Incremental benefit of 80-lead electrocardiogram body surface mapping over the 12-lead electrocardiogram in the detection of acute coronary syndromes in patients without ST-elevation myocardial infarction: Results from the Optimal Cardiovascular Diagnostic Evaluation Enabling Faster Treatment of Myocardial Infarction (OCCULT MI) trial

BACKGROUND

The initial 12-lead (12L) electrocardiogram (ECG) has low sensitivity to detect myocardial infarction (MI) and acute coronary syndromes (ACS) in the emergency department (ED). Yet, early therapies in these patients have been shown to improve outcomes.

OBJECTIVES

The Optimal Cardiovascular Diagnostic Evaluation Enabling Faster Treatment of Myocardial Infarction (OCCULT-MI) trial was a multicenter trial comparing a novel 80-lead mapping system (80L) to standard 12L ECG in patients with chest pain and presumed ACS. This secondary analysis analyzed the incremental value of the 80L over the 12L in the detection of high-risk ECG abnormalities (ST-segment elevation or ST depression) in patients with MI and ACS, after eliminating all patients diagnosed with ST-elevation MI (STEMI) by 12L ECG.

METHODS

Chest pain patients presenting to one of 12 academic EDs were diagnosed and treated according to the standard care of that site and its clinicians; the clinicians were blinded to 80L results. MI was defined by discharge diagnosis of non-ST-elevation MI (NSTEMI) or unstable angina (UA) with an elevated troponin. ACS was defined as discharge diagnosis of NSTEMI or UA with at least one positive test result (troponin, stress test, angiogram) or revascularization procedure.

RESULTS

  Of the 1,830 patients enrolled in the trial, 91 patients with physician-diagnosed STEMI and 225 patients with missing 80L or 12L data were eliminated from the analysis; no discharge diagnosis was available for one additional patient. Of the remaining 1,513 patients, 408 had ACS, 206 had MI, and one had missing status. The sensitivity of the 80L was significantly higher than that of the 12L for detecting MI (19.4% vs. 10.4%, p = 0.0014) and ACS (12.3% vs. 7.1%, p = 0.0025). Specificities remained high for both tests, but were somewhat lower for 80L than for 12L for detecting both MI and ACS. Negative and positive likelihood ratios (LR) were not statistically different between groups. In patients with severe disease (defined by stenosis > 70% at catheterization, percutaneous coronary intervention, coronary artery bypass graft, or death from any cause), the 80L had significantly higher sensitivity for detecting MI (with equivalent specificity), but not ACS.

CONCLUSIONS

Among patients without ST elevation on the 12L ECG, the 80L body surface mapping technology detects more patients with MI or ACS than the 12L, while maintaining a high degree of specificity.

[Relationship between reference point potential and potential distribution of normal electrocardial field on the thoracic surface of healthy individuals]

OBJECTIVE

To explore the effect of reference point on the potential distribution of normal cardioeleclric field of healthy individuals.

METHODS

Two different reference points including central terminal and right forehead were applied to record electrocardiogram simultaneously from 15 testing points (V(1)-V(6), V(7)-V(9), V(3R)-V(8R)) of Wilson lead (RL) and the same testing points (HV(1)-HV(9), HV(3R)-HV(8R)) of head-chest (HC) lead around the torso of healthy individuals. Chi-square test was performed to observe statistical difference between the HCECGs and RLECGs according to different shapes of QRS and T waves.

RESULTS

Among 120 healthy individuals, deformed ECGs appeared in V(1) and HV(3R)-HV(8R) leads, with 20% (24/120) inverted T wave in V(1) lead, 100% (120/120) in V(3R)-V(8R) leads, wide or deep Q wave 100% (120/120) in V(4R)-V(8R) leads. However, in the corresponding HC-lead system, T waves were all positive, and QRS waves were upright as the pattern of rs, RS or qRs. There was statistical difference in the form of ECG between V(1), V(3R)-V(8R) of Wilson lead and the corresponding HC-lead (P<0.05). The distribution of normal cardioeleclric field related to QRS-T wave was of all-round outward shape by HC-lead, and of roughly bipolar shape by Wilson lead for inverted QRS-T wave on the right thoracic surface.

