Home About us Contact
Kinds of QTc
Terms modified by QTc
Differences in sino-atrial and atrio-ventricular function with age and sex attributable to the Scn5a+/, mutation in a murine cardiac modelACTA PHYSIOLOGICA, Issue 1 2010
Abstract Aim:, To investigate the interacting effects of age and sex on electrocardiographic (ECG) features of Scn5a+/, mice modelling Brugada syndrome. Methods:, Recordings were performed on anaesthetized wild-type (WT) and Scn5a+/, mice and differences attributable to these risk factors statistically stratified. Results:,Scn5a+/, exerted sex-dependent effects upon sino-atrial function that only became apparent with age. RR intervals were greater in old male than in old female Scn5a+/,. Atrio-ventricular (AV) conduction was slower in young female mice, whether WT and Scn5a+/,, than the corresponding young male WT and Scn5a+/,. However, PR intervals lengthened with age in male but not in female Scn5a+/, giving the greatest PR intervals in old male Scn5a+/, compared with either old male WT or young male Scn5a+/, mice. In contrast, PR intervals were similar in old female Scn5a+/, and in old female WT. QTc was prolonged in Scn5a+/, compared with WT, and female Scn5a+/, compared with female WT. Age-dependent alterations in durations of ventricular repolarization relative to WT affected male but not female Scn5a+/,. Thus, T-wave durations were greater in old male Scn5a+/, compared with old male WT, but indistinguishable between old female Scn5a+/, and old female WT. Finally, analysis for combined interactions of genotype, age and sex demonstrated no effects on P wave and QRS durations and QTc intervals. Conclusion:, We demonstrate for the first time that age, sex and genotype exert both independent and interacting ECG effects. The latter suggest alterations in cardiac pacemaker function, atrio-ventricular conduction and ventricular repolarization greatest in ageing male Scn5a+/,. [source]
The effect of sertindole on QTD and TPTEACTA PSYCHIATRICA SCANDINAVICA, Issue 5 2010
Nielsen J, Andersen MP, Graff C, Kanters JK, Hardahl T, Dybbro J, Struijk JJ, Meyer JM, Toft E. The effect of sertindole on QTD and TPTE. Objective:, Recent research suggests that other surrogate markers than QTc, including QTc dispersion and Tpeak-Tend, may better correlate with cardiac arrhythmia risk. While sertindole significantly prolongs the QTc interval, the effects on other markers of arrhythmia risk, such as QTc dispersion and Tpeak-Tend are unknown. Method:, Digital 12-lead ECG was recorded at baseline and at steady-state in 37 patients switched to sertindole. ECG was analysed for Fridericia-corrected QT duration (QTcF), QT dispersion and Tpeak-Tend. Results:, From a baseline QTcF of 407 ± 22 ms, mean QTcF prolongation during sertindole treatment was 20 ± 23 ms, P < 0.01. No effect on QTc dispersion was found (,1 ± 11 ms; P = 0.41). No increased duration of the Tpeak-Tend interval from baseline was found (+7 ± 21 ms; P = 0.05). Conclusion:, These findings might be related to the absence of confirmed Torsade de Pointes (TdP) cases related to sertindole exposure, despite sertindole's QTc prolonging effects. [source]
Effect of insulin infusion on electrocardiographic findings following acute myocardial infarction: importance of glycaemic controlDIABETIC MEDICINE, Issue 2 2009
R. M. Gan
Abstract Aims, To determine the effects of insulin infusion and blood glucose levels during acute myocardial infarction (AMI) on electrocardiographic (ECG) features of myocardial electrical activity. Methods, ECGs at admission and 24 h were examined in a randomized study of insulin infusion vs. routine care for AMI patients with diabetes or hyperglycaemia. Results were analysed according to treatment allocation and also according to average blood glucose level. Results, ECG characteristics were similar at admission in both groups. Patients allocated to conventional treatment had prolongation of the QT interval (QTc) after 24 h but those receiving infused insulin did not. In patients with a mean blood glucose in the first 24 h > 8.0 mmol/l, new ECG conduction abnormalities were significantly more common than in patients with mean blood glucose , 8.0 mmol/l (15.0% vs. 6.0%, P < 0.05). Conclusions, Prevention of QTc prolongation by administration of insulin may reflect a protective effect on metabolic and electrical activity in threatened myocardial tissue. Abnormalities of cardiac electrical conduction may also be influenced by blood glucose. [source]
QT interval prolongation in association with impaired circadian variation of blood pressure and heart rate in adolescents with Type 1 diabetesDIABETIC MEDICINE, Issue 11 2007
Abstract Aims, The aim of our study was to assess diurnal blood pressure (BP) and heart rate variability and their possible relationship to the duration of the QT interval in adolescents with Type 1 diabetes. Methods, In 48 normotensive, normoalbuminuric diabetic adolescents, with a mean (± sd) age of 17.3 (± 4.1) years and a mean (± sd) diabetes duration of 8.5 (± 3.3) years, 24-h ambulatory BP was recorded. In addition, 24-h heart rate (HR) monitoring was performed and QT and corrected QT (QTc) intervals were estimated as indices of autonomic function. The patients were divided into two groups according to the absence of a decrease (non-dippers) or the presence of a decrease (dippers) in nocturnal diastolic BP (DBP). Results, In comparison with the dippers, the non-dippers showed reduced mean 24-h HR (79.6 vs. 84.0 beats/min, P = 0.05) and reduced mean daytime HR (81.3 vs. 86.0 beats/min, P = 0.05). The QT interval was prolonged in the non-dippers (366.3 vs. 347.5 ms, P = 0.015), and end systolic (28.7 vs. 25.9 mm, P = 0.004) and end diastolic left ventricular diameters (47.8 vs. 45.5 mm, P = 0.037) were greater. In stepwise multiple regression, HR variables were the most important factors affecting DBP ratio or the duration of the QT interval. Conclusions, In conclusion, normotensive diabetic adolescents with impaired nocturnal BP reduction also have impaired autonomic function tests, in association with prolonged QT interval and increased left ventricular diameters. These findings suggest that diabetic adolescents who have the ,non-dipper' phenomenon may need close follow-up for the possible development of vascular complications, such as cardiac arrhythmias and left-ventricular hypertrophy. [source]
