QT Interval in Patients with Unstable Angina and Non‐Q Wave Myocardial Infarction

Background: Non‐Q wave mvocardial infarction (NQMI) and unstable angina (UAP) have similar clinical presentations and similar ST‐T changes on the electrocardiogram. The purpose of this study was to assess whether changes in QT interval might help differentiating between these entities. Methods: The QT intervals of 52 patients hospitalized with NQMI were compared to those of 52 patients hospitalized for UAP. All patients had repeated ECG for at least 4 days. Results: Maximal QTc in patients with NQMI was significantly longer than in patients with UAP (475 vs 439 ms, P < 0.0001). QTc on the admission ECG was 450 ms in patients with NQMI compared to 417 ms in UAP P < 0.005). QTc > 460 ms was present in 48% patients with NQMI and in 19% of UAP patients. Maximal QT prolongation was observed within 36 hours of admission with return to normal within 96 hours. QT dispersion was within normal range, being longer in patients with NQMI than patients with UAP (55 vs 43 ms, P < 0.003). QT prolongation was not associated with increased frequency of arrhythmia. The cause of QT prolongation in NQMI may be related to the damage of subendocardial layer exposing the M cells layer which markedly prolong action potential duration. Conclusion: Transient QT prolongation is observed in about half of patients with NQMI. These ECG changes may help differentiating between patients with NQMI and UAP already on admission. A.N.E. 2002;7(4):343–348     

Changes of the T-wave amplitude and angle: an early marker of altered ventricular repolarization in hypertension

BACKGROUND: The heterogeneity of ventricular repolarization is an important proarrhythmic factor. QT dispersion has been proposed to reflect the inhomogeneity of ventricular repolarization, but a poor reproducibility limits its clinical applicability. Reliable noninvasive methods to quantify abnormalities in ventricular repolarization are still lacking. The T-loop morphology analysis is a novel method aimed at quantifying ventricular repolarization. HYPOTHESIS: To test the ability of the T-loop morphology analysis to discriminate between hypertensive patients and healthy subjects, 105 hypertensive patients (mean age 63.6 +/- 12.3 years) and 110 healthy controls (mean age 49.7 +/- 14.3 years) were evaluated. METHODS: The maximum QT interval (QT maximum), the minimum QT interval (QT minimum), and their difference (QT dispersion) were calculated from a digitally recorded 12-lead electrocardiogram (ECG) in both study groups. X, Y, and Z leads were reconstructed from the 12-lead ECG, and the amplitude of the maximum T vector (T amplitude) and the angle between the maximum T vector and X axis (T angle) were calculated from the projection of the T loop in the frontal plane. RESULTS: T amplitude (p < 0.001), T angle (p = 0.05), and QT dispersion (p = 0.04) were significantly different between hypertensive patients and controls, while QT maximum (p = 0.14) and QT minimum (p = 0.35) did not differ between the groups. T amplitude was the only marker which differed between hypertensive patients without ECG criteria for left ventricular hypertrophy and controls (p = 0.002). CONCLUSIONS: T-loop features and particularly T amplitude are significantly different between hypertensive patients and healthy controls and may serve as early markers of repolarization abnormalities in a hypertensive population.     

短QT综合征新进展

短QT综合征(Short QT Syndrome,SQTS),是一种发生于非器质性心脏病的恶性心律失常,表现为多形性室性心动过速及心室颤动,引起反复晕厥、心脏骤停及猝死,心电图以短QT间期为显著特征。虽然SQTS发病率较低,但临床致死性极高,值得关注和重视。     

Catecholaminergic Polymorphic Ventricular Tachycardia with QT Prolongation

The QT interval in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT) is typically normal. However, CPVT patients are sometimes misdiagnosed as concealed long QT syndrome (LQTS), because patients with LQTS also manifest with syncope or sudden death following periods of exertion or extreme emotion. We report a CPVT patient with a pathogenic RyR2 mutation associated with a marked QT prolongation, which normalized after flecainide therapy.     

Circadian Variation and Waking Hour Dynamics of the QT Interval

Background: The incidence of sudden cardiac death is maximal in the morning hours. Although ventricular arrhythmias have been implicated as a potential mechanism, and several neurohumoral factors affecting myocardial excitability have been shown to be raised in the early morning hours, it is not known if there is any circadian variation in the dynamics of ventricular repolarization when studied on a beat-to-beat basis. The objective of this study was to examine the range, diurnal variations, and circadian distribution of the variability of the QT interval in healthy subjects. Method: We developed and validated a new method for continuous measurement of QT intervals from 24-hour Holter recordings. The QT intervals measured semi-automatically were corrected by a linear regression formula derived independently for each patient from his own QT and RR values in 32 healthy males (20 ± 0.4 years). QT variability was assessed by the mean standard deviation of the average of consecutive uncorrected QT intervals (SDA-QT Index) and corrected QT intervals (SDA-QTc index) over 5-minute segments. The rate-dependent changes of the QT interval were studied as a function of the slope of the regression line between the QT and RR values. Results: The average QTc range was mean (SD) 79 (± 28) ms; the average maximal QTc interval was 481 (± 24) ms. The 95% upper confidence limit for the mean 24-hour QTc interval was 443 ms. The RR, QT, and QTc intervals were longer, while the SDA-QT and SDA-QTc indices were shorter during sleep. Hourly averages of the SDA-QT and SDA- QTc index revealed a sudden increase in QT variability in the first hour of waking (P < 0.0001 and P = 0.006). Conclusion: The dynamic behavior of the QT interval shows significant diurnal variations. The maximal QTc interval over 24 hours is longer than previously assumed. The period shortly following awakening is characterized by a peak in the variability of the QT interval. These changes may be indicative of autonomic instability during the early waking hours and correspond with the peak incidence of sudden arrhythmic death.     

