Methods of Assessment and Clinical Relevance of QT Dynamics

The dependence on heart rate of the QT interval has been investigated for many years and several mathematical formulae have been proposed to describe the QT interval/heart rate (or QT interval/RR interval) relationship. While the most popular is Bazett’s formula, it overcorrects the QT interval at high heart rates and under-corrects it at slow heart rates. This formulae and many others similar ones, do not accurately describe the natural behaviour of the QT interval. The QT interval/RR interval relationship is generally described as QT dynamics. In recent years, several methods of its assessment have been proposed, the most popular of which is linear regression. An increased steepness of the linear QT/RR slope correlates with the risk of arrhythmic death following myocardial infarction. It has also been demonstrated that the QT interval adapts to heart rate changes with a delay (QT hysteresis) and that QT dynamics parameters vary over time. New methods of QT dynamics assessment that take into account these phenomena have been proposed. Using these methods, changes in QT dynamics have been observed in patients with advanced heart failure, and during morning hours in patients with ischemic heart disease and history of cardiac arrest. The assessment of QT dynamics is a new and promising tool for identifying patients at increased risk of arrhythmic events and for studying the effect of drugs on ventricular repolarisation

Screening for QT Prolongation in the Emergency Department: Is There a Better “Rule of Thumb?”

Introduction: Identification of QT prolongation in the emergency department (ED) is critical for appropriate monitoring, disposition, and treatment of patients at risk for torsades de pointes (TdP). Unfortunately, identifying prolonged QT is not straightforward. Computer algorithms are unreliable in identifying prolonged QT. Manual QT-interval assessment methods, including QT correction formulas and the QT nomogram, are time-consuming and are not ideal screening tools in the ED. Many emergency clinicians rely on the “rule of thumb” or “Half the RR” rule (Half-RR) as an initial screening method, but prior studies have shown that the Half-RR rule performs poorly as compared to other QT assessment methods. We sought to characterize the problems associated with the Half-RR rule and find a modified screening tool to more safely assess the QT interval of ED patients for prolonged QT.Methods: We created graphs comparing the prediction of the Half-RR rule to other common QT assessment methods for a spectrum of QT and heart rate pairs. We then proposed various modifications to the Half-RR rule and assessed these modifications to find an improved “rule of thumb.”Results: When compared to other methods of QT correction, the Half-RR rule appears to be more conservative at normal and elevated heart rates, making it a safe initial screening tool. However, in bradycardia, the Half-RR rule is not sufficiently sensitive in identifying prolonged QT. Adding a fixed QT cutoff of 485 milliseconds (ms) increases the sensitivity of the rule in bradycardia, creating a safer initial screening tool.Conclusion: For a rapid and more sensitive screening evaluation of the QT interval on electrocardiograms in the ED, we propose combining use of the Half-RR rule at normal and elevated heart rates with a fixed uncorrected QT cutoff of 485 ms in bradycardia

Optimisation of variables for studying dilepton transverse momentum distributions at hadron colliders

In future measurements of the dilepton ($Z/\gamma^*$) transverse momentum, \Qt, at both the Tevatron and LHC, the achievable bin widths and the ultimate precision of the measurements will be limited by experimental resolution rather than by the available event statistics. In a recent paper the variable \at, which corresponds to the component of \Qt\ that is transverse to the dilepton thrust axis, has been studied in this regard. In the region, \Qt\ $<$ 30 GeV, \at\ has been shown to be less susceptible to experimental resolution and efficiency effects than the \Qt. Extending over all \Qt, we now demonstrate that dividing \at\ (or \Qt) by the measured dilepton invariant mass further improves the resolution. In addition, we propose a new variable, \phistarEta, that is determined exclusively from the measured lepton directions; this is even more precisely determined experimentally than the above variables and is similarly sensitive to the \Qt. The greater precision achievable using such variables will enable more stringent tests of QCD and tighter constraints on Monte Carlo event generator tunes.Comment: 8 pages, 5 figures, 2 table

Quiet Time for Mechanically Ventilated Patients in The Medical Intensive Care Unit

