心房颤动患者体表心电图QT间期的变化

探讨心房颤动(简称房颤)患者体表心电图QT间期的变化。入选81例房颤患者和71例对照者,测量Ⅰ导联和V2导联QT间期,根据Bazett公式计算QTc。结果:窦性心律时V2导联QT间期可测量性略高于Ⅰ导联,而房颤时相反。V2导联测得的QTc比Ⅰ导联长。房颤组与对照组比较,窦性心律时Ⅰ导联和V2导联的QTc两组间均无明显差异;房颤发作时Ⅰ导联QTc较对照组延长(429.01±43.08msvs408.50±31.93ms,P<0.05);V2导联QTc较对照组也延长(444.45±33.16msvs414.82±25.57ms,P<0.05)。房颤组房颤发作时与窦性心律时的自身对照比较,V2导联的QTc也延长(448.63±31.59msvs426.22±29.08ms,P<0.05)。结论:房颤患者在房颤发作时QTc延长,而房颤患者窦性心律时QTc与对照组无差异。     

阵发性房颤终止后长间歇患者心电图指标分析

目的探讨阵发性房颤终止后长间歇患者窦性心律时心电图指标的特征及长间歇可能的机制。方法阵发性房颤的患者170例,根据房颤发作终止后是否出现≥2 s的RR长间歇,分为长RR间歇组(长间歇组)70例和无长RR间歇组(对照组)100例。比较两组年龄、性别、房颤病史、基础疾病、黑矇或晕厥的发生率、心脏超声学指标、抗心律失常药物使用情况的差异。同时比较两组患者窦性心律时的心电图指标,包括24 h窦性平均心率、静息心率、Ⅱ导联P波时限和振幅、PR间期、QRS时限、QT间期、QTc间期、ST段形态、T波形态、有无传导异常、有无右束支和左束支传导阻滞、有无Brugada波和J波。结果两组患者黑矇或晕厥的发生率有明显差异(P<0.001);两组患者的窦性24 h平均心率、窦性静息心率、PR间期、QT间期及QTc间期的平均水平差异有统计学意义(P<0.05)。结论阵发性房颤患者房颤终止后窦性心律时心电图出现心率减慢、PR间期延长、QT间期和QTc间期延长者有出现阵发性房颤终止后长间歇的可能。     

阵发性心房颤动发作特点的研究

目的：分析阵发性心房颤动（房颤）的发作特点。方法：42例阵发性房颤患者分成有器质性心脏病和无可发现的器质性心脏病2例,共进行45次24h动态心电图检查,对比房颤发作前30min和1min的窦性心室率,以及诱发和不诱发房颤的房性早搏的配对间期（PP′）和早搏指数（PI）。结果：随机抽取53例次的阵发性房颤样本。房颤发作前30min和1min的平均窦性心室率改变不显著。但14例次（33％）和15例次（36％）房颤发作前1min的窦性心室率＜60次／min,与53个不诱发房颤的房性早搏相比。48个诱发房颤的房性早搏的PP′间期和PI均显著缩短（P＜0．001）。有器质性心脏病和无器质性心脏病的2组阵发性房颤患者的各项观察指标差异均显著性。结论：短配对间期的房性早搏是阵发性房颤的独立诱发因素,部分患者的房颤发作与心动过缓有关,采取相应的治疗措可能预防房颤的发生。     

交接性逸搏心律伴短QT间期1例

患者男性，80岁。临床诊断：冠心病、病窦综合征。心电图各导联均无窦性P波，QRS波为室上性（图略）。图1为V1导联，R-R间距1．94s，频率31次／分，QRS波形态、时间正常，R波前后无逆行P波，为交接性节律。QT间期426ms，QTc间期297ms。按Rautaharju等提出的测量QT间期预测公式QTp（ms）=656／（1＋心率／100），本例QT间期预测值为501ms[656／（1＋31／100）]，实测值是预测值的85#（426ms／501ms）。心电图诊断：①窦性静止；②过缓性交接性逸搏心律；③短QT间期；④双结病变。     

