Hanna A. Pipberger

Clinical application of a second generation electrocardiographic computer program

An electrocardiographic computer program based on multivariate analysis of orthogonal leads (Frank) was applied to records transmitted daily by telephone from the Veterans Administration Hospital, West Roxbury, Mass., to the Veterans Administration Hospital, Washington, D. C. A Bayesian classification procedure was used to compute probabilities for all diagnostic categories that might be encountered in a given record. Computer results were compared with interpretations of conventional 12 lead tracings. Of 1,663 records transmitted, 1,192 were selected for the study because the clinical diagnosis in these cases could be firmly established on the basis of independent, nonelectrocardiographic information. Twenty-one percent of the records were obtained from patients without evidence of cardiac disease and 79 percent from patients with various cardiovascular illnesses. Diagnostic electrocardiographic classifications were considered correct when in agreement with documented clinical diagnoses. Of the total sample of 1,192 recordings, 86 percent were classified correctly by computer as compared with 68 percent by conventional 12 lead electrocardiographic analysis. Improvement in diagnostic recognition by computer was most striking in patients with hypertensive cardiovascular disease or chronic obstructive lung disease. The multivariate classification scheme functioned most efficiently when a problem-oriented approach to diagnosis was simulated. This was accomplished by a simple method of adjusting prior probabilities according to the diagnostic problem under consideration.

Analysis of the Normal and Abnormal Vectorcardiogram in Its Own Reference Frame

Vectorcardiograms from 296 patients with a variety of ECG abnormalities were compared with normal standards obtained from 249 subjects without evidence of heart disease. A reference frame based on the spatial orientation of QRS loops rather than on conventional plane projections was used. Burgers polar vector and Schellongs QRS plane form the main parameters of such a reference frame. Spatial QRS orientation is defined by one term, the polar vector, which is perpendicular to the QRS plane. The direction of this vector can be determined through rotation of the QRS loop into its principal plane by means of a VCG lead resolver. Further analysis of QRS in its principal plane then becomes independent of inter-individual variability in spatial QRS direction. Separation between normal and abnormal was used as an indicator for the diagnostic quality of various measurements. Two corrected orthogonal lead systems designed by Schmitt and Frank were used for the study. These systems did not differ appreciably in the extent of normal ranges nor in the discrimination between normal and abnormal. The polar vector appeared as the best indicator for abnormalities. In 65 per cent of the pathologic cases this parameter was found outside normal limits. Measurements derived from the contour and principal axes of QRS planes improved the recognition rate for abnormalities. Ratios expressing the degree of QRS planarity, however, contributed little to diagnostic accuracy. The QRS-T angle obtained in the QRS plane improved the recognition rate mainly in the series with ventricular hypertrophies. It could be demonstrated that without evaluation of time and voltage criteria between 85 and 100 per cent of all pathologic records could be recognized as abnormal when the vectorcardiograms were analyzed in their own reference frame. Thus, it appeared that this method of analysis has a considerable diagnostic potential and compares favorably with those used more commonly in clinical electrocardiography and vectorcardiography.

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.

Display and analysis of electrocardiographic data

Abstract A review of the most common types of electrocardiographic display and analysis, including those developed more recently, was given. Advantages and disadvantages of scalar lead recordings, vector loop displays, curves of spatial magnitude, orientation and velocity, polar vectors and Eigenvectors were evaluated. Analysis of data from these displays was compared with analysis by digital computer, which is based almost exclusively on numerical terms. Since graphic display of numerical operations proved impractical, the question was raised, whether or not display of electrocardiographic data represents an unnecessary restraint for efficient analysis. A new method of differential electrocardiography is described. It is based on computed ranges of various diagnostic entities. Leads which discriminate best between diagnostic groups can be obtained by resolution of orthogonal leads. Some of the results of large scale computations can thus be incorporated in routine electrocardiography. Quantitative comparison of various analytical procedures showed a marked superiority of spatial parameters over scalar leads recorded in sequence. Rates of diagnostic recognition were best when a series of instantaneous vectors was available for QRS, S-T and T. The ventricular gradient, polar vectors, Eigenvectors and curves of spatial magnitude, orientation and velocity were found less efficient for diagnostic classification.

The electrocardiogram in epidemiologic investigations. A new classification system.

A new coding system for ECG abnormalities was developed, based on Franks 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.

Computer analysis of changes in frank vectorcardiograms of 666 normal infants in the first 72 hours of life

Frank vectorcardiograms (VCGs) were collected on magnetic tape for 666 normal newborn infants at 1, 6, 12, 24, 36, 48, 60, and 72 hours after birth and analyzed by computers. The final total included 1,337 VCGs for white babies and 413 for blacks. No previous report has been made for the normal neonate with such a large sample, and no previous substantiation exists of possible age or sex differences at this early age. This study establishes a statistically significant change in vectorcardiographic patterns over the first three days, specifically in the measurements P duration, QRS duration, maximal spatial QRS amplitude, S in lead x, and T in lead z, as well as for several time-normalized QRS vectors. (P less than or equal to .005.) Racial differences were significant for T waves in lead z. This study supports the use of vectorcardiographic standards sensitive to the age of the newborn as well as to race.

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.

Computer analysis of ventricular conduction defects.

Computer criteria for LAHB and LPHB were described together with limits of normal for ortogonal leads. These differ significantly from those used for conventional 12-lead ECG, indicating the need for specific LAHB and LPHB criteria in orthogonal electrocardiography. Multivariate analysis with a likelihood ratio test was used for the separation of records with conduction defects with and without MI. The total number of records was 847. The recognition rate for MI in the presence of LVCD was 66%. In the presence of RVCD, MI was diagnosed correctly in only 55%. This relatively poor result was probably due to the relatively large number of combinations of RCVD with LAHB or LPHB.