Reduction of QTD - A Novel Marker of Successful Reperfusion in NSTEMI. Pathophysiologic Insights by CMR

Background/Objectives: Non-ST segment elevation myocardial infarction (MI) poses similar detrimental long-term prognosis as ST-segment elevation MI. No marker on ECG is established to predict successful reperfusion in NSTEMI. QT dispersion is increased by myocardial ischemia and reduced by successful restoration of epicardial blood flow by PCI. Whether QT dispersion reduction translates to smaller infarcts and thus indicates successful reperfusion is unknown.We hypothesized that the relative reduction of QT dispersion (QTD-R_rel ) on a standard ECG in acutely reperfused NSTEMI is related to infarct size and infarct transmurality as assessed by delayed enhancement CMR (DE-CMR).Methods and Results: 69 patients with a first acute NSTEMI were included. QTD-R_rel was stratified according to LV function and volumes, infarct transmurality and size as assessed by DE-CMR. Extensive myocardial infarction was defined as above median infarct size.LV function and end-systolic volume were only mildly related to QTD-R_rel . QTD-R_rel was inversely related to infarct size (r=-0.506,p=0.001) and infarct transmurality (r=-0.415, p=0.001). QTD-R_rel was associated with extensive myocardial infarction in univariate analysis (odds ratio (OR) 0.958, CI 0.935-0.982; p=0.001). Compared to clinical and angiographic data QTD-R_rel remained the only independent predictor of non-transmural infarcts (OR 1.110, CI 1.055-1.167; p=0.049).Conclusion: In patients with acute Non-ST-Segment Myocardial infarction QTd-R_rel calculated on a surface ECG prior and post PCI for restoration of epicardial blood flow detects small, non-transmural infarcts as assessed by delayed enhancement CMR. Thus, QTd-R_rel can indicate successful reperfusion therapy.     

Q-Tcd对乳腺癌表阿霉素化疗致心肌损伤的早期预测价值

目的：：探讨Q-T 间期离散度(Q-Tcd)预测表阿霉素导致早期心肌损伤的应用价值。方法：44例乳腺癌患者均采用含表阿霉素的方案化疗,使用剂量为75mg/m2,治疗1-5个周期。根据肌钙蛋白Ⅰ水平将患者分为心肌损伤组和未发生心肌损伤组,比较患者的Q-T间期离散度和心脏超声结果。结果：44例患者中心肌损伤组16例、未发生心肌损伤组28例。心肌损伤组患者Q-T间期离散度明显高于未发生心肌损伤组(P<0.05）;两组心脏超声左室舒张末期前后径、左室射血分数比较差异无统计学意义(P>0.05）。结论：表阿霉素对心肌损伤的评价指标中,Q-T间期离散度较左室舒张末期前后径和射血分数更为敏感,对表阿霉素致心肌病具有预测价值。     

永久起搏器和埋藏式心脏复律除颤器（ICD）在遗传性长QT综合征患者中的应用

目的总结合并窦性心动过缓的遗传性长QT综合征（以下简称遗传性LQTS）患者植入永久起搏器和埋藏式心脏复律除颤器（以下简称ICD）的治疗效果,对比分析这两种治疗在预防患者猝死中的差异。方法对我院从2003年6月到2013年6月出院诊断为遗传性LQTS合并窦性心动过缓、植入了永久起搏器或ICD的全部21例患者,结合门诊、电话和程控随访了解患者的生存状况、手术并发症以及晕厥、室性恶性心律失常的发作情况。结果起搏器组男性2例,女性9例,年龄39.3±14.3岁,随访时间50.6±26.3个月,1例患者猝死,2例患者再发晕厥前兆,其中1例最终更换为ICD。ICD组男性2例,女性8例,年龄34.5±11.9岁,随访时间61.4±43.5个月,3例患者接受了ICD的适当治疗,另2例患者接受了ICD的不适当治疗,1例患者术后出现囊袋感染,1例患者更换为永久起搏器。治疗有效率在起搏器组及ICD组分别为72.7%（8/11）和100.0%（10/10）,未达到统计学差异（p=0.21）。不良事件发生率在起搏器组及ICD组分别为27.3%（3/11）和30.0%（3/10）,也未达到统计学差异（p=0.63）。结论对于不能植入ICD的合并窦性心动过缓的遗传性LQTS患者,植入永久起搏器可能是一个较好的替代方法,但对于QTc≥539ms的患者,只有植入ICD才能预防猝死。植入ICD后长期无心脏事件发生的患者,根据患者意愿,可考虑更换为永久起搏器。