Long Runs of Non-Sustained Ventricular Tachycardia on 24-Hour Ambulatory Electrocardiogram Predict Major Arrhythmic Events in Patients with Idiopathic Dilated Cardiomyopathy

This study examined the prognostic significance of the rate and length of non-sustained (NS) ventricular tachycardia (VT) on 24-hour ambulatory electrocardiograms (ECG) recorded in 343 patients with idiopathic dilated cardiomyopathy (IDC) in the prospective Marburg Cardiomyopathy study. NSVT was defined as ≥3 consecutive ventricular premature beats at >120 bpm. During 52 ± 21 months of follow-up, major arrhythmic events defined as sustained VT, VF, or sudden cardiac death occurred in 46 of 343 patients (13%). Patients with 3–4 beat runs of NSVT had a similar arrhythmia-free survival as patients without NSVT on baseline 24-hour ambulatory ECG. The incidence of major arrhythmic events during follow-up increased significantly from 2% per year in patients without NSVT, to 5% per year in patients with 5–9 beat runs of NSVT, to 10% per year in patients with ≥10 beat runs of NSVT (P < 0.05). Unlike the length, the rate of NSVT was similar in patients with versus without subsequent major arrhythmic events (163 ± 23 vs 160 ± 24 bpm). Thus, the length but not the rate of NSVT on 24-hour ambulatory ECG was a predictor of major arrhythmic events in patients with IDC. The presence of NSVT with ≥10 beat runs on ambulatory ECG was associated with a particularly high risk of major arrhythmic events.     

Does heart rate identify sudden death survivors? Assessment of heart rate, QT interval, and heart rate variability

The objective was to test whether the circadian variability of several electrocardiographic variables distinguishes sudden cardiac death survivors from heart disease patients without a history of cardiac arrest and from normal subjects. Heart rate, heart rate variability, and QT interval have been reported to identify survivors of sudden cardiac death. Computer-assisted continuous QT measurement and heart rate variability analysis were performed on 24-hour Holter records for three groups: (1) 14 sudden death survivors; (2) 14 control patients with diagnosis and therapy matched to survivors; and (3) 14 healthy subjects. There were no significant differences in 24-hour mean RR and QT intervals between groups. However, heart rate was significantly different between the three groups at night but not during the day because the expected nighttime decline was markedly blunted in survivors and somewhat blunted in control patients. The QT interval and frequency domain heart rate variability measures followed a similar circadian pattern. The mean QTc was significantly longer in control patients. The QTc had a wide range in all groups, but less in sudden death survivors. Of ten common time and frequency domain heart rate variability indices, only SDANN and SDNN were significantly lower in sudden death survivors. Reduced circadian variation of heart rate, with marked blunting of the nighttime heart rate decline, identifies sudden cardiac death survivors as well as does SDANN and SDNN, and, in contrast to heart rate variability measures, can easily be obtained from a Holter report without complex calculations.     

Determinant of QT Dispersion in Patients with Hypertrophic Cardiomyopathy

KAWASAKI, T., et al. : Determinant of QT Dispersion in Patients with Hypertrophic Cardiomyopathy. QT dispersion is thought to reflect a regional difference in repolarization process although QT interval is composed of depolarization and repolarization. This study was designed to investigate the effect of depolarization and repolarization on QT dispersion in hypertrophic cardiomyopathy. Standard 12-lead ECG was recorded in 70 hypertrophic cardiomyopathy patients with anteroseptal wall hypertrophy (HC-As), 8 patients with lateral wall hypertrophy (HC-L), 8 patients with diffuse hypertrophy (HC-D), and 46 normal controls. QRS, JTc, maximum and minimum QTc, and QTc dispersion were compared. The maximum QTc was greater in HC-As and HC-L than in the control; the minimum QTc was similar in all 3 groups; consequently, QTc dispersion was greater in HC-As and HC-L. In HC-D, the maximum QTc and the minimum QTc were greater than the control, which produced QTc dispersion similar to that in the control. JTc did not differ among 4 groups. In hypertrophic cardiomyopathy, both QTc and QRS duration were increased in the leads coinciding with the left ventricular portion of localized hypertrophy. We conclude that QTc dispersion depended on the heterogeneity of QRS duration or depolarization rather than repolarization, which in fact may be ascribed to the regionally different hypertrophy of the left ventricle in hypertrophic cardiomyopathy. (PACE 2003; 26[Pt. I]:819–826)     

