Electrocardiographic and ventriculographic recovery patterns in Q wave myocardial infarction.

To further define the capacity for recovery after acute phase electrical and mechanical injury in patients with Q wave myocardial infarction who were treated with standard measures, 120 lead body surface potential maps and radionuclide angiograms were recorded at day 5 before discharge and month 6 after infarction in 23 patients with a first infarction (12 anterior and 11 inferior by standard 12 lead electrocardiographic criteria). In addition to assessment of spatial changes in electrocardiographic and wall motion patterns, five quantitative variables were evaluated: minimal Q zone integral, sigma Q wave integral, maximal ST integral, left ventricular ejection fraction and left ventricular wall motion abnormality score. From day 5 to month 6 after infarction, the only change in the inferior infarction group was a gain in sigma Q wave (-91 +/- 40 mu V X s X 10(2) to -68 +/- 24 mu V X s X 10(2); p less than 0.05). In contrast, all variables improved over the same time period in the anterior infarction group: Q zone minimum, -34 +/- 20 to -24 +/- 13 mu V X s (p less than 0.05); sigma Q wave, -160 +/- 122 X 10(2) to -120 +/- 90 mu V X s X 10(2) (p less than 0.05); ST maximum, 44 +/- 19 to 18 +/- 9 mu V X s (p less than 0.01); ejection fraction, 54 +/- 7 to 63 +/- 17% (p less than 0.05); and wall motion score, 6 +/- 3 to 3 +/- 3 (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of best electrocardiographic leads for diagnosing myocardial infarction by statistical analysis of body surface potential maps.

This study describes a practical approach for the extraction of diagnostic information from body surface potential maps. Body surface potential map data from 361 subjects were used to identify optimal subsets of leads and features to distinguish 184 normal subjects from 177 patients with myocardial infarction (MI). Multivariate analysis was performed on 120-lead data, using as features instantaneous voltage measurements on time-normalized QRS and STT waveforms. Several areas on the map, most of which were located outside the precordial region, contained leads with important discriminant features; 2 of the 3 limb leads (aVR and aVF) also exhibited high diagnostic capability. A total of 6 features (mostly STT measurements) from 3 locations accounted for a specificity of 95% and a sensitivity of 95%; these were the right subclavicular area, the left posterior axillary region and the left leg. As a comparison, the same number of features from the standard 12-lead electrocardiogram yielded a sensitivity of 88% for a specificity of 95%. To investigate the repeatability of the results, the entire population was separated into a training set (100 normal subjects and 100 patients with MI) and a testing set (84 normal subjects and 77 patients with MI); computing a discriminant function on the training set and applying it to the testing set only moderately deteriorated the diagnostic classification. It is concluded that this approach achieves efficient information extraction from body surface potential maps for improved diagnostic classification.

Body surface potential maps with low-level exercise in isolated left anterior descending coronary artery disease.

One hundred and twenty-lead body surface potential maps (BSPMs) were recorded at rest, at immediate cessation of exercise and after 1 (early) and 5 minutes (late) of recovery in 14 patients with isolated, critical, left anterior descending (LAD) coronary artery stenosis. Exercise endpoints, at an average peak rate of 98 +/- 13, were usual pain worsening in 13 LAD patients, and diagnostic ST depression in lead V5 in 1 patient. Twelve patients also had positive thallium scans. BSPMs were also recorded in 8 normal subjects who exercised to peak heart rates similar to those of the LAD subjects. Spatially, there were similar exercise changes in QRS and ST-segment integral patterns over the precordium and inferior torso in both groups. These were transient in the control group but persisted to late recovery in the LAD group, particularly for ST integral. Quantitatively, multivariate analysis revealed significant temporal differences between the 2 groups. However, the only independent BSPM variable was the sum of ST integral decrease, averaging --2,323 +/- 1,809 microV.s for normal patients between rest and immediate cessation of exercise, compared with -3,828 +/- 2,329 microV.s for the LAD patients (p less than 0.05). Late recovery minus rest difference averaged -1,264 +/- 1,080 microV.s for normal subjects and -2,575 +/- 1,844 microV.s for LAD patients (p less than 0.01). To control for the physiologic changes of exercise, the ST integral temporal differential maps of the normal subjects were subtracted from those of the LAD patients and the sum of negative intergroup differences was assumed to reflect only ischemia. Correlation of ST integral ischemia values at immediate cessation of exercise and late recovery was high (r = 0.88); however, intertechnique correlations of the BSPM variables with quantitative angiographic scores and thallium perfusion scan scores revealed generally low r values (range 0 to 0.52). These data demonstrate that ischemic repolarization changes are detectable and quantifiable by BSPM at low levels of cardiac stress in patients with 1-vessel disease when the usual electrocardiographic criteria of myocardial ischemia are frequently absent. The data further suggest that ST integral changes reflective of myocardial ischemia persist well after the exercise recovery period and that they are complementary to, rather than substitutionary for, other indirect measures of myocardial ischemia.

