冠心病室性心律失常患者的QT间期变异性与室性心律失常的相关分析

目的 现已明确冠心病患者发生猝死与恶性室性心律失常密切相关，本文旨在探讨冠心病患者Q-T间期变异性与发生室性心律失常的相关性。方法 采用动态心电图分析54例冠心病室性心律失常患者24hQ-T间期变异性。结果 冠心病室性心律失常患者24hQ-T间期变异性明显减低。结论 冠心病室性心律失常患者24h Q-T间期变异性较正常人明显减低，其发生心律失常的可能性将明显增加。     

Dispersion of QT and QTc interval in healthy children, and effects of sinus arrhythmia on QT dispersion

Objective—To determine the normal values of QT and QTc dispersion and the effects of sinus arrhythmia on QT dispersion in healthy children.
Patients and setting—The study was carried out in a university hospital on 372 local schoolchildren (200 male, 172 female), aged seven to 18 years.
Methods—The QT and preceding RR intervals of at least one sinus beat were measured manually in a range of nine to 12 leads on standard 12 lead surface ECGs. The corrected QT interval was computed by the method of Bazett. Dispersion of QT and QTc were defined as (1) the difference between the maximum and minimum QT and QTc intervals occurring in any of the 12 leads (QTD and QTcD), (2) the standard deviation of the QT and QTc interval in the measurable leads (QT-SD and QTc-SD).
Results—There was no significant difference in QT, QTc, and RR dispersion between girls and boys. Overall 53% of children had sinus arrhythmia. Although QTD and QT-SD were not affected by sinus arrhythmia, both QTcD and QTc-SD were significantly greater in children with sinus arrhythmia than in those without (QTcD: 52.9 (17.4) v 40.9 (13.1); QTc-SD: 17.5 (5.9) v 13.2 (4.0); p < 0.001).
Conclusions—As calculation of QTc dispersion is affected by sinus arrhythmia, which is common in childhood, we suggest that QT dispersion should not be corrected for heart rate in children.

Keywords: QT dispersion;  heart rate;  children;  sinus arrhythmia     

Fetal cardiac repolarization abnormalities

Abnormal cardiac repolarization renders the heart susceptible to lethal ventricular tachyarrhythmias, increasing the risk of sudden cardiac death in all ages; however, little is known about the incidence and etiology of T-wave abnormalities in utero. In this study, magnetocardiography was used to better define fetal T-wave characteristics, including the QT interval in the normal fetus, and to characterize T-wave abnormalities in the fetus with arrhythmia. The QT interval and T-wave alternans were assessed from magnetocardiographic recordings obtained at 14 to 39 weeks' gestation from 120 fetuses. Of these fetuses, 78 were from uncomplicated pregnancies and 42 had various forms of fetal arrhythmia (supraventricular tachycardia in 14, congenital atrioventricular block in 17, long QT syndrome with Torsades de pointes in 1, ventricular tachycardia in 2, sinus bradycardia in 4, and bradycardia due to blocked premature atrial contractions in 4). Although the corrected QT interval in normal sinus rhythm was accurately described by Bazett's formula, the corrected QT interval in fetal arrhythmia exhibited a systematic deviation at heart rate extremes. The dependence of the QT interval on the RR interval in arrhythmia was approximately described by QT alpha RR0.8. T-wave alternans was detected in 7 fetuses with arrhythmia, often in association with QT prolongation, suboptimal outcome, or fetal demise. The results of our study have demonstrated that QT-interval abnormalities exist and can be detected in fetal patients. The potential importance of T-wave assessment in the fetus with cardiac arrhythmia was evidenced by the high incidence of marked QT prolongation and T-wave alternans in the fetuses with suboptimal outcomes.     

QT interval: A measure of drug action

Historically, QT prolongation, occurring with or without drug therapy, has been considered primarily as a clinical marker for risk of arrhythmia. However, as understanding of cardiac repolarization improves and ability to measure accurately small changes in QT interval increases, the QT interval will be used as a marker for drug action as well. In addition, QT prolongation may prove to be a valuable tool for detecting and quantifying risk of arrhythmia due to drugs. This has been emphasized recently by the experience with terfenadine. Use of the QT interval as a marker for toxicity and efficacy will require sensitive and specific methods that are currently being developed and validated. The current methodologies for detecting small changes in the QT interval and the significance of those changes are discussed.     