Circadian Profile of QT Interval and QT Interval Variability in 172 Healthy Volunteers

BONNEMEIER, H., et al .: Circadian Profile of QT Interval and QT Interval Variability in 172 Healthy Volunteers. The limited prognostic value of QT dispersion has been demonstrated in recent studies. However, longitudinal data on physiological variations of QT interval and the influence of aging and sex are few. This analysis included 172 healthy subjects (89 women, 83 men; mean age   38.7 ± 15   years). Beat-to-beat QT interval duration (QT, QTapex [QTa], T_end[Te]), variability (QTSD, QTaSD), and the mean R-R interval were determined from 24-hour ambulatory electrocardiograms after exclusion of artifacts and premature beats. All volunteers were fully active, awoke at approximately 7:00 am , and had 6–8 hours of sleep. QT and R-R intervals revealed a characteristic day-night-pattern. Diurnal profiles of QT interval variability exhibited a significant increase in the morning hours (6–9 am ; P < 0.01) and a consecutive decline to baseline levels. In female subjects the R-R and T_end intervals were significantly lower at day- and nighttime. Aging was associated with an increase of QT interval mainly at daytime and a significant shift of the T wave apex towards the end of the T wave. The circadian profile of ventricular repolarization is strongly related to the mean R-R interval, however, there are significant alterations mainly at daytime with normal aging. Furthermore, the diurnal course of the QT interval variability strongly suggests that it is related to cardiac sympathetic activity and to the reported diurnal pattern of malignant ventricular arrhythmias. (PACE 2003; 26[Pt. II]):377–382)     

Video-Assisted Thoracoscopic Sympathectomy for Congenital Long QT Syndromes

LI, J., et al .: Video-Assisted Thoracoscopic Sympathectomy for Congenital Long QT Syndromes. The feasibility, safety, and effectiveness of video-assisted thoracoscopic sympathectomy (VATS) for congenital long QT syndrome were assessed in four patients who had frequent syncopal events before the surgeries. Under general anaesthesia, the pleural cavity was entered via two small incisions in the left third and fifth intercostal spaces at the mid-axillary line. The left thoracic sympathetic chain was identified and resected from T2-T5. The lower one third of the left stellate ganglion was also resected. VATS resulted in a significant shortening in corrected QT intervals (QTc) in three patients, the average QTc of the four patients immediately before and after VATS was   538 ± 76   and   512 ± 57 ms   , respectively   (P = 0.047)   . The heart rate remained unchanged after the VATS (   67 ± 4   vs   69 ± 4 beats/min, P > 0.05   ). There were no major perioperative complications apart from mild ptosis of the left upper eyelid in one patient who recovered in the following days. There was no recurrence in syncopal events after a 3-month follow-up. VATS is a safe and effective technique for left cardiac sympathectomy in patients with congenital long QT syndromes. (PACE 2003; 26[Pt. I]:870–873)     

Circadian Rhythm of the Corrected QT Interval: Impact of Different Heart Rate Correction Models

