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QT Peak (qt + peak)
Selected AbstractsPredictive Value of Admission Electrocardiography in Patients With Heart FailureCONGESTIVE HEART FAILURE, Issue 4 2008Karolina M. Zareba MD Admission electrocardiography (ECG) in heart failure (HF) patients provides important diagnostic information; however, there are limited data regarding the prognostic significance of ECG parameters for predicting cardiac events (CEs). The ECGs of 246 patients admitted with acute HF were evaluated for heart rate, rhythm, QRS and ST-T wave abnormalities, QTc duration, QT peak corrected (QTpc), T amplitude, and axis. The end points included rehospitalization for a CE or death during 30-day follow-up. There were 71 (29%) patients with CEs. In patients with CEs, atrial fibrillation (AF) was observed more frequently (27% vs 13%, respectively; P=.009) and QTpc was shorter (370±43 vs 386±44 ms, respectively; P=.020). Multivariate logistic regression analysis revealed that QTpc ,360 ms and AF were predictive of CE after adjustment for clinical covariates. In conclusion, apart from AF, the presence of short QTpc ,360 ms is independently associated with increased risk of rehospitalization or death in HF patients. [source] Mechanisms of Ventricular Fibrillation Initiation in MADIT II Patients with Implantable Cardioverter DefibrillatorsPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 2 2008RYAN ANTHONY M.D. Background:The availability of stored intracardiac electrograms from implantable defibrillators (ICDs) has facilitated the study of the mechanisms of ventricular tachyarrhythmia onset. This study aimed to determine the patterns of initiation of ventricular fibrillation (VF) in Multicenter Automatic Defibrillator Implantation Trial (MADIT) II patients along with associated electrocardiogram (ECG) parameters and clinical characteristics. Methods:Examination of stored electrograms enabled us to evaluate the rhythm preceding each episode of VF and to calculate (intracardiac) ECG parameters including QT, QT peak (QTp), coupling interval, and prematurity index. Results:Sixty episodes of VF among 29 patients (mean age 64.4 ± 2.5 years) were identified. A single ventricular premature complex (VPC) initiated 46 (77%) episodes whereas a short-long-short (SLS) sequence accounted for 14 (23%) episodes. Of the 29 patients studied, 23 patients had VF episodes preceded by a VPC only, two patients with SLS only, and four patients with both VPC and SLS-initiated episodes. There were no significant differences between initiation patterns in regards to the measured ECG parameters; a faster heart rate with SLS initiation (mean RR prior to VF of 655 ± 104 ms for SLS and 744 ± 222 ms for VPC) approached significance (P = 0.06). The two patients with SLS only were not on ,-blockers compared to 83% of the VPC patients. Conclusion:Ventricular fibrillation is more commonly initiated by a VPC than by a SLS sequence among the MADIT II population. Current pacing modes designed to prevent bradycardia and pause-dependent arrhythmias are unlikely to decrease the incidence of VPC-initiated episodes of VF. [source] Clinical Implications of QRS Duration and QT Peak Prolongation in Patients with Suspected Coronary Disease Referred for Elective Cardiac CatheterizationANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 2 2008M. Nadeem Attar M.D., M.R.C.P. Background: The electrocardiogram (ECG) remains a simple, universally available, and prognostically powerful investigation in heart failure, and acute coronary syndromes. We sought to assess the prognostic utility of clinical, angiographic, and simple ECG parameters in a large cohort of patients undergoing elective cardiac catheterization (CC) for known or suspected coronary artery disease. Methods: Consecutive consenting patients undergoing CC for coronary disease were enrolled at a single tertiary center. Patient data, drug therapy, catheter reports, and ECG recordings were prospectively recorded in a validated electronic archive. The primary outcome measure was death or nonfatal myocardial infarction (MI) over 1 year or until percutaneous or cardiac surgical intervention. Independent prognostic markers were identified using the Cox proportional hazard model. Results: A total of 682 individuals were recruited of whom 17(2.5%) died or suffered a nonfatal MI in 1 year. In multivariate analysis QRS duration (ms) (HR 1.03 95% CI 1.01,1.05, P = 0.003), extent of coronary disease (HR 2.01 95% CI 1.24,3.58, P = 0.006), and prolonged corrected QT peak interval in lead I (HR 1.02 95% CI 1.00,1.03, P = 0.044) were independently associated with death or nonfatal MI. Receiver-operator characteristic (ROC) analysis for the multivariate model against the primary end point yielded an area under the curve of 0.759 (95% CI 0.660,0.858), P < 0.001. Conclusions: QRS duration and QT peak are independently associated with increased risk of death or nonfatal MI in stable patients attending for coronary angiography. [source] Anomalous charge relaxation in channels of pentacene-based organic field-effect transistors: a charge transient spectroscopy studyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2006I. Thurzo Abstract Two types of Si/SiO2/pentacene organic field-effect transistors (OFET) with bottom Au-source (S) and , drain (D) electrodes were examined by charge transient spectroscopy (QTS), applying pulsed bias ,UDS to the channel of an OFET with floating gate electrode. The transient charge Q (t ), flowing through the channel after the removal of the bias pulse, was processed at a constant temperature by a three-channel correlator yielding the signal ,Q = Q (t1) , 3/2Q (2t1) + 1/2Q (4t1), the scanned delay t1 being related to the trailing edge of the bias pulse. Most of the QTS spectra were characterized by peaks of ,Q (t1) with FWHM corresponding to discrete time constants ,m , t1m, while scanning t1 from 2 ,s to 0.1 s. The common feature of the QTS spectra was a linear dependence of the peak height ,Qm on ,UDS for both polarities of the latter, thereby resembling what is expected for dielectric relaxation (polarization). Some devices showed anomalous (reversed) sign of the signal with respect to the polarity of ,UDS, or even features like transitions from the correct sign to the reversed one. In order to customize the anomalies, a model is presented which ignores injection of excess charge carriers and takes into account two contributions to the total transient charge: a/space charge of intrinsic charge carriers piled up at the blocking Au-electrodes during the pulse, relaxing with the dielectric relaxation time ,D = ,0,r/, (, being conductivity of the organics); b/orientation of molecular dipoles (,dip) in the relaxing electric field of the space charge. It is the dipolar component that is responsible for the anomalous charge flow direction manifested by the signal reversal. The origin of the permanent dipole moment of the otherwise non-polar pentacene molecules may be either attached excess or missing atoms (vacancies) of the defect molecules [J. E. Northrup and M. L. Chabinyc, Phys. Rev. B 68, 041202 (2003)]. In cases of non-blocking contacts the dipolar relaxation would lead to QTS peaks of correct sign, to be distinguished from possibly non-negligible contribution of the dielectric relaxation in the semiconductor. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||