恶性快速性室性心律失常的发作方式及其临床意义

探讨恶性快速性室性心律失常的发作方式及其临床意义,分析64例在入院后至少发生≥1次由室性早搏(简称室早)诱发的恶性快速性室性心律失常患者发作时与发作前后的常规12导联心电图或持续心电监护心电图。结果:根据诱发恶性快速性室性心律失常的室早的联律间期及其前间歇的长短,64例的发作方式大致可分为以下几种类型:①单纯室早诱发;②长间歇依赖性室早诱发,此型根据基础心律QT(U)间期的长短又可分为:a.QT间期正常;b.长QT(U)间期两种形式。不同发作方式之干预措施亦异。结论:恶性快速性室性心律失常是由不同形式的室早所诱发的,他们具有不同的临床、心电学特征及干预措施。     

老年高血压伴左室肥厚的QT离散度与心律失常相关性的临床观察

目的　观察老年高血压伴左室肥厚病人的 QT离散度与心律失常的关系。方法　选择 32例老年健康人和 90例老年高血压病人进行体表心电图、超声心动图和动态心电图检查 ,作 QT离散度测定。结果　 (1 )高血压伴左室肥厚组的 QT离散度明显大于健康对照组及高血压非左室肥厚组。 (2 )高血压伴心律失常组的 QT离散度明显大于健康对照组及高血压非心律失常组。 (3)高血压伴左室肥厚组其心律失常发生率明显高于健康对照组。结论　高血压伴左室肥厚病人的 QT离散度明显增高 ,其心律失常发生率也显著增高     

Clinical investigation on the patients with tachyarrhythmic syncope with special reference to comparative study between long QT syndrome and ventricular tachycardia without long QT interval

The long QT syndrome (LQTS) is one of the important diseases that may lead to sudden death mainly in childhood, however etiology and pathogenesis are still poorly understood. The group studied consisted of 6 patients with a history of ventricular tachyarrhythmic syncope, 3 with long QT syndrome (LQTS) and 3 without long QT interval, and of 4 patients with ventricular tachycardia without syncopal episode. Their ages ranged from 5 years to 17 years. Histopathology of endomyocardial biopsy was nonspecific and mild in two cases but in one patient with LQTS, who had several episodes of syncope and refractory ventricular arrhythmia, remarkable subendocardial fibrosis, interstitial fibrosis and hypertrophy of myocytes were demonstrated. As far as ventricular tachycardia without long QT interval was concerned, in the patients with VT with syncope, histopathological abnormalities were more remarkable than in those without syncope. Electrophysiological findings in the patients with LQTS showed no characteristic findings, but only mild abnormalities with functional atrioventricular conduction disturbance on programmed atrial pacing. No inducible VT was demonstrated. Although electrophysiologic study and endomyocardial biopsy are of limited value, such studies are considered to be worthwhile for treating ventricular arrhythmias, and making a prognosis of the patients with tachyarrhythmic syncope and LQTS.     

Torsade de pointes associated with moxifloxacin: a rare but potentially fatal adverse event

Torsade de pointes occuring due to a long QT interval is a rare but potentially fatal arrhythmia. Acquired long QT develops most commonly because of drugs that prolong ventricular repolarization. It has been reported that fluoroquinolone antimicrobials prolong the corrected QT interval but rarely cause torsade de pointes. A patient with torsade de pointes risk factors (female sex, advanced age, extreme bradycardia and renal failure) who developed the condition on the fourth day of 400 mg/day of oral moxifloxacin treatment is presented. After the moxifloxacin was stopped, the corrected QT interval normalized and a permanent cardiac pacemaker was implanted. During 11 months of follow-up, arrhythmia did not recur.     