Prevalence and clinical relevance of corrected QT interval prolongation during methadone and buprenorphine treatment: a mortality assessment studyADDICTION, Issue 6 2009
ABSTRACT Aims To determine the prevalence of corrected QT interval (QTc) prolongation among patients in opioid maintenance treatment (OMT) and to investigate mortality potentially attributable to QTc prolongation in the Norwegian OMT programme. Participants and setting Two hundred OMT patients in Oslo were recruited to the QTc assessment study between October 2006 and August 2007. The Norwegian register of all patients receiving OMT in Norway (January 1997,December 2003) and the national death certificate register were used to assess mortality. Mortality records were examined for the 90 deaths that had occurred among 2382 patients with 6450 total years in OMT. Design and measures The QTc interval was assessed by electrocardiography (ECG). All ECGs were examined by the same cardiologist, who was blind to patient history and medication. Mortality was calculated by cross-matching the OMT register and the national death certificate register: deaths that were possibly attributable to QTc prolongation were divided by the number of patient-years in OMT. Findings In the QTc assessment sample (n = 200), 173 patients (86.5%) received methadone and 27 (13.5%) received buprenorphine. In the methadone group, 4.6% (n = 8) had a QTc above 500 milliseconds; 15% (n = 26) had a QTc interval above 470 milliseconds; and 28.9% (n = 50) had a QTc above 450 milliseconds. All patients receiving buprenorphine (n = 27) had QTc results <450 milliseconds. A positive dose-dependent association was identified between QTc length and dose of methadone, and all patients with a QTc above 500 milliseconds were taking methadone doses of 120 mg or more. OMT patient mortality, where QTc prolongation could not be excluded as the cause of death, was 0.06/100 patient-years. Only one death among 3850 OMT initiations occurred within the first month of treatment. Conclusion Of the methadone patients, 4.6% had QTc intervals above 500 milliseconds. The maximum mortality attributable to QTc prolongation was low: 0.06 per 100 patient-years. [source]
Cardiac function and antiepileptic drug treatment in the elderly: A comparison between lamotrigine and sustained-release carbamazepineEPILEPSIA, Issue 8 2009
Summary Purpose:, To investigate the comparative effects of carbamazepine (CBZ) and lamotrigine (LTG) on electrocardiography (ECG) parameters in elderly patients with newly diagnosed epilepsy. Methods:,, The study was conducted in the Norwegian subcohort (n = 108) of an international randomized double-blind 40-week trial, which compared the efficacy and tolerability of LTG and sustained-release CBZ in patients aged 65 and older with newly diagnosed epilepsy. Target maintenance doses were 400 mg/day for CBZ and 100 mg/day for LTG, with adjustments based on clinical response. Patients with significant unpaced atrioventricular (AV) conduction defect were excluded. Resting 12-lead ECG recordings were made under standardized conditions at pretreatment (baseline) and at the 40-week study visit (treatment visit). Changes in QRS interval (primary endpoint), heart rate (HR), PQ, and QTc (HR-corrected QT) intervals were assessed and compared between groups. Results:, Of the 108 patients randomized, 33 discontinued prematurely because of adverse events (n = 24, none of which was cardiac) or other reasons (n = 9), and 15 were nonevaluable due to incomplete ECG data. None of the assessed ECG parameters differed significantly between groups at baseline. No significant ECG changes were recorded between baseline and treatment visit for QRS duration and QTc intervals, whereas HR fell and PQ intervals increased slightly on both treatments. However, there were no differences between groups in changes from baseline to treatment visit. There were no significant relationships between individual ECG changes and serum drug concentrations, except for QTc intervals, which decreased slightly with increasing CBZ concentrations. The proportion of patients with ECG parameters outside the normal range at treatment visit was similar to that recorded at baseline. Discussion:, Clinically significant ECG changes are not common during treatment with CBZ or LTG in elderly patients with no preexisting significant AV conduction defects. [source]
Myocardial perfusion defects in Bartter and Gitelman syndromesEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 12 2008
ABSTRACT Background, Normotensive hypokalaemic tubulopathies (Bartter and Gitelman syndromes (BS/GS)) are genetic diseases that are considered benign. However, QT prolongation, left ventricular dysfunction and reduction of cardiac index upon exercise leading to arrhythmias and sudden cardiac death have been reported in these patients. Hence, we aimed to verifying whether an isometric exercise could represent a useful tool for the identification of patients at risk for future cardiac events. Patients and methods, Myocardial function (MF) and perfusion, evaluated as myocardial blood flow (MBF) of 10 BS/GS patients and 10 healthy controls, were investigated at rest and during isometric exercise. MF and MBF were evaluated using quantitative two-dimensional and myocardial contrast echocardiography. Results, BS/GS patients had normal baseline MF and MBF. During exercise in BS/GS patients, corrected QT (QTc) was prolonged to peak value of 494 ± 9·1 ms (P < 0·001). In controls, MF increased from resting to peak exercise (left ventricular ejection fraction: 65 ± 4% to 78 ± 5%, P < 0·003) while in seven BS/GS patients (Group 1) it declined (64 ± 5% to 43 ± 9%, P < 0·001). Myocardial perfusion increased upon exercise in controls as shown by changes of its markers: , (a measure of myocardial flow velocity; 0·89 ± 0·12 vs. 0·99 ± 0·12, P < 0·001) and myocardial blood volume (14·4 ± 2 vs. 20·2 ± 0·25, P < 0·001), while in Group 1 BS/GS it decreased (0·87 ± 0·15 vs. 0·67 ± 0·15, P < 0·001; and 14·5 ± 1·9 vs. 8·3 ± 0·22, P < 0·001, respectively). Conclusions, Our results document for the first time that exercise induce coronary microvascular and myocardial defects in BS/GS patients. Therefore, this may challenge the idea that BS/GS are benign diseases. In addition, the diagnostic approach to these syndromes should include an in-depth cardiac assessment in order to identify patients at higher risk. [source]
