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QTc Value (qtc + value)
Selected AbstractsQT Interval Correction in Patients with CirrhosisJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 1 2007ANDREA ZAMBRUNI M.D. Introduction: QT interval prolongation is a common electrophysiological abnormality in patients with cirrhosis. As QT interval varies with the heart rate, many QT correction formulas have been proposed, the Bazett's one being the most criticized because it overcorrects the QT interval and may be misleading. This study focused on the QT-RR relationship in patients with cirrhosis to derive a population-specific QT correction formula. Methods: One hundred cirrhotic patients of different etiology and severity and 53 healthy controls comparable for age and sex were enrolled. The QT-RR relationship was analyzed in patients by five regression analysis models to derive the population-specific QT-RR equation. The QTc was calculated and compared with those calculated by four common QT correction formulas (Bazett, Fridericia, Framingham, and Hodges). The correlation coefficient QTc-RR was calculated as a measure of the independence of QTc from the original RR interval. Results: In patients the QT-RR relationship was best described by the power equation "QT = 453.65 × RR1/3.02" (R2= 0.41), similar to the Fridericia's formula. Bazett's formula led to the longest QTc (P < 0.0001), which was still significantly influenced by the RR interval (R =,0.39; P < 0.0001), while the estimated equation led to a QTc value not influenced by RR (R =,0.014). Conclusion: Bazett's correction should be avoided in patients with cirrhosis because it still provides a rate-dependent QTc value and might be misleading, particularly when assessing the overall preoperative cardiac risk and the effect of drugs affecting the QT interval. In its place, our formula or that of Fridericia can be confidently employed. [source] Influence of promethazine on cardiac repolarisation: a double-blind, midazolam-controlled studyANAESTHESIA, Issue 6 2009R. Owczuk Summary Drugs used in anaesthesia may provoke torsadogenic changes in cardiac repolarisation. The aim of this study was to assess the effect of promethazine on the parameters of ventricular repolarisation: QTc interval and transmural dispersion of repolarisation. Forty patients were randomly allocated to receive promethazine (25 mg) or midazolam (2.5 mg). Changes in the ECG and arterial blood pressure were recorded. Correction of QT interval was calculated using Bazett's formula and Fridericia's correction; transmural dispersion of repolarisation was determined as Tpeak,Tend time. Significant prolongation of QT interval, corrected with both formulae, was detected in patients receiving promethazine, while no change in the QTc value was observed in the midazolam group. There were no significant differences in Tpeak,Tend time either between or within the groups. In conclusion, promethazine induces significant QTc prolongation but the lack of influence on transmural dispersion of repolarisation makes the risk of its torsadogenic action very low. [source] Effects of Head-Up Tilt-Table Test on the QT IntervalANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2010Michael Findler M.D. Background. The QT interval shortens in response to sympathetic stimulation and its response to epinephrine infusion (in healthy individuals and patients with long QT syndrome) has been thoroughly studied. Head-up tilt-table (HUT) testing is an easy way to achieve brisk sympathetic stimulation. Yet, little is known about the response of the QT interval to HUT. Methods. We reviewed the electrocardiograms of HUT tests performed at our institution and compare the heart rate, QT, and QTc obtained immediately after HUT with the rest values. Results. The study group consisted of 41 patients (27 females and 14 males) aged 23.9 ± 8.4 years. Head-up tilting led to a significant shortening of the RR interval (from 825 ± 128 msec at rest phase to 712 ± 130 msec in the upward tilt phase, P < 0.001) but only to a moderate shortening of the QT interval (from 363.7 ± 27.9 msec during rest to 355 ± 30.3 msec during upward tilt, P = 0.001). Since the RR interval shortened more than the QT interval, the QTc actually increased (from 403 ± 21.5 msec during rest phase to 423.2 ± 27.4 msec during upward tilt, P < 0.001). The QTc value measured for the upward tilt position was longer than the resting QTc value in 33 of 41 patients. Of those, 4 male patients and 2 female patients developed upward-tilt QTc values above what would be considered abnormal at rest. Conclusions. During HUT the QT shortens less than the RR interval. Consequently, the QTc increases during head-up tilt. Ann Noninvasive Electrocardiol 2010;15(3):245,249 [source] Cyamemazine metabolites: effects on human cardiac ion channels in-vitro and on the QTc interval in guinea pigsJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 11 2008William Crumb Monodesmethyl