CONCLUSION

The normal distribution of electrocardial field is determined by the potential of the reference point. The forehead of HC-lead seems to be better than the central terminal as the reference point of the lead system.

Spatiotemporal correlation analyses: a new procedure for standardisation of DC magnetocardiograms

There is a lack of standard methods for the analysis of magnetocardiograms (MCGs). MCG signals have a shape similar to the ECG (P wave, QRS complex, T wave). High-quality multichannel recordings can indicate even slight disturbances of de- and repolarisation. The purpose of our study was to apply a new approach in the analysis of signal-averaged DC-MCGs. DC-MCGs (31-channel) were recorded in 182 subjects: 110 patients after myocardial infarction and 72 controls. Spatiotemporal correlation analysis of the QRS complex and T wave patterns throughout the entire heart cycle was used to analyse homogeneity of de- and repolarisation. These plots were compared to standard ECG analyses (electrical axis, Q wave, ST deviation, T polarity and shape). Spatiotemporal correlation analyses seem to be applicable in assessing the course of electrical repolarisation with respect to homogeneity. MCG provided all diagnostic information contained in common ECG recordings at high significance levels. The ECG patterns were included in 5/8 of our parameters for electrical axis, 6/8 for Q-wave, 7/8 for ST deviation and 5/8 for T-polarity based on two time series of correlation coefficients. We conclude that our spatiotemporal correlation approach provides a new tool for standardised analysis of cardiac mapping data such as MCG.

Contactless magnetocardiographic mapping in anesthetized Wistar rats: evidence of age-related changes of cardiac electrical activity

Magnetocardiography (MCG) is the recording of the magnetic field (MF) generated by cardiac electrophysiological activity. Because it is a contactless method, MCG is ideal for noninvasive cardiac mapping of small experimental animals. The aim of this study was to assess age-related changes of cardiac intervals and ventricular repolarization (VR) maps in intact rats by means of MCG mapping. Twenty-four adult Wistar rats (12 male and 12 female) were studied, under anesthesia, with the same unshielded 36-channel MCG instrumentation used for clinical recordings. Two sets of measurements were obtained from each animal: 1) at 5 mo of age (297.5 ± 21 g body wt) and 2) at 14 mo of age (516.8 ± 180 g body wt). RR and PR intervals, QRS segment, and QTpeak, QTend, JTpeak, JTend, and Tpeak-end were measured from MCG waveforms. MCG imaging was automatically obtained as MF maps and as inverse localization of cardiac sources with equivalent current dipole and effective magnetic dipole models. After 300 s of continuous recording were averaged, the signal-to-noise ratio was adequate for study of atrial and ventricular MF maps and for three-dimensional localization of the underlying cardiac sources. Clear-cut age-related differences in VR duration were demonstrated by significantly longer QTend, JTend, and Tpeak-end in older Wistar rats. Reproducible multisite noninvasive cardiac mapping of anesthetized rats is simpler with MCG methodology than with ECG recording. In addition, MCG mapping provides new information based on quantitative analysis of MF and equivalent sources. In this study, statistically significant age-dependent variations in VR intervals were found.

[Heart activation course on isochrone maps in normal subjects]

Body surface potential mapping (BSPM) is a method providing a noninvasive assessment of the changes ongoing in the electric field of the heart. In the present study, the weakly recognized kind of the surface maps--isochrone maps that reflect in the best manner a pathway of the depolarization front propagation within the heart conduction system. BSPM was obtained using a HPM-7100 Fukuda Denshi system, which enables collecting a synchronic electrocardiographic recordings from 87 electrodes in the cylindrical system. The study population constituted 30 healthy subjects (15 females and 15 males) with the mean age of 23.9 +/- 4.56 years. The considered electrocardiogram from the all subjects appeared to be within the normative range. In order to obtain a pattern reflecting a depolarization trajectory in the human heart, the ventricular activation time maps (VAT), on the plane and superficial, were constructed with the own software. On the basis of the VAT maps obtained from the examined group, the group-mean VAT map for the normal subjects was created. Isochrone maps render much more information about heart activation spread than the standard 12-leads electrocardiography system. Using isochrone maps, one can monitor precisely a depolarization trajectory in the individual heart portions. The values and distribution of isochrones determine a velocity of activation propagation within the heart conduction system. Analysis of the isochrone maps collected in the normal subjects confirmed the activation pathway of the ventricles, starting from atrioventricular junction, via His bundle and its branches and finally to the myocardium through Purkinje fibres. In the examined group, no significant differences in relation to the isochrones distribution were found, therefore the group-mean VAT map was assumed as a reference pattern. The pattern of distribution and values of VAT map established for the normal subjects can be used in the further investigations concerning a diagnosis of the heart conduction system disturbances.

