Fred Kornreich

Effect of electrode positioning on ECG interpretation by computer

The aim of this study was to assess the variability in automated electrocardiogram (ECG) interpretation due to electrode positioning variations. Such variations were simulated by using a set of 746 body surface potential mappings from apparently healthy individuals and patients with myocardial infarction or left ventricular hypertrophy. Four types of electrode position changes were simulated, and the effect on ECG measurements and diagnostic classifications was determined by a computer program. At most 6% of the cases showed important changes in classification for longitudinal shifts. Transversal shifts causes less than 1.5% of important changes. An expert cardiologist, who analyzed a subset of 80 cases, agreed with the computer in 38 of 40 cases in which it made no change. In the 40 cases with large diagnostic changes, the cardiologist made no change in 18 cases. The effect of electrode position changes on ECG classification by an expert cardiologist was about half of the effect determined by computerized ECG classification. The effects on classification are significant; therefore, correct placement of chest electrodes remains mandatory.

Improved prediction of left ventricular mass by regression analysis of body surface potential maps

Electrocardiographic left ventricular (LV) hypertrophy involving ST-T abnormalities, in addition to high QRS voltages, is associated with increased risk of cardiovascular disease mortality. Unfortunately, conventional electrocardiographic criteria have limited utility in the quantitative assessment of LV hypertrophy. Body surface potential maps, which contain diagnostic information not present in commonly used lead systems, were recorded from 117 thoracic sites and 3 limb electrodes in 72 normal subjects and 84 patients with LV hypertrophy. Multiple regression analysis was performed separately for 54 women and 102 men on 120-lead data, using as features instantaneous voltages on time-normalized P, PR, QRS and ST-T waveforms. Leads and features for optimal prediction of echocardiographically determined LV mass were selected. A total of 6 features from 3 torso sites in men, and from the same 3 sites plus 2 others in women, yielded correlations between echocardiographic and electrocardiographic estimates of LV mass of 0.89 and 0.88, respectively. The standard errors of the estimate (SEE), or average errors in predicting LV mass from the regression equations, were 31 and 22 g, respectively. The single most potent predictor in both sexes was a mid-QRS voltage measured on a lead positioned 10 cm below V1; QRS duration, late QRS and early-to-mid T-wave amplitudes recorded in the lower left flank contributed significantly to the performance of both regression models. The optimal electrode sites for electrocardiographic prediction of LV mass were outside the conventional lead locations.(ABSTRACT TRUNCATED AT 250 WORDS)

Interpolation of body surface potential maps

The performance of four methods for interpolation of body surface potential maps (BSPMs) for different electrode grid densities was assessed. This study is part of a research project on the influence of the variability of 12-lead electrocardiograms on computer interpretation due to small electrode position changes. Interpolated BSPMs can be used to simulate this variability. The set of BSPMs studied, derived from a 117-electrode grid with relatively many electrodes on the left precordial part of the thorax, consisted of 232 cases without abnormalities, 277 with infarction, and 237 with left ventricular hypertrophy. The interpolation methods used were fast Fourier transforms, Chebyshev polynomials, linear functions, and cubic splines (CS). In the horizontal plane, a reference signal was first interpolated and, thereafter, resampled using 11 different sets of electrodes with the number of electrodes ranging from 18 down to 8. In the vertical direction, five grids with electrodes only on the front of the thorax and nine grids with electrodes on the front and back were examined. As a performance measure for interpolation, mean absolute error (MAE) was used: the absolute differences between the reference signal and the interpolated signal, averaged over the QRS on all maps. All methods showed deteriorating performance for decreasing grid density. In the horizontal direction, CS proved to be slightly superior to other methods for the left precordial electrodes for all but the densest grid (e.g., MAE = 22.8 microV vs MAE > 24.8 microV for a 12-electrode grid). For electrodes not in that area, CS performed the best as well (MAE = 16.1 microV for the same grid), with differences with the other methods being small (MAE > 16.4 microV). In the vertical direction, CS showed the best results on the front, both for the dense nonperiodic (MAE = 19.1 microV vs MAE > 26.6 microV for a 6-electrode grid) and periodic grids (MAE = 25.1 microV vs MAE > 26.6 microV for a 12-electrode grid). Linear functions performed best for sparse nonperiodic grids and sparse periodic grids for electrodes on the back, with the difference with CS for the last case being small. The method CS performed best overall, and is recommended for interpolating BSPMs.