Long term effects of hormone replacement therapy on heart rate variability, QT interval, QT dispersion and frequencies of arrhythmia

BACKGROUND: The aim of the study was to investigate the effects of a long term (1 year) hormone replacement therapy (HRT) on QT interval, QT dispersion (QTd) frequencies of arrhythmia and heart rate variability (HRV) parameters. METHODS: Forty-six healthy postmenopausal women (mean age; 55.34+/-4.21) as a hormone replacement therapy group and 25 healthy premenopausal women (mean age; 35.36+/-6.06) as a control group were prospectively enrolled to the study. Hormone replacement therapy group was divided into two groups; estrogen replacement therapy (ERT) group (n=23) and progestin-estrogen replacement therapy (PERT) group (n=23). Standard 12 lead electrocardiograms and 24-h ambulatory Holter recording were obtained to evaluate the effects of one year of ERT and PERT on QT intervals, QTd, frequencies of arrhythmias and HRV parameters. RESULTS: Long term use of ERT increases QT interval, QTd, in the frequencies of arrhythmia and HRV indexes of parasympathetic activity; however, the increase in frequencies of arrhythmia was not statistically significant (p>0.05). Long term use of PERT did not effected QT interval, QTd, frequencies of ventricular arrhythmia and HRV parameters (p>0.05). Frequency of supraventricular tachycardia increased in post-treatment PERT group was compared with pre-treatment PERT group. CONCLUSION: These findings supported the hypothesis that estrogen may directly modulate ventricular repolarization. But progestin do not effect the ventricular repolarization. However, these findings must be supported with a large-scale study.     

Gatifloxacin and prolonged QT interval

We report the case of a 54-year-old woman who, while being treated for acute sinusitis with gatifloxacin, presented with syncope and was found to have a markedly prolonged QT interval. After stopping gatifloxacin, the QT interval normalized. We speculate that her episode of syncope was caused by a ventricular arrhythmia that resulted from an increased QT interval.     

Update on intensive care ECG and cardiac event monitoring

This brief review is aimed primarily as a resource for the clinician and summarizes recent advancementsin electrocardiographic monitoring in the intensive care unit. Emphasis is placed on recent advances in ICU ECGand cardiac event monitoring with particular attention to arrhythmia detection in patients following myocardialinfarction. Specific topics addressed include: clinical indicators of impending arrhythmic events and suddendeath, signal averaged ECG, QT dispersion, ST segment fluctuation, T-wave alternans, QT interval beat-to-beatvariability, heart rate variability, and advances in automated arrhythmia detection.     

缺血心肌复极离散及迷走神经的保护作用

探讨急性心肌缺血后 ,迷走神经刺激对心室肌不同部位复极时程和复极离散的影响 ,及其对缺血心肌的保护作用。结扎兔冠状动脉左室支 (LVB) ,制备急性心肌缺血模型。分离、结扎并剪断双侧颈迷走、心交感神经 ,电刺激迷走神经外周端。心室复极时程以心外膜电图 (EPG)的QT间期及采用玻璃微电极技术记录的心肌细胞动作电位时程 (APD)表示。分别测定迷走神经刺激前后及缺血前后LVB支配区 (缺血区 )及非支配区 (非缺血区 )的QT间期及APD值。结果 :迷走神经刺激使正常心室肌不同部位的QT间期、APD均有明显缩短 (P <0 .0 5 )。急性心肌缺血后 ,缺血区与非缺血区的QT间期分别是 14 8.6 7± 10 .4 4vs 15 9.5 0± 14 .71ms(P <0 .0 5 ) ;APD90 分别是 :12 8.75±17.84vs 138.0 0± 11.2 2ms(P <0 .0 5 ) ;APD50 分别是 :74 .6 7± 12 .15vs 85 .0 0± 6 .78ms(P <0 .0 5 )。迷走神经刺激后 ,缺血区与非缺血区QT间期、APD差值明显缩小 ,分别是 ,QT间期 :5 .5 8± 1.0 1vs 12 .83± 4 .34ms(P <0 .0 5 ) ;APD904 .5 0± 0 .98vs 11.2 5± 7.0 9ms(P <0 .0 5 ) ;APD50 5 .4 1± 1.2 2vs 12 .5 0± 6 .19ms(P <0 .0 5 )。心肌缺血后心室易损期(VVP)明显延长 34± 2 2 .6 1ms,迷走神经刺激后VVP明显缩短至 11.75± 7.72m     