Effects of adrenaline and potassium on QTc interval and QT dispersion in manEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 2 2003
Abstract Background Hypoglycaemia alters cardiac repolarization acutely, with increases in rate-corrected QT (QTc) interval and QT dispersion (QTd) on the electrocardiogram (ECG); such changes are related to the counterregulatory sympatho-adrenal response. Adrenaline produces both QTc lengthening and a fall in plasma potassium (K+) when infused into healthy volunteers. Hypokalaemia prolongs cardiac repolarization independently however, and therefore our aim was to determine whether adrenaline-induced repolarization changes are mediated directly or through lowered plasma K+. Materials and methods Ten healthy males were studied on two occasions. At both visits they received similar l- adrenaline infusions but on one occasion potassium was also administered; infusion rates were adjusted to maintain circulating K+ at baseline. The QTc interval, QTd, peripheral physiological responses and plasma adrenaline and potassium concentrations were measured during both visits. Results The QTc interval and QTd increased both with and without potassium clamping. Without K+ replacement, mean (SE) QTc lengthened from 378 (5) ms to a final maximum value of 433 (10) ms, and QTd increased from 36 (5) ms to 69 (8) ms (both P < 0·001). During K+ replacement, QTc duration at baseline and study end was 385 (7) ms and 423 (11) ms, respectively (P < 0·001), and QTd 38 was (4) ms and 63 (5) ms (P = 0·001). Conclusions These data suggest that disturbed cardiac repolarization as a result of increases in circulating adrenaline occurs independently of extracellular potassium. A direct effect of adrenaline upon the myocardium appears the most likely mechanism. [source]
Effects of acute vagal nerve stimulation on the early passive electrical changes induced by myocardial ischaemia in dogs: heart rate-mediated attenuationEXPERIMENTAL PHYSIOLOGY, Issue 8 2008
Carlos L. Del Rio
Parasympathetic activity during acute coronary artery occlusion (CAO) can protect against ischaemia-induced malignant arrhythmias; nonetheless, the mechanism mediating this protection remains unclear. During CAO, myocardial electrotonic uncoupling is associated with autonomically mediated immediate (i.e. type 1A) arrhythmias and can modulate pro-arrhythmic dispersion of repolarization. Therefore, the effects of acutely enhanced or decreased cardiac parasympathetic activity on early electrotonic coupling during CAO, as measured by myocardial electrical impedance (MEI), were investigated. Anaesthetized dogs were instrumented for MEI measurements, and left circumflex coronary arterial occlusions were performed in intact (CTRL) and vagotomized (VAG) animals. The CAO was followed by either vagotomy (CTRL) or vagal nerve stimulation (VNS, 10 Hz, 10 V) in the VAG dogs. Vagal nerve stimulation was studied in two additional sets of animals. In one set heart rate (HR) was maintained by pacing (220 beats min,1), while in the other set bilateral stellectomy preceded CAO. The MEI increased after CAO in all animals. A larger MEI increase was observed in vagotomized animals (+85 ± 9 ,, from 611 ± 24 ,, n= 16) when compared with intact control dogs (+43 ± 5 ,, from 620 ± 20 ,, n= 7). Acute vagotomy during ischaemia abruptly increased HR (from 155 ± 11 to 193 ± 15 beats min,1) and MEI (+12 ± 1.1 ,, from 663 ± 18 ,). In contrast, VNS during ischaemia (n= 11) abruptly reduced HR (from 206 ± 6 to 73 ± 9 beats min,1) and MEI (,16 ± 2 ,, from 700 ± 44 ,). These effects of VNS were eliminated by pacing but not by bilateral stellectomy. Vagal nerve stimulation during CAO also attenuated ECG-derived indices of ischaemia (e.g. ST segment, 0.22 ± 0.03 versus 0.15 ± 0.03 mV) and of rate-corrected repolarization dispersion [terminal portion of T wave (TPEc), 84.5 ± 4.2 versus 65.8 ± 5.9 ms; QTc, 340 ± 8 versus 254 ± 16 ms]. Vagal nerve stimulation during myocardial ischaemia exerts negative chronotropic effects, limiting early ischaemic electrotonic uncoupling and dispersion of repolarization, possibly via a decreased myocardial metabolic demand. [source]
Cardiovascular effects of high dose venlafaxine XL in patients with major depressive disorderHUMAN PSYCHOPHARMACOLOGY: CLINICAL AND EXPERIMENTAL, Issue 3 2007
Abstract Objective To assess cardiovascular safety profile of high dose Venlafaxine XL in patients with major depression. Method Effects of high dose venlafaxine (mean 346.15,mg;) on the cardiovascular system in 37 patients with major depressive disorder were evaluated: BP, ECG (PR, QT, QRSD and QTc intervals) and heart rate. Results 12.5% of patients developed hypertension after starting treatment with venlafaxine. There was an association between heart rate and the dose of venlafaxine although not statistically significant. There was no association between dose of venlafaxine and PR, QT, QRSD and QTc intervals. One patient on 300,mg who was hypertensive and on other medications that may prolong QTc, had mildly prolonged QTc. However this was not clinically significant. Conclusion This study of subjects on high dose venlafaxine (mean 346.15,mg; range 225,525,mg) did not demonstrate any clinical or statistically significant effects on electrocardiogram (ECG) parameters including PR, QT, QRSD and QTc interval. Copyright © 2007 John Wiley & Sons, Ltd. [source]
QT Interval Correction in Patients with CirrhosisJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 1 2007
ANDREA 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]
Clinical Course and Risk Stratification of Patients Affected with the Jervell and Lange-Nielsen SyndromeJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 11 2006
ILAN GOLDENBERG M.D.