Objective: Sleep disruption occurs frequently in critically ill patients. The primary aim of this study was to examine the effect of quiet time (QT) on patient sedation frequency, sedation and delirium scores; and to determine if consecutive QTs influenced physiologic measures (heart rate, mean arterial blood pressure and respiratory rate). Method: A prospective study of a quiet time protocol was conducted with 72 adult patients on mechanical ventilation. Setting: A Medical Intensive Care Unit (MICU) in the Midwest region of the United States. Results: Sedation was given less frequently after QT (p = 0.045). Those who were agitated prior to QT were more likely to be at goal sedation after QT (p \u3c 0.001). Although not statistically significant, the majority of patients who were negative on the Confusion Assessment Method (CAM-ICU) prior to QT remained delirium free after QT. Repeated measures analysis of variance (ANOVA) for three consecutive QTs showed a significant difference for respiratory rate (p = 0.035). Conclusion: QT may influence sedation administration and promote patient rest. Future studies are required to further understand the influence of QT on mechanically ventilated patients in the intensive care unit

Quantum Drinfeld Modules II: Quantum Exponential and Ray Class Fields

This is the second in a series of two papers presenting a solution to Manin's Real Multiplication program \cite{Man} in positive characteristic. If $K$ is a quadratic and real extension of $\mathbb{F}_{q}(T)$ and $\mathcal{O}_{K}$ is the integral closure of $\mathbb{F}_{q}[T]$ in $K$, we associate to each modulus $\mathfrak{M}\subset \mathcal{O}_{K}$ the {\it unit narrow ray class field} $K^{\mathfrak{M}}$: a class field containing the narrow ray class field, whose class group contains an additional contribution coming from $\mathcal{O}^{\times}_{K}$. For $f\in K$ a fundamental unit, we introduce the associated {\it quantum Drinfeld module} $\rho^{\rm qt}_{f}$ of $f$: a generalization of Drinfeld module whose elements are multi-points. The main theorem of the paper is that $$K^{\mathfrak{M}}=H_{\mathcal{O}_{K}} ( {\sf Tr}(\rho^{\rm qt}_{f}[\mathfrak{M}]), {\sf Tr}(\rho^{\rm qt}_{f^{-1}}[\mathfrak{M}]))$$ where $H_{\mathcal{O}_{K}}$ is the Hilbert class field of $\mathcal{O}_{K}$ and ${\sf Tr}(\rho^{\rm qt}_{f}[\mathfrak{M}])$, ${\sf Tr}(\rho^{\rm qt}_{f^{-1}}[\mathfrak{M}])$ are the groups of traces of $\mathfrak{M}$ torsion points of $\rho^{\rm qt}_{f}$, $\rho^{\rm qt}_{f^{-1}}$.Comment: 41 page

Vector boson production at hadron colliders: transverse-momentum resummation and leptonic decay

We consider the transverse-momentum (qT ) distribution of Drell-Yan lepton pairs produced, via W and Z/γ∗ decay, in hadronic collisions. At small values of qT , we resum the logarithmically-enhanced perturbative QCD contributions up to next-to-next- to-leading logarithmic accuracy. Resummed results are consistently combined with the known O(αS2 ) fixed-order results at intermediate and large values of qT . Our calculation includes the leptonic decay of the vector boson with the corresponding spin correlations, the finite-width effects and the full dependence on the final-state lepton(s) kinematics. The computation is encoded in the numerical program DYRes, which allows the user to apply arbitrary kinematical cuts on the final-state leptons and to compute the corresponding distributions in the form of bin histograms. We present a comparison of our results with some of the available LHC data. The inclusion of the leptonic decay in the resummed cal- culation requires a theoretical discussion on the qT recoil due to the transverse momentum of the produced vector boson. We present a qT recoil procedure that is directly applica- ble to qT resummed calculations for generic production processes of high-mass systems in hadron collisions.Fil: Catani, Estefano. Universita Degli Studi Di Firenze; ItaliaFil: de Florian, Daniel Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología. Centro Internacional de Estudios Avanzados; ArgentinaFil: Ferrera, Giancarlo. Università degli Studi di Milano; ItaliaFil: Grazzini, Massimiliano. Universitat Zurich; Suiz