US Naval Research Laboratory focus issue: introduction.

Rather than concentrate on a single topic, this feature issue presents the wide variety of research in optics that takes place at a single institution, the United States Naval Research Laboratory (NRL) and is analogous to an NRL feature issue published in Applied Optics in 1967. NRL is the corporate research laboratory for the Navy and Marine Corps. It conducts a broadly based multidisciplinary program of scientific research and advanced technological development in the physical, engineering, space, and environmental sciences related to maritime, atmospheric, and space domains. NRL's research is directed toward new and improved materials, techniques, equipment, and systems in response to identified and anticipated Navy needs. A number of articles in this issue review progress in broader research areas while other articles present the latest results on specific topics.

Optics research at the U.S. Naval Research Laboratory.

The Naval Research Laboratory (NRL) was established in Washington, DC in 1923 and is the corporate laboratory for the U.S. Navy and Marine Corps. Today NRL is a world-class research institution conducting a broad program of research and development (R&D), including many areas of optical science and technology. NRL is conducting cutting-edge R&D programs to explore new scientific areas to enable unprecedented Navy capabilities as well as improving current technologies to increase the effectiveness of Navy and other Department of Defense systems. This paper provides a broad overview of many of NRL's achievements in optics. Some of the remaining articles in this feature issue will discuss NRL's most recent research in individual areas, while other articles will present more detailed historical perspectives of NRL's research concerning particular scientific topics.

Direct visualization of the slow pathway using voltage gradient mapping: a novel approach for successful ablation of atrioventricular nodal reentry tachycardia.

AIMS: Ablation of atrioventricular nodal reentry tachycardia (AVNRT) has become treatment of choice because of a high success and low complication rate. Most ablations are successful in utilizing an anatomic approach, but anatomic variance, unusual pathway locations, or multiple pathways may complicate the procedure. Visualization of the slow pathway could expedite ablation success and enhance safety. Our purpose is to determine whether voltage gradient mapping can directly image the slow pathway and aid successful ablation of AVNRT. METHODS AND RESULTS: Three-dimensional voltage maps of the right atrial septum were constructed from intracardiac recordings obtained by contact mapping. Voltage values were adjusted until low-voltage bridging was observed within the Triangle of Koch. Forty-eight consecutive patients undergoing ablation for inducible AVNRT, underwent voltage gradient mapping. The slow pathway was identified in all 48 patients via its corresponding low-voltage bridge. Ablation of the slow pathway associated low-voltage bridges in 48 patients was successful in preventing reinduction following the first lesion in 43 of 48 patients. Five patients had multiple slow pathways and >1 lesion was required to prevent reinduction. Repeat mapping confirmed the absence of low-voltage connections previously observed in all 48 patients. CONCLUSION: Voltage gradient mapping can assist in visualization of the slow pathway. Ablation of the associated low-voltage bridge results in loss of slow pathway function and significant changes in the post-ablation voltage map. We conclude that voltage gradient mapping offers the ability to target the slow pathway for successful ablation.

Substrate Targeted Ablation of Atrial Fibrillation Guided by High Density Voltage Mapping: Long-Term Results.

BACKGROUND: Long-term ablation results for atrial fibrillation (AF) have been disappointing, particularly for non-paroxysmal AF (NPAF). We hypothesize fibrosis in paroxysmal AF (PAF) and NPAF would be reflected in voltage fragmentation and visualized by high density mapping. Targeted ablation of discrete low voltage bridges (LVB) would eliminate endocardial fragmentation and should have a positive effect on long-term sinus rhythm (SR) survival. OBJECTIVE: To assess the efficacy of LVB ablation on SR survival in patients with PAF and NPAF, as well as, determine its impact on P wave duration (PWD) and LA volume (LAV). METHODS: 56 patients (29PAF/26NPAF) had a voltage gradient map (VGM) created, high and low voltage limits were adjusted to image LVB. Ablation was performed until no LVB were observed. Baseline PWD and LAV were obtained and reassessed 6 months' post ablation. Patients were followed for 5 years with intermittent monitors. RESULTS: Termination of AF in NPAF was 88%. PWD normalized in PAF and were normal in NPAF post ablation. LAV decreased significantly in NPAF. At 5 years, SR was observed in 89% of PAF and 67% of NPAF. CONCLUSIONS: 1. LVB ablation terminates AF in NPAF 88%; 2. Both PWD and LAV were improved; 3. Maintenance of SR was observed in 89% and 67% (PAF vs NPAF); 4. The present study demonstrates efficacy of a simplified, individualized, and unified methodology for AF ablation.

Assessment of the accuracy of two gutta-percha gauges used to alter gutta-percha tip diameter.

This study sought to compare the accuracy of two gauges used to alter gutta-percha (GP) cone tips. Randomly selected size 20 cones (with tapers of 0.02, 0.06, 0.10, or 0.12) were trimmed to size 50 (N= 10/taper/gauge) for an overall sample of 80 cones. Accuracy of the altered cone tips was determined by calculating the difference (in %) between the altered tip diameter and the expected tip diameter (0.50 mm). A two-factor ANOVA revealed significant differences (p < or = 0.05) in altered tip accuracy as a result of GP gauge and cone taper. The results suggest that the SybronEndo gauge performs accurately regardless of the cone taper, while the Maillefer gauge was accurate only when used to alter cones with a 0.02 taper.