Background:The corrected QT interval (QTc) according to Bazett's formula (QTc = QT/RR 1/2 ) has been used in clinical practice. Bazett's formula, however, overcorrects the QT interval at fast heart rates and undercorrects it at low heart rates. Guidelines and some investigators have recommended using Fridericia's formula (QTc = QT/RR 1/3 ) in these cases, especially in tachycardic subjects. The aim of the present study was to determine cutoffs for QTc suitable for screening pediatric subjects with prolonged QT intervals, based on manually measured values corrected by Fridericia's formula in a large number of subjects. Methods and Results:Three consecutive QT and RR intervals were measured in 4,655, 4,655, and 5,273 1st, 7th, and 10th graders, aged 6, 12, and 15 years, respectively. Each QT interval was corrected by Fridericia's formula, and mean values were calculated. Determination of the cut-offs for screening was based on the prevalence of abnormal electrocardiographic phenotypes of 1:1,164 and on the upper 0.025 percentile in the QTc distribution derived from previous studies. The tentative cut-offs suitable for screening subjects with prolonged QT intervals were 430 ms for 1st graders, 445 ms for 7th graders, and 440 and 455 ms for 10th grade boys and girls, respectively. Conclusions:These tentative cut-offs can be used to screen subjects with prolonged QT intervals in the clinical setting. Further studies are needed to confirm their validity. (Circ J 2010; 74: 1663 - 1669
ong QT syndrome (LQTS) is a rare disorder characterized by prolonged ventricular repolarization and a high risk of cardiac events, including sudden cardiac death. 1,2 Among the mutations thus far identified in specific ion channel genes causing LQTS, 3-6 KCNQ1 and KCNH2 have been most commonly identified, and they are known to cause the LQT1 and LQT2 forms, respectively. Recent studies have reported that LQTS-related cardiac events tend to occur under specific circumstances in a genespecific manner. 7 In the LQT1 form, exercise and swimming are the most common triggers, whereas in the LQT2 form they are strong emotions, sleep, and rest. 7 Results of experimental studies suggest that the interval between the peak and the end of the T wave in a transmural electrocardiogram (ECG) reflects the transmural dispersion of repolarization (TDR) when a normal upright T wave is present, and that TDR is linked to the genesis of torsade de pointes. [8][9][10] When complex (inverted, notched or biphasic, and triphasic) T waves are present, the interval from the nadir of the initial negative T wave to the end of the T wave is representative of the TDR. 11 However, the definition of the interval representative of TDR on a clinical surface ECG remains a subject of controversy when the T wave shows a notched or a bifid configuration. [12][13][14][15][16] There has not been a clinical report of the use of the interval from the nadir of the initial negative T wave to the end of the T wave as the definition of the interval representative of TDR when the notched or a bifid T wave is present.A face immersion test was reported to induce an abnormally prolonged QT interval and notched T waves in children and adolescent with LQTS, 17 suggesting that the same test would induce a prolongation of the TDR in these young patients. We used the face immersion test to examine the QT intervals and compare the T wave configuration on ECG before and after treatment with the aim of determining whether the interval representative of TDR based on the experimental study can be adapted for use in the clinical setting, assuming that the decrease in the QTc interval after treatment is associated with a decrease in the TDR. Methods Study PopulationInclusion criteria for the present study were children and adolescents with LQTS who had been treated and undergone a face immersion test before and after treatment. The 3 boys and 2 girls comprised 3 cases of the LQT1 form (KCNQ1 mutation; 2 families) and 2 of the LQT2 form (KCNH2 mutation, 2 families) ( Table 1). ControlsTo determine the normal range of the QT intervals during the face immersion test, 31 control children and adolescents (23 boys, 8 girls; mean age, 12 years; range, 6-17 years) were also examined. Normal ranges were defined as the mean ± 2SD. Background It has been shown experimentally that the interval from the nadir of the initial negative T wave to the end of the T wave is representative of transmural dispersion of repolarization (TDR) when complex T waves are present. In the clinical setting,...
Background and objectivesIt is sometimes difficult to obtain antigen‐negative red blood cells (RBCs) for patients with antibodies against RBCs. However, the frequency and severity of the adverse reactions have not been well elucidated. Here, we conducted a multi‐institutional collaborative study to clarify the background, frequency and clinical significance of antigen‐positive RBC transfusions to patients with the respective antibodies.Materials and methodsThe survey included the background of patients, antigens on RBCs transfused, total amount of antigen‐positive RBCs transfused, results from antibody screen and direct antiglobulin tests, specificity of antibodies, adverse reactions and efficacies. All antibodies were surveyed regardless of their clinical significance.ResultsIn all, 826 cases containing 878 antibodies were registered from 45 institutions. The main reasons for antigen‐positive RBC transfusions included ‘negative by indirect antiglobulin test’ (39%) and ‘detection of warm autoantibodies’ (25%). In 23 cases (3% of total), some adverse reactions were observed after antigen‐positive RBC transfusion, and 25 antibodies (9 of 119 clinically significant and 16 of 646 insignificant antibodies) were detected. Non‐specific warm autoantibodies were detected in 9 cases, anti‐E in 5 cases, 2 cases each of anti‐Lea, anti‐Jra or cold alloantibodies, and 1 case each of anti‐Dib, anti‐Leb or anti‐P1. Other antibodies were detected in 2 further cases. Five (22%) of these 23 cases, who had anti‐E (3 cases) or anti‐Jra (2 cases), experienced clinically apparent haemolysis.ConclusionsAdverse reactions, especially haemolysis, were more frequently observed in cases with clinically significant antibodies than those with clinically insignificant antibodies (P < 0·001).
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