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  • Blackwell Science Inc  (114)
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  • 1
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: The aim of this study was to compare the reproducibility and sensitivity of four commonly used methods for QT interval assessment when applied to ECG data obtained after infusion of ibutilide. Methods: Four methods were compared: (1) 12-lead simultaneous ECG (12-SIM), (2) lead II ECG (LEAD II), both measured on a digitizing board, (3) 3-LEAD ECG using a manual tangential method, and (4) a computer-based, proprietary algorithm, 12SL™ ECG Analysis software (AUT). QT intervals were measured in 10 healthy volunteers at multiple time points during 24 hours at baseline and after single intravenous doses of ibutilide 0.25 and 0.5 mg. Changes in QT interval from baseline were calculated and compared across ECG methods, using Bland–Altman plots. Variability was studied using a mixed linear model. Results: Baseline QT values differed between methods (range 376–395 ms), mainly based on the number of leads incorporated into the measurement, with LEAD II and 3-LEAD providing the shortest intervals. The 3-LEAD generated the largest QT change from baseline, whereas LEAD II and 12-SIM generated essentially identical result within narrow limits of agreement (0.4 ms mean difference, 95% confidence interval ± 20.5 ms). Variability with AUT (standard deviation 15.8 ms for within-subject values) was clearly larger than with 3-LEAD, LEAD II, and 12-SIM (9.6, 10.0, and 11.3 ms). Conclusion: This study demonstrated significant differences among four commonly used methods for QT interval measurement after pharmacological prolongation of cardiac repolarization. Observed large differences in variability of measurements will have a substantial impact on the sample size required to detect QT prolongation in the range that is currently advised in regulatory guidance.
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  • 2
    Electronic Resource
    Electronic Resource
    350 Main Street , Malden , MA 02148 , USA , and 9600 Garsington Road , Oxford OX4 2DQ , UK . : Blackwell Science Inc
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: Measures of QT dynamics express repolarization abnormalities that carry prognostic information, but the reproducibility of beat-to-beat QT dynamics has never been established. The QT interval is prolonged at night, but how the circadian rhythm and heart rate influence the dynamic QT measurements is still unsettled. The aims of the present study were: (1) to describe the reproducibility of beat-to-beat QT dynamics with respect to intrasubject, between-subject, and between-observer variability and (2) to describe the normal range, circadian variation, and heart rate dependence of QT dynamics. Methods: Ambulatory Holter recordings were performed three times on 20 healthy volunteers and were analyzed by two experienced cardiologists. Slope and intercept of the QT/RR regression, the variability of QT and R-R intervals expressed as the standard deviation, and the relation between QT and RR variability expressed as a variability ratio were measured among other QT dynamics. Results: The reproducibility of all QT dynamics was good. All QT dynamics showed circadian variation when calculated on an hourly basis. The day/night variation in slope could be explained by the differences in heart rate, whereas the day/night variation in intercept was heart rate independent. Conclusion: The present study shows that reliable automatic QT measurements could be performed, encouraging further evaluation of the clinical value of QT dynamics in risk stratification of cardiac patients.
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  • 3
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: Congenital long QT syndrome (LQTS) is caused by mutations in the cardiac Na+ or K+ channels that result in a prolonged QTc interval and increased QT dispersion. Na+ channel blockers and K+ can reverse the repolarization abnormalities in the Na+ channel variant (LQT3) and K+ channel variant (LQT1, LQT2), respectively. The phenotype of LQTS can be difficult to recognize, especially when the QTc interval is mildly prolonged. Additional noninvasive testing methods are needed to enhance the diagnosis of LQTS. This study compared the response of the QTc interval and QT dispersion to a sequential lidocaine/K+ infusion in LQTS patients with borderline QTc interval prolongation and control patients as a means of diagnosing LQTS. Methods: In this study, eight LQTS patients with borderline QTc, defined as QTc 〈 470 ms, and 10 healthy controls received sequential lidocaine/K+ infusion. Results: At baseline, LQTS patients had a longer QTc (446 ± 29 vs 416 ± 28 ms, P 〈 0.05) but similar QT dispersion (43 ± 14 vs 29 ± 10 ms) compared to controls. After lidocaine administration, baseline QTc and QT dispersion did not change in either LQTS or controls. One LQTS patient had a 54 ms (12%) reduction in his QTc but no change in QT dispersion. Following K+ infusion, baseline QTc and QT dispersion decreased by 9% (P 〈 0.005) and 45% (P 〈 0.005), respectively in LQTS. No effect was seen in control patients, where QTc and QT dispersion shortened by 1% (5 ± 14 ms) and 20% (6 ± 7 ms), respectively, compared to baseline. The combined lidocaine/K+ infusion had a sensitivity, specificity, and accuracy of 88%, 100%, and 94%, respectively, in diagnosing LQTS. Conclusions: A simplified sequential lidocaine/K+ challenge is accurate in diagnosing LQTS among patients with borderline QTc prolongation.
