extent of myocardial injury in patients with acute anterior or lateral wall infarction. Estimates have been based on various QRS- and ST-T-derived parameters, including amplitude sum of ST elevations. Application of the electrodes, commonly 35, is cumbersome and time-consuming with the critically ill. A subset of 5 or 7 selected leads can be applied instead, and the remaining leads calculated from that subset with minimal loss of QRS and ST-T information. Maps were recorded from 100 patients within 72 hours of onset of anterior or lateral infarct. Optimal lead subsets for QRS and ST-T feature extraction were found by the sequential selection method of Lux. Subsets numbering between 2 and 15 leads were derived, with their lead-transform coefficients. Measures to estimate goodness of fit for reconstructed leads included correlations, error-to-signal ratios and root-mean-square errors. These measures were calculated separately over the QRS and ST-T complexes. Reconstructions from a 7-lead subset had a mean 0.92 correlation with ST-T in the original leads and root-mean-square error of only 0.04 mV. Sum of ST elevation differed by only 2% between original leads and reconstructions based on 5 or more leads. To confirm repeatability, lead-transform coefficients were also calculated from a training population of 50 patients and applied to the maps of the other 50.

The orthogonal electrocardiogram as risk indicator for the prediction of myocardial infarction and/or cardiac death.

In a prospective study on Coronary Heart Disease (CHD) orthogonal electrocardiograms (Frank) were recorded annually for ten years from 1,444 asymptomatic, middle-aged males with a mean age of 57.4 +/- 10.6 years. Cases with overt or suspected CHD were excluded. The purpose of the study was to identify risk indicators in electrocardiograms and to compare them with other known risk factors used for prediction of acute CHD events such as myocardial infarction (MI) and/or cardiac death (CD). Such acute events occurred in 88 cases. Pre-event ECGs of these acute events were compared with all others without events, using logistic regression analysis. Identified ECG risk indicators were then compared with other known risk factors such as smoking, blood pressure, cholesterol, age, weight, etc. The predictive power of the ECG, derived mainly from the ST-T complex, exceeded all others by a wide margin. The amplitude of the first 1/8 of the ST-T complex in lead x (similar to V5-V6) together with relative body weight proved best when one pre-event record was available. Prediction improved when ECG changes between two pre-event recordings were included. Precision of measurements by computer appeared essential for improvements in CHD prediction.

Scalar, planar, and spatial measurements of the Frank vectorcardiogram in normal infants and children.

Frank-lead vectorcardiograms (VCGs) were obtained from 1222 normal infants and children. By means of the Pipberger computer system, 176 different scaler and vector measurements obtained from each VCG were correlated with height, weight, race, sex, torso length, chest circumference, and chest diameters to determine the effect of anthropometric indices on the VCG wave forms. Because 5509 tests of statistical significance were performed, correlation coefficients and tests of statistical significance are reported only with p less than 0.001. Height, weight, torso length, and chest circumference show good correlation with QT interval, but these findings are reflective of the decrease in heart rate with age. The VCG does not show consistent correlations with constitutional variables when stratified by age, sex, or race. There were six instances of VCG parameters significantly greater in black children, and four instances of VCG parameters significantly greater in white children. All racial differences, while statistically significant, are small by clinical, hand measurement standards. There were 22 VCG values in boys which exceeded those in girls and only one VCG value in girls which exceeded those in boys. In the pediatric age group, racial differences in VCG wave forms are small and clinically insignificant. The Frank-lead system adequately corrects for constitutional variables in infants and children. Adequate evaluation of pediatric VCGs requires stratification of data according to age and sex.

Year-to-year variation of the orthogonal electrocardiogram and vectorcardiogram among 243 normal white males.