Non-Q-wave acute myocardial infarction: body surface potential map and ventriculographic patterns.

Day 5 body surface map and radionuclide angiographic patterns were compared among 56 patients with first non-Q-wave or Q-wave acute myocardial infarction (AMI). Three radionuclide angiographic patterns were recognized in patients with non-Q infarction: no wall motion abnormalities (n = 8), single-segment wall motion abnormalities (n = 10) and multiple-segment wall motion abnormalities (n = 9). In contrast, only 2 radionuclide angiographic patterns were identified in patients with Q-wave infarction: multiple-segment wall motion abnormalities (n = 25) and single-segment wall motion abnormalities (n = 4). The Q-wave distributions of 14 of 18 patients with non-Q infarction with 0 or 1 wall motion abnormalities were normal; 2 patients had "missed" anterior; 1 patient had inferior; and 1 had posterior AMI patterns. Of 9 patients with non-Q infarction who had multiple-segment wall motion abnormalities, 8 had infarct Q waves on the posterior torso. Q-wave patterns in patients with anterior (n = 17) and inferior (n = 12) Q-wave infarctions were typical and homogeneous for each group. Quantitative analysis of minimum Q-zone integral, sigma Q-wave integrals, ST-integral maximum, wall motion abnormality score and ejection fraction revealed no differences between patients with non-Q-wave and those with inferior Q-wave infarction. In contrast, patients with anterior AMI had significantly more abnormal values of all variables than either of the other groups. Overall, the data support the concept of non-Q-wave AMI as a distinct, if heterogeneous, pathophysiologic entity.(ABSTRACT TRUNCATED AT 250 WORDS)

Frequent ventricular ectopic activity without underlying cardiac disease: analysis of 45 subjects.

Forty-five subjects, aged 2 weeks to 62 years, who presented with frequent (greater than 100/day) ventricular ectopic beats (VEBs) and without evidence of underlying cardiac disease were studied. The spectrum of ventricular dysrhythmia was assessed by 24-hour ambulatory electrocardiography and exercise tolerance test. Sinus rhythm was the prevailing rhythm in all subjects. VEB frequency averaged 444 +/- 454 per hour (range 0 to 1,863) over the 24-hour monitoring period and was not significantly different during waking or sleeping periods. There was no simple correlation of VEB frequency with prevailing sinus rate (r = -0.0006; p = not significant [NS]). The prevalence of complex VEBs (multiform, R-on-T and repetitive) was relatively high (18 of 45 patients), and was equally distributed about the median VEB frequency of 314 VEBs/hour (7 of 18 versus 11 of 18; NS). Of the 43 subjects who had exercise tests, 37 had VEBs during the preexercise rest phase, compared with only 11 at peak exercise (p less than 0.0001). To assess the short-term natural history of the VEBs, 27 subjects had repeat clinical examinations and 24-hour electrocardiograms at a mean interval of 8 months. All remained well. Although there was considerable individual temporal variability of VEB frequency in this subgroup, there was no significant change in group mean values (415 +/- 409 VEBs/hour initially versus 401 +/- 383 VEBs/hour at follow-up study; NS). The relative temporal constancy of VEB frequency in the group as a whole was also reflected in a high linear correlation of VEB frequency at initial and follow-up studies (r = 0.816; p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac rhythm, rate and ventricular repolarization properties in infants at risk for sudden infant death syndrome: comparison with age- and sex-matched control infants.

