短QT间期的心电图诊断标准探讨

目的用2种已报道的诊断标准研究一组心电图短QT间期者所占比例,并比较2种方法的异同。方法随机选取547例健康人,做常规12导联心电图,准确测量QT间期,根据RR间期(RR)和心率(HR)计算QT间期校正值(QTc)和QT间期预计值(QTp),以QT相似文献   

冠状动脉血管成形术对QT离散度的影响及其意义

为阐明冠状动脉血管成形术（CA）对QT离散度（QTd）的影响，并探讨其意义。我们分析48例（心绞痛14例，心肌梗塞34例）CA术前后1天内所记录的心电图，测算QT、QTd、心率校正QT间期（QTc）和心率校正QT离散度（QTcd）。病例分为：心绞痛CA成功组、心肌梗塞CA成功组和CA失败组，分别对3组的4项指标作术前与术后比较。结论：前两组本前与本后QT和QTc差异均无显著性，但术后QTd和QTcd较术前显著减小（分别为38±13vs65±15ms，1．2±0．5vs2．4±0．8；38±16vs66±25ms，1．3±0．6vs2．1±0．9，P均＜0．001）。CA失败组术前后4项指标差异均无显著性。结论：成功的CA能显著减小心绞痛和心肌梗塞患者的QTd，提示可能改善患者的预后；术后QTd减小可能反映了顿抑或冬眠心肌的“苏醒”，并表明梗塞区尚有存活心肌。     

Inaccurate electrocardiographic interpretation of long QT: The majority of physicians cannot recognize a long QT when they see one

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, >80% of arrhythmia experts but <50% of cardiologists and <40% 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 = 0.82, 0.44, and < 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 <25% of cardiologists and noncardiologists. CONCLUSIONS: Most physicians, including many cardiologists, cannot accurately calculate a QTc and cannot correctly identify a long QT.     

Rate-independent QT shortening during exercise in healthy subjects: terminal repolarization does not shorten with exercise

Introduction: QT interval for a given heart rate differs between exercise and recovery (QT hysteresis) due to slow QT adaptation to changes in heart rate. We hypothesized that QT hysteresis is evident within stages of exercise and investigated which component of the QT contributes to hysteresis. Methods and Results: Nineteen healthy volunteers performed a staged exercise test (four stages, 3 min each). Continuous telemetry was analyzed with software to compare QT intervals in a rate‐independent fashion. QRST complexes during each minute were sorted by RR interval, and complexes in bins of 20 ms width were signal‐averaged. QT and QTp (onset of QRS to peak T wave) were measured, and terminal QT calculated (peak to end of T wave, Tpe = QT – QTp). QT, QTp, and Tpe at the same heart rate were compared between the first and last minute of each stage. QT shortened from the first to last minute of exercise in each stage (Stage I: 358 ± 30 to 346 ± 25 ms, P < 0.001; Stage II: 342 ± 27 to 331 ± 24 ms, P = 0.003; Stage III: 329 ± 21 to 322 ± 18 ms, P = 0.03; Stage IV: 313 ± 22 to 303 ± 23 ms, P = 0.005). QTp also shortened in each stage, while Tpe was unchanged. Conclusion: QT hysteresis occurs during exercise in normals, and the major determinant is shortening of the first component of the T wave. Terminal repolarization (peak to end of T wave), a surrogate for transmural dispersion of repolarization, does not shorten significantly with exercise.     

QT interval dispersion pattern in patients with acute ischemic stroke: Does the site of infarction matter?

BACKGROUND:

QT interval dispersion (QTD) is an independent predictor of outcome following acute neurological events.

OBJECTIVES:

To explore QTD patterns and their relation to the affected cerebral region in patients with acute ischemic stroke.