SMETANA, P., et al .: Circadian Rhythm of the Corrected QT Interval: Impact of Different Heart Rate Correction Models . A reduced circadian pattern in the QTc interval has been repeatedly reported to provide prognostic information in cardiac patients. However, the results of studies in healthy subjects in which different heart rate correction formulas were used are inconsistent regarding the presence and extent of diurnal variations in QTc. This study compared the diurnal variations in QTc obtained with four frequently used heart rate correction models with those based on individually optimized heart rate correction. In 53 subjects (25 men aged 27 ± 7 years and 28 women aged 27 ± 9 years) 12-lead digital ECGs were obtained every 30 seconds during 24 hours. The QT interval was measured automatically by six different algorithms provided by a commercially available device. The QT/RR relation was estimated by four common heart rate correction models and by an individually optimized correction model, QTc = QT/RR^α. In each 24-hour recording, RR, QT, and QTc intervals of separate ECG samples were averaged over 10-minute intervals. Marked differences were found in the extent of the circadian pattern of QTc obtained with different formulas for heart rate correction. Under and overcorrection of the QT interval resulted in significant over- or underestimation of the circadian pattern. Thus, the extent of circadian variation in QTc depends highly on the heart rate correction formula used. To obtain proper insight regarding diurnal variation in QTc prolongation during pharmacologic therapy and/or to assess higher risk due to impaired autonomic regulation of ventricular repolarization, individualized heart rate correction is necessary. (PACE 2003; 26[Pt. II]:383–386)     

Abnormal Nocturnal Heart Rate Variability and QT Dynamics in Patients with Brugada Syndrome

Background: In Brugada syndrome (BSY), most of the ventricular arrhythmic events are nocturnal, suggesting an influence of the autonomic nervous system.
Methods: In 46 patients (mean age = 41 ± 14 years, 43 men) with electrocardiograms (ECG) consistent with BSY and structurally normal hearts, we measured heart rate variability (HRV) and QT dynamics (QT/RR slopes) on 24-hour ambulatory ECG. Type 1 BSY-ECG was spontaneous in 23 (50%) and induced in 23 patients.
Results: History of syncope was present in 23 patients (50%). Programmed ventricular stimulation induced ventricular tachyarrhythmias (VTA) in 13 patients (28%). A single patient developed ventricular tachycardia during a mean follow-up of 34 months. Compared to a control group matched for age and sex, HRV was decreased over 24 hours and during nighttime in patients with BSY (SDNN 122 ± 44 vs 93 ± 36 ms, P = 0.0008 and SDANN 88 ± 39 vs 54 ± 24 ms, P < 0.0001). QTend /RR slopes were decreased over 24 hours in patients with BSY (0.159 ± 0.05 vs 0.127 ± 0.05, P = 0.003) and particularly at night (0.123 ± 0.04 vs 0.089 ± 0.04, P = 0.0001). QTend /RR slopes were significantly decreased during nighttime in patients with spontaneous versus provoked BSY-ECG patterns. By contrast, HRV and QT/RR slopes were similar in symptomatic and asymptomatic patients, whether VTA were induced or not.
Conclusions: Patients with a BSY-ECG pattern had lower HRV and QT/RR slopes than control subjects during nighttime. High-risk patients with spontaneous BSY-ECG patterns had the lowest nocturnal QTend/RR slopes. These unique repolarization dynamics might be related to the frequent nocturnal occurrence of VTA in BSY.     

Sensing Through the Esophagus for Temporary Atrial Synchronous Ventricular VDD Pacing

The purpose of this study was to evaluate the effectiveness and safety of temporary VDD pacing using an esophageal electrode for sensing of the atrial electrogram. We studied 15 patients, 8 men and 7 women, aged 77 ± 2 years (mean ± SE, range 61–90), with severe atriovenfricular (AV) conduction disturbances. A 24-hour beat-to-beat ECG analysis was used to evaluate the effectiveness of the pacing system and special tests were performed to test the stability of pacing and sensing. The system performed satisfactorily in 12 of the 15 patients. The 24-hour Holter ECG monitoring revealed the following percentages of beats: 96.32 ± 0.5 VDD, 2.92 ± 0.6 VVI, and 0.14 ± 0.05 paced beats resulting from pseudosensing. All the latter were single, with no bigeminy or salvos. The results of the stability tests were as follows: the percentage of VDD beats was significantly lower than the 24-hour mean when the patient lay on his right side (92.8 ± 0.5, P < 0.001), during the swallowing of liquids (91.26 ± 0.4, P < 0.001) and soft foods (84.2 ± 1.4, P < 0.001), and during coughing (94.2 ± 0.6, P < 0.001). The percentage of VVI type beats increased in these four cases (6.7 ± 0,5, 7.2 ± 0.3, 13.2 ± 1.2 and 4.8 ± 0.4, respectively, P < 0.001 in each case). The percentage of ectopic beats due to pseudosensing did not change significantly during any of the tests. These results indicate that the method described is a safe and effective technique for temporary VDD pacing.     