Introduction: Data regarding risk factors and clinical course of patients affected with Jervell and Lange-Nielsen syndrome (JLNS), an autosomal recesssive form of the congenital long-QT syndrome (LQTS), are limited to several reported cases and a retrospective analysis. Methods and Results: We prospectively followed-up 44 JLNS patients from the U.S. portion of the International LQTS Registry and compared their clinical course with 2,174 patients with the phenotypically determined dominant form of LQTS (Romano-Ward syndrome [RWS]) and a subgroup of 285 patients with type 1 LQTS (LQT1). Mean (±SD) corrected QT interval (QTc) in the JLNS, RWS, and LQT1 groups were 548 ± 73, 500 ± 48, and 502 ± 46 msec, respectively (P < 0.001). The cumulative rates of cardiac events from birth through age 40 among JLNS and RWS patients were 93% (mean [±SD] age: 5.0 ± 7.0 years) and 54% (mean [±SD] age: 14.2 ± 9.3 years), respectively (P < 0.001). The JLNS:RWS and JLNS:LQT1 adjusted hazard ratios (HR) for cardiac events were highest among patients with a baseline QTc ,550 msec (HR = 15.83 [P < 0.001] and 13.80 [P < 0.001], respectively). Among JLNS patients treated with beta-blockers, the cumulative probability of LQTS-related death was 35%; defibrillator therapy was associated with a 0% mortality rate during a mean (±SD) follow-up period of 4.9 ± 3.4 years. Conclusions: Patients with JLNS experience a high rate of cardiac and fatal events from early childhood despite medical therapy. Defibrillator therapy appears to improve outcome in this high-risk population, although longer follow-up is needed to establish its long-term efficacy. [source]
Congenital Short QT Syndrome and Implantable Cardioverter Defibrillator Treatment:JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 12 2003
Inherent Risk for Inappropriate Shock Delivery
Introduction: A congenital short QT interval constitutes a new primary electrical abnormality associated with syncope and/or sudden cardiac death. We report on the initial use of implantable cardioverter defibrillator (ICD) therapy in patients with inherited short QT interval and discuss sensing abnormalities and detection issues. Methods and Results: In five consecutive patients from two unrelated European families who had structurally normal hearts, excessively shortened QT intervals, and a strong positive family history of sudden cardiac death, ICDs were placed for primary and secondary prevention. Mean QT intervals were 252 ± 13 ms (QTc 287 ± 13 ms). Despite normal sensing behavior during intraoperative and postoperative device testing, 3 of 5 patients experienced inappropriate shock therapies for T wave oversensing 30 ± 26 days after implantation. Programming lower sensitivities and decay delays prevented further inappropriate discharges. Conclusion: The congenital short QT syndrome constitutes a new clinical entity with an increased risk for sudden cardiac death. Currently, ICD treatment is the only therapeutic option. In patients with short QT interval and implanted ICD, increased risk for inappropriate therapy is inherent due to the detection of short-coupled and prominent T waves. Careful testing of ICD function and adaptation of sensing levels and decay delays without sacrificing correct arrhythmia detection are essential. (J Cardiovasc Electrophysiol, Vol. 14, pp. 1273-1277, December 2003) [source]
Location of Mutation in the KCNQ1 and Phenotypic Presentation of Long QT SyndromeJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 11 2003
Ph.D., WOJCIECH ZAREBA M.D.
