U Wave Variability in the Surface ECG

A 72‐year‐old man with heart failure, left ventricular dysfunction (ejection fraction 20%), prior ischemic stroke, COPD, and exacerbation of chronic renal failure was admitted in our unit. Serum potassium was 6.1 mmol/L, calcium concentration was at the lower normal range 2.15 mmol/L, and NT‐pro‐BNP was 28,900 pg/mL. The surface 12‐lead electrocardiogram (ECG) showed sinus rhythm at 60 bpm, PR interval 160 ms, QRS duration 115 ms, QT interval 460 ms, and left ventricular hypertrophy criteria. Negative T waves in leads I, II, aVL, and V₄–V₆ were also seen. In leads V₄–V₆, negative U waves were observed in concordance with negative T waves. In all precordial leads, beat‐to‐beat U‐wave polarity variability was observed as a polarity variation from negative to positive with associated and stable negative T waves, in a beat‐to‐beat alternate morphology.     

Weighing the QT Intervals with the Slope or the Amplitude of the T Wave

Objective: The reproducibility of QT interval measurements is low, even for the mean QT interval based on the standard ECG. In this study we analyzed whether the reproducibility of the mean weighed QT interval was better than the simple mean QT interval. The weighing was based on the amplitude of the T wave or the slope of the steepest tangent on the terminal part of the T wave. Material and methods: 12‐lead ECGs of 130 postmyocardial infarction patients were obtained. The QT intervals were measured by the tangent‐method on two occasions by the same observer Mismatch QT intervals were defined as QT intervals that were measured at only one occasion. Sixteen ECGs were rejected. The data were split into 34 and 80 ECGs for optimization and validation of the weighing, respectively. The weighed QT dispersion was calculated as the weighed mean of the three longest minus the weighed mean of the three shortest QT intervals. Results: Weighing with the slope increased the reproducibility by 41% (P = 3 10^‐6), but weighing with the amplitude reduced it by 20% (P = 0.02). However, if measurements with errors above 75 ms were rejected, weighing with the slope or the amplitude increased the reproducibility with 26% and 20% (P = 0.02), respectively. Weighing did not change the reproducibility of the weighed QT dispersion. Conclusion: Weighing with the slope improved the reproducibility of the mean weighed QT interval. However, if measurements with errors above 75 ms were rejected, weighing with the amplitude also increased the reproducibility. Weighing did not change the reproducibility of the weighed QT dispersion. Weighing is particularly efficient at reducing the negative impact of mismatch QT intervals on the reproducibility. A.N.E. 2002;7(1):4–9     

Increased Chaos of Beat-to-Beat QT Interval Variability in Patients with Congestive Cardiac Failure: Decreased Chaos of QT with Clinical Improvement

There is increasing evidence supporting the additional utility of nonlinear techniques such as chaos analysis of heart rate (HR) time series as indictors of prognosis in cardiac patients. Prolongation of rate-corrected QT interval, QTc, is strongly associated with sudden cardiac death. Recent studies of beat-to-beat QT interval variability (QTV) have shown that an increase in QTV is associated with increased sympathetic activity. QTvi, a QT variability index (QT variance corrected for mean QT divided by HR variance corrected for mean HR), is also a predictor of sudden cardiac death. We studied the utility of a measure of chaos, the Largest Lyapunov Exponent (LLE) of beat-to-beat HR and QT time series at baseline and after treatment in patients with congestive heart failure (CHF). We compared beat-to-beat HR and QT interval data in 23 patients with CHF and 19 age-matched normal controls. The ECG data were acquired in lead II configuration at a sampling rate of 1000 Hz. CHF patients had a significantly lower LLE of HR and a significantly higher LLE of QT time series than did normal controls. Clinical improvement in a subgroup of these patients was associated with a decrease in QT-LLE and a decrease in LLEqthr (LLE-QT/LLE-HR). These results demonstrate a decreased chaos of HR and increased chaos of QT time series in patients with CHF suggesting decreased cardiac vagal and increased sympathetic function in patients with CHF. Nonlinear measures may prove to be of additional utility to linear measures as surrogate end points to evaluate treatment effect in these patients.     