Using 24-hour ambulatory electrocardiographic recordings and 120-lead body surface potential maps, prevailing cardiac rate and rhythm, incidence and frequency of dysrhythm and rate and pattern of ventricular repolarization at the body surface were compared in 17 infants at risk for sudden infant death syndrome (SIDS) and 17 age- and sex-matched control subjects. Sinus rhythm was the prevailing rhythm in both study groups and there were no intergroup differences in average overall awake or asleep sinus rates, nor in temporal variability of sinus rate. Atrial and ventricular ectopic activity were equally uncommon in both study groups. Although there were smooth and bipolar body surface distributions of ST-T and QRST time integrals in both study groups, the average rate of ventricular repolarization (QTc), measured from the 12-lead electrocardiogram, 120-lead body surface potential maps and 24-hour electrocardiography, was consistently shorter in the at-risk group than in the control group. However, temporal variability of QTc was not different between the 2 groups. Thus, significant cardiac dysrhythm and QT prolongation are not found in infants at increased risk for SIDS. Rather, there is an abbreviated ventricular repolarization interval in at-risk infants. In combination with the findings of intergroup similarity of average sinus rate and temporal variability of sinus rate and ventricular repolarization rate, the data suggest a subtle, constant difference in cardiac autonomic activity, most likely an increase in sympathetic tone, in at-risk subjects. The role of this altered cardiac autonomic activity in the causation of SIDS remains undetermined.

Cardiac function at rest and with exercise in the chronic fatigue syndrome.

To evaluate a possible cardiac pathophysiology of the chronic fatigue syndrome, we compared the resting cardiac function and exercise performance of 41 patients to those of an age-matched and sex-matched normal control group. Persistent fatigue following an acute apparently viral illness was the major complaint of all patients; none had specific cardiac symptoms nor abnormal physical findings. Electrocardiographic spatial patterns were normal in the patients, and there were no differences in the body surface sum of positive T-wave integrals between the patients (240 microV.x 10(2) +/- 107 microV.s x10(2)) and control (244 microV.x 10(2) +/- 108 microV.s x 10(2) subjects. Twenty-four hour ambulatory ECGs revealed no differences in sinus rates and incidences of ventricular dysrhythmias in the two populations. Left ventricular dimensions and systolic fractional shortening values were also similar in both groups; moreover none of the patients had segmental wall motion abnormalities. On graded exercise testing, 20 of 32 normal subjects achieved target (85 percent of age-maximum) heart rates, compared to four of 31 patients (p less than 0.001). The duration of exercise averaged 12 +/- 4 minutes for the normal subjects and 9+/- 4 minutes for the patients (p less than 0.01). The temporal profile of exercise heart rates was dissimilar in the two groups, with patients' rates consistently and progressively less than those of normal subjects. Peak heart rate averaged 152 +/- 16 beats per minute for the normal group vs 124 +/- 19 beats per minute for the patients (p less than 0.0001); in age-related terms, respectively, 82 +/- 6 percent of the maximum heart rate vs 66 +/- 10 percent (p less than 0.0001). Thus, patients with chronic fatigue syndrome have normal resting cardiac function but a markedly abbreviated exercise capacity characterized by slow acceleration of heart rate and fatigue of exercising muscles long before peak heart rate is achieved.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac effects of common viral illnesses.

We compared the clinical, electrocardiographic and echocardiographic findings of 32 patients during the acute and recuperative phases of viral illness with similar data from a healthy age- and sex-matched normal control group. During the acute phase, no patient had cardiac symptoms and none had clinical evidence of left ventricular or valvular dysfunction, nor pericarditis. Electrocardiograms revealed no differences in mean sinus rate or ectopic dysrhythm between the two groups. Spatial 12- and 120-lead body surface electrocardiographic patterns were normal in 30 patients; two others had nonspecific T wave abnormalities. There were no differences in echo-determined left ventricular cavity size or systolic shortening fraction between the two groups. Three patients had segmental ventricular hypokinesis; 17 patients had small pericardial effusions. Data herein suggest effects on myocardial electrical and mechanical function in patients with viral illness. It may be prudent for such patients to minimize cardiac stress during illness.

Indirect measurement of infarct size. Correlative variability of enzyme, radionuclear angiographic, and body-surface-map variables in 34 patients during the acute phase of first myocardial infarction.

To gain a correlative perspective of indirect indications of the size of a myocardial infarct, we measured several body-surface electrocardiographic variables and several enzyme and radionuclear angiographic indicators of an infarct's size in 34 patients during the acute phase of first infarction. We found that bivariate correlations ranged widely, from an r value of 0.05 to an r value of 0.92, but were significantly (p less than 0.001) higher when variables from the same technique were correlated (mean r, 0.60 +/- 0.27), as opposed to correlations of variables from different techniques (mean r, 0.27 +/- 0.18). Trivariate comparisons among techniques produced significantly (p less than 0.001) higher r values, but the highest, an r value of 0.76 (total wall motion abnormality score; peak lactic dehydrogenase level; ST-segment integral maximum), indicated that even in this best case, only about 60 percent of the variation of one variable was dependent on or due to the two other variables. These data demonstrate that multiple indirect quantitative indicators of myocardial injury can vary widely in their correlations within the same population of infarcts, and much remains unknown in their relationships during the acute phase. Caution should be exercised, therefore, in their clinical application to predict an infarct's size in individual patients with acute myocardial infarction.