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  • 4
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: Coronary slow flow (CSF) is characterized by delayed opacification of coronary arteries in the absence of epicardial occlusive disease. In this study, we aimed to determine endothelin-1 (ET-1), nitric oxide (NOx) levels and time domain heart rate variability (HRV) parameters in patients with CSF and relationship among these parameters. Methods: Thirty-three patients with CSF detected in the coronary angiography (17 females; mean age 55 ± 7) and 19 patients with normal coronary flow (10 females; mean age 54 ± 11) as a control group were enrolled in the study. Patients were divided into two groups according to exercise testing as if positive (group A, n = 8) or negative (group B, n = 25). Results: Plasma ET-1 levels were higher in the group A patients (28.7 ± 17.4 pg/ml) than that of group B (15.9 ± 10.6 pg/ml) and control group (6.0 ± 5.7 pg/ml); and higher in group B patients than that of control group (P 〈 0.05). Although groups A and B did not differ according to plasma NOx levels (23.4 ± 13.5 μmol/L vs. 32.8 ± 22.7 μmol/L, P 〉 0.05), NOx levels in group A were lower than the control group (23.4 ± 13.5 μmol/L versus 42.5 ± 15.9 μmol/L, P 〈 0.05). Time domain HRV parameters were decreased in all patient groups. This was more prominent in group A. Additionally, HRV parameters were negatively correlated with ET-1 and TIMI frame counts. TIMI frame count was also significantly correlated with ET-1 and NOx levels (r = 0.61, P 〈 0.0001, r =−0.30, P 〈 0.05). Upon intravascular ultrasonography investigation, the common finding was longitudinally extended massive calcification throughout the epicardial arteries. Mean intimal thickness was 0.50 ± 0.13 mm (group A; 0.58 ± 0.11 mm, group B 0.47 ± 0.12 mm, P = 0.029). Conclusions: The present study demonstrated that in patients with CSF, both increased plasma ET-1, decreased plasma NOx and diffuse atherosclerosis may cause the decrease in HRV by effecting myocardial blood flow.
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  • 5
    Electronic Resource
    Electronic Resource
    350 Main Street , Malden , MA 02148 , USA , and 9600 Garsington Road , Oxford OX4 2DQ , UK . : Blackwell Science Inc
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Objective: The purpose of this study was to report a novel electrocardiographic (ECG) phenomenon in acute pulmonary embolism characterized by QT interval prolongation with global T-wave inversion. Methods: Among a total of 140 study patients with a confirmed diagnosis of acute pulmonary embolism, patients who fulfilled the inclusion criteria for QT interval prolongation with global T-wave inversion were examined. Each of these patients had undergone a detailed clinical evaluation including testing for myocardial injury and echocardiography. Results: QT interval prolongation with global T-wave inversion was found in five patients (age 51–68 years) with acute pulmonary embolism. Four were women. Acute pulmonary embolism was diagnosed by ventilation-perfusion scan in three patients and by spiral computed tomography in other two patients. None of the patients had any right or left ventricular regional wall motion abnormalities on echocardiography. All patients had changes characteristic of hemodynamically significant pulmonary embolism, including right ventricular stunning or hypokinesis and dilatation in five patients with paradoxical septal motion in four. Acute coronary syndrome was ruled out in each patient by clinical evaluation, serial ECGs and cardiac markers, and lack of regional wall motion abnormalities on echocardiography. Prolongation of QT intervals (QTc 456–521 ms) with global T-wave inversion was noted on presentation. The ECG changes gradually resolved in 1 week in all patients with appropriate treatment of acute pulmonary embolism. One patient died. None of the patients developed torsade de pointes. Conclusions: Acute pulmonary embolism may occasionally result in reversible QT interval prolongation with deep T-wave inversion, and, thus should be considered among the acquired causes of the long QT syndrome.