急性心肌梗死患者心室复极变异研究

目的描述急性心肌梗死(AMI)患者24小时心室复极变异性。方法对65例AMI患者和80例正常人行24小时Holter检测,人工编辑QRS-T波群模板,计算机辅助测定QT间期、RR间期、QT变异度(QTV)、心率变异性SDNN,计算QT变异系数(QTCV)、及QT变异度指数(QTVI)。结果①AMI组较正常对照组平均心率减慢(68.02±12.01bpmvs.73.57±7.65bpm,P<0.01),平均QT间期延长(382.96±37.07msvs.367.66±25.58ms,P<0.05),而两组QTc无显著差异(405.13±19.87ms,vs.404.1±18.65ms,P>0.05)。②AMI组24hQTV和QTCV显著低于正常对照组(25.03±9.91msvs.29.95±7.27ms,P<0.01;0.066±0.03vs.0.081±0.02,P<0.01)。③AMI组24小时QTVI较正常组显著增高(-0.45±0.41vs.-0.76±0.25,P<0.01)。结论AMI患者较正常对照组全天QT变异度和QT变异系数显著降低,可能与交感神经受损、心率变异降低有关。去除心率变异影响后,AMI患者QT变异度指数增高,心室复极变异增大。推测AMI造成的心肌缺血和心肌坏死,导致心室复极变异增大。QTVI可能是一个新的AMI电生理紊乱预测指标。     

运动试验QT离散度变化与心肌缺血或T波改变相关性的研究

目的 :探讨运动试验QT离散度 (QTd)变化与心肌缺血和T波变化的相关性及评价QTd的临床应用价值。方法 :2 4 2例经冠脉造影证实冠心病而静息心电图正常 ,平板运动试验阳性 (冠心病组 )和 16 8例静息心电图有T波低平、双向、倒置或有u波 ,平板运动试验心电图正常 ,并经冠脉造影及其他检查排除器质性心脏病 (非器质性心脏病组 )。观察两组平板运动试验QTd的变化与心肌缺血和T波变化的相关性。结果 :设QTd >5 0ms为异常 ,冠心病组运动前QTd异常率为18% ,运动后为 80 % ;非器质性心脏病组运动前QTd异常率为 84 % ,运动后为 12 %。QTd的变化与T波改变相关 ,r=0 .86 ,P <0 .0 1;与冠心病运动后单纯缺血性ST段下移无相关性。结论 :运动试验QTd变化与心肌缺血无相关性 ,QTd异常不能判断心肌复极不均一性进而预测恶性心律失常或心脏猝死 ,而只是反映T波非特异性异常的一个粗浅的量化指标     

Relation between Beat‐to‐Beat QT Interval Variability and T‐Wave Amplitude in Healthy Subjects

Objectives: Elevated beat‐to‐beat QT interval variability (QTV) has been associated with increased cardiovascular morbidity and mortality.The aim of this study was to investigate interlead differences in beat‐to‐beat QTV of 12‐lead ECG and its relationship with the T wave amplitude. Methods: Short‐term 12‐lead ECGs of 72 healthy subjects (17 f, 38 ± 14 years; 55 m, 39 ± 13 years) were studied. Beat‐to‐beat QT intervals were extracted separately for each lead using a template matching algorithm. We calculated the standard deviation of beat‐to‐beat QT intervals as a marker of QTV as well as interlead correlation coefficients. In addition, we measured the median T‐wave amplitude in each lead. Results: There was a significant difference in the standard deviation of beat‐to‐beat QT intervals between leads (minimum: lead V₃ (2.58 ± 1.36 ms), maximum: lead III (7.2 ± 6.4 ms), ANOVA: P < 0.0001). Single measure intraclass correlation coefficients of beat‐to‐beat QT intervals were 0.27 ± 0.18. Interlead correlation coefficients varied between 0.08 ± 0.33 for lead III and lead V₁ and 0.88 ± 0.09 for lead II and lead aVR. QTV was negatively correlated with the T‐wave amplitude (r =–0.62, P < 0.0001). There was no significant affect of mean heart rate, age or gender on QT variability (ANOVA: P > 0.05). Conclusions: QTV varies considerably between leads in magnitude as well as temporal patterns. QTV is increased when the T wave is small.     