Selection of optimal recording sites for limited lead body surface potential mapping: a sequential selection based approach

Background

In this study we propose the development of a new algorithm for selecting optimal recording sites for limited lead body surface potential mapping. The proposed algorithm differs from previously reported methods in that it is based upon a simple and intuitive data driven technique that does not make any presumptions about deterministic characteristics of the data. It uses a forward selection based search technique to find the best combination of electrocardiographic leads.

Methods

The study was conducted using a dataset consisting of body surface potential maps (BSPM) recorded from 116 subjects which included 59 normals and 57 subjects exhibiting evidence of old Myocardial Infarction (MI). The performance of the algorithm was evaluated using spatial RMS voltage error and correlation coefficient to compare original and reconstructed map frames.

Results

In all, three configurations of the algorithm were evaluated and it was concluded that there was little difference in the performance of the various configurations. In addition to observing the performance of the selection algorithm, several lead subsets of 32 electrodes as chosen by the various configurations of the algorithm were evaluated. The rationale for choosing this number of recording sites was to allow comparison with a previous study that used a different algorithm, where 32 leads were deemed to provide an acceptable level of reconstruction performance.

Conclusion

It was observed that although the lead configurations suggested in this study were not identical to that suggested in the previous work, the systems did bear similar characteristics in that recording sites were chosen with greatest density in the precordial region.

Additional electrocardiographic leads in the ED chest pain patient: right ventricular and posterior leads

In the evaluation of the patient with chest pain, the 12-lead electro cardiogram is a less-than-(ECG) perfect indicator of acute myocardial infarction (AMI), particularly when used early in the course of the acute ischemic event; this relative insensitivity for AMI results from many different issues, including a less-than-optimal imaging of certain areas of the heart. It has been suggested that the sensitivity of the 12-lead ECG can be improved if 3 additional body surface leads are used in selected individuals. Acute posterior (PMI) and right ventricular myocardial infarctions are likely to be underdiagnosed, because the standard lead placement of the 12-lead ECG does not allow these areas to be assessed directly. Additional leads frequently used include leads V(8) and V(9), which image the posterior wall of the left ventricle, and lead V(4R), which reflects the status of the right ventricle. The standard ECG coupled with these additional leads constitutes the 15-lead ECG, the most frequently used additional lead ECG in clinical practice. The use of the additional leads might not only confirm the presence of AMI, but also provide a more accurate reflection of the true extent of myocardial damage.

Beyond the 12 lead: review of the use of additional leads for the early electrocardiographic diagnosis of acute myocardial infarction

Despite known limitations, the standard 12 lead ECG is the principal risk stratification device for patients presenting with chest pain to the ED. However, it has a sensitivity of less than 60% for MI. One reason for this is that the standard placement of chest leads fails to interrogate many areas of the myocardium. Various workers have addressed this problem through the use of additional leads or body surface mapping. Additional leads on the posterior and right thoracic surface have been shown to give additional information, which may be important to the emergency physician. This review demonstrates the need for additional leads in the acute setting and makes recommendations about the utility of using additional leads in the ED.

Recording locations in multichannel magnetocardiography and body surface potential mapping sensitive for regional exercise-induced myocardial ischemia

INTRODUCTION

This study aimed to identify the optimal locations in multichannel magnetocardiography (MCG) and body surface potential mapping (BSPM) to detect exercise-induced myocardial ischemia.

