Prevalence of long and short QT in a young population of 41,767 predominantly male Swiss conscripts (original) (raw)
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Journal of the American College of Cardiology, 2006
Almost 50 years after the first description of congenital long QT syndrome (LQTS), where QT interval prolongation was recognized as the hallmark of a new pathologic entity associated with sudden cardiac death (1), the simple linear measurement of QT interval still stands as the strongest independent predictor of cardiac events in LQTS patients. Prolonged corrected QT interval (QTc) was a powerful independent risk factor for cardiac event (syncope or cardiac arrest) since the initial analysis of patients enrolled in the International LQTS Registry (2-3). Subsequent analyses confirmed that finding (4-10). Incremental changes of QT interval carried higher risk for sudden death, and a cutoff of QTc Ͼ500 ms consistently identified higher-risk patients. Most analyses of the International LQTS Registry were based on QT interval measured on the first available electrocardiogram (ECG) (6-8). This was done to avoid possible selection bias, because symptomatic patients tended to have more ECG recordings than asymptomatic subjects, and to limit possible effects of concomitant therapies, which were less likely to be present in the earliest ECG. See page 1047 The study by Goldenberg et al. (11) in this issue of the Journal first evaluated possible incremental benefit of follow-up ECG on risk stratification. Its main results were that maximum QTc, rather than baseline QTc, was better correlated with risk of cardiac events during follow-up and that an increased number of ECG tracings may improve risk stratification. The major clinical implications are that serial ECG tracings should be routinely obtained during clinical follow-up of LQTS patients and that changes of QT interval duration may be monitored to evaluate the effect of therapies in LQTS patients.
Heart Rhythm, 2005
BACKGROUND Physicians in all fields of medicine may encounter patients with long QT syndrome (LQTS). It is important to define the percentage of physicians capable of distinguishing QT intervals that are long from those that are normal because LQTS can be lethal when left untreated. OBJECTIVES The purpose of this study was to define the percentage of physicians in the different disciplines of medicine who can recognize a long QT when they see one. METHODS We presented the ECGs of two patients with LQTS and two healthy females to 902 physicians (25 world-renowned QT experts, 106 arrhythmia specialists, 329 cardiologists, and 442 noncardiologists) from 12 countries. They were asked to measure the QT, calculate the QTc (the QT interval corrected for the heart rate), and determine whether the QT is normal or prolonged. RESULTS For patients with LQTS, Ͼ80% of arrhythmia experts but Ͻ50% of cardiologists and Ͻ40% of noncardiologists calculated the QTc correctly. Underestimation of the QTc of patients with LQTS and overestimation of the QTc of healthy patients were common. Interobserver agreement was excellent among QT experts, moderate among arrhythmia experts, and low among cardiologists and noncardiologists (kappa coefficient ϭ 0.82, 0.44, and Ͻ 0.3, respectively). Correct classification of all QT intervals as either "long" or "normal" was achieved by 96% of QT experts and 62% of arrhythmia experts, but by only Ͻ25% of cardiologists and noncardiologists. CONCLUSIONS Most physicians, including many cardiologists, cannot accurately calculate a QTc and cannot correctly identify a long QT.
J-Shaped Association Between QTc Interval Duration and the Risk of Atrial Fibrillation
Journal of the American College of Cardiology, 2013
The aim of this study was to investigate whether the heart rate-corrected QT (QTc) interval on the electrocardiogram (ECG) is associated with the onset of atrial fibrillation (AF). Background Patients with hereditary short-QT or long-QT syndromes, representing the very extremes of the QT interval, both seem to have a high prevalence of AF. Methods A total of 281,277 subjects were included, corresponding to one-third of the population of the greater region of Copenhagen. These subjects underwent digital ECG recordings in a general practitioner's core facility from 2001 to 2010. Data on drug use, comorbidities, and outcomes were collected from Danish registries. Results After a median follow-up period of 5.7 years, 10,766 subjects had developed AF, of whom 1,467 (14%) developed lone AF. Having a QTc interval lower than the first percentile (372 ms) was associated with a multivariate-adjusted hazard ratio of 1.45 (95% confidence interval: 1.14 to 1.84; p ¼ 0.002) of AF, compared with the reference group (411 to 419 ms). From the reference group and upward, the risk of AF increased with QTc interval duration in a doseresponse manner, reaching a hazard ratio of 1.44 (95% confidence interval: 1.24 to 1.66, p < 0.001) for those with QTc intervals !99th percentile (!464 ms). The association with respect to longer QTc intervals was stronger for the outcome of lone AF, as evidenced by a hazard ratio of 2.32 (95% confidence interval: 1.52 to 3.54, p < 0.001) for having a QTc interval !99th percentile (!458 ms). Conclusions In this large ECG study, a J-shaped association was found between QTc interval duration and risk of AF. This association was strongest with respect to the development of lone AF.