QRS Amplitude of ECG in Normal Humans: Effects of Orthostatic Challenge on Linear and Nonlinear Measures of Beat-to-Beat Variability

When respiratory signal is not available, it can be derived from the surface electrocardiogram (ECG) with some limitations. This is particularly useful to understand the contribution of respiratory variability in several conditions where there is an increased risk of cardiovascular mortality. ECG-derived respiratory signal is also more valuable in situations of 24-h ECG records, where the continuous respiratory signal is not usually available. We have previously shown that respiratory variability in tidal volume significantly increases during standing posture compared to supine posture. In this study, we obtained respiratory signal derived from the ECG in 17 normal adult controls without a history of heart disease and quantified the time of occurrence of peaks and amplitudes or the QRS complex and performed cross-spectral analysis between R-R (interbeat) interval and the QRS-amplitude time series sampled at 4 Hz. Our findings show that the supine QRS amplitude HF power (0.15–0.5 Hz) correlates significantly with the R-R HF power (r (0.62; n (17; p ((0.004). However, this was negatively correlated in standing posture (r (−0.5; n (17; p (0.04). While there was a significant decrease of R-R HF power upon standing (p(0.01), there was a significant increase in QRS amplitude HF power (p (0.004). These findings indicate that the variability of QRS amplitude behaves differently in standing posture compared to R-R time series and thus the supine QRS amplitudinal changes may reflect more closely, the respiratory variability. These findings are discussed in relation to the increased QRS amplitude variability in conditions such as coronary artery disease and other populations at risk for increased cardiac mortality.     

应用体表心电图测定QT离散度的错误概念及其理由的探讨

目的　自Ｃａｍ ｐｂｅｌｌ等提出ＱＴ离散度（ＱＴｄ）以来,临床上普遍采用,用心电图（ＥＣＧ）来测ＱＴ间期,其有长短,只因心向量（ＶＣＧ）在某个导联轴上的投影量不同所致,并不能代表某局部的ＱＴ间期,因此有必要深入探讨。方法　选择临床诊断明确的数千例同时有ＥＣＧ和ＶＣＧ者,从中选出有ＱＴｄ 异常者（≥５０ ｍ ｓ）和长ＱＴ者１００ 例。结果　１．ＱＴｄ 异常可见于正常人,儿童老年均可。２．ＱＴｄ异常受心率影响很大,心率慢时有异常ＱＴｄ,而心率增快时ＱＴｄ 可转为正常。３．ＱＴｄ 异常与有无恶性室性心律失常无关,而与其ＱＴ 是否延长密切相关。结论　我们认为测量ＱＴ间期并分析其ＥＣＧ 和ＶＣＧ应密切结合临床,目前对ＱＴｄ 的分析应慎重,不宜滥用     

Seasonal Variability of QT Dispersion in Healthy Young Males

Background: There are few data related to the seasonal influences on the QT dispersion. Methods: We analyzed the effects of seasons on QT dispersion in a large group of healthy young males. We studied the seasonal variability of QT dispersion in 523 healthy male subjects aged 22 ± 4 years (ranging from 20 to 26). Four seasonal 12‐lead resting electrocardiograms (ECGs) recorded at double amplitude were performed at 25 mm/s at intervals of 3 months. Subsequent ECGs were recorded within 1 hour of the reference winter recording. QT dispersion was defined as the difference between the longest and the shortest mean QT intervals. Results: There was a significant seasonal variation in QT dispersion (P = 0.001) , with the largest QT dispersion in winter (71 ± 18 ms) and the smallest one in spring (43 ± 19) . Conclusion: There exists a significant seasonal variation in QT dispersion of healthy subjects and such variability should be taken into consideration in the evaluation process of QT dispersion.     

Reproducibility of Minimum,Maximum and Median QT Intervals in the 12‐Lead Resting ECG