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.     

Age and Gender Influences on Rate and Duration of Paroxysmal Atrial Fibrillation

The influence of age and gender on the character of paroxysmal atrial fibrillation (PAF) has not been described. Methods: The heart rate (HR) during PAF in patients receiving placebo or antiarrhythmic therapy was analyzed. Data from 177 24-hour Holter recordings were analyzed to mark the onset and termination of PAF and converted into RR interval files. PAF episodes lasting at least 2 minutes and containing ± 20% noise were included. HR during the first 30-second segment versus during the remainder of the episode, and the duration of PAF episodes were compared among groups of different ages and sex (Wilcoxon test). Results: 236 episodes from 55 recordings in 32 patients (all patients: 61.4 ± 12.8 years; men (19): 58.5 ± 12.6 years; women (13) 65.5 ± 12.4 years, P = ns for difference in age) fulfilled the inclusion criteria. Women had a higher mean heart rate at AF onset (123 ± 35 beats/min vs 115 ± 20 beats/min, P = 0.02) and during the remainder of the episode (120 ± 25 beats/min vs 112 ± 22 beats/min at the start, P = 0.01, and 116 ± 26 beats/min vs 108 ± 18 beats/min subsequently, P = 0.01). Episodes tended to be longer in women (mean 89.8 min vs 50.5 min, P = NS) and in the aged (mean 83.8 min vs 46.9 min, P = NS). Conclusion: PAF episodes are associated with faster heart rates and last longer in women, which may reflect differing autonomic responses to AF. A slower ventricular rate during PAF in older patients probably reflects an increasing prevalence of impaired atrioventricular conduction.     

Alteration of QT Rate Dependence Reflects Cardiac Autonomic Imbalance in Patients with Obstructive Sleep Apnea Syndrome

QT rate dependence is one of the major properties of ventricular repolarization with its circadian and autonomic modulations. The authors postulated that dynamic alterations in QT interval adaptation could help characterize patients with cardiac autonomic alterations, like those with obstructive sleep apnea syndrome (OSAS). To assess ventricular repolarization features in patients with OSAS, QT parameters and their dynamicity along RR intervals were compared from 24-hour ECG data of patients with and without this syndrome, assessing cardiac autonomic nervous system equilibrium by means of time-domain and frequency-domain analyses of heart rate variability (HRV). The study group consisted of 74 consecutive patients referred to the Sleep Laboratory for clinically suspected OSAS. The syndrome was confirmed in 30 (40.5%) patients according to standard polysomnographic criteria. QT length related to heart rate (HR) was found significantly shorter for HR < 70 beats/min in patients with OSAS   (−1.32 ± 0.35)   compared with patients without OSAS   (−1.99 ± 0.40; P < 0.01)   . This flattened relationship was correlated with the severity of the sleep related disorder. Using multiple linear regression analysis, the apnea/hypopnea index and nocturnal normalized high frequencies (HFnu) were the most significant predictors of the QT/RR slope   (R = 0.61; P < 0.0001)   . OSAS is significantly associated with a flattened relationship between QT duration and RR interval at low HRs. The alteration of cardiac parasympathetic tone occuring in severe OSAS patients may explain this altered rate dependent adaptation of myocardial repolarization. (PACE 2003; 26[Pt. I]:1446–1453)     

The 12-lead electrocardiogram in patients with subarachnoid hemorrhage: early risk prognostication

Objective

The aim of this study was to investigate if the electrocardiographic (ECG) abnormalities assessed early in the emergency department (ED) are associated with the in-hospital mortality of the patients with spontaneous subarachnoid hemorrhage (SAH).