Exercise body surface potential mapping in single and multiple coronary artery disease.

Body surface ST integral maps were recorded in 36 coronary artery disease (CAD) patients at: rest; peak, angina-limited exercise; and, 1 and 5 min of recovery. They were compared to maps of 15 CAD patients who exercised to fatigue, without angina, and eight normal subjects. Peak exercise heart rates were similar (NS) in all groups. With exercise angina, patients with two and three vessel CAD had significantly (p less than 0.05) greater decrease in the body surface sum of ST integral values than patients with single vessel CAD. CAD patients with exercise fatigue, in the absence of angina, had decreased ST integrals similar (NS) to patients with single vessel CAD who manifested angina and the normal control subjects. There was, however, considerable overlap among individuals; some patients with single vessel CAD had as much exercise ST integral decrease as patients with three vessel CAD. All CAD patients had persistent ST integral decreases at 5 min of recovery and there was a direct correlation of the recovery and peak exercise ST changes. Exercise ST changes correlated, as well, with quantitative CAD angiographic scores, but not with thallium perfusion scores. These data suggest exercise ST integral body surface mapping allows quantitation of myocardium at ischemic risk in patients with CAD, irrespective of the presence or absence of ischemic symptoms during exercise. A major potential application of this technique is selection of CAD therapy guided by quantitative assessment of ischemic myocardial risk.

The effect of torso geometry on magnetocardiographic isofield maps.

Using a computer model of a realistically shaped human torso with lungs and intraventricular blood masses, we have assessed how torso geometry and composition affect the extracorporal magnetic field produced by a current dipole in the centre of the ventricular mass. The magnetic induction vector B arising from the dipole has been calculated at points of a precordial measuring grid and the influence of boundaries has been assessed qualitatively, by comparing contour maps of the B component normal to the torso's frontal plane. We found that the maps reflected relatively faithfully the underlying dipolar source for the homogeneous torso and even for the torso with lungs. However, the intraventricular blood masses caused a noticeable rotation of the maps' extrema. Both lungs and blood masses tended to swing the distribution towards the distribution that would have been caused by a dipole oriented along the anatomical axis of the heart.

Two-dimensional Fourier spectrum of QRST integral maps in classification of patients prone to ventricular arrhythmia.

Two-dimensional Fourier spectra of QRST integral maps, obtained by body surface potential mapping, were analyzed to identify subjects prone to ventricular arrhythmia, when they have not been identified by the extrema count method. The diagnostic performance (84.38 percent) of the peak value of the Fourier spectrum as a classifier for subjects prone to ventricular arrhythmia showed an improvement of 3.65 percent over the use of the extrema count method as a classifier.

Magnetocardiographic functional localization using a current dipole in a realistic torso.

We describe a fast and numerically effective biomagnetic inverse solution using a moving dipole in a realistic homogeneous torso. We applied the localization model and high-resolution magnetocardiographic mapping to localize noninvasively the ventricular preexcitation site in ten patients suffering from Wolff-Parkinson-White syndrome. In all cases, the computed localization results were compared to the results obtained by invasive catheter technique. Using a standard-size torso model in all cases, the average 3-D distance between the computed noninvasive locations and the invasively obtained results was 2.8 +/- 1.4 cm. When the torso was rescaled to better match the true shape of the subject in five cases, the 3-D average was improved to 2.2 +/- 1.0 cm. This accuracy is very satisfactory, suggesting that the method would be clinically useful.

Q-wave infarction: pathophysiology of body surface potential map and ventriculographic patterns in anterior and inferior groups.

