Reproducibility of Computerized Measurements of QT Interval from Multiple Leads at Rest and During Exercise

Background: Accurate measurement of the QT interval is important for diagnosing long QT syndrome (LQTS), and in research on determinants of ventricular repolarization time. We tested automatic analysis of QT intervals from multiple ECG leads on chest. Methods: Eleven healthy volunteers and 10 genotyped LQTS patients were tested at rest and during exercise with a bicycle ergometer twice 1–31 months apart. Electrocardiograms were recorded with the body surface potential mapping system, and 12 precordial channels were selected for analysis. Averaged QT peak and QT end intervals were determined with an automated algorithm, and the difference QT end minus QT peak (Tp‐e) was calculated. Repeatability was assessed by coefficient of variation (CV) between measurements. Results: Within one test at rest the QT end intervals were highly repeatable with CV 0.6%. In repeated tests CV was 4.4% for QT end interval and 3.5% when the QT interval was corrected for heart rate. In exercise test at specified heart rates, mean CV was 3.0% for QT end and 2.9% for QT peak interval. The CV of Tp‐e interval was 10.2% at rest, and 9.3% in exercise test. Reproducibility was comparable between healthy subjects and LQTS patients. Conclusions: The BSPM system with automated analysis produced accurate and highly repeatable QT interval measurements. Reproducibility was adequate also over prolonged time periods both at rest and in exercise stress test. The method can be applied in studying duration of ventricular repolarization time in different physiologic and pharmacologic interventions.     

多巴酚丁胺负荷实验对家猪急性冬眠心肌模型QT离散度影响的实验研究

目的 观察多巴酚丁胺负荷期间QT离散度(QTd)的变化情况,探讨其临床意义.方法 对13只小型中国家猪采用闭胸介入法制备急性冬眠心肌模型(右冠状动脉为靶血管),利用多巴酚丁胺超声负荷实验(DSE,0～40 μg·Kg-1·min-1)检出冬眠心肌,之后成功复灌,处死动物,对心脏行TTC大体染色及光镜检查.分别于模型制备前后、DSE期间及复灌后观察QTd的变化情况.结果 ①10只动物(76.92%)成功制备成模型,病理检查未示心肌坏死改变.②模型制备成功后QTd较正常状态明显增加[(68.75±5.33)ms和(25.00±1.77)ms,P＜0.05];复灌后明显降低[(35.62±3.47)ms和(68.75±5.33)ms,P＜0.05],与正常状态差异无统计学意义[(35.62±3.47)ms和(25.00±1.77)ms,P＞0.05].③DSE期间QTd呈现先降低后增加的双相反应的变化趋势.④模型制备成功后的QTd与DSE检出的急性冬眠心肌节段数呈中等程度的负相关(r=-0.64,P＜0.05).结论 ①.急性冬眠心肌动物模型的QTd明显增加,早期有效复灌可降低QTd.②DSE期间急性冬眠心肌模型的QTd呈现双相反应趋势.③急性冬眠心肌模型的QTd是反映冬眠心肌数量的指标之一.     

The cardiac effects of terfenadine after inhibition of its metabolism by grapefruit juice

Objective: To determine whether the pharmacokinetics and electrocardiographic pharmacodynamics of terfenadine are affected by the concomitant administration of grapefruit juice. Methods: Six healthy volunteers were recruited for a balanced cross-over study. Each volunteer received 120 mg terfenadine 30 min after drinking 300 ml of either water or freshly squeezed grapefruit juice. The alternative treatment was administered on the second study day 2 weeks later. Measurements of the area under the terfenadine plasma concentration-time curve (AUC), maximum terfenadine concentration (C_max) and the time to maximum concentration (t_max) were made, and the corrected QT (QTc) interval was measured from the surface electrocardiogram. Results: Terfenadine was quantifiable in plasma in all 6 subjects on both study days for up to 24 h post-dosing. The AUC of terfenadine was significantly increased by concomitant grapefruit administration (median values 40.6 vs 16.3 ng · ml⁻¹ · h), as was the C_max (median values 7.2 vs 2.1 ng · ml⁻¹). The t_max was not significantly increased and there was no significant change in the median QTc interval despite the increased terfenadine levels. The 95% confidence interval for the difference in the change in QTc interval at C_max was −13 to +38 ms. Conclusion: Administration of grapefruit juice concomitantly with terfenadine may lead to an increase in terfenadine bioavailability, but the increase observed in this study did not lead to significant cardiotoxicity in normal subjects. However, this does not exclude the risk of cardiotoxicity in high-risk subjects given greater doses of grapefruit juice over longer periods of time. Received: 14 October 1996 / Accepted in revised form: 10 December 1996     

QT离散度对急危重病人预后的评估

目的　研究QT离散度对急危重病人预后的预测价值。方法　死亡组 4 7例、疾病组 4 0例和正常组 4 3例。记录 12导联心电图 ,人工测量各导联R -R间期和QT间期 ,计算R -R、QTc、QTd和QTcd。结果　死亡组的R -R、QTc、QTd和QTcd分别为 0 5 6 2± 0 2 2 0ms、0 35 6± 0 0 6 9ms、0 0 5 6± 0 0 33ms和 0 0 79± 0 0 4 6ms ;疾病组的R -R、QTc、QTd和QTcd分别为0 80± 0 134ms、0 4 16± 0 0 3ms、0 0 34± 0 0 14ms和 0 0 39± 0 0 16ms;正常组的R -R、QTc、QTd和QTcd分别为 0 82 5± 0 0 88ms、0 4 0 2± 0 0 3ms、0 0 2 7± 0 0 15ms和 0 0 31± 0 0 15ms。比较死亡组、疾病组和正常组发现 ,死亡组和疾病组的R -R、QTc、QTd和QTcd存在显著差异 (P分别 <0 0 0 1、<0 0 0 2 5、<0 0 0 1和 <0 0 0 1)。死亡组和正常组的R -R、QTc、QTd和QTcd存在显著差异 (P分别 <0 0 0 1、<0 0 0 2 5、<0 0 0 1和 <0 0 0 1)。结论　QTd对急危重病人的预后有一定的预测价值 ;但其它临床应用价值存在局限性 ,有待进一步探索。     

直接PTCA对急性心肌梗死的QT离散度的影响

目的　观察直接PTCA对急性心肌梗死 (AMI)患者QT离散度 (QTd)及QTc离散度 (QTcd)的影响。方法　对 30例AMI患者行直接PTCA ,使病变血管血流达到TIMI血流 3级 ,于PTCA术前、术后 2h、4 8h作同步 12导心电图并测量QTd及QTcd ,然后与 30例正常人对照。结果　AMI组与正常对照组间QTd及QTcd有极显著差异 (P <0 .0 1)。有室性心律失常的AMI患者其QTd和QTcd高于无室性心律失常患者 ,但差异无显著性(P >0 .0 5 ) ,PTCA术后其QTd和QTcd下降 (P <0 .0 1) ,室性心律失常好转。结论　成功的直接PTCA可降低AMI患者的QTd和QTcd ,减少室性心律失常的发生 ,改善预后