Methods

We studied prospectively a cohort of 222 adult patients with spontaneous SAH in an ED. A 12-lead ECG was performed for these patients in the ED. The patients were stratified into nonsurvivors and survivors based on the in-hospital mortality. The clinical characteristics, heart rate, corrected QT interval (QTc) and 7 predefined morphologic abnormalities were compared between these 2 groups of patients.

Results

Compared with the survivors (n = 178), the nonsurvivors (n = 44) had significantly slower heart rate (75 ± 23 vs 83 ± 16, P = .018) and more prolonged QTc (492 ± 58 vs 458 ± 40, P = .001). There were significantly higher frequency of occurrence of ECG morphologic abnormalities (66% vs 37%, P = .001) and nonspecific ST- or T-wave changes (NSSTTCs; 32% vs 12%, P = .015) in the nonsurvivors compared with those in the survivors. Multiple logistic regression model identified QTc (odds ratio, 1.0; 95% confidence interval, 1.0-1.0; P = .005) and NSSTTC (odds ratio, 3.3; 95% confidence interval, 1.0-10.7; P = .047) as the significant ECG variables associated with in-hospital mortality.

Conclusions

The occurrence of NSSTTC and prolonged QTc assessed early in the ED are independently associated with the in-hospital mortality in adult patients with spontaneous SAH.     

Risk assessment of R-on-T event based on modeled QT-RR relationship

Background: R‐on‐T event is a well‐known trigger of ventricular tachycardia (VT) and ventricular fibrillation (VF). We propose a method to estimate the risk of R‐on‐T event from the inter‐beat (RR) intervals based on modeled QT‐RR relationship. Methods: We retrospectively analyzed the Spontaneous Ventricular Tachyarrhythmia Database and the HAWAI Registry, which include a total of 397 RR interval recordings from 116 implantable cardioverter defibrillator patients. For each RR interval time series, QT intervals were estimated from the weighted average of preceding RR intervals using Bazett, Fridericia, and linear formulas. The risk score (RS) of each cycle was calculated to quantify the probability of R‐on‐T event based on the timing of R‐wave relative to the estimated T‐end. We identified 52,440 ectopic beats (EBs) episodes, 280 nonsustained VT (NSVT) episodes, and 352 sustained VT/VF episodes. The RS of episode onset and the prematurity index (PMI) of the initiating beat were compared. Results: Using different QT‐RR models, R‐on‐T events were respectively detected in 9% EB, 45% NSVT, 69% VT/VF (Bazett); in 6% EB, 41% NSVT, 65% VT/VF (Fridericia); and in 7% EB, 42% NSVT, 66% VT/VF (linear). No R‐on‐T event was found in normal beats. Consistent among three QT‐RR models, the RS of episode onset rises sharply from EB to NSVT and to VT/VF episodes. In contrast, no trend in PMI is found. Conclusions: The risk of R‐on‐T can be estimated from RR intervals, based on modeled QT‐RR relationship. An episode onset with higher RS has increased risk of developing into NSVT or VT/VF. (PACE 2011; 700–708)     

Congestive Heart Failure and VVI Pacing Mode: Dynamic Behavior of the Dispersion of Ventricular Repolarization