Background: Heterogeneity in the recovery of ventricular refractory periods is an important factor in the development of ventricular arrhythmia. The QT dispersion (QTD) is increasingly used to measure this heterogeneity but its clinical value is limited due to methodological problems. QTD is defined as the maximum minus the minimum QT intervals that are suspected to be the least reproducible of the QT measurements. Objective: To analyze the reproducibility of the minimum, maximum and median QT intervals. Material: One database consisted of 356 subjects: 169 with diabetes and 187 nondiabetic control persons. The other database consisted of 110 subjects with remote myocardial infarction: 55 with no history of arrhythmia, and 55 with a recent history of ventricular tachycardia or fibrillation. Methods: 12‐lead surface ECGs were recorded with an amplification of 10 millimeters per millivolt at a paper speed of 50 mm/s. QT was measured manually by the tangent‐method. The reproducibility was calculated from measurements of QT in successive beats. Results: The standard deviation (SD) of QTs reproducibility was 9 ms for the arrhythmia data and 8 ms for the diabetes data. The reproducibility of QT_max and QT_min were on average 30% and 15% worse than for QT_median. The SD of QT_max was significantly higher than for QT_median in both database (P < 0.001), whereas SD of QT_min was only significantly higher than for QT_median for the diabetes data (P < 0.001). Conclusions: The reproducibility of QT_min and in particular QTmax was significantly lower than for QT_median. This indicates that the QT dispersion is based on the least reproducible of the QT measurements. A.N.E. 2000;5(4):354–357     

Reproducibility,Circadian Variability,and Limit Values of Ventricular Late Potentials in Healthy Men

Objectives: The aim of the study was to examine the reproducibility of late potential parameters over time and to assess the influence of circadian rhythm, type of activity (rest, exercise) and autonomous state on these parameters in healthy subjects. Background: Late potentials are used as a marker for an elevated arrhythmic risk in patients after myocardial infarction. The method is increasingly used in cardiovascular hospital departments. However, the relatively high percentage of false-positive results compared to the outcome of electrophysiological testing precludes its more general use. Methods: In a population of healthy volunteers, the normal values, the reproducibility, and the dependence from a circadian rhythm of ventricular late potentials were examined. The dependence of the late potentials from the type of activity was studied. Results: The limit values of the late potential parameters found in this study did not differ from the proposed standard limits in the Euro-American guidelines. Circadian variability of heart rate and duration of QRS and QT-interval were documented. No circadian variation was found in the late potential parameters in the subjects studied. The values for late potential parameters did not significantly differ in measurements repeated after 24 hours and 7 days, thus resulting in good reproducibility. The heart rate changes induced by ergometry and autonomous blockade had no influence on late potential parameters. Conclusions: Late potential parameters are reproducible and are not changed significantly by circadian rhythm, type of activity, or autonomous state in these healthy volunteers.     

Power Spectral Changes of Spontaneous Beat-to-Beat Variability of the RT Interval in Patients with Coronary Artery Disease

Objective: This study sought to evaluate the spontaneous beat-to-beat variability of the RT interval (RTV) as a marker of autonomic balance at the ventricle in patients with coronary artery disease (CAD), as heart rate variability (HRV) primarily reflects sympathovagal interactions at the sinus node. Methods: ECG and peripheral blood pressure signals were analyzed in supine and passive head-up tilt in 19 patients with CAD. RT intervals were measured between the maximum of the QRS complex and the maximum of the T wave. Power spectral analysis of RR intervals, RT intervals, systolic and diastolic pressure were performed using discrete Fourier transformation. We calculated the area under the spectral density curve in the low (LF = 0.05–0.18 Hz) and high frequency range (HF = 0.18–0.50 Hz). Results: Tilting results in a decrease of HF in HRV to 45%± 10% (P < 0.05) and an increase of HF in RTV to 266%± 83% (P < 0.01). Total RTV was 2.4% of total HRV. In systolic blood pressure variability HF increased to 396%± 124% (P < 0.05), in diastolic blood pressure variability to 231%± 69% (P < 0.05). Conclusion: If the transfer-function of sympathetic activity to the ventricle and to the sinus node are similar, the increase of HF in RTV cannot be explained by the increase in sympathetic activity induced by tilting. It is most likely a mechanical phenomenon induced by respiration synchronous changes of the position of the heart in the thorax and transferred variabilities of the central venous pressure that can also be identified in systolic and diastolic pressure variabilities.     

Spatial Properties of QT and the T‐Wave Morphology

Objective: To describe the relation between the QT interval and the T‐wave morphology. Material and methods: Frank orthogonal leads X, Y, Z of one subject and resting 12‐lead ECG of 40 subjects. QT was measured by the tangent method. The QT values are organized according to the anatomic orientation of the leads: I, ‐aVR, II, aVF, III, ‐aVL, ‐I, aVR, ