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Biomedical subjects

R L Lux

Publications and source records attributed to R L Lux.

At least 91 records · Page 5Linked to original sources
PubMed1982

Application of body surface mapping to exercise testing: S-T80 isoarea maps in patients with coronary artery disease.

Body surface electrocardiographic maps were recorded before and after exercise in 25 men with angiographically documented coronary disease. Torso potential distributions at 192 locations were derived from a 32 lead electrode array using methods previously described in our laboratory. The S-T segment was characterized by the spatial distribution of the integral of S-T segment voltage over 80 ms (S-T80). Body surface regions where the S-T80 areas were =8 mV . ms or greater were identified in 18 of 25 patients. The most negative S-T80 site on the map was called the "S-T80 minimum." The S-T80 minima were located 1 or 2 electrode rows away from the standard V4--V6 electrode positions in 6 of 18 patients who developed S-T80 areas of -8 mV . ms or greater. Our data suggest that standard electrocardiographic leads may not be optimal for identifying S-T segment depression in all patients with coronary disease. Furthermore, body surface mapping during exercise provides a more quantitative and qualitative method for characterizing the ischemic response to exercise.

Adult↗
PubMed1982

The QRST deflection area of electrograms during global alterations of ventricular repolarization.

Changes of refractory period and QRST deflection area in cardiac electrograms due to localized myocardial warming and altered cycle length were determined. Localized myocardial warming consistently resulted in increased QRST deflection area which was highly correlated with reduction of refractory period. Similar reductions of refractory period by decreased cycle length were associated with insignificant changes of small QRST areas and significant reductions of larger QRST areas. The different effect of local thermal alteration of repolarization and global alteration due to cycle length changes is experimental evidence that QRST deflection area depends on differences in duration of ventricular repolarization properties. The finding of decreased deflection area with decreased cycle length is also evidence of decreased disparity of repolarization properties of normal myocardium at rapid heart rates.

Animals↗
PubMed1982

Relation of canine atrial activation sequence to anatomic landmarks.

Activation sequence in the atria was investigated in 35 dogs. The atria were studied as four regions, and activation sequence in one region was determined in each experiment. In each region 60 electrograms were recorded simultaneously from bipolar electrodes. The maximal first derivative of the electrograms was taken as activation time. Dried atrial specimens, which permitted identification of pectinate muscles, crista terminalis, and the axis of fiber direction, were prepared. Nonuniform activation was demonstrated with more rapid conduction over the long axis of fiber direction and in Bachmann's bundle, crista terminalis, and pectinate muscles. These regions of rapid conduction were the same during sinus rhythm and ectopic and retrograde activation. Findings confirm the presence of paths with relatively rapid conduction in the atria and demonstrate that these are related to gross anatomic features. Findings also demonstrate that the paths are accessible to activation from multiple sites rather than insulated conduction paths with limited sites for entry and exit of activation.

Animals↗
PubMed1982

Electrocardiographic body surface potential mapping.

This article is intended as a review of the field of electrocardiographic body surface potential mapping. The problems associated with measurement of potential distributions will be described, along with the various techniques of data acquisition and display that have evolved over the past decade. Description of mapping applications as they apply to clinical and experimental electrocardiography are presented. The article has been written from a historical perspective, although emphasis is placed on current, state-of-the-art approaches.

Data Display↗
PubMed1981

Sequences of early and late phases of repolarization on dog ventricular epicardium.

