QT interval prolongation and risk for cardiac events in genotyped LQTS-index children.

Congenital long-QT syndrome (LQTS) is an inherited cardiac disorder with a disturbance in repolarization characterized by a prolonged QT interval on the surface electrocardiogram and life-threatening ventricular tachycardia. Publications from the International LQTS Registry have provided information that the cardiac risk may be influenced by gender, genotype, exposure to arrhythmia triggers, and previous cardiac events. In children, early-onset of disease, changes in life style, and medical treatment is a sensitive issue and significant, gender-related differences of a first life-threatening event were reported. Thus, we investigated the clinical features of a large genotyped population of LQTS-index children (age < or =16 years) upon a single-center experience and determined risk factors for symptoms. Of 83 children [mean corrected QT interval (QTc) 510 +/- 74 ms], 89% had LQT1, -2, or -3. Nine patients (11%) were identified as having Jervell and Lange-Nielsen syndrome. Among symptomatic children (n = 51, 61%), syncope was the most prevalent symptom at initial presentation (49%); however, aborted cardiac arrest (ACA) occurred in 33% and sudden cardiac death (SCD) in 18%, respectively, as the initial manifestation. During a mean follow-up period of 5.9 +/- 4.7 years, 31% of the children developed symptoms while on therapy (86% syncope, 9% ACA, 5% SCD). Statistical analyses of risk factors for cardiac events showed that the QTc >500 ms was a strong and significant predictor for cardiac events during follow-up (p = 0.02). Furthermore, a prior syncope [hazard ratio (HR), 4.05; 95% confidence interval (CI), 1.1 to 15.0; p = 0.03] or an ACA (HR, 11.7; 95% CI, 3.1 to 43.4; p = <0.001) identified children with an increased risk for recurrent cardiac events compared to asymptomatic LQT children. LQTS-index children manifest with a high percentage of severe symptoms. Among presently validated risk factors for LQTS, a QTc interval >500 ms and a history of prior syncope or ACA were strong predictors for recurrent cardiac events.

Spectra of electron-beam pumped XeF lasers.

An analysis is presented of the lasing spectrum of the rovibronic XeF(B-X) transition as observed in an electron-beam pumped laser. The intricate spin-split rotational and vibrational structure in the 35.1- and 353-nm lasing emission is investigated, and insight is gained on the processes responsible for the vibrational, rotational, and spin inhomogeneities manifested in the spectra. Explanations of the data are developed in terms of near-resonant vibration-rotation energy transfer, rotational relaxation rate differences in the B and X states, rapid dissociation of the rotational resonances near the dissociation limit of the ground state, relatively slow collisional spin relaxation, and optical coupling of spin states. The implications for narrowband extraction in the 351- and 353-nm bands are noted. The rotational relaxation rates of the X and B states of XeF are estimated in the Appendix.

Mechanisms for improved XeF laser performance at elevated temperatures.

Lasing spectra and output efficiency have been measured for four Ne/Xe/NF(3) laser mixtures from 300 to 450 K. These high resolution spectra have been correlated with a theoretical rotational bandhead structure to identify rotational states contributing to two narrowband emissions in the 351-nm band. Rotationalvibrational population shifts appear to be the most important mechanisms responsible for the increase in laser efficiency with temperature. Increased ground-state dissociation and decreased narrowband absorption may not be as important as previously thought.