Introduction: Recent data showed that long QT syndrome (LQTS) patients with mutations in the pore region of the HERG (LQT2) gene have significantly higher risk of cardiac events than subjects with mutations in the non-pore region. The aim of this study was to determine whether there is an association between the location of mutations in the KCNQ1 gene and cardiac events in LQT1 patients. Methods and Results: The study population consisted of 294 LQT1 patients with KCNQ1 gene mutations. Demographic, clinical, and follow-up information was compared among subjects with different locations of KCNQ1 mutations defined as pre-pore region including N-terminus (1,278), pore region (279,354), and post-pore region including C-terminus (>354). Cardiac events observed during follow-up from birth until age of last contact or age 40 years were defined as syncope, cardiac arrest, or sudden death. There were 164 (56%) LQT1 patients with pre-pore mutations, 101 (34%) with pore mutations, and 29 (10%) with post-pore mutations. QTc duration did not differ significantly among the three subgroups (mean QTc = 494, 487, and 501 ms, respectively). There was no significant difference between groups with regard to the risk of cardiac events by age 40 years. Conclusion: There are no significant differences in clinical presentation, ECG parameters, and cardiac events among LQT1 patients with different locations of KCNQ1 mutations. These findings indicate that factors other than location of mutation influence clinical phenotype in patients with LQT1 mutations. (J Cardiovasc Electrophysiol, Vol. 14, pp. 1149-1153, November 2003) [source]
QTc interval and QTc dispersion during haemodiafiltrationNEPHROLOGY, Issue 6 2004
SUMMARY: Background and Aim: Our aim was to evaluate QTc interval and QTc dispersion in 27 end-stage renal disease (ESRD) patients undergoing Acetate Free Biofiltration (AFB) in order to ascertain any correlations between the electrrocardiographic (ECG) parameters, serum Na+, K+, Ca++, Mg++ and intraerythrocytic Mg++ (Mg++e) concentrations. All measures were made at t0 (session beginning), t1 (first hour), t2 (second hour), t3 (third hour), and t4 (session end). Results: Blood pressure, heart rate, bodyweight and total ultrafiltration in the three dialysis sessions were constant. A significant progressive increase occurred in serum Ca++ during the sessions, while there was a significant diminution in serum K+. The pattern for Mg++ concentrations in serum and erythrocytes differed: in serum it decreased, whereas Mg++e increased. At t4, the QTc interval was reduced to a significant extent with respect to the baseline value. QTc dispersion significantly increased at t1 without there being significant variations at other times with respect to t0. At t2, t3 and t4, values promptly returned to baseline levels. QTc had a negative correlation with serum Ca++ levels at t4. In contrast, an inverse correlation was found between QTc dispersion and serum K+ at t1. No other correlations could be found between any other electrolytes, QTc interval or QTc dispersion. Conclusion: In conclusion, the decrease observed in the QTc interval at the end of an AFB session was inversely related to serum Ca++ concentrations. Moreover, an increase in QTc dispersion occurred during the first hour of the session, and was negatively correlated with serum K+. [source]
QT Interval Variability and Adaptation to Heart Rate Changes in Patients with Long QT SyndromePACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 1 2009
JAN N, MEC M.D.
Background: Increased QT variability (QTV) has been reported in conditions associated with ventricular arrhythmias. Data on QTV in patients with congenital long QT syndrome (LQTS) are limited. Methods: Ambulatory electrocardiogram recordings were analyzed in 23 genotyped LQTS patients and in 16 healthy subjects (C). Short-term QTV was compared between C and LQTS. The dependence of QT duration on heart rate was evaluated with three different linear models, based either on the RR interval preceding the QT interval (RR0), the RR interval preceding RR0 (RR -1), or the average RR interval in the 60-second period before QT interval (mRR). Results: Short-term QTV was significantly higher in LQTS than in C subjects (14.94 ± 9.33 vs 7.31 ± 1.29 ms; P < 0.001). It was also higher in the non-LQT1 than in LQT1 patients (23.00 ± 9.05 vs 8.74 ± 1.56 ms; P < 0.001) and correlated positively with QTc in LQTS (r = 0.623, P < 0.002). In the C subjects, the linear model based on mRR predicted QT duration significantly better than models based on RR0 and RR -1. It also provided better fit than any nonlinear model based on RR0. This was also true for LQT1 patients. For non-LQT1 patients, all models provided poor prediction of QT interval. Conclusions: QTV is elevated in LQTS patients and is correlated with QTc in LQTS. Significant differences with respect to QTV exist among different genotypes. QT interval duration is strongly affected by noninstantaneous heart rate in both C and LQT1 subjects. These findings could improve formulas for QT interval correction and provide insight on cellular mechanisms of QT adaptation. [source]
Video-Assisted Thoracoscopic Sympathectomy for Congenital Long QT SyndromesPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 4p1 2003
LI, J., et al.: Video-Assisted Thoracoscopic Sympathectomy for Congenital Long QT Syndromes. The feasibility, safety, and effectiveness of video-assisted thoracoscopic sympathectomy (VATS) for congenital long QT syndrome were assessed in four patients who had frequent syncopal events before the surgeries. Under general anaesthesia, the pleural cavity was entered via two small incisions in the left third and fifth intercostal spaces at the mid-axillary line. The left thoracic sympathetic chain was identified and resected from T2-T5. The lower one third of the left stellate ganglion was also resected. VATS resulted in a significant shortening in corrected QT intervals (QTc) in three patients, the average QTc of the four patients immediately before and after VATS was538 ± 76and512 ± 57 ms, respectively(P = 0.047). The heart rate remained unchanged after the VATS (67 ± 4vs69 ± 4 beats/min, P > 0.05). There were no major perioperative complications apart from mild ptosis of the left upper eyelid in one patient who recovered in the following days. There was no recurrence in syncopal events after a 3-month follow-up. VATS is a safe and effective technique for left cardiac sympathectomy in patients with congenital long QT syndromes. (PACE 2003; 26[Pt. I]:870,873) [source]