Monophasic action potentials from 32 to 43 epicardial sites were recorded with concentric suction electrodes in 11 dogs during atrial pacing at a constant rate. The duration of action potentials and the sequence of repolarization referenced to the onset of ventricular activation at 50% of the highest plateau amplitude and the end of the action potential were determined. These quantities were correlated with activation sequence determined from action potential upstrokes. On the anterior ventricular surface, both 50% and 100% repolarization sequences were qualitatively similar to activation sequence and showed positive correlation coefficients. On the posterior ventricular surface, 50% and 100% repolarization sequences had little qualitative resemblance to activation sequence and showed lower correlation coefficients. Correlations between the patterns of 100% repolarization and action potential duration were significantly higher on the posterior than the anterior ventricular surface. These findings demonstrate that activation sequence has less influence on repolarization sequence on the posterior than the anterior wall and that action potential duration is the major determinant of repolarization sequence on the posterior wall. These findings extend previous descriptions of the normal sequence of ventricular repolarization and the relative roles of activation and action potential duration in determining that sequence. The study also showed differences between the sequences of 50% and 100% repolarization suggesting different slopes of action potential downstrokes at various ventricular sites with steeper slopes at the posterior basal and upper anterolateral left ventricular wall. This finding adds new detail to previous descriptions of the distribution of intrinsic ventricular recovery properties.

Action Potentials↗
PubMed1981

Redundancy reduction for improved display and analysis of body surface potential maps. I. Spatial compression.

The Karhunen-Loeve technique of random process representation was investigated as a method of quantitatively characterizing body surface potential maps. One hundred ninety-two lead body surface potential maps from 124 normal subjects and 97 patients with independently documented heart disease were used in the study. Each map frame in QRS and ST-T of 34 maps in a test set was represented as a linear sum of orthonormal distributions derived from the covariance matrix estimated from all QRS frames in the 221 training maps. A 16:1 reduction in spatial data of the test set was achieved with rms errors of 45 and 21 microV in QRS and ST-T, respectively. Results suggest that 12 independent waveforms, derived from the 192 measured ECGs, may be used in place of those 192 ECGs. In addition to providing a convenient and familiar method of display for map data, the technique puts the data in an appropriate form for quantitative statistical analysis.

Cardiomegaly↗
PubMed1981

Redundancy reduction for improved display and analysis of body surface potential maps. II. Temporal compression.

This paper describes use of the Karhunen-Loeve expansion to identify and reduce temporal redundancy in electrocardiographic body surface potential maps (192 body surface leads recorded simultaneously at 1 kHz/channel for approximately 600 msec). Temporal data compression of about 20 to 1 was obtained with accurate representation of the original data. Use of separate sets of orthonormal basis functions for QRS and ST-T provided a more accurate representation than the basis derived from QRST. Combined with the spatial compression described in the preceding paper, overall map data compression of about 320 to 1 was obtained without significant loss of accuracy of representation or map appearance. With both spatial and temporal compression the 100,000 numbers which typically comprise a single cardiac complex were accurately represented by 216 coefficients. Using basis functions derived from a single cardiac complex were accurately represented by 216 coefficients. Using basis functions derived from a training set of 221 maps, the estimated average rms error of representation was 60 microV during the ST-T. For 34 test maps which were not part of the training set, measured average errors were 64 microV during the QRS and 23 microV during the ST-T. This technique provides a basis for quantification of the diagnostic content of maps and automated classification of maps.

Adult↗
PubMed1980

Body surface distribution of QRS deflection areas in experimental ventricular preexcitation.

The utility of QRS isoarea maps for recognition of preexcitation sites was evaluated in chronic experiments in dogs. Pacing electrodes were surgically implanted on the atrium and ventricular sites near the AV ring. Electrocardiograms from 192 torso sites were simultaneously recorded during pacing of the atrium together with each of the ventricular sites. Time phase of atrial and ventricular stimuli was varied to yield both preexcitation with clear delta waves and more subtle forms of preexcitation with sites activated earlier than normal but after onset of the normal QRS. QRS area maps were determined by integrating QRS amplitudes at 1 msec intervals over the QRS duration. Results showed a systematic relation between the body surface location of the minimum in the QRS area maps and the preexcitation site. In additon there was a linear relation between the magnitude of maximum and minima in the QRS isoarea maps over different degrees of preexcitation, and the slope of curves showing this relation differed for different sites of preexcitation. Findings suggest that a single display of the QRS isoarea map may permit identification and localization of preexcitation including subtle forms occurring after the onset of the QRS.