动态心电图在房性早搏诱发阵发性心房颤动诊断中的应用

目的研究动态心电图在房性早搏诱发阵发性心房颤动中的应用，并分析阵发性心房颤动和房性早搏的关系。方法选取我院2010年1月至2013年2月收治的48例阵发性房颤动患者，所有患者经动态心电图确诊。分析48例患者阵发性房颤次数、诱发房颤的房早前周期、房早联律间期，未诱发房颤的房早间期及房早前周期。结果诱发房颤的房早联律间期为（814±102）ms，未诱发房颤的房早间联律间期为（710±124）ms，诱发比未诱发明显提前，两组比较差异具有统计学意义（P〈0．05）；诱发房颤的房早联律间期为（325．8±34．5）ms，未诱发房颤的房早联律间期为（510．2±38．5）ms，诱发比未诱发明显短，两组比较差异具有统计学意义（P〈0．05）。结论房性早搏联律间期与房性早搏始动及房早前周期有一定的关系，动态心电图在诊断阵发性心房颤动中具有无创、高效、可靠、重复性好等优点。     

伊布利特对冷冻球囊消融术后仍为持续性心房颤动患者的转复疗效

目的评估伊布利特在行冷冻消融术后仍为持续性房颤(简称房颤)患者中的转复疗效及安全性。方法回顾分析单中心收治应用冷冻球囊消融治疗持续性房颤消融术后仍为房颤,并于术中应用伊布利特转复的患者临床资料,包括临床基线特征、术中QTc间期改变值、冷冻程序结束时的A-A间期及并发症,术后随访包括房颤复发和其它心血管事件。结果 33例行冷冻球囊消融的持续性房颤患者入组,在冷冻消融程序结束时均保持为房颤,应用了伊布利特静脉输注。20例在伊布利特输注结束20 min内房颤终止,13例仍需要同步直流电复律转复窦性心律,伊布利特的转复成功率为60.6%。转复窦性心律后的QTc间期较输注伊布利特前明显延长[(455±81) ms vs (381±46) ms,P<0.001],4例出现血流动力学障碍的并发症(12.1%),均发生于房颤终止转复窦性心律之时或之后,其中3例转复窦性心律后的QTc间期发生了明显的延长。与伊布利特复律失败组相比,伊布利特转复成功组的患者房颤病程更短[(17.4±14.7)个月vs (55.8±59.6)个月,P=0.04],而冷冻程序结束时的平均AA间期长于复律失败组[(251±20) ms vs(221±36)ms,P=0.004]。术后1年内75.8%的患者能维持窦性心律。结论伊布利特可对冷冻球囊消融术后仍为持续房颤的患者有效地转复窦性心律,但会延长患者的QTc间期。伊布利特转复成功的患者房颤病程更短,而冷冻消融程序结束时的A-A间期更长。     