METHODS

We studied 17 healthy controls and 24 coronary artery disease (CAD) patients with stenosis in one of the main coronary artery branches: left anterior descending (LAD) in 11 patients, right (RCA) in 7 patients, and left circumflex (LCX) in 6 patients. MCG and BSPM signals were recorded during a supine bicycle stress test. The capability of a recording location to separate the groups was quantified by subtracting the mean signal amplitude of the normal group from that of the patient group during the ST segment and at the T-wave apex, and dividing the resulting amplitude difference by the corresponding standard deviation within all subjects.

RESULTS

In MCG the optimal location for ST depression was at the right inferior grid for the RCA, at the mid-inferior grid for the LCX, and in the middle of these locations for the LAD subgroup (mean ST amplitudes: CAD -80 +/- 360fT, controls 610 +/- 660fT; p < 0.001). In BSPM it was on the left upper anterior thorax for the LAD, left lower anterior thorax for the RCA, and on the lower back for the LCX subgroup (mean ST amplitudes: CAD -39 +/- 61 microV and controls 38 +/- 38 microV; p < 0.001). In MCG the optimal site for T-wave amplitude decrease was the same as the one for the ST depression. In BSPM it was on the middle front for the LAD, on the back for the LCX and on the left abdominal area for the RCA group. In accordance with electromagnetic theory, the largest ST segment and T-wave amplitude changes took place in MCG in locations orthogonal to those in BSPM.

CONCLUSION

This study identified magnetocardiographic and BSPM recording locations which are sensitive for detecting transient myocardial ischemia by evaluation of the ST segment as well as the T-wave. These locations strongly depend on ischemic regions and are outside the conventional 12-lead ECG recording sites.

Geometrical aspects of the interindividual variability of multilead ECG recordings

The electrocardiogram (ECG) as measured from healthy subjects shows a considerable interindividual variability. This variability is caused by geometrical as well as by physiological factors. In this study, the relative contribution of the geometrical factors is estimated. In addition a method aimed at correcting for these factors is described. First, a measure (RV) for quantifying the overall variability is presented, and for healthy individuals its value is estimated as 0.52. Next, based on a simulation study using the individual (heart-lung-torso) geometry of 25 subjects, the variability caused by geometrical factors is estimated as 0.40, indicating that in healthy subjects the RV for healthy individuals resulting from electrophysiology is of the order of 0.33. In an evaluation of the correction procedure, applied to realistic, simulated body surface potentials, it is shown that RV caused by geometrical factors can be reduced from 0.40 to 0.06. When applying the correction procedure to measured ECG data no reduction of the RV value could be demonstrated. These results indicate that the involved procedure of the inverse computation of a cardiac equivalent source, at the present time, is of insufficient quality to cash in on the substantial reduction of RV values from 0.52 down to 0.33 that might be obtainable.

On selecting a body surface mapping procedure

Throughout the world, various procedures related to body surface mapping have evolved. The large differences in these procedures make multicenter studies difficult. This paper discusses the problems involved in selecting the number of leads, lead placement, and map format. Methods are highlighted that have been developed for pooling of the data as obtained by different centers. Recommendations are included to newcomers in the field. (The work stems from an international study, the Noninvasive Evaluation of the Myocardium, a study group sponsored by the European Commission, which has as one of its objectives the standardization of body surface mapping procedures.)

The absolute voltage and the lead vector of Wilson's central terminal

The absolute potential value of Wilson's central terminal was calculated at 2 msec intervals during a cardiac cycle in 60 clinical cases. Starting from the body surface potential data at 128 thoracic locations, the effect of immersion of the body into an infinite conductor on the surface potential was calculated to obtain values with reference to zero potential at infinity. The conductivity of the outside medium was then made to approach zero. Comparison of the result with the original map showed nearly a constant shift of the potential, corresponding to the voltage of Wilson's terminal. In addition, the cardiac vector was calculated as the first approximation of the cardiac electromotive force and the lead vector of Wilson's terminal was obtained in order that the scalar product of the cardiac vector and the lead vector approximated the observed voltage of Wilson's terminal. The results indicate that the voltage of the Wilson electrode depended on the surface voltage with a peak value near the maximal QRS force in most of the cases. The peak voltage of Wilson's terminal was either positive or negative, and was 0.15 mV in absolute value on average. Voltage variations of Wilson's terminal during a cardiac cycle were 0.20 mV as an average of all cases. The voltage of Wilson's terminal also depended on the direction of the equivalent cardiac vector. The lead vector of Wilson's terminal was found to be directed superiorly in most of the cases. The average magnitude of the lead vector of Wilson's terminal was 0.097 omega/cm, which corresponded to about 1/4 of that of lead I.