Animals↗
PubMed1980

Variability of the body surface distributions of QRS, ST-T and QRST deflection areas with varied activation sequence in dogs.

Distributions of QRS, ST-T and QRST areas of 192 lead body surface ECG's were measured in dogs for multiple activation orders. Qualitatively, the distributions of QRST area were found to be strikingly similar over all activation orders in contrast to the distributions of QRS or ST-T areas. Quantitative results showed that variability of the QRST areas over all activation orders was consistently less than those of either QRS or ST-T. The factor responsible for the QRS deflection is ventricular activation sequence while those responsible for the ST-T deflection are both activation sequence and ventricular recovery properties. Since the total QRST deflection area was largely independent of activation sequence it is likely the quantity is an index of ventricular recovery properties. The significance of this relation is that QRST deflection area may permit evaluation of intrinsic ventricular recovery properties in the presence of abnormal ventricular activation as occurs with intraventricular conduction disorders and ectopic origin of excitation. Evaluation of intrinsic ventricular recovery properties may also permit recognition of states at risk of ventricular arrhythmias due to increased disparity of these properties.

Animals↗
PubMed1980

Ventricular recovery properties and QRST deflection area in cardiac electrograms.

We measured QRST deflection areas in cardiac surface electrograms of dogs and determined their relation to changes of refractory period induced by localized myocardial warming. Refractory period changes and QRST deflection areas were highly correlated with an average correlation of 0.95 over multiple activation sequences. For a single activation sequence, refractory period change was also highly correlated with ST-T deflection area, but over multiple activation sequences this correlation was reduced and the pooled variance of ST-T deflection areas was over 18 times greater than that of QRST area. No relation between QRST deflection area and the absolute value of refractory period over various cardiac sites was evident. Findings suggest that a particular set of ventricular recovery properties cannot be defined on the basis of QRST deflection areas, but that changes of recovery properties can be recognized on that basis.

Action Potentials↗
PubMed1980

Detailed activation sequence in the region of electrically induced ventricular fibrillation in dogs.

We determined the details of ventricular activation sequence during the onset of ventricular fibrillation in 6 dogs. Unipolar electrograms were simultaneously recorded from 192 ventricular epicardial sites evenly spaced in a 3 by 3 cm square area surrounding 2 central sites to which stimuli for inducing fibrillation were delivered. In 5 dogs, 2 to 10 msec duration pulses with amplitudes of 150 to 220 v were used to induce fibrillation, and in 1 dog, 3 successive permature stimuli of 3 v intensity were used to induce fibrillation. In 2 dogs the pattern of activation at the onset of fibrillation was compatible with local reentrant paths near the stimulus site. Fibrillation was induced with a single high intensity pulse in both of these dogs. In the other 4 dogs, the pattern of activation at the onset of fibrillation was highly suggestive of reentrant paths distant from the stimulating electrodes. In 3 of these dogs fibrillation was induced by a single high intensity pulse and in the other it was induced by 3 repetitive stimuli. Activation patterns resembling supraventricular activation occurred prior to fibrillation in the latter animal. The data demonstrate 2 distinct modes of onset of electrically induced ventricular fibrillation. The findings support local reentry in the region of the stimulus site as the mode of onset of fibrillation in some animals and possible reentry at sites distant from the stimulus site with participation of the specialized conduction system in other animals. The differences in mode of onset of electrically induced fibrillation may be responsible for instability of fibrillation threshold measurements in some animals. In addition the role of the specialized conduction system in the onset of fibrillation may be responsible for the effects of sympathetic and vagal stimulation on fibrillation threshold.

Animals↗
PubMed1979

Clinically practical lead systems for improved electrocardiography: comparison with precordial grids and conventional lead systems.