阵发性心房颤动发作之前的基础房律特性分析

目的探讨阵发性心房颤动(简称房颤)发作之前的基础房律特性,了解其房律特性是否与房颤发生相关。方法对动态心电图数据库中的8 000份原始电子资料(均由杭州百慧医疗设备有限公司生产的动态心电图记录仪记录),采用相应的软件,在浏览栏中,使用结论"阵发性心房颤动"搜索,寻获相应病例数据,编号,集中备份,再对备份数据采用散点图及逆向技术精细分析。观察到阵发性房颤起始节律后,在此时刻点截取12导联心电图,存储在指定硬盘中,以便后续采用Windows照片查看器将图片放大至适当程度测量房颤发作前Ⅱ、aVR、V_1导联上的P波时限和振幅。统计房颤发生前后各1 h的窦性心律和房颤时的平均心率,以及1 h窦性心律中发生的房性早搏(简称房早)、成对房早、二联律房早以及房性心动过速(简称房速)的个或次数。当阵发性房颤病例(阵发性房颤组)确定后,根据其组病例顺号,按性别匹配在同样的数据库中寻找窦性心律合并房早的病例(对照组),再根据房颤发作前1 h的时刻,在对照组中病例的相应时刻,统计1 h的窦性心率以及房性异位心搏的相应指标,截取一段12导联心电图,作相应存盘,后续采用前述同样方法测量Ⅱ、aVR、V_1导联上P波时限和振幅。结果共获取阵发性房颤79例,最终阵发性房颤组55例(有1例基础节律为心房扑动,故除外),对照组56例。两组年龄比较,无显著差异[(68.7±9.8)岁vs(66.2±15.1)岁,P>0.05]。房颤发作后1 h平均心率明显增快[(99±21)次/分vs(70±12)次/分,P<0.001]。与对照组比较,阵发性房颤组窦性心律时,单个房早的发生无明显差异(中位数:31.0 vs 43.5,P>0.05),而成对、二联律房早以及房速的发生明显增加(中位数:4.0 vs 0;3.0 vs 0;1.0 vs 0;P<0.001)。Ⅱ、aVR和V_1导联上的P波时限和振幅都明显增加[如Ⅱ导联:(112.73±15.92)ms vs(96.61±14.05)ms;(0.176±0.060)mV vs(0.141±0.050)mV,P均<0.001];P波时限和振幅的异常率亦明显增加(如Ⅱ导联,P波时限≥110 ms,75%vs 24%;P波振幅≥0.25 mV,19%vs 4%,P均<0.01,V_1导联,P波时限≥110 ms,24%vs 11%;P波振幅≥0.20 mV,11%vs 0,P均<0.001)。在Ⅱ导联上,1例在房颤开始发作前8个房波为倒置,而在aVR导联上为正向。在V_1导联上,P波的形态分布在两组中无明显差异,但在阵发性房颤组中,有2例P波呈完全负向,在房颤发作之前有小于1 000 ms的心房扑动或颤动的发生,而P波时限和振幅均在正常范围之内。结论①阵发性房颤发作后心室率变快;②房颤发作与其发作之前的成对、二联律房早以及房速发作频度增高有关;③房颤发作与P波的时限延长和振幅增高相关;④房颤的发作可能与房间传导径路变化相关。     

长QT综合征患者植入心律转复除颤器后成功消融心房颤动一例

1.临床资料:患者女,48岁,反复心悸伴晕厥2年,曾于当地医院诊断为“阵发性心房颤动(房颤)”,给予静脉滴注胺碘酮及电复律治疗,但仍有反复心悸发作.20个月前于某院诊为“遗传性长QT综合征,室性心动过速(室速)、心室颤动(室颤),阵发性房颤,窦性心动过缓”,植入心律转复除颤器(ICD,7230型,美国Medtronic公司),术后服用胺碘酮.5个月后出现甲状腺功能减退而改用普萘洛尔20 mg,每日3次口服.近20d心悸症状明显,ICD放电次数较前增加,患者焦虑恐惧,不敢下床活动,严重影响生活质量[1].其姐姐于30岁时猝死.既往无冠心病、高血压史.心电图示:窦性心律,心率53次/min,QTc 0.605 s(图1);经食管超声心动图示左心房42 mm,未见血栓形成;动态心电图示阵发性房颤,伴室内差异性传导.住院期间曾发作心悸伴ICD放电1次.ICD程控示:ICD放电时,为快速心室率房颤发作,RR间期为190 ～340 ms(图2).入院诊断为遗传性长QT综合征,室速、室颤,单腔ICD植入术后,阵发性房颤伴ICD误放电;窦性心动过缓,焦虑状态.     

心房颤动患者消融术中应用伊布利特提高手术即刻疗效

目的 观察在心房颤动(房颤)射频消融术中使用伊布利特( ibutilide,Ibu)对消融即刻疗效的作用.方法 99例经充分线性消融仍为房颤或转为左心房心房扑动(LAFL)的患者,静脉推注Ibu,推注中若复律立即停止;注射完lmg后10 min仍未转复者,可重复注射但总量≤2 mg.在静脉推注Ibu的同时重复标测并加强消融.记录给药前后心律变化,测量复律后的QT间期和RR间期.术后心电监护至少12 h.结果 静脉推注Ibu并加强消融复律者77例(77.8％),其余22例患者中16例接受体外同步电复律,13例(81％)成功转复;l例LAFL经超速抑制转为窦性心律;最终仍为房颤者6例、LAFL 2例.给药至成功转复时间2～41 min.Ibu用量0.4～2.0 mg(平均1.04 mg).手术结束时91例恢复窦性心律,校正的QT间期(QTc)为364 ～ 599 (469±40) ms,其中70例(76.9％ )QTc≥440 ms、16例(17.6％ )QTc≥500 ms.无严重药物不良反应发生.结论 对经充分线性消融仍为房颤或转为LAFL患者,静脉推注Ibu并加强消融能提高手术即刻疗效.     

