Analysis of the Corrected QT Before the Onset of Nonsustained Ventricular Tachycardia in Patients with Hypertrophic Cardiomyopathy

BARANOWSKI, R., et al .: Analysis of the Corrected QT Before the Onset of Nonsustained Ventricular Tachycardia in Patients with Hypertrophic Cardiomyopathy. This study examined ventricular repolarization before the onset of 37 episodes of nonsustained ventricular tachycardia (NSVT) in 26 untreated patients with hypertrophic cardiomyopathy (HCM). Fourteen episodes were recorded in patients with a history of cardiac arrest or patients who died suddenly during follow-up. The QT interval was measured beat-by-beat on 24-hour ambulatory electrocardiograms. Mean 24-hour, hourly QTc and QTc of the last 10 beats prior to NSVT, consisted of 4–50 cycles (mean   9 ± 10   ), at the fastest rates of 100–175 beats/min (mean 122 ± 22) were analyzed. NSVT was more prevalent during nighttime (23 episodes), than during daytime (14 episodes,   P < 0.05   ). No significant differences were observed between mean 24-hour, mean hourly QTc during the hour with NSVT, and QTc of the last 10 cycles prior to onset of NSVT. QTc was significantly longer in patients with a history of sudden cardiac death (SCD) or who died suddenly during follow-up than in survivors. The 24-hour QT variability was higher in nonsurvivors than in survivors (   -39 ± 6   vs   33 ± 6 ms, P = 0.03   ). Episodes of NSVT in untreated patients with hypertrophic cardiomyopathy were more frequent during the nighttime. The 24-hour QT variability was higher in nonsurvivors than in survivors. (PACE 2003; 26[Pt. II]:387–389)     

Clinical Value of Electrocardiographic Parameters in Genotyped Individuals with Familial Long QT Syndrome

MOENNIG, G., et al. : Clinical Value of Electrocardiographic Parameters in Genotyped Individuals with Familial Long QT Syndrome. Rate corrected QT interval (QTc) and QT dispersion (QTd) have been suggested as markers of an increased propensity to arrhythmic events and efficacy of therapy in patients with long QT syndrome (LQTS). To evaluate whether QTc and QTd correlate to genetic status and clinical symptoms in LQTS patients and their relatives, ECGs of 116 genotyped individuals were analyzed. JTc and QTc were longest in symptomatic patients (  n = 28  ). Both QTd and JTd were significantly higher in symptomatic patients than in asymptomatic (  n = 29  ) or unaffected family members (  n = 59  ). The product of QTd/JTd and QTc/JTc was significantly different among all three groups. Both dispersion and product put additional and independent power on identification of mutation carriers when adjusted for sex and age in a logistic regression analysis. Thus, symptomatic patients with LQTS show marked inhomogenity of repolarization in the surface ECG. QT dispersion and QT product might be helpful in finding LQTS mutation carriers and might serve as additional ECG tools to identify asymptomatic LQTS patients.     

QT Interval Variability and Adaptation to Heart Rate Changes in Patients with Long QT Syndrome

Background: Increased QT variability (QTV) has been reported in conditions associated with ventricular arrhythmias. Data on QTV in patients with congenital long QT syndrome (LQTS) are limited.
Methods: Ambulatory electrocardiogram recordings were analyzed in 23 genotyped LQTS patients and in 16 healthy subjects (C). Short-term QTV was compared between C and LQTS. The dependence of QT duration on heart rate was evaluated with three different linear models, based either on the RR interval preceding the QT interval (RR₀), the RR interval preceding RR₀ (RR_-1), or the average RR interval in the 60-second period before QT interval (mRR).
Results: Short-term QTV was significantly higher in LQTS than in C subjects (14.94 ± 9.33 vs 7.31 ± 1.29 ms; P < 0.001). It was also higher in the non-LQT1 than in LQT1 patients (23.00 ± 9.05 vs 8.74 ± 1.56 ms; P < 0.001) and correlated positively with QTc in LQTS (r = 0.623, P < 0.002). In the C subjects, the linear model based on mRR predicted QT duration significantly better than models based on RR₀ and RR_-1. It also provided better fit than any nonlinear model based on RR₀. This was also true for LQT1 patients. For non-LQT1 patients, all models provided poor prediction of QT interval.
Conclusions: QTV is elevated in LQTS patients and is correlated with QTc in LQTS. Significant differences with respect to QTV exist among different genotypes. QT interval duration is strongly affected by noninstantaneous heart rate in both C and LQT1 subjects. These findings could improve formulas for QT interval correction and provide insight on cellular mechanisms of QT adaptation.     