To define and relate the body surface electrocardiographic and left ventricular wall motion patterns in the acute phase of Q-wave infarction, we recorded 120-lead body surface potential maps and radionuclear angiograms in 29 patients on the fifth day of their first infarction. By standard 12-lead electrocardiographic criteria, 17 patients were designated as anterior infarction and 12 as inferior infarction. Body surface map infarct patterns in the anterior group were characterized primarily by abnormal Q-wave, negative Q-zone and positive ST-segment integral patterns over the anterior torso and little reciprocal change. The maps of the inferior patient group were characterized primarily by depolarization and repolarization infarct patterns over the inferior torso and marked reciprocal changes in all integral patterns over the anterior torso. Both groups displayed infarct patterns over a common area of the right anterior-inferior torso. In the anterior group depolarization minima and repolarization maxima were clustered in a small precordial area; in the inferior group the same extrema were widely scattered over the inferior torso, both anteriorly and posteriorly. Segmental left ventricular wall motion analysis revealed that the 3 most commonly and most severely involved segments were the same in both infarct groups--apical, infero-apical and antero-lateral. Basal septum and antero-basal segmental dysfunction were exclusive to the anterior group; postero-lateral and infero-basal involvement, to the inferior group.(ABSTRACT TRUNCATED AT 250 WORDS)

Antidepressant drugs and heart electrical field.

Some antidepressant drugs, especially tricyclic ones--(TCA), have cardiovascular side effects. To compare the effects of antidepressant drugs, the electrocardiogram (ECG), vectorcardiogram (VCG), and body surface maps (BSM) were recorded in psychiatric patients without cardiovascular diseases treated by a) TCA amitriptyline or dosulepin (daily dose 50-200 mg, 22 patients), b) lithium (serum level 0.66 +/- 0.08 meq/l, 21 patients), c) selective serotonine reuptake inhibitor citalopram (daily doses 20-60 mg, 30 patients), and in 23 control patients. In the TCA-treated patients, the heart rate was increased, QT and RR intervals shortened (p < 0.01, antimuscarinic effect). This was not observed in lithium- and citalopram-treated patients. All antidepressants decreased the absolute maximum values of depolarization isointegral maps, lithium and TCA reduced the initial and citalopram the later phase of depolarization. Citalopram slightly diminished the amplitude of the R wave. The results confirm the antimuscarinic effects of TCA in therapeutic doses and specify the intraventricular effects of antidepressants.

The inverse problem of electrocardiography: a solution in terms of single- and double-layer sources of the epicardial surface.

An approach to the inverse problem of electrocardiography that involves an estimation of the electric potentials (double-layer equivalent sources) on the heart's epicardial surface from the electrocardiographic potentials that are measurable on the body surface has received considerable attention. This report deals with a heretofore unexplored extension of this approach, one that yields, in addition to the electric potentials on the epicardial surface, the normal components of their gradients (single-layer equivalent sources). We show that this formulation has at least three advantages over the formulation in term of epicardial potentials alone: (1) single-layer equivalent sources, which reflect the flow of current across the epicardial surface, are well suited for the imaging of regional ischemia and infarction; (2) the transfer matrix linking the epicardial and body-surface potentials for this formulation is less ill conditioned than that for the formulation in terms of potentials alone; (3) the input vector for inverse calculations consists of spatially filtered (rather that directly measured and therefore noise) body-surface potentials. To establish the feasibility of this new formulation of the inverse problem and to compare it with the formulation in terms of potentials alone, we used a realistically shaped boundary-element model of human torso. By calculating singular values less ill conditioned. We then directly calculated epicardial and body-surface potentials for a single dipole located centrally and for three simultaneously active dipoles located eccentrically in the torso's heart region and used these results to test three methods that are prerequisites of a successful inverse solution: Tikhonov regularization, linearly constrained least squares, and an L-curve method. The feasibility of the new formulation was demonstrated by the fact that the method based on the linearly constrained least squares improved on overregularized Tikhonov solutions over a wide range of regularization parameters, and it yielded solutions that were more accurate than the best-possible Tikhonov solutions. Moreover, the L-curve solution procedure, which requires no a priori information about the solution, yielded slightly underregularized, but accurate, estimates for the optimal regularization parameter and the corresponding best-possible Tikhonov solution. Our results also showed that replacing--in the interest computational economy--quadrature formulas for the planar triangles with various approximate formulas for the nodes of the model reduces the accuracy of the inverse solution.

Value of simulated body surface potential maps as templates in localizing sites of ectopic activation for radiofrequency ablation.