炎症在老年性心房颤动中的作用

目的探讨炎症在老年性心房颤动（AF）、心房重构的发生及持续中的作用。方法选择88例老年患者,其中持续性房颤组30例,阵发性房颤组30例,窦性心律组28例。所有入选患者进行心脏超声心动图检查,并检测患者外周血高敏C-反应蛋白（hs—CRP）、血管紧张素转换酶（ACE）水平。结果外周血hs—CRP、ACE水平持续性房颤组为（8．9±2．6）mg／ml、（89．7±11．3）U／L,阵发性房颤组为（4．7±2．3）mg／ml、（39．6±10．6）U／L,窦性心律组为（1．9±0．7）mg／ml、（36．8±10．5）U／L。持续性房颤组外周血ACE、hs—CRP水平高于阵发性房颤组和窦性心律组（P〈0．05）,阵发性房颤组外周血hs—CRP水平高于窦性心律组（P〈0．05）,阵发性房颤组ACE水平与窦性心律组相比差异无统计学意义（P〉0．05）。结论外周血hs—CRP、ACE水平增高与心房颤动的发生和持续可能相关。     

A comparison of commonly used QT correction formulae: The effect of heart rate on the QTc of normal ECGs

The corrected QT interval (QTc) is widely used in pharmaceutical studies and clinical practice. Bazett’s QT correction formula is still the most popular, despite Simonson’s warning in 1961 that it could not be recommended. Other QTc formulae, e.g. Fridericia, Framingham, and Hodges, are also used. This study compares these four formulae using 10,303 normal ECGs recorded from four US hospitals. QT intervals were measured by the same computer program on ECGs confirmed by physicians. The distributions of QTc based on Fridericia, Framingham, and Hodges formulae were similar but Bazett’s was significantly wider. The global group QTc-heart rate (HR) correlation coefficients were calculated as Bazett 0.33, Fridericia 0.24, Framingham 0.26, and Hodges 0.11, with the uncorrected QT-HR correlation being 0.82. Overall by far, Hodges QTc is significantly less correlated with HR compared to the others. Certain subgroup correlations of gender and low, mid, or high HR show that one individual formula can out-perform the others, whereby automated selection of QT correction formula based on the patient’s HR and gender could be implemented as another option in products. The upper normal limits of corrected QTc were determined by excluding the top 2% from the global distribution charts as follows: Bazett 483 ms, Fridericia 460 ms, Framingham 457 ms, and Hodges 457 ms. Whether for males and/or females, the middle range of HR from 60 to 99 bpm has similar upper normal limits of QTc for all formulae except Bazett. Numerous references recommend 420 to 440 ms as the threshold for reporting prolonged QTc when using Bazett’s formula. Based on this database, 30% of apparently normal ECGs would be reported as having abnormal QT intervals for the 440 ms threshold, or 10% if 460 ms is chosen, compared to <2% for the other formulae. It was also noted that QT has a linear trend with HR but not with RR.     