cyamemazine and cyamemazine sulfoxide, the two main metabolites of the antipsychotic and anxiolytic phenothiazine cyamemazine, were investigated for their effects on the human ether-à-go-go related gene (hERG) channel expressed in HEK 293 cells and on native INa, ICa, Ito, Isus or IK1 of human atrial myocytes. Additionally, cyamemazine metabolites were compared with terfenadine for their effects on the QT interval in anaesthetized guinea pigs. Monodesmethyl cyamemazine and cyamemazine sulfoxide reduced hERG current amplitude, with IC50 values of 0.70 and 1.53 ,M, respectively. By contrast, at a concentration of 1 ,M, cyamemazine metabolites failed to significantly affect INa, Ito, Isus or IK1 current amplitudes. Cyamemazine sulfoxide had no effect on ICa at 1 ,M, while at this concentration, monodesmethyl cyamemazine only slightly (17%), albeit significantly, inhibited ICa current. Finally, cyamemazine metabolites (5 mg kg,1 i.v.) were unable to significantly prolong QTc values in the guinea pig. Conversely, terfenadine (5 mg kg,1 i.v.) significantly increased QTc values. In conclusion, cyamemazine metabolite concentrations required to inhibit hERG current substantially exceed those necessary to achieve therapeutic activity of the parent compound in humans. Moreover, cyamemazine metabolites, in contrast to terfenadine, do not delay cardiac repolarization in the anaesthetized guinea pig. These non-clinical findings explain the excellent cardiac safety records of cyamemazine during its 30 years of extensive therapeutic use. [source] Effects of Head-Up Tilt-Table Test on the QT IntervalANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2010Michael Findler M.D. Background. The QT interval shortens in response to sympathetic stimulation and its response to epinephrine infusion (in healthy individuals and patients with long QT syndrome) has been thoroughly studied. Head-up tilt-table (HUT) testing is an easy way to achieve brisk sympathetic stimulation. Yet, little is known about the response of the QT interval to HUT. Methods. We reviewed the electrocardiograms of HUT tests performed at our institution and compare the heart rate, QT, and QTc obtained immediately after HUT with the rest values. Results. The study group consisted of 41 patients (27 females and 14 males) aged 23.9 ± 8.4 years. Head-up tilting led to a significant shortening of the RR interval (from 825 ± 128 msec at rest phase to 712 ± 130 msec in the upward tilt phase, P < 0.001) but only to a moderate shortening of the QT interval (from 363.7 ± 27.9 msec during rest to 355 ± 30.3 msec during upward tilt, P = 0.001). Since the RR interval shortened more than the QT interval, the QTc actually increased (from 403 ± 21.5 msec during rest phase to 423.2 ± 27.4 msec during upward tilt, P < 0.001). The QTc value measured for the upward tilt position was longer than the resting QTc value in 33 of 41 patients. Of those, 4 male patients and 2 female patients developed upward-tilt QTc values above what would be considered abnormal at rest. Conclusions. During HUT the QT shortens less than the RR interval. Consequently, the QTc increases during head-up tilt. Ann Noninvasive Electrocardiol 2010;15(3):245,249 [source] Electrocardiographic Transmural Dispersion of Repolarization in Patients with Inherited Short QT SyndromeANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2008Olli Anttonen M.D. Background: Short QT syndrome (SQTS) carries an increased risk for sudden cardiac death. However, only a short QT interval does not express the risk of ventricular arrhythmias. Thus, additional evaluation of the repolarization abnormality in SQTS patients is essential. In experimental models of SQTS, increased transmural dispersion of repolarization (TDR) and its electrocardiographic counterpart T-wave peak to T-wave end interval (TPE) appeared critical for induction of polymorphic ventricular tachycardia (PMVT). In a clinical study with acquired long QT syndrome patients, TPE/QT ratio > 0.28 indicated arrhythmia risk. We hypothesized that the TPE/QT ratio would be greater in SQTS patients than in control subjects. Methods and Results: We compared the behavior of the electrocardiographic TDR in three seriously symptomatic SQTS patients of unknown genotype presenting baseline QTc values <320 ms and in nine healthy age-matched control subjects. We determined QT and TPE intervals as well as TPE/QT ratio from 24-hour ECG recordings using a computer-assisted program. Diurnal average of TPE/QT ratio was 0.28 ± 0.03 in SQTS patients and 0.21 ± 0.02 in control subjects (P = 0.01). SQTS patients had also lesser capacity to change TPE intervals from steady-state conditions to abrupt maximal values than control subjects. Conclusion: SQTS patients have increased and autonomically uncontrolled electrocardiographic TDR. According to experimental SQTS models, the present results may in part explain increased vulnerability of SQTS patients to ventricular arrhythmias. [source] | ||||||||||