METHODS:

Thirty patients with first acute ischemic stroke (the first stroke the patients had ever experienced) (study group) and 30 healthy controls (control group) were enrolled. Patients underwent magnetic resonance imaging to confirm and localize cerebral damage. Patients in the study group were further subdivided according to the site of infarction into four subgroups – namely, cortical, subcortical, brain stem and cerebellar infarctions, as well as according to insular involvement. All included subjects underwent 12-lead electrocardiography to measure QTD and corrected QT dispersion (QTcD).

RESULTS:

In the study group, both QTD and QTcD on the first hospitalization day were significantly higher than in the control group (P<0.05 for both). Similarly, in the study group, both QTD and QTcD values on the first hospitalization day were significantly higher than the respective values on the third day (P<0.001 for both). No significant differences were found among the four territorial subgroups, or between right- and left-sided subgroups, regarding QT interval measurements, whether on the first or third day (P>0.05 for all). However, ‘first-day’ QTD and QTcD of patients with insular involvement were significantly higher than in those without such involvement (P<0.001 for both).

CONCLUSIONS:

Both QTD and QTcD increased significantly in patients with acute ischemic stroke during the first hospitalization day. This increase of ‘first-day’ QTD and QTcD was significantly higher in patients with insular involvement than in those without such involvement.     

QT Dispersion in Healthy Chinese Children and Adolescents

Background: QT dispersion (QT_d) reflects the interlead difference in QT interval. It may provide a measure of repolarization inhomogeneity. Studies on QT_d mainly involve adults, while QT_d in children are less well studied. The aim of this study was to evaluate QT_d in healthy children and assess the relationship of gender, age, and anthropometric parameters, viz. weight (W), height (H), body mass index (BMI), and body surface area (BSA) to QT_d. Methods: Five hundred and one Chinese children and adolescents (243 boys, 258 girls) with no history of cardiovascular diseases were studied. Their ages ranged from 6.3 to 17.5 years. Surface 12-lead electrocardiograms were measured in each child at rest. QT and R-R intervals in each of the 12 leads were manually measured at a magnification of 2X. QT was corrected to QT_c according to Bazett's formula. QT_d was calculated as the difference between the maximum and minimum QT of the measured leads, while corrected QT_d (QT_cd) was the difference between the maximum and minimum QT_c of the measured leads. Adjusted QT_d was QT_cd divided by the square root of the number of measurable leads. Results: Mean QT_d of all subjects was 34 ms (95% Cl 33.6–35.1 msl. Mean QT_d for boys and girls was 35 ms and 34 ms, respectively (P = 0.18). Mean QT_cd for the whole group was 47 ms (95% Ci 45.8–48.2 ms), while mean adjusted QT_cd was 14 ms (95% Cl 13.8–14.5 ms). There were no significant gender differences in QT_cd or adjusted QT_cd. Weak negative correlation existed between age and QT_d, QT_d and adjusted QT_cd (r =?0.22, r =?0.26, r =?0.21, respectively, P < 0.001 Similarly, QT_cd also had a weak significant negative correlation with W (r =?0.20), H (r =?0.21) and BSA (r =?0.22), P < 0.001. However, multiple stepwise regression analysis revealed that only age was significantly related to QT_cd (R2 = 0.066) and QT_d (R2 = 0.059), P < 0.001. Conclusions: The results of this study indicate a trend of decreasing QT_d and QT_cd with increasing age, supported by multiple regression analysis. However indices of QT_d in children are not influenced by anthropometry. This information may be useful for the clinical application of QT_d in children. A.N.E. 1999;4(3):281–285     