QRST changes during and after percutaneous transluminal coronary angioplasty

This study reports preliminary results on 45 patients who underwent percutaneous transluminal coronary angioplasty (PTCA); 120-lead data (including the 12-lead standard electrocardiogram [ECG]) were recorded before, during, and after balloon inflation. Twenty-one patients underwent PTCA for left anterior descending coronary disease, 13 for right coronary artery disease, and 10 for left circumflex; 1 patient had combined left anterior descending and right coronary artery disease. In each patient, voltage data recorded during the various phases of the procedure were compared with the patients own baseline data. In 18 patients, 120 leads were also recorded 24 hours after PTCA. In this study, the usefulness of the standard 12-lead ECG was investigated in locating the coronary artery being occluded, in elucidating the mechanisms of the QRS changes, and in identifying changes occurring 24 hours after completion of the procedure. Results indicate that the observation of ST elevation in the 12-lead ECG may lead to ambiguous interpretation. Also, limiting observation to ST-T patterns alone instead of including QRS changes further hampers correct identification of the involved vessel. QRS modifications during inflation are interpreted as conduction disturbances, although other mechanisms are evoked: study of surface maps may contribute to the understanding of these mechanisms. Changes present 24 hours later are visible in the standard leads, but again, in the absence of the thoracic potential distribution, these are difficult to interpret. These changes were different from those observed after cessation of inflation at the end of the procedure. It is hypothesized that next-day changes may reflect reperfusion injury and/or represent myocardial stunning. Presence of injury and reversibility of changes require further investigation. Also, biochemical markers such as creatine kinase-MB mass, creatine kinase-MB activity, myoglobin, and troponin-T may help elucidate the significance of these findings.

Effective extraction of diagnostic ECG waveform information using orthonormal basis functions derived from body surface potential maps

A common basis of orthogonal waveform functions was derived from 128 lead body surface potential maps of 405 subjects. Twelve such orthogonal functions or frames were adequate for reconstruction of original ECGs from the beginning of QRS to the end of T. A larger number of frames (18) was required when basis functions were derived separately for QRS (10) and ST-T segments (8). Diagnostic information content of the coefficients of the orthogonal basis functions was evaluated in comparison with Minnesota Code criteria for myocardial infarction and with a more advanced multivariate ECG analysis program (Pipberger Program). This was done by deriving a linear discriminant function for separating normals from ECGs of patients with myocardial infarction and testing the discriminant in a different test population of infarcts and normals. The diagnostic accuracy of orthogonal basis functions was as good as that of Pipbergers program and considerably better than that of the Minnesota Code. The classification method described is insensitive to noise and errors in detecting QRS and T wave onsets and offsets or in selecting proper baseline for amplitude measurements. The robustness and enhanced classification stability with respect to noise and minor wave detection errors is a potential advantage particularly in serial ECG comparison.

Supplemented standard 12-lead electrocardiogram for optimal diagnosis and reconstruction of significant body surface map patterns

In this study, based on 120-lead body surface potential maps (BSPMs), we explored the improvement in electrocardiogram (ECG) diagnosis obtained by adding additional leads and using estimation of unmeasured leads. We found that adding a few leads observed to be optimal for diagnosis or signal capture combined with the existing 12-lead ECG improves diagnostic performance. Separately, using reconstruction (estimation) of BSPMs and using diagnostic criteria derived for maps also improve diagnostic performance over that provided by the recorded 12-lead ECG alone. Combining these 2 ideas, namely, addition of optimal leads and estimation of BSPMs improves performance even more.