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  • 6
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
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  • 7
    Electronic Resource
    Electronic Resource
    350 Main Street , Malden , MA 02148 , USA , and 9600 Garsington Road , Oxford OX4 2DQ , UK . : Blackwell Science Inc
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: Recently, we identified a novel mutation of SCN5A (1795insD) in a large family with LQTS3. The aim of this study was to assess whether the various proposed corrections of the QT interval to heart rate help to improve the identification of carriers of the mutant gene. Methods: The study group consisted of 101 adult family members: 57 carriers and 44 noncarriers (mean age 44.6 ± 14.6 and 40.3 ± 12.8 years, respectively). In all individuals a 12-lead ECG, exercise ECG, and 24-hour Holter ECG were obtained. Results: Correction for heart rate significantly improved the diagnostic performance of the QT interval. Diagnostic performance of the Bazett formula was similar to that of the newer formulas (Fridericia, Hodges, Framingham, and a logarithmic formula). At a cut-off value of 440 ms, the Bazett corrected QT interval was associated with a sensitivity and specificity of 90% and 91%, respectively. Using the 24-hour Holter ECG, a prolonged QTc at heart rates less than 60 beats/min was almost pathognomonic for genetic mutation (sensitivity and specificity both 99%), whereas the QTc calculated at the lowest heart rate using Bazett's formula provided full discrimination. Conclusion: In the present family, the resting ECG gave a good indication about the presence or absence of genetic mutation but a 24-hour Holter recording was mandatory to ascertain the diagnosis. In the diagnosis of this form of LQTS3, Bazett's formula was at least as good as other proposed corrections of the QT interval to heart rate.
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  • 9
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: There is a significant difference in repolarization on the surface ECG between men and women. The effect of testosterone on repolarization of myocardium may provide a basis for the physiological and pathophysiological importance of these distinctions between sexes. The purpose of this study is to compare the repolarization characteristics of surface ECG in patients with secondary hypogonadotropic hypogonadism to those of healthy men and women. Methods: The study consisted of 45 consecutive patients with the diagnosis of secondary hypogonadotropic hypogonadism (study group) and age-, weight- and height-matched normal healthy men (n = 35) and women (n = 39) (control group). 12-lead ECG recordings were obtained and electronic calipers were used for measurements of ECG repolarization variables. ECG variables were compared with those of control groups. Results: J point amplitude (0.12 ± 0.07 vs 0.05 ± 0.05 mV, respectively), T max (0.74 ± 0.28 vs 0.60 ± 0.27 mV, respectively), T wave area (81 ± 36 vs 60 ± 29 mVms, respectively) and T wave descending time (93 ± 16 vs 85 ± 15 ms, respectively) were significantly higher in healthy subjects than hypogonadal men. In comparison with those of healthy women, hypogonad males have higher J point (0.05 ± 0.05 vs 0.02 ± 0.02 mV), taller T wave (0.60 ± 0.27 vs 0.34 ± 0.13 mV), consequently less T wave area (60 ± 29 vs 34 ± 16 mVms), ascending (62 ± 18 vs 53 ± 11) and descending angle (67 ± 17 vs 55 ± 12). Corrected QT was not different among groups. Conclusions: Testosterone deprivation in hypogonadotropic hypogonadism attenuates J point, T wave peak, T wave area, and T wave descending time, but does not reach to the level of those in healthy women. Testosterone has no effect on QT interval in this group of age. Hormone replacement therapy of these patients will provide informative contribution.
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  • 10
    Electronic Resource
    Electronic Resource
    350 Main Street , Malden , MA 02148 , USA , and 9600 Garsington Road , Oxford OX4 2DQ , UK . : Blackwell Science Inc
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Aim: Prolongation of P wave time and increase of its dispersion as an independent predictor of atrial fibrillation. In patients with paroxysmal atrial fibrillation (PAF) as in healthy people, exercise augments sympathetic activity and therefore can cause the development of atrial fibrillation. The aim of this study is to evaluate the effect of exercise on P wave dispersion and to predict the development of atrial fibrillation. Methods: One hundred and ninety-eight patients (93 women, 105 men, mean age: 59.05 ± 11.01 years) having the diagnosis of PAF were included in the study. The left atrial diameter of all these patients was more than 4.0 cm. One hundred and fifty-five patients (72 females, 83 males, mean age: 58.41 ± 10.79 years), with left atrial diameter more than 4.0 cm and without PAF were taken as control group. Symptom limited exercise test with modified Bruce protocol was performed on all patients. Rest, maximum exercise and recovery, and first, third, and fifth-minute 12-derivation ECG was taken in all patients. The velocity of ECG was adjusted to 50 mm/s; shortest and largest P wave durations were measured and P wave dispersion was calculated. Results: The mean left atrial diameter was 4.41 ± 0.58 cm in PAF patients and 4.38 ± 0.48 cm in control group. No differences were found between PAF patients with the controls in exercise time (10.38 ± 2.93 vs 10.81 ± 2.75 minutes); METs (6.98 ± 1.72 vs 7.28 ± 1.75 minutes); resting heart rate (79.13 ± 14.86 vs 79.69 ± 10.43 bpm); peak heart rate (146.83 ± 23.21 vs 146.94 ± 16.13 bpm). Maximum exercise P wave duration and P wave dispersion were greater than the rest measurements in PAF group (respectively P 〈 0.0001 and P = 0.0004). Conclusion: In PAF patients, P wave dispersion is significantly longer at rest, maximum exercise and recovery time than in a control group without PAF.
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