Systematic Comparisons of Electrocardiographic Morphology Increase the Precision of QT Interval Measurement

Decreased intrasubject variability of QTc values is needed to increase the power and reduce the size of the so-called thorough QT studies. One source of QTc variability is the lack of systematic measurements when electrocardiograms (ECG) with closely matching morphologies are not measured in an exactly corresponding way. The inaccuracy can be eliminated by postprocessing of QT measurements by ECG pattern matching. This study tested the effects of pattern matching in ECG measurements in two populations of healthy subjects (n = 48 + 56) and in a population of patients with advanced Parkinson's disease (n = 130) in whom both day-time and night-time data were available. Intrasubject QTc variability was measured by intrasubject standard deviations (SD) of QTc values obtained with manual measurements before and after pattern-matching measurement alignments. In each subject, QT values (n = 230–320) in one drug-free long-term ECG recording were evaluated. The pattern-matching adjustment of the QT measurement decreased the intrasubject QTc variability from 5.2 ± 1.0 to 4.5 ± 1.0 ms (P < 10⁻¹⁴) from 6.4 ± 1.7 to 5.5 ± 1.6 ms (P < 10⁻¹⁰) from 5.6 ± 1.5 to 4.6 ± 1.4 ms (P < 10⁻³⁴) and from 6.1 ± 1.9 to 5.0 ± 1.7 ms (P < 10⁻³³), in the two populations of healthy subjects and in the day-time and night-time recordings of Parkinson's disease patients, respectively. Hence, morphological pattern adjustment of QT interval measurements improves the quality of the QT data with substantial practical implications. Reductions in intrasubject QTc variability were reproducibly found in different populations and thus the technology might be recommended for every thorough QT/QTc study. Noticeable reductions of necessary study size are likely achievable in this way.     

Torsades de pointes in congenital long QT syndrome following low-dose orphenadrine

We report the case of a woman, affected by congenital long QT syndrome (LQTS), who experienced three syncopal episodes shortly after the assumption of a low dose of orphenadrine. The ECG revealed a QT interval of 600 ms, and the corrected QT interval (QTc) was 537 ms. No structural cardiac disease was demonstrated by echocardiography. Orphenadrine treatment was discontinued. During the first 12 h of monitoring, three short-lasting, asymptomatic episodes of torsades de pointes occurred. No other sustained ventricular arrhythmia was revealed at Holter monitoring in the following days. During the ensuing 6 months, the patient remained asymptomatic, and the QTc did not change. Orphenadrine is an analogue of diphenhydramine, an antihistaminic drug that produces sodium channel blockade similar to that caused by quinidine and other Class Ia antiarrhythmic drugs. Our case rises the suspicion that orphenadrine could cause life-threatening arrhythmias in LQTS even at a low dose, and independently from concomitant assumption of potentially QT-prolonging drugs.     

QT Duration and Dispersion in Patients with Anomalous Origins of Coronary Arteries

Background: Coronary artery anomalies have been reported to show various symptoms ranging from chest pain and dyspnea to cardio-respiratory arrest and sudden death. In this study, we attempted to assess the changes in QT interval duration and dispersion in anomalous origins of coronary arteries (AOCA).
Methods: Nineteen AOCA patients (mean age: 52 ± 11 years) and 30 healthy control subjects (mean age: 50 ± 12 years) were included in the study. Minimum and maximum corrected QT intervals, and corrected QT dispersion were calculated. The two groups were compared in terms of QT dispersion and QT duration.
Results: There was no difference between the two groups in terms of baseline demographic characteristics. Maximum corrected QT intervals (QTc max), minimum corrected QT intervals (QTc min), and corrected QT dispersion were higher in AOCA patients than controls (452 ± 38 vs 411 ± 25 ms [P = 0.0001], 402 ± 31 vs 383 ± 28 ms [P = 0.048], and 51 ± 30 vs 28 ± 12 ms [P = 0.001], respectively).
Conclusion: In the patients with anomalous origins of coronary arteries, QT dispersion that is an indicator of sudden cardiac death and arrhythmias frequency increased. QTc max, QTc min, and corrected QT dispersion are higher in patients with anomalous origin of the coronary artery than in control subjects.     

Extreme QT prolongation during therapeutic hypothermia after cardiac arrest due to long QT syndrome

During therapeutic hypothermia, QT interval is prolonged. In patients with congenital long QT syndrome (LQTs), a longer QT interval was associated with significantly increased risk of cardiac arrest (CA). Therefore, therapeutic hypothermia may have proarrhythmic effects in survivors of CA due to congenital LQTs. A 27-year-old man was resuscitated from CA due to congenital LQTs type 3 and Brugada syndrome. Torsade de pointes (TdP) recurred spontaneously on admission (body temperature, 36.9°C). During mild hypothermia therapy, QTc increased from 499 (36.9°C) to 667 milliseconds (33.8°C), although TdP was not induced. A 13-year-old boy with congenital LQTs type 1 underwent therapeutic hypothermia after resuscitation. Short-acting β-blocker was administered intravenously during this treatment. The QTc increased from 534 (36.4°C) to 626 milliseconds (34.3°C). However, TdP did not recur during mild hypothermia therapy. In both patients, electrolyte abnormalities were checked frequently and corrected immediately. QT prolongation remained a couple of days after completion of rewarming. The withdrawal of sedative drugs and extubation were not pursued before QT shortening reached to a plateau. Both patients were fully recovered from neurologic damage. During therapeutic hypothermia, QT interval was extremely prolonged, although TdP did not recur in 2 patients with congenital LQTs. Therapeutic hypothermia may be beneficial for comatose survivors of CA due to LQTs.     