Analysis of the Corrected QT Before the Onset of Nonsustained Ventricular Tachycardia in Patients with Hypertrophic CardiomyopathyPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 1p2 2003
BARANOWSKI, R., et al.: Analysis of the Corrected QT Before the Onset of Nonsustained Ventricular Tachycardia in Patients with Hypertrophic Cardiomyopathy. This study examined ventricular repolarization before the onset of 37 episodes of nonsustained ventricular tachycardia (NSVT) in 26 untreated patients with hypertrophic cardiomyopathy (HCM). Fourteen episodes were recorded in patients with a history of cardiac arrest or patients who died suddenly during follow-up. The QT interval was measured beat-by-beat on 24-hour ambulatory electrocardiograms. Mean 24-hour, hourly QTc and QTc of the last 10 beats prior to NSVT, consisted of 4,50 cycles (mean9 ± 10), at the fastest rates of 100,175 beats/min (mean 122 ± 22) were analyzed. NSVT was more prevalent during nighttime (23 episodes), than during daytime (14 episodes,P < 0.05). No significant differences were observed between mean 24-hour, mean hourly QTc during the hour with NSVT, and QTc of the last 10 cycles prior to onset of NSVT. QTc was significantly longer in patients with a history of sudden cardiac death (SCD) or who died suddenly during follow-up than in survivors. The 24-hour QT variability was higher in nonsurvivors than in survivors ( -39 ± 6vs33 ± 6 ms, P = 0.03). Episodes of NSVT in untreated patients with hypertrophic cardiomyopathy were more frequent during the nighttime. The 24-hour QT variability was higher in nonsurvivors than in survivors. (PACE 2003; 26[Pt. II]:387,389) [source]
Temporary Disturbances of the QT Interval Precede the Onset of Ventricular Tachyarrhythmias in Patients with Structural Heart DiseasesPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 10 2002
BJÖRN HENRIK DIEM
DIEM, B.H. et al.: Temporary Disturbances of the QT Interval Precede the Onset of Ventricular Tach-yarrhythmias in Patients with Structural Heart Diseases. An increase in sinus rate prior to ventricular tachyarrhythmias has been demonstrated in previous studies. There is no clear data available concerning changes in ventricular de- and repolarization prior to ventricular tachyarrhythmias, especially in patients with structural heart disease. Therefore, the aim of this study was to analyze the QT and QTc interval (Bazett's formula immediately before the onset of ventricular tachyarrhythmias in stored electrograms of patients with ICDs. The study analyzed 228 spontaneous ventricular tachyarrhythmia episodes in 52 patients (mean age 64 ± 10 years, 49 men, 3 women) and compared them with 146 electrograms of baseline rhythm recorded during regular ICD follow-up. Mean ventricular cycle length (CL), QT interval, and QTc were measured before the onset of ventricular tachyarrhythmia and during baseline rhythm. Prior to ventricular tachyarrhythmias onset, CL was significantly shorter than during baseline rhythm (714 ± 139 vs 828 ± 149 ms, P < 0.0001). By contrast, the QT interval (430 ± 67 ms) and QTc interval (518 ± 67 ms) were significantly prolonged before the onset of ventricular tachyarrhythmias as compared to baseline rhythm (QT 406 ± 67 ms, QTc 450 ± 61 ms; P < 0.0001). CL, QT, and QTc changes were independent of concomitant treatment with antiarrhythmic drugs. Ventricular tachyarrhythmias are preceded by a significant prolongation of the QT and QTc intervals. This phenomenon may represent a greater than normal disparity of repolarization recovery times possibly facilitating the development of ventricular tachyarrhythmias. [source]
Clinical Value of Electrocardiographic Parameters in Genotyped Individuals with Familial Long QT SyndromePACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 4 2001
MOENNIG, G., et al.: Clinical Value of Electrocardiographic Parameters in Genotyped Individuals with Familial Long QT Syndrome. Rate corrected QT interval (QTc) and QT dispersion (QTd) have been suggested as markers of an increased propensity to arrhythmic events and efficacy of therapy in patients with long QT syndrome (LQTS). To evaluate whether QTc and QTd correlate to genetic status and clinical symptoms in LQTS patients and their relatives, ECGs of 116 genotyped individuals were analyzed. JTc and QTc were longest in symptomatic patients (n = 28). Both QTd and JTd were significantly higher in symptomatic patients than in asymptomatic (n = 29) or unaffected family members (n = 59). The product of QTd/JTd and QTc/JTc was significantly different among all three groups. Both dispersion and product put additional and independent power on identification of mutation carriers when adjusted for sex and age in a logistic regression analysis. Thus, symptomatic patients with LQTS show marked inhomogenity of repolarization in the surface ECG. QT dispersion and QT product might be helpful in finding LQTS mutation carriers and might serve as additional ECG tools to identify asymptomatic LQTS patients. [source]
Successful uses of magnesium sulfate for torsades de pointes in children with long QT syndromePEDIATRICS INTERNATIONAL, Issue 2 2006
Abstract Background: Administration of magnesium sulfate (MgSO4) is an effective and safe treatment for torsades de pointes (TdP) associated with acquired long QT syndrome (LQTS) in adults. As for children, there are few reports focusing on it. The authors discuss the efficacy of MgSO4 for TdP in children with congenital and acquired LQTS. The authors also discuss the optimal administration dosage and serum magnesium (SMg) concentration during MgSO4 therapy. Methods: The authors studied seven consecutive LQTS children undergoing MgSO4 therapy for TdP. Of the seven children, five were congenital LQTS and two were acquired LQTS. A bolus injection of MgSO4 was given intravenously over 1,2 min followed by continuous infusion for the next 2,7 days. Results: Of the seven patients, six responded completely to the initial bolus. The bolus dosage was 5.9 ± 3.8 mg/kg (range, 2.3,12 mg/kg) in these six, and the other remaining one (neonate with congenital LQTS) required a total of 30 mg/kg until complete abolishment. The continuous infusion was given at rates of 0.3,1.0 mg/kg per h and patients did not show recurrence of TdP. The SMg concentration was 3.9 ± 1.0 mg/dL (2.9,5.4 mg/dL) immediately after bolus injection. The mean corrected QT (QTc) interval before and after bolus injection did not show significant difference. Conclusion: Intravenous infusion of MgSO4 was effective for TdP in children with LQTS, and MgSO4 abolished TdP without shortening the QTc interval. The optimal bolus dosage, infusion rates and SMg concentration were 3,12 mg/kg, 0.5,1.0 mg/kg per h and 3,5 mg/dL, respectively. [source]