The state of body surface mapping in Japan

In Japan, body surface mapping (BSM) started in 1974. A huge amount of data has been accumulated regarding basic researches and clinical applications. Recent work on BSM in Japan is summarized here, with the goals of establishing a normal database and diagnostic criteria by using the standardized mapping system. The standard systems used in Japan are the HPM-7100 and the VCM-3000, manufactured by Fukuda-Denshi (Tokyo, Japan) under the supervision of a committee of the Japanese Circulation Society. The number of leads in this system is 87 (59 on front, 28 on back). As a basic study, a computer simulation was carried out on bundle branch block with myocardial infarction (MI), on late potentials in MI, and finally, on the solution of the inverse problem. The database of 606 normal subjects was established regarding age and sex, and a "departure index" (the grade of deviation from normal: the difference between a patient's data the normal mean divided by the normal SD) was proposed. Using the departure index, diagnostic criteria were proposed for the ischemic site, MI site, hypertrophic site of the ventricle, etc. The origin of the ventricular premature contractions was determined by the site of minima and maxima of the QRS and QRST isointegral maps. The site of accessory pathways was determined by the site of minimum less than -0.15 mV on the BSM. For the prediction of patients prone to ventricular tachycardia (VT), several approaches were tried such as multipolar patterns of QRST isointegral maps, Wigner distribution, late potentials with relation to endo- or epicardial delayed potentials, body surface distribution of specific frequency band (25-50 Hz) obtained from fast Fourier transform analysis, and nondipolarity of the QRST isointegral map. To improve the ablation procedure of VT, the author developed a technique to determine the precise location of the VT focus in pace mapping using a correlation matrix between VT and pace maps. To ensure the longevity of the BSM, a reduction of the number of leads has been proposed. The usefulness of BSM has been confirmed and the technique accepted in Japan for daily clinical diagnosis.

[Data base for body surface potential maps of normal populations--normal data base by the Japanese Circulation Society Task Force Committee on Criteria for Body Surface Mapping]

In order to evaluate the normal ranges of the body surface potential maps, data from normal healthy subjects were compiled by the Japanese Circulation Society Task Force Committee on Criteria for Body Surface Mapping (Chairman: Shoji Yasui, Nagoya National Hospital). The subjects met all the following criteria; (1) normal physical findings; (2) no heart or lung diseases; (3) no hypertension (160/90 mmHg); (4) normal 12-lead electrocardiogram; (5) normal chest roentgenogram (may be omitted in children); (6) normal findings in exercise test in subjects 40 years of age or older; and (7) no major morbidity. Body surface mapping data were recorded by use of 87-lead mapping systems, HPM-5100, HPM-6500, and VCM-3000 (Fukuda Denshi, and Chunichi Denshi), or 128-lead mapping systems Cardiovision (Tokyo Technological University-Teijin), and Cardiomap (Gakken). To construct the database, each original set of body surface mapping data was copied to an MS-DOS file. Data recorded by a 128-lead mapping system was transformed into an 87-lead system data. Next, each individual data was transformed into a file of common format with a header containing clinical information, and the onset and offset of each electrocardiographic waves. From these secondary files, mean and standard deviation of each electrocardiographic lead were calculated for instantaneous voltages of P wave, QRS wave, and ST-T; time integrals of P, QRS, and QRST; and ventricular activation time, to subgroups divided age and gender. All these data were stored in a optical disk, and also mean and standard deviation for subgroups were stored in a set of floppy disks.(ABSTRACT TRUNCATED AT 250 WORDS)