QT prolongation on the electrocardiogram in diabetic autonomic neuropathy

Patients with Type 1 diabetes and autonomic neuropathy have an increased risk of sudden death for which the mechanism remains obscure. Prolongation of the QT interval on the electrocardiogram may occur with sympathetic dysfunction and is also associated with ventricular arrhythmia and sudden death. We have therefore measured the QT interval in patients with Type 1 diabetes with normal, borderline, and definitely abnormal autonomic function tests and in non-diabetic control subjects. The maximum QT interval was measured on 12-lead electrocardiograms recorded at rest and then plotted against the RR interval. The QT interval was above the upper 95% limit for the non-diabetic control subjects in 5 diabetic patients with abnormal autonomic function tests (33%), but in no cases with normal or borderline tests. Multivariate analysis confirmed that autonomic score contributed significantly (p less than 0.025) to the variance in QT interval. The raw Valsalva ratio alone also contributed significantly to the variance in QT interval (p = 0.025). Heart rate variability, heart rate response to standing, age, sex, and the presence of symptoms of autonomic neuropathy did not contribute significantly.     

Polymorphous ventricular tachycardia: clinical characterization, therapy, and the QT interval

Forty-five consecutive patients with polymorphous ventricular tachycardia (PVT) were studied. The arrhythmia proved to be of a drug-related cause in 27 and due to an electrolyte disorder in four patients. Coexistent cardiac diseases without metabolic or drug-related abnormalities included ischemic heart disease in three, cardiomyopathy in three, and mitral valve prolapse in two. PVT was exercise-induced in four and associated with bradyarrhythmias in two. A prolonged QT or corrected QT interval was inconsistently related to the occurrence of PVT. In patients in whom PVT was induced by certain type I drugs, other type I antiarrhythmic drugs were usually either ineffective or resulted in aggravation of arrhythmia. For the group as a whole, treatment with lidocaine resulted in inconsistent beneficial effects, while cardiac pacing was almost universally effective for those with drug-induced PVT, regardless of the length of the QT interval. Long-term amiodarone therapy proved safe and effective for 12 of the 24 patients with drug-induced PVT who required long-term therapy for their original arrhythmia. We conclude that identification of PVT is the key clinical issue and that the QT interval is not necessarily the prime abnormality nor the variable to be considered in predicting success of therapy. Temporary cardiac pacing appears to be very effective in the short-term management of these patients. Use of type I antiarrhythmic agents in patients with drug-induced PVT generally resulted in aggravation of arrhythmia. In contrast, long-term amiodarone therapy for control of the original arrhythmia appears to be a promising approach for those with PVT associated with type I agents.     

Relation between QT dispersion and ventricular arrhythmias in uncomplicated isolated mitral valve prolapse

Complications of mitral valve prolapse (MVP), among which serious ventricular arrhythmia and sudden death are of major importance, affect many individuals due to the high incidence of MVP itself in the community despite the actual low incidence of these complications. The present study investigated the incidence and distribution of ventricular arrhythmias according to their severity and relationship with the QT interval and dispersion of repolarization in uncomplicated isolated MVP (IMVP) cases. Fifty-eight uncomplicated IMVP patients, 33 patients with accompanying tricuspid valve prolapse (TVP), to compare its relationship with ventricular arrhythmia, and 60 age- and sex-matched control subjects were enrolled in the study. Individuals with accompanying cardiac or systemic disease, or who were on drug therapy that could potentially affect QT characteristics, were excluded. The incidence of ventricular arrhythmia was 48% in the IMVP group and 64% in the TVP group; the difference was statistically insignificant. In addition, the differences of the QT and Q peak T values were insignificant, whereas QT dispersion (QTd) and Q peak T dispersion (QpeakTd) values were significantly higher in the patient group (60+/-14, 54+/-14 ms, respectively) compared with the control group (42+/-10, 38+/-10 ms, respectively, p<0.001). Complex ventricular arrhythmias (Lown Grade > or =III) in the IMVP group had a significant relationship with QTd and QpeakTd (p<0.001), but not with QT or QpeakT. As a result of the study, it is concluded that TVP accompanying MVP does not increase the incidence of ventricular arrhythmia, that ventricular arrhythmia is related to QT dispersion rather than QT interval in IMVP, that the QT dispersion is a fairly good marker for identifying the high-risk group for serious ventricular arrhythmia and sudden death, and that QpeakT dispersion measurement is an additional indicator that could be an alternative when QT is difficult to determine in conditions such as high heart rate or the presence of U wave.     