Impact of baseline ECG collection on the planning, analysis and interpretation of ,thorough' QT trialsPHARMACEUTICAL STATISTICS: THE JOURNAL OF APPLIED STATISTICS IN THE PHARMACEUTICAL INDUSTRY, Issue 2 2009
Abstract The current guidelines, ICH E14, for the evaluation of non-antiarrhythmic compounds require a ,thorough' QT study (TQT) conducted during clinical development (ICH Guidance for Industry E14, 2005). Owing to the regulatory choice of margin (10,ms), the TQT studies must be conducted to rigorous standards to ensure that variability is minimized. Some of the key sources of variation can be controlled by use of randomization, crossover design, standardization of electrocardiogram (ECG) recording conditions and collection of replicate ECGs at each time point. However, one of the key factors in these studies is the baseline measurement, which if not controlled and consistent across studies could lead to significant misinterpretation. In this article, we examine three types of baseline methods widely used in the TQT studies to derive a change from baseline in QTc (time-matched, time-averaged and pre-dose-averaged baseline). We discuss the impact of the baseline values on the guidance-recommended ,largest time-matched' analyses. Using simulation we have shown the impact of these baseline approaches on the type I error and power for both crossover and parallel group designs. In this article, we show that the power of study decreases as the number of time points tested in TQT study increases. A time-matched baseline method is recommended by several authors (Drug Saf. 2005; 28(2):115,125, Health Canada guidance document: guide for the analysis and review of QT/QTc interval data, 2006) due to the existence of the circadian rhythm in QT. However, the impact of the time-matched baseline method on statistical inference and sample size should be considered carefully during the design of TQT study. The time-averaged baseline had the highest power in comparison with other baseline approaches. Copyright © 2008 John Wiley & Sons, Ltd. [source]
A comparison of the effect on QT interval between thiamylal and propofol during anaesthetic induction,ANAESTHESIA, Issue 7 2010
Summary The aim of this study was to determine the effect of thiamylal and propofol on heart rate-corrected QT (QTc) interval during anaesthetic induction. We studied 50 patients undergoing lumbar spine surgery. Patients were administered 3 ,g.kg,1 fentanyl and were randomly allocated to receive 5 mg.kg,1 thiamylal or 1.5 mg.kg,1 propofol as an induction agent. Tracheal intubation was performed after vecuronium administration. Heart rate, mean arterial pressure, bispectral index score, and 12-lead electrocardiogram were recorded at the following time points: just before (T1) and 2 min after (T2) fentanyl administration; 2 min after anaesthetic administration (T3); 2.5 min after vecuronium injection (T4); and 2 min after intubation (T5). Thiamylal prolonged (p < 0.0001), but propofol shortened (p < 0.0001), the QTc interval. [source]
Effects of sevoflurane on QT parameters in children with congenital sensorineural hearing lossANAESTHESIA, Issue 1 2009
H. S. Kim
Summary Sevoflurane prolongs the QT interval (QTI). Patients with congenital sensorineural hearing loss (SNHL) often have a prolonged QTI. This study was to investigate the effects of sevoflurane on the QTI in SNHL and control children. Thirty patients with SNHL and 30 controls were studied. The corrected QT interval (QTc), interval from peak to end of T wave (Tp-e) and QT variability index (QTVI) were analysed. QTc and Tp-e were estimated by the average QTc and Tp-e measured beat-by-beat for 15 min. Heart rate power spectral analysis was performed. In both groups, QTc and QTVI increased during anaesthesia, but Tp-e did not change. There were no differences in QTc, QTVI, Tp-e, low- and high-frequency power between the two groups. In both groups, sevoflurane lengthened the QTc and QTVI intervals but not Tp-e. [source]
Effects of Head-Up Tilt-Table Test on the QT IntervalANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2010
Michael 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]
Optimization of Repolarization during Biventricular Pacing: A New Target in Patients with Biventricular Devices?ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 1 2010
Cengizhan Türko, lu M.D.
Background: Evaluation of repolarization during sequentional biventricular pacing. Methods: Patients with biventricular devices, and left ventricular leads placed to the basal part of lateral left ventricular wall were enrolled. QRS, QTc, JTc, and corrected Tpeak-Tend intervals were compared during sequentional biventricular, left ventricular, and right ventricular pacing. Results: Five patients with nonischemic and five with ischemic cardiomyopathy due to anterior myocardial infarction were enrolled. No correlation was observed between values of repolarization among patients. The optimal values of repolarization were significantly different from values of echocardiographically guided hemodynamic optimization. Two patients with biventricular pacing-induced ventricular fibrillation were successfully treated by reprogramming of V-V delay according to interventricular delay resulting in shorter Tpeak-Tend interval, although delayed effect of amiodarone in one of these patients cannot be ruled out. Conclusions: Patients with biventricular devices may be prone to development of ventricular arrhythmias depending on programmed V-V interval. We suggest that optimization of repolarization may be performed in patients with biventricular pacemakers in the absence of backup ICD and those with frequent episodes of ventricular tachyarrhythmias, although this finding deserves further study. Ann Noninvasive Electrocardiol 2010;15(1):36,42 [source]
Long QT Syndrome in African-AmericansANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 1 2010
Thomas Fugate II B.S.