Location and magnitude of ST changes in acute myocardial infarction by analysis of body surface potential maps

ST-segment changes in acute myocardial infarction (MI) are attributed to injury currents generated by acutely ischemic cardiac tissue. Electrodes directly overlying the injured zone usually record ST-segment elevation while those positioned in opposite areas of the torso show secondary or reciprocal ST depression (“mirror images”). Detection of ST changes depends on the characteristics of the lesion (age, size, location, orientation, intensity) and, particularly, on the electrode placement used to record the surface electrocardiographic (ECG) signals. The standard 12-lead ECG is the most commonly used and easiest noninvasive method for deciding those patients who are eligible for thrombolytic therapy. For patients to be included in the treatment protocol, several criteria are required: acute typical chest-pain of ischemic origin, elevated heart-specific enzymes, and diagnostic ST elevation on admission. ’ Unfortunately, large areas of the thoracic surface are left unexplored by the standard electrode positions, particularly the posterolateral, posterior, and basal portions of the left ventricle, as well as the entire right ventricle. As a consequence, patients with ST elevation in areas not interrogated by the conventional electrodes will not be included in the protocol and will not benefit from thrombolytic therapy.

Diagnostic features of body surface potential maps in patients with myocardial ischemia and normal resting 12-lead electrocardiograms

Body surface maps recorded from 35 ischemic patients with normal resting 12-lead electrocardiograms were compared with those obtained from 36 age- and sex-matched normal subjects. From instantaneous maps of each subject 187 variables were derived relating to the configuration (80 variables) and magnitude (104 variables) of the potential distribution and duration of the electrocardiographic intervals (3 variables). By using stepwise discriminant analysis we selected 3 variables whose linear combination enabled us to correctly allocate 91% of the study population (jacknife procedure; specificity 92%, sensitivity 91%). To substantiate the validity of the results the discriminant function was tested on a new independent population consisting of 27 ischemic patients and 54 normal subjects from another laboratory. A proper allocation was obtained in 86% of the cases (specificity 87%, sensitivity 85%). The large number of correctly classified ischemic patients and the repeatability of the results indicate that the adopted criteria are good markers of ischemic heart disease.

Multigroup diagnosis of the standard 12-lead electrocardiogram.

Most studies on diagnostic classification of the electrocardiogram (ECG) deal with only two diagnostic categories at once, for example normals versus anterior myocardial infarction, normals versus inferior myocardial infarction, or normal versus left ventricular hypertrophy. ~-5 Such procedures can be helpful for selecting optimal measurements and providing better insight in diagnostic criteria, and in some important applications, such as monitoring patients with acute myocardial infarction, a normal versus myocardial infarction setting may suffice. Bigroup comparisons, however, are not realistic in clinical practice, where often more than two diagnostic entities must be considered. 6 The multigroup approach was first developed by Pipberger et al. 7 Other investigators have since then applied multivariate statistical techniques for classification of both the vectorcardiogram (VCG) and the ECG in a multigroup setting. 8-1~ The set of measurements to be entered into the multigroup classification scheme generally results from pooling the most disciminating variables selected from each pairwise comparison. The total accuracy--percentage of correctly classified subjects--has varied from 63% to 87%, depending on the lead system, the number of groups, and whether prior probabilities were used. Most reports have placed greater emphasis on the

Best ECG leads for diagnosing acute myocardial infarction by multivariate analysis of body surface potential maps

The authors compared 120-lead body surface potential map (BSPM) data from 131 patients with acute myocardial infarction (MI) and 159 normal control subjects (N). The MI population was stratified according to the location of ventricular wall motion abnormalities using technetium-99m-labeled blood pool imaging into 76 patients with anterior MI (AMI), 32 patients with inferior MI (IMI), and 23 patients with posterior MI (PMI). Stepwise discriminant analysis was performed for each pairwise comparison (AMI vs N, IMI vs. N, and PMI vs. N) using as measurements the ST magnitude in 120 electrode sites from each individual. Two leads from areas with the most abnormal ST changes achieved optimal classification in each MI class, and five of these six leads were outside the precordial electrode positions. In each bigroup classification, the first and best measurement corresponded to ST depression while the second represented ST elevation. Sensitivities at a specificity level of 95% were 82% for AMI, 93% for PMI, and 100% for IMI.<<ETX>>