When assessing patients' serial ECG changes, the clinician implicitly compares those changes to the limits of change expected in a healthy population. Prospective epidemiological studies, too, develop their criteria from the limits of normal serial ECG changes. Surprisingly then, few studies have reported normal limits for changes between serial ECGs taken six months or longer apart, and all are based on small samples. The present study has a large sample size: 243 white middle-aged and older males, after exclusions for heart disease. Each had at least four consecutive annual examinations with ECGs. Limits of serial variability were computed for 52 measurements. The ECG measurements included durations, amplitudes, ratios, angles and spatial magnitudes. Clinical measurements included blood pressure, cholesterol relative weight and hemoglobin. Year-to-year ECG variabilities were compared to day-to-day variabilities of the same measurements reported earlier. Year-to-year variation was virtually identical to the reported day-to-day variation in most measurements. In only two measurements was year-to-year variation over 25% greater than the reported day-to-day variation.

A new microcomputer-based ECG analysis system.

A new automated ECG system using advances in microprocessor technology and computerized electrocardiography is described. This microcomputer-based system is self-contained and mobile. It acquires both the 12-lead and orthogonal lead (Frank) electrocardiograms and analyzes the latter within minutes. Software includes the program developed in the Veterans Administration which uses advanced statistical classification techniques and a large well-documented patient data base. Diagnostic probabilities are computed using a Bayesian approach. Diagnostic performance has been tested using independent clinical criteria and found to be quite accurate. This system enables the clinician to immediately review the computer's identifications, measurements, and diagnostic classifications and quickly use these results in clinical decision making. Serial comparisons are readily made since all previous recordings are stored on floppy diskettes. The use of microprocessors in this system makes it economically feasible for practicing physicians.

The impact of an ECG computer analysis program on the cardiologist's interpretation. A cooperative study.

Nine experienced electrocardiographers and the ECG computer program developed in the Veterans Administration (AVA 4.0) were evaluated against ECG-independent evidence of 180 patients' true diagnoses. A cross section of cardiac abnormalities was included. Each reader was given the 12-lead and orthogonal 3-lead ECG. The impact of ECG computer reports on the interpretations by the nine readers was evaluated by comparing their interpretations before and after the addition of a computer report. Using only high probability statements, the average accuracy of ECG diagnosis by the nine readers was 54%. It increased to 62% when the computer report was added. Computer interpretation was correct in 76%. It was shown that the Bayesian classification method together with multivariate analysis, used in the VA program, are mainly responsible for the improvement in diagnostic accuracy.

The electrocardiogram in epidemiologic investigations. A new classification system.

A new coding system for ECG abnormalities was developed, based on Frank's orthogonal ECG leads. In contrast to other systems, such as the Minnesota Code (MC), the new system was based on data collected prospectively in a cooperative study of 5031 records. The records were classified solely on the basis of non-ECG information. A record sample from normal women was also available. The large data base allowed stratification of ECG criteria according to sex and race. ECG criteria were determined at two levels of sensitivity and specificity. Specificity was 80-100% at the first level and 90-90% at the second. The new system has fewer criteria than other codes, which leads to reduction of coding errors and coding time. For common problems in differential diagnosis, optional criteria were included. A computer program for automated coding was also developed.

Q-wave abnormalities in chronic obstructive pulmonary disease and myocardial infarction.

ECGs taken from patients with chronic obstructive pulmonary disease (COPD) frequently mimic myocardial infarction (MI), and may, therefore, cause diagnostic difficulties for the physician. In many previous studies, criteria to differentiate electrocardiographically between COPD and MI were either untested in large numbers of cases or too complicated for routine use. This study was undertaken to find simple new criteria, using scalar measurements which are easily obtainable in clinical practice. To assure the stability and repeatability of our results, the accuracy of these criteria was tested in a large series of cases. Three-hundred and ninety-six (396) cases of COPD and eight-hundred and seventy-eight (878) cases of MI comprised the material for this study. The COPD cases were grouped into two: a training set of 266 cases and a test set of 130 cases. There were three MI subgroups: AMI-344 cases, PDMI-449 cases, and LMI-85 cases. By applying the proposed ECG criteria specifically on the "COPD--MI mimics," we were able to reduce the number of potentially mis-diagnosed COPD cases (based purely on Q-wave abnormality) from 158 cases (40% of all COPD cases) to 71 cases (18%).