The Evaluation of a Borderline Long QT Interval in an Asymptomatic Patient
Cardiac Electrophysiology Clinics, 2012
The incidence of long QT syndrome (LQTS) is approximately 1 in 2500, but 25% to 50% of patients may demonstrate a normal or borderline long QT interval. The rate of life-threatening arrhythmias in patients with LQTS with normal corrected QT intervals is very low (approximately 0.13% per year) but higher (>10-fold) than that in unaffected family members. Avoidance of QT-prolonging medications and routine therapy with highly efficacious b-blockers significantly reduce life-threatening arrhythmia. Therefore, identification of the index case and affected family members is critical. Comprehensive clinical history taking, rest and provocative electrocardiographic testing, and targeted genetic testing assists in diagnosing patients with LQTS with normal or borderline QT intervals.
QT interval in 24-hour ambulatory ECG recordings from 60 healthy adult subjects
Journal of Electrocardiology, 1991
QT and RR intervals were measured in 24-hour electrocardiographic (ECG) recordings from 60 healthy subjects randomly selected among participants in the Copenhagen City Heart Study. Five men and five women of each IO-year age group between the ages of 20 and 79 were included. The mean of three consecutive RR and QT intervals was calculated from ECG strips recorded at 1000, 1400, 1800, 2200, 0200, and 0600 hours in each subject. The RR interval varied between 728 ms at 1400 hours and 984 ms at 0600 hours, and the uncorrected QT interval between 358 ms at 1400 hours and 417 ms at 0200 hours. The QT interval corrected for heart rate by Bazett's formula varied between 418 ms at 0600 hours and 428 ms at 1000 hours, and the QT interval corrected by the regression equation of this study varied between 396 ms at 1400 hours and 422 ms at 0200 hours. Multiple regression analysis of uncorrected data yielded a partial regression coefficient for heart rate influence of 0.14. After correction by Bazett's formula, a statistically significant effect of heart rate remained (partial regression coefficient-0.08, t =-9.93, p <O.OOOl). In addition to the influence of heart rate, the analysis revealed a statistically significant effect of hour of day (F = 11.30; DF 5, 286; p <O.OOOl) and gender (F = 6.24; DF 1, 53; p <0.05), whereas age in the range of 20-79 years had no significant effect. The QT intervals of this study differed from the values measured in standard ECG recordings but not from those of other Holter studies. It is recommended that the QT interval be corrected for heart rate, gender, and hour of day before being classified as normal or abnormal.
The association of QT interval components with atrial fibrillation
Annals of noninvasive electrocardiology : the official journal of the International Society for Holter and Noninvasive Electrocardiology, Inc, 2017
Although abnormalities of the QT interval are associated with atrial fibrillation (AF), it is unclear whether ventricular depolarization (QRS duration) or repolarization (JT interval) is a more important marker of AF risk. This analysis included 4,181 (95% white; 59% women) participants from the Cardiovascular Health Study (CHS) who were free of baseline AF and major intraventricular delay. A linear scale was used to compute heart rate adjusted QT (QTa), QRS (QRSa ), and JT (JTa ) intervals. Prolonged QTa , QRSa , and JTa were defined by values greater than the sex-specific 95th percentile for each measurement. AF events were ascertained during the annual study electrocardiograms and from hospitalization discharge data. Cox regression was used to compute hazard ratios (HR) and 95% confidence intervals (CI) for the associations of prolonged QTa , QRSa , and JTa with AF, separately. Over a mean follow-up of 12.1 years, a total of 1,236 (30%) AF events were detected. An increased risk ...