Correlation of Heart Rate Variability Parameters and QT Interval in Patients After PTCA of Infarct Related Coronary Artery as an Indicator of Improved Autonomic Regulation

The purpose of this study was to determine if PTCA of the infarct related coronary artery (IRA) in the late phase of myocardial infarction (MI) can improve autonomic regulation of sinus rhythm and electrical stability of the myocardium measured by heart rate variability (HRV), QT, QTc, and its dispersion (QTd) and if any correlation exists among these measures. The study was performed in 25 patients (21 male, age: 50 ± 9 years, EF: 52%± 11%) in the late phase of MI (2.5 ± 1.5 months). HRV parameters were calculated automatically. QT, QTc, and QTd were measured manually from a 12-lead surface ECG (50 mm/s). All measurements were made before and 3–5 days after PTCA. Day and night parameters of HRV were sampled over two periods: 2 pm to 10 pm (day) and 10 pm to 6 am (night). Parameters of HRV measured from whole recordings were significantly higher after successful PTCA: SDRR (116 31 vs 128 ± 38 ms), SD (55 ± 17 vs 62 ± 22 ms), rMSSD (30 ± 13 vs 36 ± 14 ms) and HF (246 ± 103 vs 417 ± 224 ms2). Significant differences were found during daytime for SD, rMSSD, and HF, and during nighttime for SDRR, SDANN. QT interval duration, QT corrected to the heart rate, and QT dispersion were significantly lower after PTCA (QTd: 54 ± 15 vs 39 ± 12 ms). There was no correlation between HRV and QT values before PTCA. High correlations were found after the procedure, particularly between QTd and nighttime HRV. Conclusions: PTCA of IRA in the late phase of MI enhances sympathovagal regulation of the cardiac rhythm and the electrical stability of the heart, which may be prognostically important.     

Evaluation of PR, RR, QT Intervals and QT Dispersion Following Stellate Ganglion Block in Chronic Shoulder–Hand Pain Patients

Abstract: Right stellate ganglion block (SGB) can increase QT interval, rate‐corrected QT interval (QTc), QT dispersion (QTD), rate‐corrected QTD (QTcD), and RR interval while left SGB can decrease these intervals in healthy volunteers. No such studies have been conducted in patients with chronic pain, hence this study was designed to investigate the effects of left and right SGB on these variables in chronic shoulder–hand pain patients. In this study, 28 patients with chronic shoulder–hand pain of at least 6 months duration were given right or left SGB depending on the shoulder affected. A 12‐lead electrocardiogram (ECG) was recorded before the block, 30 minutes and 60 minutes after the block. PR interval, RR interval, QT interval were recorded in all 12 leads while QTc, QTD, and QTcD were calculated. Right SGB was performed in 21 patients. A significant decrease (P < 0.05) in PR interval and a significant increase (P < 0.05) in RR interval, QT interval, and QTc interval were observed. QTD showed a significant increase (P < 0.05) only at 30 minutes after right SGB. Left SGB was performed in seven patients. A significant decrease (P < 0.05) in QT interval was observed throughout the study period, while QTc showed a significant decrease (P < 0.05) only at 60 minutes after the block. We conclude that right SGB induces significant increase of QT interval, RR interval, QTc interval, QTD, and a significant decrease of PR interval while left SGB produces a significant decrease in QT and QTc intervals in patients with chronic shoulder–hand pain.     

急性心肌梗死患者经皮冠脉介入治疗前后校正QT间期、校正Tp-e间期、Tp-e/QT的变化及其预测价值

目的观察急性ST段抬高型心肌梗死(STEMI)患者成功行经皮冠脉介入治疗(PCI)术前术后校正QT间期、校正Tp-e间期、Tp-e/QT的变化,分析这些指标与恶性心律失常事件(MAE)的相关性,探讨其预测价值。方法 STEMI患者40例,12 h内成功行PCI术,分别测算术前及术后100 min梗死相关导联QTc、Tp-ec、Tp-e/QT,随访三个月后MAE情况。40例正常心电图做对照。结果 (1)STEMI组QTc、Tp-ec、Tp-e/QT在发病12 h内明显升高(P<0.05),PCI术后降低(P<0.05),但与对照组仍差异有统计学意义(P<0.05)。(2)STEMI组以PCI术前QTc440ms为节点分组,随访三个月组间MAE发生差异无统计学意义(P>0.05);而以Tp-ec 100ms和Tp-e/QT 0.25为节点,组间MAE发生有统计学意义。结论急性STEMI患者Tp-ec,尤其是Tp-e/QT比值增加,与恶性心律失常事件相关,是预测急性STEMI后恶性心律失常事件的指标。