Computer analysis of the orthogonal electrocardiogram and vectorcardiogram in 257 patients with aortic valve disease.

In most electrocardiographic studies of left ventricular hypertrophy the hypertrophy has had different causes. This study examined the performance of the Frank orthogonal electrocardiogram in 257 patients with aortic valve disease, 90 with predominant aortic stenosis and the remaining 167 with predominant aortic insufficiency. Optimal measurements suggested for routine electrocardiographic diagnosis of left ventricular overload resulted in recognition of 64 percent of cases of aortic stenosis and 74 percent of cases of aortic insufficiency with a 6 percent false positive rate. Multivariate analysis techniques improved performance: 82 percent of the aortic stenosis records and 78 percent of the aortic insufficiency records were correctly recognized as showing left ventricular overload; the false positive rate was 5 percent. Although many electrocardiographic measurements were significantly correlated with the aortic valve gradient, correlations were not high enough for use in predicting the severity of the aortic stenosis. Comparison of electrocardiographic variables in aortic stenosis and aortic insufficiency demonstrated a wide overlap between groups, and the electrocardiographic changes of aortic stenosis could not be differentiated from those of aortic insufficiency.

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.

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.

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.

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.

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.

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.

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.