Electrogram analysis and pacing are complimentary for recognition of abnormal conduction and far-field potentials during substrate mapping of infarct-related ventricular tachycardia.

BACKGROUND Mapping to identify scar-related ventricular tachycardia re-entry circuits during sinus rhythm focuses on sites with abnormal electrograms or pace-mapping findings of QRS morphology and long stimulus to QRS intervals. We hypothesized that (1) these methods do not necessarily identify the same sites and (2) some electrograms are far-field potentials that can be recognized by pacing. METHODS AND RESULTS From 12 patients with coronary disease and recurrent ventricular tachycardia undergoing catheter ablation, we retrospectively analyzed electrograms and pacing at 546 separate low bipolar voltage (<1.5 mV) sites. Electrograms were characterized as showing evidence of slow conduction if late potentials (56%) or fractionated potentials (76%) were present. Neither was present at (13%) sites. Pacing from the ablation catheter captured 70% of all electrograms. Higher bipolar voltage and fractionation were independent predictors for pace capture. There was a linear correlation between the stimulus to QRS duration during pacing and the lateness of a capturing electrogram (P<0.001), but electrogram and pacing markers of slow conduction were discordant at 40% of sites. Sites with far-field potentials, defined as those that remained visible and not captured by pacing stimuli, were identified at 48% of all pacing sites, especially in areas of low bipolar voltage and late potentials. Initial radiofrequency energy application rendered 74% of targeted sites electrically unexcitable. CONCLUSIONS Far-field potentials are common in scar areas. Combining analysis of electrogram characteristics and assessment of pace capture may refine identification of substrate targets for radiofrequency ablation.

Analysis of ozone and water vapor field measurement data /

Mode of access: Internet.

Problems of administration and supervision in modern elementary schools; a syllabus in two volumes. vol. 1-2. Based on an analysis of 472 questionnaires obtained from active elementary school principals in the field,

Mode of access: Internet.

Sinkhole-type subsidence over abandoned coal mines in St. David, Illinois : mine subsidence report, St. David, Illinois : a field survey and analysis of mine subsidence of abandoned coal mines in St. David, Illinois /

"June, 1980."

The geomagnetic field, its description and analysis

Mode of access: Internet.

Regional analysis of production adjustments in the major field crops : historical and prospective : an application of spatial linear programming /

Literature cited and selected references: p. 38-41.

Regional location of production of major field crops at alternative demand and price levels, 1975; a linear programing analysis,

Issued in cooperation with Iowa State University of Science and Technology, Agriculture and Home Economics Experiment Station, and the Center for Agricultural and Economic Development.

Assessing soil compaction on forest inventory & analysis phase 3 field plots using a pocket penetrometer /

"April 2004."

An isotopic analysis of geothermal brine and calcite scaling from the Blue Mountain geothermal field, Winnemucca, Nevada

Understanding, and controlling, the conditions under which calcite precipitates within geothermal energy production systems is a key step in maintaining production efficiency. In this study, I apply methods of bulk and clumped isotope thermometry to an operating geothermal energy facility in northern Nevada to see how those methods can better inform the facility owner, AltaRock Energy, Inc., about the occurrence of calcite scale in their power plant. I have taken water samples from five production wells, the combined generator effluent, shallow cold-water wells, monitoring wells, and surface water. I also collected calcite scale samples from within the production system. Water samples were analyzed for stable oxygen isotope composition (d18O). Calcite samples were analyzed for stable oxygen and carbon (d13C) composition, and clumped isotope composition (D47). With two exceptions, the water compositions are very similar, likely indicating common origin and a well-mixed hydrothermal system. The calcite samples are likewise similar to one another. Apparent temperatures calculated from d18O values of water and calcite are lower than those recorded for the system. Apparent temperatures calculated from D47 are several degrees higher than the recorded well temperatures. The lower temperatures from the bulk isotope data are consistent with temperatures that could be expected during a de-pressurization of the production system, which would cause boiling in the pipes, a reduction in system temperature, and rapid precipitation of calcite scale. However, the high apparent temperature indicated by the D47 data suggests that the calcite is depleted in clumped isotopes given the known temperature of the system, which is inconsistent with this hypothesis. This depletion could instead result from disequilibrium isotopic fractionation during the aforementioned boil events, which would make both the apparent d18O-based and D47-based temperatures unrepresentative of the actual water temperature. This research can help improve our understanding of how isotopic analyses can better inform us about the movement of water through geothermal systems of the past and how it now moves through modern systems. Increased understanding of water movement in these systems could potentially allow for more efficient utilization of geothermal energy as a renewable resource.

An object-oriented designed finite-difference time-domain simulator for electromagnetic analysis and design in MRI - application to high field analyses

This paper presents a finite-difference time-domain (FDTD) simulator for electromagnetic analysis and design applications in MRI. It is intended to be a complete FDTD model of an MRI system including all RF and low-frequency field generating units and electrical models of the patient. The pro-ram has been constructed in an object-oriented framework. The design procedure is detailed and the numerical solver has been verified against analytical solutions for simple cases and also applied to various field calculation problems. In particular, the simulator is demonstrated for inverse RF coil design, optimized source profile generation, and parallel imaging in high-frequency situations. The examples show new developments enabled by the simulator and demonstrate that the proposed FDTD framework can be used to analyze large-scale computational electromagnetic problems in modern MRI engineering. (C) 2004 Elsevier Inc. All rights reserved.