肺动脉高压患者心率校正QT间期和QT离散度的研究

目的:检测肺动脉高压(pulmonary hypertension,PH)患者的心率校正的QT间期(heartrate-corrected QT interval,QTc)和QTc离散度(QTc dispersion,QTcd),并评价其与肺动脉压力的关系。方法:入选2003年12月至2008年7月因初步诊断为PH而进行右心导管术的患者。记录静息12导联心电图,手工测量QT间期并用Bazett公式进行校正。根据平均肺动脉压,将患者分为对照组,轻-中度PH组和重度PH组。结果:共入选201例患者。男性患者的QTc和QTcd在3组间差异无统计学意义。女性患者中,重度PH组的QTc比对照组高〔(436.1±39.4)msvs.(407.6±24.8)ms,P=0.037〕,重度PH组的QTcd(68.5±20.9)ms高于对照组(45.1±12.6)ms和轻-中度组(58.6±14.7)ms(P=0.002;P=0.003)。此外,女性患者的QTc和QTcd与平均肺动脉压正相关(r=0.207,P=0.03;r=0.236,P=0.012)。结论:本组资料中女性PH患者的QTc和QTcd与平均肺动脉压正相关,且在重度PH患者中显著增高,有待于进一步探讨。     

Preferred QT Correction Formula for the Assessment of Drug‐Induced QT Interval Prolongation

Drug‐Induced QTc Interval Assessment. Introduction: There is debate on the optimal QT correction method to determine the degree of the drug‐induced QT interval prolongation in relation to heart rate (ΔQTc). Methods: Forty‐one patients (71 ± 10 years) without significant heart disease who had baseline normal QT interval with narrow QRS complexes and had been implanted with dual‐chamber pacemakers were subsequently started on antiarrhythmic drug therapy. The QTc formulas of Bazett, Fridericia, Framingham, Hodges, and Nomogram were applied to assess the effect of heart rate (baseline, atrial pacing at 60 beats/min, 80 beats/min, and 100 beats/min) on the derived ΔQTc (QTc before and during antiarrhythmic therapy). Results: Drug treatment reduced the heart rate (P < 0.001) and increased the QT interval (P < 0.001). The heart rate increase shortened the QT interval (P < 0.001) and prolonged the QTc interval (P < 0.001) by the use of all correction formulas before and during antiarrhythmic therapy. All formulas gave at 60 beats/min similar ΔQTc of 43 ± 28 ms. At heart rates slower than 60 beats/min, the Bazett and Framingham methods provided the most underestimated ΔQTc values (14 ± 32 ms and 18 ± 34 ms, respectively). At heart rates faster than 60 beats/min, the Bazett and Fridericia methods yielded the most overestimated ΔQTc values, whereas the other 3 formulas gave similar ΔQTc increases of 32 ± 28 ms. Conclusions: Bazett's formula should be avoided to assess ΔQTc at heart rates distant from 60 beats/min. The Hodges formula followed by the Nomogram method seem most appropriate in assessing ΔQTc. (J Cardiovasc Electrophysiol, Vol. 21, pp. 905‐913, August 2010)     

交感神经张力对犬QT滞后现象的影响

目的 探讨交感神经张力改变对犬QT滞后现象的影响.方法 用右心房（RA）起搏为基本方法造成犬心率的动态变化,静脉注射异丙基肾上腺素（ISO）或普萘洛尔干预交感神经张力,设计5套实验方案：A：RA增减频起搏;B：静脉注射ISO;C：普萘洛尔＋RA增减频起搏;D：普萘洛尔＋静脉注射ISO;E：毁损窦房结＋小剂量ISO持续静脉注射＋RA增减频起搏.同时记录犬的体表心电图,测量RR间期和QT间期,绘制QT-RR曲线,并计算QT滞后指数.比较不同实验方案的QT滞后指数,观察交感神经张力改变对QT滞后现象的影响.结果 方案A的QTe滞后指数和QTp滞后指数显著低于方案B[QTe：（0.56±4.56） ms对（17.96±8.22） ms,P＜0.05; QTp：（0.50±3.14） ms对（11.33±13.47） ms,P＜0.05].方案A的QTe滞后指数和方案C相比差异无统计学意义[（0.56±4.56）ms对（2.34±2.84）ms,P＞0.05],但QTp滞后指数高于方案C[（0.50±3.14）ms对（-5.45±2.13）ms,P＜0.05].方案B和方案D相比,QTe滞后指数和QTp滞后指数均差异无统计学意义.方案C的QTe滞后指数和QTp滞后指数均显著低于方案D[QTe：（2.34±2.84） ms对（15.77±14.89） ms,P＜0.05;QTp：（-5.45±2.13）ms对（17.12±10.47）ms,P＜0.05].方案A的QTe滞后指数明显低于方案E[（0.56±4.56） ms对（8.42±7.86） ms,P＜0.05],QTp滞后指数差异无统计学意义.方案B的QTe滞后指数和QTp滞后指数显著高于方案E[QTe：（17.96±8.22）ms对（8.42±7.86） ms,P＜0.05; QTp：（11.33±13.47） ms对（0.62±7.46）ms,P＜0.05].结论 交感神经过度兴奋是引起QT滞后现象的重要原因,交感神经对QT滞后的影响并不依赖于心率的动态改变.QT滞后的程度与交感神经兴奋程度相关,轻度的交感神经兴奋主要影响T波终末部.     

