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Biomedical subjects

Robert L Lux

Publications and source records attributed to Robert L Lux.

9 recordsLinked to original sources
PubMed2006

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.

Algorithms↗
PubMed2003

Cycle length sequence dependent repolarization dynamics.

Cardiac repolarization, particularly its heterogeneity, is known to play a significant role in arrhythmogenesis. Steepness of cardiac restitution, or the cycle length dependency of repolarization, has also been implicated as a condition that favors occurrence of reentrant arrhythmias. However, most assessments of heterogeneity and restitution are based on static observations and do not directly account for the extent or heterogeneity of dynamic changes. The uncertainty and unpredictability of arrhythmias and the difficulty of identifying patients most at risk may possibly be explained by the lack of consideration of dynamic changes of repolarization, its heterogeneity and time varying restitution. In this brief article, we show the global changes in repolarization that occur in normal canine hearts in response to programmed cycle length sequences. Specifically, we show the beat-to-beat tracking of repolarization during rapid (step) changes in cycle length as well as linear up and down (sawtooth) changes, and random cycle length sequences. The measurement and robust characterization of the dynamic repolarization response to specific cycle length sequences may offer an opportunity to characterize the substrate for arrhythmias to a greater extent than has been possible to date. Although there is no guarantee that characterization of repolarization dynamics will provide definitive means to identify patients at risk, such assessment will, at a minimum, put into perspective the role that repolarization dynamics may play in detecting states of increased arrhythmia risk. Another potential use of these techniques is in the assessment of repolarization in patients undergoing EP testing, pharmacological therapies or during other provocative testing.

Animals↗
PubMed2002

Electrocardiographic potential correlations: rationale and basis for lead selection and ECG estimation.

Einthoven gave to us the electrocardiogram. Electrocardiographic mapping demonstrated that localized electrophysiological events and phenomena have localized body surface electrocardiographic manifestations. Clinical electrocardiography has given us "reasonably good" means (criteria) with which to detect and characterize medically significant cardiac conditions, events, and diseases. However, clinical electrocardiography is imperfect, largely as a consequence of inadequate or redundant spatial sampling. This compromises the sensitivity and specificity of diagnosing cardiac diseases for which electrocardiographic manifestations are present but undetected due to imperfect sampling that results in a low signal-to-noise ratio for the specific abnormality. Correlation structure of body-surface potential distributions between and across populations or individuals provides important insight into and justification for the selection and use of "limited", "reduced", or "derived" lead systems aimed at improving the capture and use of electrocardiographic information. In this paper, we show the electrocardiographic voltage correlation relationships that occur on the body surface, across groups of subjects, either with or without cardiac disease. In addition, we demonstrate the correlation relationships between torso-surface and epicardial-surface potential distributions in experiments incorporating isolated canine hearts in a human-shaped torso tank. Analysis of these correlation relationships provides an explanation for the long-standing success of clinical electrocardiography but also suggests the means to improve its performance by incorporating new leads and/or their estimation from appropriately selected leads.

Body Surface Potential Mapping↗
PubMedDate not supplied

Spatial methods of epicardial activation time determination in normal hearts.

The purpose of this study was to demonstrate errors in activation time maps created using the time derivative method on fractionated unipolar electrograms, to characterize the epicardial distribution of those fractionated electrograms, and to investigate spatial methods of activation time determination. Electrograms (EGs) were recorded using uniform grids of electrodes (1 or 2 mm spacing) on the epicardial surface of six normal canine hearts. Activation times were estimated using the time of the minimum time derivative, maximum spatial gradient, and zero Laplacian and compared with the time of arrival of the activation wave front as assessed from a time series of potential maps as the standard. When comparing activation times from the time derivative for the case of epicardial pacing, spatial gradient and Laplacian methods with the standard for EGs without fractionation, correlations were high (R2 = 0.98, 0.98, 0.97, respectively). Similar comparisons using results from only fractionated EGs (R2 = 0.85,0.97,0.95) showed a lower correlation between times from the time derivative method and the standard. The results suggest an advantage of spatial methods over the time derivative method only for the case of epicardial pacing where large numbers of fractionated electrograms are found.

Action Potentials↗