Background: We evaluated the risk factors and clinical course of Long QT syndrome (LQTS) in African-American patients. Methods: The study involved 41 African-Americans and 3456 Caucasians with a QTc , 450 ms from the U.S. portion of the International LQTS Registry. Data included information about the medical history and clinical course of the LQTS patients with end points relating to the occurrence of syncope, aborted cardiac arrest, or LQTS-related sudden cardiac death from birth through age 40 years. The statistical analyses involved Kaplan-Meier time to event graphs and Cox regression models for multivariable risk factor evaluation. Results: The QTc was 29 ms longer in African-Americans than Caucasians. Multivarite Cox analyses with adjustment for decade of birth revealed that the cardiac event rate was similar in African-Americans and Caucasians with LQTS and that beta-blockers were equally effective in reducing cardiac events in the two racial groups. Conclusions: The clinical course of LQTS in African-Americans is similar to that of Caucasians with comparable risk factors and benefit from beta-blocker therapy in the two racial groups. Ann Noninvasive Electrocardiol 2010;15(1):73,76 [source]
Correction for QT/RR Hysteresis in the Assessment of Drug-Induced QTc Changes,Cardiac Safety of GadobutrolANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2009
M.D., Marek Malik Ph.D.
Background: The so-called thorough QT/QTc (TQT) studies required for every new pharmaceutical compound are negative if upper single-sided 95% confidence interval (CI) of placebo and baseline corrected QTc prolongation is <10 ms. This tight requirement has many methodological implications. If the investigated drug has a fast action and ECGs cannot be obtained at stable heart rates, QT/RR hysteresis correction is needed. Methods: This was used in a TQT study of gadobutrol. The TQT study was a randomized double-blind five-times crossover study of three doses of gadobutrol (0.1, 0.3, and 0.5 mmol/kg) that was placebo and positive effect controlled (moxifloxacin 400 mg). The study enrolled 50 healthy subjects with data of all periods. QT/RR hysteresis was assessed from prestudy exercise test ECGs. Among others, comparisons were made between population heart rate correction without hysteresis considerations and combined population heart rate and hysteresis correction. Results: The highest heart rate increase (placebo and baseline controlled) of 13.1 beats per minute (90% CI 9.9,16.4) occurred 1 minute after the administration of the highest dose of gadobutrol. Without hysteresis consideration, the highest ,,QTc were 9.91 ms (90% CI 8.01,11.81) while with hysteresis correction, these values were 7.62 ms (90% CI 6.37,8.87), thus turning a marginally positive TQT study into a negative finding. Conclusion: Hence, omitting hysteresis correction from episodes of fast heart rate changes may lead to incorrect conclusions. Despite substantial rate acceleration, accurate hysteresis correction confirms that gadobutrol does not have any effects on cardiac repolarization that would be within the limits of regulatory relevance. [source]
T-Wave Morphology in Short QT SyndromeANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2009
Olli Anttonen M.D.
Background: Short QT syndrome (SQTS) is an inherited disorder characterized by a short QT interval and vulnerability to ventricular tachyarrhythmias. The diagnostic criteria for this syndrome are not well defined, since there is uncertainty about the lowest normal limits for the corrected QT (QTc) interval. Objective: The aim of this study was to determine whether T-wave morphology parameters are abnormal in short QT subjects and whether those parameters can help in the diagnosis of SQTS. Methods and Results: We describe three families (10 patients) with short QT intervals (QTc 310 ± 32 ms). Seven subjects had suffered serious arrhythmic events and three were asymptomatic. T-wave morphology was assessed using the principal component analysis (PCA). QTc was significantly shorter and T-wave amplitude in lead V2 higher in the short QT subjects compared to healthy controls (n = 149), (P < 0.001 for both). The total cosine of the angle between the main vectors of the QRS and T-wave loops (TCRT) was markedly abnormal among the symptomatic patients with short QT syndrome (n = 7) (TCRT ,0.14 ± 0.55 vs 0.36 ± 0.51, P = 0.019). None of the three asymptomatic patients with short QT but without a history of arrhythmic events had an abnormally low TCRT. Conclusion: Our observations suggest that patients with a short QT interval and a history of arrhythmic events have abnormal T-wave loop parameters. These electrocardiogram (ECG) features may help in the diagnosis of SQTS in addition to the measurement of the duration of QT interval from the 12-lead ECG. [source]
Familial Aggregation and Heritability of Electrocardiographic Intervals and Heart Rate in a Rural Chinese PopulationANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 2 2009
Jianping Li M.D., Ph.D.
Background: Estimates of the genetic influences on electrocardiographic (ECG) parameters are inconsistent in previous reports, and no such studies have been performed in China. So we estimated genetic contributions to PR and QRS intervals and the rate-adjusted QT interval (Bazett's QTc) in a Chinese rural population. Methods: A total of 2909 subjects from 847 families were enrolled in the current study. Genetic contributions to ECG parameters were estimated in two ways: correlation coefficients among family members (father-mother, parent-offspring, first sibling-other sibling) and the heritability of each of the ECG parameters. Results: Our results showed significant correlations among family members on theses parameters: the correlation coefficients for PR interval, QRS duration, QTc interval, and HR, between parent-sibling, and sibling-sibling were 0.17 and 0.13, 0.18 and 0.23, 0.22 and 0.28, 0.19 and 0.18, respectively. The heritability for PR interval, QRS duration, QTc interval, and HR were estimated as 0.34, 0.43, 0.40, and 0.34, respectively. Conclusion: Genetic factors, together with the environmental and other cofactors contribute no more than 60% to the variance of the ECG intervals, supporting the concept that multiple factors, including gene-gene and gene-environment interactions could influence ECG interval phenotypes, and genetic factors play a major role. [source]