The use of limited leads for estimating total body surface potential distributions was investigated as a practical solution to the problem associated with extensive electrocardiographic sampling used in surface potential mapping. Two practical, limited lead sets of 32 leads each were derived and contrasted to a set of 30 precordial leads similar to those used in ST-segment and QRS mapping for estimating infarct size, and to a set of nine leads simulating those used in conventional 12-lead examinations. The two arrays, one of which excluded posterior sites for use in recumbent patients, showed little difference in ability to estimate 192 lead measured maps (average rms voltage error of 35 muV and average correlation coefficient of 0.97). The 30- and 9-lead arrays consistently showed twice the voltage (72 muV) and poorer pattern estimation (average correlation coefficient of 0.91) than either of the 32 lead arrays. These findings indicate the need for 20-35 properly located electrodes for accurate total body surface potential estimation. They also show that there is no difference in the abilities of a 30-lead precordial array and conventional leads to estimate maps.

Arrhythmias, Cardiac↗
PubMed1978

The relation of localized myocardial warming to changes in cardiac surface electrograms in dogs.

We studied the relationship of the size and severity of alteration of recovery properties in localized areas to changes in cardiac surface electrograms in experiments on six open-chest dogs. Alterations in recovery properties were induced thermally because size and severity of the affected area could be controlled on the basis of physical principles which were modeled. We recorded unipolar electrograms from 75 cardiac surface sites simultaneously during stimulation of atria and pulmonary conus in control periods and in the presence of warmed areas of varying sizes and intensities. Size of the areas was controlled by the diameter of an aperture through which a light source was directed. Intensity was controlled by the light source excitation voltage. Myocardial temperature was monitored with a thermistor. The QRS, STT, and QRST deflection areas were determined by computer processing and displayed as isoarea maps. Difference maps also were determined by subtracting control QRST isoarea maps from those obtained in the presence of warmed areas. QRST area difference maps were related closely to the size and severity of the thermally induced changes in recovery properties. With areas of the same size and increasing myocardial temperatures, the magnitude of the change in QRST area increased, and the gradient of contour lines between the affected and unaffected areas increased. When myocardial temperature at the center of the warmed area was kept constant and the size of the warmed area was increased, the affected cardiac surface area increased, but the number of isoarea contours remained approximately the same. These findings suggest that the change in QRST isoarea maps may be a useful indicator of lesion size when combined with an index of lesion severity such as the QRST area change in the electrogram with the maximum change. QRST areas during both activation orders were similar, suggesting that the QRST area is independent of changes in activation sequence.

Action Potentials↗
PubMed1977

Diagnosis of old inferior myocardial infarction by body surface isopotential mapping.

Body surface isopotential maps obtained from 28 patients with old inferior wall myocardial infarction were compared with maps from 120 normal subjects. The 12 lead electrocardiogram of 8 of the 28 patients (29 percent) with inferior wall infarction was normal or showed only nondiagnostic ST-T wave abnormalities at the time the isopotential maps were obtained. In all patients with inferior wall infarction the isopotential map showed a minimum (area of negative potentials) on the inferior or right thoracic surface during the early portions of the QRS complex. This finding was observed in patients with normal or nonspecific abnormalities in the 12 lead electrocardiogram as well as those with QRS abnormalities. By contrast, the minimum during the early QRS complex in normal subjects was located on the right upper back and shoulder region...

Back↗
PubMed1976

The expression of normal ventricular repolarization in the body surface distribution of T potentials.

Isopotential maps from 120 normal subjects were obtained from 192 simultaneously recorded electrocardiographic leads. Maps were plotted at 1 msec intervals during the QRS and 5 msec intervals during the ST-T deflection. Repetition of QRS features was evident during all but the first few msec of the initial half of serial T maps. This suggests similarities of the normal sequence of ventricular excitation and recovery. Such similarities have been demonstrated by direct studies but are not evident from other electrocardiographic examinations. Serial maps during later portions of the T wave showed decreasing intensity of potentials with little change of body surface locations. This also correlates with an established feature of ventricular repolarization, namely that potential difference boundaries with stable locations are widely distributed during part of that process. Findings suggest isopotential maps show features of ventricular recovery not apparent from less extensive examinations.

Action Potentials↗