对QT离散度实质的探讨

为探讨ＱＴ离散度（ＱＴｄ）的真实意义，观察１３９例急性心肌梗死（ＡＭＩ，ＡＭＩ组）及１０９例正常人（对照组）的最长ＱＴ间期（ＱＴｍａｘ）、校正ＱＴｍａｘ（ＱＴｃｍａｘ）及ＱＴｄ的变化。结果：①ＡＭＩ组的ＱＴｍａｘ、ＱＴｃｍａｘ和ＱＴｄ均显著高于对照组（分别为４２２．６０±３０．５１ｍｓｖｓ３８２．４６±２３．４０ｍｓ、４６０．２１±２８．９６ｍｓｖｓ３８８．５１±２０．１５ｍｓ、５９．８０±２８．４０ｍｓｖｓ３９．４３±１２．２１ｍｓ，Ｐ均＜０．００１）。②ＡＭＩ组中发生严重室性心律失常（ＶＡ）患者（１１４例）的ＱＴｍａｘ、ＱＴｃｍａｘ、ＱＴｄ与无ＶＡ的患者（２５例）相比，均有显著差异（分别为４４８．５８±３３．４０ｍｓｖｓ４１６．１０±３５．３０ｍｓ、４８１．４３±３５．１７ｍｓｖｓ４３９．６０±２７．１０ｍｓ、６６．９０±２０．７２ｍｓｖｓ４８．３２±２３．６１ｍｓ，Ｐ均＜０．００１）。认为ＡＭＩ时ＱＴｄ系Ｔ向量环在不同导联上的“投影”差异所引起的，其异常的本质是ＱＴ间期延长     

正常成人QTmax,QTmin在十二导心电图的分布规律及临床意义

目的 找出正常成人最大ＱＴ间期（ＱＴｍａｘ）和最小ＱＴ间期（ＱＴｍｉｎ）在十二导心电图的分布规律,提高ＱＴ离散度的敏感性。方法 在５８２例正常成人进行十二导心电图同步记录检查,找出ＱＴｍａｘ和ＱＴｍｉｎ在各导联的数量和在十二导心电图中的分布规律,统计各导联缺失和不同导联组合缺失时的ＱＴ离散度均值,观察其对ＱＴｄ的影响。结果 ５８２例心电图平均ＱＴｄ３５．３±９．５ｍｓ,各导联ＱＴ间期均值ａｖＬ最小     

Assessment of the sensitivity of detecting drug-induced QTc changes using subject-specific rate correction

Aims

To quantify the sensitivity of QT heart-rate correction methods for detecting drug-induced QTc changes in thorough QT studies.

Methods

Twenty-four-hour Holter ECGs were analyzed in 66 normal subjects during placebo and moxifloxacin delivery (single oral dose). QT and RR time series were extracted. Three QTc computation methods were used: (1) Fridericia's formula, (2) Fridericia's formula with hysteresis reduction, and (3) a subject-specific approach with transfer function-based hysteresis reduction and three-parameter non-linear fitting of the QT–RR relation. QTc distributions after placebo and moxifloxacin delivery were compared in sliding time windows using receiver operating characteristic (ROC) curves. The area under the ROC curve (AUC) served as a measure to quantify the ability of each method to detect moxifloxacin-induced QTc prolongation.

Results

Moxifloxacin prolonged the QTc by 10.6 ± 6.6 ms at peak effect. The AUC was significantly larger after hysteresis reduction (0.87 ± 0.13 vs. 0.82 ± 0.12, p < 0.01) at peak effect, indicating a better discriminating capability. Subject-specific correction further increased the AUC to 0.91 ± 0.11 (p < 0.01 vs. Fridericia with hysteresis reduction). The performance of the subject-specific approach was the consequence of a substantially lower intra-subject QTc standard deviation (5.7 ± 1.1 ms vs. 8.8 ± 1.2 ms for Fridericia).

Conclusion

The ROC curve provides a tool for quantitative comparison of QT heart rate correction methods in the context of detecting drug-induced QTc prolongation. Results support a broader use of subject-specific QT correction.     