Critical evaluation of the twin peaked P wave ("pseudo-P mitrale") in orthogonal electrocardiograms.

The present study was performed to evaluate the specificity of twin peaked P wave (TWPP) for left atrial overload (LOA) in orthogonal ECGs. A total of 2093 ECGs recorded with Frank's corrected orthogonal leads were used for analysis. It can be concluded from the present study that (1) TWPP is diagnostically non-specific and its mere existence cannot imply the existence of LAO, and (2) a time interval between the beginning of the P wave and the second peak in lead Y of more than 76 msec, is the most useful parameter available for identifying LAO, especially mitral value disease.

Performance of conventional orthogonal and multiple-dipole electrocardiograms in estimating left ventricular muscle mass.

For estimating left ventricular mass (LVM), ECG criteria for left ventricular hypertrophy (LVH) were selected from conventional 12-lead ECGs, orthogonal three-lead ECGs, and multiple-dipole ECGs (MDECG). The three cardiograms were recorded in 139 patients for whom the degree of LVH was independently determined from biplane ventriculograms. Tested ECG criteria included Sokolow-Lyon measurements for the 12-lead ECG; for the orthogonal ECG, maximal QRS magnitude in the horizontal plane, R duration in the z-lead and Jxyz (spatial magnitude of point J); and for the 126 leads of the MDECG, the dipole activity (DA) of the septum and the free left ventricular wall. Correlation coefficients between LVM and the 12-lead ECG, three-lead ECG and MDECG were 0.61, 0.78 and 0.89, respectively, with corresponding errors of estimated LVM of 103, 82 and 60 g. More complex recording and analytic methods clearly led to increased accuracy in LVM estimates. However, the large error of estimate may limit practical applicability of such correlations. For classification of subjects into normal and above-normal categories, a likelihood ratio was also used and led to a maximum performance index of 86% with MDECG measurements.

Effects of electrode area on electrocardiographic voltages.

Effects of two different sizes of chest electrodes--100 and 750 mm2 area--on x and z Frank leads were determined using electrocardiographic data from 25 subjects. In most cases, differences in Rx and Rz were below 50 uV, but in nine cases (36%) differences exceeded this value for either Rx or Rz or both. In six cases, differences exceeded 100 uV. For an additional 20 subjects, standard precordial leads were recorded using the same two electrode sizes. QRS amplitudes were significantly affected for V4 but not for V1 or V6. Variability caused by electrode size is greater than that caused by beat-to-beat variation and is comparable to that found in day-to-day variation. Interchangeability of data among ECG recording laboratories can be significantly improved by standardizing electrode size for precordial electrodes.

Electrode position effects on Frank lead electrocardiograms.

Frank lead electrocardiograms were recorded from 149 normal and abnormal adult males using four different electrode placements. All chest electrodes were placed at: (1) the fourth intercostal space level, (2) the fifth intercostal space level, (3) the fourth intercostal space level with V4 substituted for C, and (4) the fifth intercostal space level with V4 substituted for C. Differences in mean values of many commonly used amplitudes and orientations were not statistically significant among the four recording methods, but amplitude differences for individual subjects were often large and difficult to predict. When V4 is substituted for C, as commonly done in some laboratories, Rx decreased and Rz increased by more than 10 per cent in about 40 per cent of the cases. In about 70 per cent of the cases, Rx and Rz changed significantly when electrode level was shifted from the fifth to the fourth intercostal space. For these 70 per cent, it does not appear possible to accurately predict increase or decrease of Rx, Rz, or QRSm. Analysis programs which depend on individual amplitude measurements are likely to be significantly affected by electrode placement. It is suggested that criteria for analysis programs developed using a specified version of the Frank system should ideally be applied only to electrocardiograms recorded in the same manner.