QTc延长预测肥厚型心肌病合并心房颤动患者导管消融术后的复发

目的:探讨肥厚型心肌病(hypertrophic cardiomyopathy,HCM)合并心房颤动患者的QTc是否与心房颤动导管射频消融术后复发相关。方法:回顾性分析2006年11月至2013年6月,在北京安贞医院第一次行导管射频消融术的HCM合并心房颤动患者共39例,收集术前心电图和其他临床资料,术后定期随访。结果:随访(14.8±11.7)个月,23例患者心房颤动消融术后复发(复发率59%)。与未复发组相比,复发组QTc显著性延长[(461±29)vs.(434±18)ms,P=0.001)]。多因素Logistic回归分析显示QTc和左心房前后径(LAD)是心房颤动复发的独立危险因素。其中,当QTc截断值为448ms时,其预测心房颤动复发的敏感性为0.81,特异性为0.78。多因素Cox回归分析表明QTc每增加10ms,心房颤动复发的风险比为1.227(95%CI:1.053~1.431,P=0.009)。与LAD单独预测术后复发相比,LAD和QTc联合能更好地预测心房颤动消融术后复发。短QTc和左心房偏小的患者无心房颤动复发。结论:QTc延长能预测HCM合并心房颤动患者导管消融术后复发。短QTc和左心房偏小的患者导管消融术后复发率低。     

A rate-independent method of assessing QT-RR slope following conversion of atrial fibrillation

Introduction: Following conversion of atrial fibrillation (AF), QT interval transiently and variably prolongs and can trigger Torsades de Pointes (TdP). However, quantitative analysis of risk in this setting is difficult because cycle length variability during AF makes rate-corrected QT impossible to calculate. In this study, a newly developed method to study heart rate dependence of the QT interval during AF was applied to assess the QT–RR relationships prior to and following cardioversion in patients with AF.
Methods and Results: Cardiac rhythm was digitized for ≥30 minutes prior to and following elective cardioversion to sinus rhythm (SR) in 12 patients. Each QT interval was placed in a "bin" (50 ms), according to the preceding RR interval. All QT intervals within a bin were averaged and RR bin-specific QT values were derived. The slope of the QT–RR relationship was much flatter in AF (0.058 ± 0.02) compared with that predicted by conventionally used QT rate corrections (0.130 [Bazett], 0.096 [Fridericia]) and much steeper after cardioversion (0.238 ± 0.14, P < 0.01 compared with AF). The method also allowed us to establish that QT at any given RR interval prolonged when SR was restored (e.g., at RR interval 800 ms: QT = 0.38 ± 0.03 second [AF] vs 0.46 ± 0.05 second [SR], P < 0.01). The longest QT values were in patients receiving sotalol or quinidine.
Conclusions: The results of this study demonstrate that QT interval can be reliably measured in AF using a method that is independent of heart rate. We also showed that cardioversion of AF acutely increases the QT interval and the steepness of the QT–RR slope.     