Body surface potential maps recorded during catheter pace mapping can facilitate the localization of the site of origin of ventricular tachycardia. In this study, we investigated the value of a realistic computer model of the human ventricular myocardium in generating body surface potential maps as templates for identifying sites of ectopic activation. Our model features an anatomically accurate geometry and an anisotropy due to transmural fibre rotation, that were reconstructed with a spatial resolution of 0.5 mm. It simulates the electrotonic interactions of cardiac cells by solving a nonlinear parabolic partial differential equation, but it behaves as a cellular automaton when the transmembrane potential exceeds the threshold value. We successfully validated our model by comparing the simulated activation sequences--described by isochronal maps, epicardial potential maps and body surface potential maps--with the measured sequences of epicardial and body surface maps reported in the literature. By systematically pacing the left ventricular and right ventricular endocardial surfaces in our ventricular model, we generated a database of 155 QRS-integral maps, which provides a high-resolution reference frame for localizing distinct endocardial pacing sites. This database promises to be a useful tool in improving the performance of catheter pace mapping used in combination with body surface potential mapping. Overall, the results demonstrate that our computer model of the human ventricular myocardium is well suited for complementing a database of QRS-integral maps obtained during clinical pace mapping and can help enhance the efficacy of the ablative treatment of ventricular arrhythmias.

Spatial resolution of body surface potential maps and magnetic field maps: a simulation study applied to the identification of ventricular pre-excitation sites.

The spatial resolution of body surface potential maps (BSPMs) and magnetic field maps (MFMs) is investigated by means of an anatomically accurate computer model of the human ventricular myocardium. BSPMs and MFMs are calculated for the simulated activation sequences initiated at 35 pre-excitation sites located along the atrioventricular (AV) ring of the epicardium. Changes in the BSPMs and MFMs corresponding to different pre-excitation sites are quantified in terms of the correlation coefficient r. The spatial resolution (selectivity) for a given pre-excitation site is defined as the half-distance between those neighbouring locations at which morphological features of maps, in terms of r, become distinct (r < 0.95). It is found that, at 28 ms after the onset of pre-excitation and with no noise added, this distance +/- SD, for all sites along the AV ring for the 117-lead BSPMs, is 0.83 +/- 0.32 cm, and for the 64-lead and 128-lead MFMs it is 1.54 +/- 0.84 cm and 1.15 +/- 0.43 cm, respectively. The findings suggest that, when features of non-invasively recorded electrocardiographic and magnetocardiographic map patterns are used for identifying accessory pathways in patients suffering from WPW syndrome, BSPMs are likely to provide more detailed information for guiding the ablative treatment than MFMs. For some sites MFMs provide more information. Both modalities may provide additional assistance to the cardiologist in locating the site of the accessory pathway.

Accuracy of single-dipole inverse solution when localising ventricular pre-excitation sites: simulation study.

Different factors are investigated that may affect the accuracy of an inverse solution that uses a single-dipole equivalent generator, in a standardised inhomogeneous torso model, when localising the pre-excitation sites. An anatomical model of the human ventricular myocardium is used to simulate body surface potential maps (BSPMs) and magnetic field maps (MFMs) for 35 pre-excitation sites positioned on the epicardial surface along the atrioventricular ring. The sites of pre-excitation activity are estimated by the single-dipole method, and the measure for the accuracy of the localisation is the localisation error, defined as the distance between the location of the best-fitting single dipole and the actual site of pre-excitation in the ventricular model. The findings indicate that, when the electrical properties of the volume conductor and lead positions are precisely known and the 'measurement' noise is added to the simulated BSPMs and MFMs, the single-dipole method optimally localises the pre-excitation activity 20 ms after the onset of pre-excitation, within 0.71 +/- 0.28 cm and 0.65 +/- 0.30 cm using BSPMs and MFMs, respectively. When the standard torso model is used to localise the sites of onset of the pre-excitation sequence initiated in four individualised torso models, the maximum errors are as high as 2.6-3.0 cm (even though the average error, for both the BSPM and MFM localisations, remains within the 1.0-1.5 cm range). In spite of these shortcomings, it is thought that single-dipole localisations can be useful for non-invasive pre-interventional planning.

Value and limitations of an inverse solution for two equivalent dipoles in localising dual accessory pathways.

Investigations were carried out into whether an equivalent generator consisting of two dipoles could be used to detect dual sites of ventricular activity. A computer model of the human ventricular myocardium was used to simulate activation sequences initiated at eight different pairs of sites positioned on the epicardial surface of the atrio-ventricular ring. From these sequences, 117-lead body surface potentials (covering the anterior and posterior torso), 64-lead magnetic field maps (above the anterior chest) and 128-lead magnetic field maps (above the anterior and posterior chest) were simulated and were then used to localise dual accessory pathways employing pairs of equivalent dipoles. Average localisation errors were 12 mm, 12 mm and 9 mm, respectively, when body surface potentials, 64-lead and 128-lead magnetic fields were used. The results of the study suggest that solving the inverse problem for two dipoles could provide additional information on dual accessory pathways prior to electrophysiological study.