Dynamic Behavior of the Dispersion of Ventricular Repolarization. The aim of this study was to evaluate the circadian variation in the spatial dispersion of ventricular repolarization in continuously paced patients with congestive heart failure (CHF). Fourteen patients (10 males, 4 females, aged 65 ± 5 years) with CHF due to dilated cardiomyopathy (DCM) and an echocardiographic ejection fraction of 28%± 3% were studied. All patients underwent AV functional RF ablation and permanent pacemaker implantation for drug refractory chronic atrial fibrillation (AF). Patients were evaluated at 1 month postimplant with a three-channel 24-hour Holter monitor, using the three plane Frank orthogonal leads (X, Y, and Z), in VVI pacing mode at 70 beats/min. For each hour, the mean value of spike-T interval dispersion of the first five beats was measured. The control group consisted of 20 patients without structural heart disease, but with AF and complete AV block, continuously paced in WI mode at 70 beats/min. The dispersion of the spike-T interval had a circadian behavior in the study population, with higher values at night and lower during the daytime. During the daytime, the mean value of spike-T interval dispersion was 39 ± 5 ms and during the nighttime it was 45 ± 7 ms (P = 0.003). Such a difference between day and night was not found in the control group (38 ± 6 ms and 40 ± 8 ms, respectively, P = NS), In the daytime period the mean value of spike-T interval dispersion of our study population was comparable to that of the control group (P = NS), while during the nighttime it was significantly higher (P = 0.0004). In conclusion, by evaluating the dispersion of ventricular repolarization in two dimensions, space and time, a circadian variation was found in paced patients with CHF due to DCM. The increased QT dispersion in these patients during the nighttime period was attributed to different effects of vagal activity in normal and abnormal myocardial areas.     

超声引导下经皮心肌内室间隔射频消融术治疗梗阻性肥厚型心肌病不增加心律失常风险：小样本一年随访研究

目的探讨24 h动态心电图评估超声引导下经皮心肌内室间隔射频消融术（PIMSRA,Liwen术式）治疗梗阻性肥厚型心肌病（HOCM）致心律失常风险。 方法选取2016年6月至2018年7月在西京医院行Liwen术式治疗HOCM患者35例,分别在Liwen术式治疗HOCM术前以及术后1年,采用24 h动态心电图获取室性心律失常、房性心律失常以及心率变异性参数,采用配对样本t检验和配对Wilcoxon符号秩和检验比较术前和术后上述参数的变化。 结果消融前后最大心率、最低心率、平均心率,差异均无统计学意义（P均>0.05）;室性早博总数、成对室性早博总、多源室性早博以及Lown′s分级,差异均无统计学意义（P均>0.05）;消融前后室上性早博总数、成对室上性早博总数、室上性心动过速总数,差异均无统计学意义（P均>0.05）;消融前后最大QT以及最大QTc无显著变化,差异均无统计学意义（P均>0.05）;消融前后心率变异性参数,差异均无统计学意义（P>0.05）。 结论Liwen术式治疗HOCM不增加术后短期心律失常风险,其远期风险需要大样本长期观察。     

Predictors of Syncope in Patients with Hypertrophic Cardiomyopathy

Background: Approximately 30% of patients with hypertrophic cardiomyopathy (HCM) suffer syncope and syncope was the only symptom associated with sudden death. However, no systematic studies in large cohorts looking at predictors of syncope are available in the literature. Therefore, we sought to determine predictors of syncope in patients with HCM.
Methods: One hundred and seventy-three consecutive patients with HCM and a mean age of 42 ± 18 years (range 10–78) underwent extensive clinical, electrocardiographic, and echocardiographic testing to identify predictors of syncope.
Results: During the mean follow-up duration of 50 months, syncope occurred in 28% of the HCM patients. Univariate analysis showed male gender, age <40 years, family history of sudden death, PR interval, QRS width, ≥2 bursts of nonsustained ventricular tachycardia (NSVT), ≥3 bursts of nonsustained supraventricular tachycardia (NSSVT), maximum left ventricular wall thickness ≥30 mm, and abnormal blood pressure response, out of 24 demographic, clinical, hemodynamic, electrocardiographic, and echocardiographic features, to be significantly associated with syncope. Of these nine variables, the only independent predictors of syncope at multivariate analysis were age <40 years (odds ratio [OR]: 4.4, 95% confidence interval [CI]: 2.2–16, P = 0.003), ≥2 bursts of NSVT (OR: 9.9, 95% CI: 2.0–46, P = 0.0001), and ≥3 bursts of NSSVT (OR: 2.7, 95% CI: 0.38–8.25, P = 0.001). The concomitant occurrence of all three variables had a sensitivity of 87% and specificity of 73% in identifying the patients with syncopal events.
Conclusions: The results of this study showed that age <40 years, bursts of NSVT, and NSSVT were independently associated with the risk of syncope in patients with HCM. Demographic data and ambulatory ECG findings could help in risk stratification of patients with HCM.     