犬短QT综合征发生心室颤动的电生理机制研究

目的：研究犬短QT综合征模型易发致命性心室颤动的电生理机制.方法：应用吡那地尔建立比格犬短QT综合征模型,利用篮状电极标测左室心内膜心肌电位.比较静脉推注吡那地尔（负荷剂量0.5 mg/kg,维持剂量每小时0.5 mg/kg）前后,QT间期、T波峰末间期（Tp-Te）、心肌细胞复极90％的动作电位（APD90）及激动恢复时间（ARI）、心室颤动周长（VF-CL）等参数的变化. 结果：与基础状态相比,吡那地尔显著缩短窦性心律和300 ms起搏时的QT间期,分别为（264±17） ms对（240±15） ms,P＜0.01;（247±7）ms对（229±10） ms,P＜0.01.应用吡那地尔后,APD90、ARI和VF-CL均较基础值显著降低,分别为（175±11） ms对（164±11） ms,P＜0.01;（156±11） ms对（147±10） ms,P＜0.01;（104±9） ms对（95±7）ms,P＜0.01.同时,Tp-Te间距较基础状态延长19％,即（35.8±3.4） ms对（44.1±1.4） ms,P＜0.01. 结论：不应期缩短和不应期心室跨壁离散度增加可能是吡那地尔诱导短QT综合征并发致命性室性心律失常的电生理基础.     

Relation between QT and RR intervals during exercise testing in atrial fibrillation.

The ability to predict the RR-QT relation over a range of heart rates was evaluated in 10 patients with atrial fibrillation (AF) and in 10 control subjects in sinus rhythm. The data from each subject were fitted by regression into 3 QT prediction formulas (the square root formula of Bazett, the cube root formula of Fridericia and the exponential formula of Sarma) applied in standard form and modified with a weighted average of the preceding 5 RR intervals. The goodness-of-fit of each formula was evaluated using mean square residual and Akaike information criterion. For AF, the mean square residuals did not differ among the 3 standard QT prediction formulas (Bazett 624 +/- 274, Fridericia 625 +/- 274 and Sarma 611 +/- 267) and among the 3 modified QT prediction formulas (Bazett 507 +/- 325, Fridericia 496 +/- 255 and Sarma 495 +/- 328). The weighted average modification produced a significant decrease in mean square residuals for all 3 equations (p less than 0.05) in all patients. These findings were confirmed by Akaike information criterion. Goodness-of-fit in sinus rhythm was similar to previously published reports, and significantly better than the fit for AF (p less than 0.0001). For 9 of the 10 patients with AF, sinus rhythm electrocardiograms were obtained and the above regression equations were used to predict QT intervals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bazett and Fridericia QT correction formulas interfere with measurement of drug-induced changes in QT interval.

BACKGROUND: The QT interval on the ECG is prolonged by more than 50 marketed drugs, an effect that has been associated with syncope and/or sudden cardiac death due to an arrhythmia. Because changes in heart rate also change the QT interval, it has become standard practice to use a correction formula, such as the Bazett formula, to normalize the QT interval to a heart rate of 60 bpm, that is, the rate-corrected QT or QTc. Numerous other formulas have been devised to make this correction, including the Fridericia, Hodges, and Framingham formulas. OBJECTIVES: The purpose of this study was to investigate how the Bazett formula and three other formulas influence assessment of the QT-prolonging effect of the potassium channel-blocking drug ibutilide. METHODS: Using a standardized physical activity protocol, the QT interval was assessed over a broad range of heart rates before and after an infusion of ibutilide (4.75 microg/kg) that produced a stable 15- to 20-ms QT prolongation in consenting normal subjects (9 men and 9 women). The QT interval was measured digitally over a range of heart rates from 60 to 120 bpm, and then four correction formulas (Bazett, Fridericia, Framingham, or Hodges) were applied. The uncorrected change in QT interval due to ibutilide was compared with the change using each of the formulas by repeated measures analysis of variance. RESULTS: At heart rates from 60 to 120 bpm, the Bazett and Fridericia correction formulas overestimated the change in QT in both men and women (P <.001). However, the Framingham and Hodges formulas did not alter the accuracy of the assessment of QT interval change. CONCLUSION: Rate correction of QT intervals using the standard Bazett and Fridericia formulas can introduce significant errors in the assessment of drug effects on the QT interval. This has implications for the clinical assessment of drug effects and for the safety assessment of new drugs under development.