QT dispersion: an indication of arrhythmia risk in patients with long QT intervals.

Homogeneity of recovery time protects against arrhythmias whereas dispersion of recovery time is arrhythmogenic. A single surface electrocardiographic QT interval gives no information on recovery time dispersion but the difference between the maximum and minimum body surface QT interval may be relevant. This hypothesis was tested by measuring the dispersion of the corrected QT interval (QTc) in 10 patients with an arrhythmogenic long QT interval (Romano Ward and Jervell and Lange-Nielsen syndromes or drug arrhythmogenicity) and in 14 patients without arrhythmias in whom the QT interval was prolonged by sotalol. QTc dispersion was significantly greater in the arrhythmogenic QT group than in the sotalol QT group. In patients with prolonged QT intervals, QT dispersion distinguished between those with ventricular arrhythmias and those without. This supports the hypothesis that QT dispersion reflects spatial differences in myocardial recovery time. QT dispersion may be useful in the assessment of both arrhythmia risk and the efficacy of antiarrhythmic drugs.     

QT dispersion: an indication of arrhythmia risk in patients with long QT intervals

Homogeneity of recovery time protects against arrhythmias whereas dispersion of recovery time is arrhythmogenic. A single surface electrocardiographic QT interval gives no information on recovery time dispersion but the difference between the maximum and minimum body surface QT interval may be relevant. This hypothesis was tested by measuring the dispersion of the corrected QT interval (QTc) in 10 patients with an arrhythmogenic long QT interval (Romano Ward and Jervell and Lange-Nielsen syndromes or drug arrhythmogenicity) and in 14 patients without arrhythmias in whom the QT interval was prolonged by sotalol. QTc dispersion was significantly greater in the arrhythmogenic QT group than in the sotalol QT group. In patients with prolonged QT intervals, QT dispersion distinguished between those with ventricular arrhythmias and those without. This supports the hypothesis that QT dispersion reflects spatial differences in myocardial recovery time. QT dispersion may be useful in the assessment of both arrhythmia risk and the efficacy of antiarrhythmic drugs.     

Azithromycin/chloroquine combination does not increase cardiac instability despite an increase in monophasic action potential duration in the anesthetized guinea pig

Prolongation of the electrocardiogram QT interval by some, but not all drugs, has been associated with increased incidence of sudden cardiac death. Current preclinical regulatory assays cannot discriminate the arrhythmia liability of these drugs. Consequently, many new medications that prolong the QT interval are not developed despite their potential therapeutic benefit. Alternans (action potential duration alternations) is a measure of cardiac instability in humans and animals associated with the onset of ventricular fibrillation. Due to potential arrhythmia risk from observed QT prolongation, alternans was assessed in the anesthetized guinea pig after azithromycin or chloroquine alone and after combination treatment at clinically relevant concentrations proposed for the management of malaria. Chloroquine alone, but not azithromycin, caused a profound increase in action potential duration but with only minimal effects on alternans (approximately 10 ms). Azithromycin alone and in combination with chloroquine showed no increase in alternans beyond vehicle baseline responses indicating no additional arrhythmia liability.     

Recurrent ventricular tachycardia in hypothyroidism--report of a case and review of the literature

A 47-year-old woman suffered from recurrent attacks of ventricular tachycardia. Her electrocardiogram showed low voltage, right bundle branch block and prolonged QT interval. Hormonal studies disclosed primary hypothyroidism. The arrhythmia responded to treatment with procainamide and did not recur following thyroid replacement therapy. The QT interval returned to normal. Five similar cases reported in the literature are reviewed, emphasizing the importance of QT prolongation, in the context of hypothyroidism, as a risk factor for the occurrence of ventricular tachycardia.     

Adrenal and extra-adrenal pheochromocytomas presenting as life-threatening ventricular arrhythmias: Report of three cases

Pheochromocytoma patients can rarely have prolonged QT interval in the ECG. We report three cases of pheochromocytoma in females presenting with ventricular arrhythmia; two had torsades de pointes and a third patient had frequent VPCs and nonsustained ventricular tachycardia. All the patients were treated with surgical removal of the tumor with complete relief of symptoms and normalization of QT interval.