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.     

Circadian and Sex-Dependent QT Dynamics

The dynamic QT relationship between the QT and RR intervals in normal individuals, including sex differences, has not been well examined. The aim of this Holter monitor-based study was to assess circadian and sex-related variations in QT dynamics in healthy subjects. The study population consisted of 50 healthy volunteers (mean age = 32 ± 6 years, 25 men), in whom 24-hour digital Holter monitoring and QT interactive, beat-by-beat analyses were performed. The mean lengths of QT and RR intervals were measured from the 24-hour recordings. In order to assess QT dynamics, QT/RR linear regression was performed, and the slope was calculated over 24 hour and for day and night periods, and both genders separately. In the whole population, the mean QT interval was 356.5 ± 19.2 ms and RR interval was 785.9 ± 80.7 ms. The mean value of the slope over 24 hour was 0.17 ± 0.03, though significantly steeper during the day (0.13 ± 0.03) than at night (0.09 ± 0.03, P < 0.001). The analysis of QT/RR dynamics over 24 hour revealed a significantly steeper slope in women (0.18 ± 0.03) than in men (0.16 ± 0.03, P = 0.006), as well as during daytime (0.14 ± 0.03 vs 0.12 ± 0.03, P = 0.04). Circadian variations and sex differences were observed in QT dynamics. The latter may explain the greater susceptibility of women to torsades de pointes during treatment with drugs that prolong repolarization.     

New Insight into Repolarization Abnormalities in Patients with Congenital Long QT Syndrome: the Increased Transmural Dispersion of Repoiarization

There is evidence from experimental studies that the time interval from the peak to the end of T-wave reflects the transmural dispersion in repolarization (electrical gradient) between myocardial "layers" (epicardial, M-cells, endocardial). Since Congenital Long QT Syndrome (LQTS) is considered to be classical disease or repolarisation abnormalities, we performed the present study to assess the transmtiral dispersion of repolarization in LQTS patients. The study group consisted of 17 patients: 7 LQTS pts and 10 pts from the control group. In each patient the 24-hour ECG recording was performed on magnetic tape. The interval from the peak to the end of the T-wave (TpTo) was automatically measured by Holter system during every hour as a measure of transmural dispersion of repolarisation. Thereafter the mean TpTo from 24-hours was calculated. In addition the spatial QT dispersion was measured from 12 lead ECG and 3 channel Holter tape as a difference between the shortest and the longest QT interval between leads. The values were compared between groups using the Anova test.
TpTo was 79,6±9,6 ms (72–92 ms) in LQTS group and 62,4±7,5 ms (51–70) in the control group (p< 0.001). In LQTS group TpTo was significantly longer at night hours 72,5±2 when compared to day hours 87,4±8 (p<0.01). The spatial QT dispersion was significantly higher in LQTS patients when compared to control, both in 12-lead standard and Holter ECG.
Congenital long QT syndrome is associated with increase in both transmural and spatial dispersion of repolarization. The extent of prolongation of the terminal portion of QT in patients with congenital long QT syndrome is greater at night sleep hours compared to daily activity.     

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.