Reproducibility of Minimum,Maximum and Median QT Intervals in the 12‐Lead Resting ECG

Background: Heterogeneity in the recovery of ventricular refractory periods is an important factor in the development of ventricular arrhythmia. The QT dispersion (QTD) is increasingly used to measure this heterogeneity but its clinical value is limited due to methodological problems. QTD is defined as the maximum minus the minimum QT intervals that are suspected to be the least reproducible of the QT measurements. Objective: To analyze the reproducibility of the minimum, maximum and median QT intervals. Material: One database consisted of 356 subjects: 169 with diabetes and 187 nondiabetic control persons. The other database consisted of 110 subjects with remote myocardial infarction: 55 with no history of arrhythmia, and 55 with a recent history of ventricular tachycardia or fibrillation. Methods: 12‐lead surface ECGs were recorded with an amplification of 10 millimeters per millivolt at a paper speed of 50 mm/s. QT was measured manually by the tangent‐method. The reproducibility was calculated from measurements of QT in successive beats. Results: The standard deviation (SD) of QTs reproducibility was 9 ms for the arrhythmia data and 8 ms for the diabetes data. The reproducibility of QT_max and QT_min were on average 30% and 15% worse than for QT_median. The SD of QT_max was significantly higher than for QT_median in both database (P < 0.001), whereas SD of QT_min was only significantly higher than for QT_median for the diabetes data (P < 0.001). Conclusions: The reproducibility of QT_min and in particular QTmax was significantly lower than for QT_median. This indicates that the QT dispersion is based on the least reproducible of the QT measurements. A.N.E. 2000;5(4):354–357     

正常中国人QT间期及QTLC与QTC比较

目的探讨中国人正常ＱＴ间期并建立依心率校正ＱＴ的线性公式模型。方法对４３２２例从出生到８５岁健康婴儿、儿童和成人心电图ＱＴ间期进行分析统计，用直线回归方法拟合依心率校正ＱＴ的线性公式模型ＱＴＬＣ，并与Ｂａｚｅｔ的ＱＴｃ比较。结果研究证明，ＱＴ间期有心率、年龄、性别和种族差别，但影响ＱＴ的主要因素是心率，用直线回归方法拟合成依心率校正ＱＴ的线性回归方程：Ｙ（ＱＴＬＣ）＝ＱＴ＋０．２１６×（１－ＲＲ），Ｒ＝０．８９１３，ＳＸ．Ｙ＝０．０２１。在校正ＱＴ的功能方面能克服Ｂａｚｅｔ的ＱＴｃ随心率快而出现过高校正ＱＴ的现象。结论心率是影响ＱＴ间期的主要因素，用心率校正ＱＴ的线性公式（（ＱＴＬＣ）明显优于Ｂａｚｅｔｔ的ＱＴｃ。（ＱＴＬＣ）校正公式在临床上可用于任何年龄     

Improvement and limitation of the reliability of automated QT measurement by recent algorithms

Background

Newer algorithms for automated QT interval measurements may be more reliable than previous algorithms.

Objective

This study compares Bazett-corrected QTc obtained by an older algorithm (Old12SL) and by 2 newer ones (New12SL and v3.19) to semiautomated measurement performed by experienced cardiologists.

Methods

A total of 6105 randomly selected electrocardiograms were classified by the cardiologists as normal (4227), borderline (1254), abnormal (575), or not analyzable (49). Errors of automated measurement were defined by more than 30 milliseconds of absolute difference between Bazett-corrected QTc obtained by automated algorithms and semiautomated measurement.

Results

The Old12SL had approximately twice as many errors (5.25%) as the New12SL (2.33%) and v3.19 (2.30%), P < .0001. Abnormal tracings resulted in more errors than did normal ones (Old12SL: 16.52% vs 3.45%, New12SL: 7.30% vs 1.51%, and v3.19: 10.61% vs 1.21%).

Conclusion

Newer automated algorithms for QT measurements are highly reliable in normal tracings. However, electrocardiogram abnormalities increase the risk of QT measurement errors.     

肥厚性心肌病患者左心室形态学改变与QT间期离散度的关系

目的探讨体表心电图上QT间期离散度（QTd）与肥厚性心肌病（HCM）左心室形态学改变的关系。方法43例HCM患者,均经二维超声心动图确诊。根据心室肥厚的部位不同,将患者分为4组:A组（室间隔肥厚）16例、B组（室间隔肥厚及左室前壁肥厚）10例、C组（室间隔肥厚、左室前壁肥厚及左室侧壁肥厚）10例、D组（室间隔肥厚及广泛左室壁肥厚）7例。在安静状态下记录同步12导联心电图（ECG）,人工测量各导联的QT间期、QRS波时间,并计算QT及QRS离散度（QTd及QRSd）。结果超声心动图检查D组的左室后壁厚度（PWT）明显大于A、B、C组,D组的室间隔厚度（IVST）/PWT明显小于A、B、C组。A、B组的QTd明显大于C、D组,差异有显著性意义。结论QTd不仅反应了左心室复极的不均一性,也反应了左心室肥厚的形态学改变的不均性。     

QT interval in cardiac amyloidosis

The aim of the study was to investigate whether cardiac amyloidosis is associated with QT interval abnormalities and ventricular arrhythmias. A controlled study of 30 patients was undertaken at a university cardiology department in a large referral hospital. Thirty patients (18 men, 12 women, mean age 56 ± 12 years) with systemic amyloidosis verified by biopsy and strong indications of cardiac amyloidosis comprised the study group, with 30 healthy age- and sex-matched individuals serving as controls. Complete M-mode and two-dimensional echocardiographic study was undertaken and QT interval and QT_c were calculated. All patients and controls underwent 24-h Holter monitoring for arrhythmias. Left ventricular (LV) wall thickening was found in all patients with cardiac amyloidosis. The LV mass in the patients with cardiac amyloidosis was significantly greater than that of the control group, as was the ratio LVmass/body surface area (p < 0.001). There was no significant difference in the max QT interval or in QT_c dispersion between the two groups, although the max QT_c was greater in the patients with cardiac amyloidosis. Patients with cardiac amyloidosis did not have a higher incidence of arrhythmias than the controls. Although patients with thickened cardiac walls due to cardiac amyloidosis have a prolonged QT_c in comparison with controls, they do not show an increase in interlead QT_c dispersion which might suggest the possibility of regional disturbances of the uniformity of repolarization. Patients with cardiac amyloidosis do not have a higher incidence of arrhythmias than controls.     

Evaluation of QT Interval Dispersion in a Multiple Electrodes Recording System versus 12‐Lead Standard ECG in an In Vitro Model

Background: QT interval dispersion (QTID) as assessed on conventional surface electrocardiogram (ECG) has been used as a clinical tool to identify patients at high risk of ventricular arrhythmia. However, the results obtained have been controversial. The main purpose of this study was to compare QTID measured from an array of 5 × 6 electrodes homogeneously distributed against the values found when the 12‐lead standard ECG was used. Methods: QTID was calculated in a modified Langendorff‐perfused rabbit heart model immersed in a cylindrical chamber. Dispersion in ventricular repolarization was artificially increased by d‐sotalol (60 μ;m) perfusion. Results: All the duration variables measured from any of the lead systems used were significantly increased after d‐sotalol perfusion. The most commonly used variables in clinical studies, such as QTID (maximum ‐ minimum), do not reach a level of statistical significance, except when measured from the 30‐electrodes array or 15 electrodes covering the left or right side of the heart. The standard deviation of the QT interval (QTI) hardly reached a significant level (P = 0.0499) when calculated from the 12‐lead standard ECG. QTID measured at the peak of the T wave exhibited the highest level of significance when calculated from any of the lead systems used. Conclusion: Thirty electrodes homogeneously distributed on the body surface can better discriminate changes in heterogeneity of repolarization. These data further support the importance of multiple recording systems for the evaluation of QTID and may help to provide an understanding of the discrepancies found in clinical applications.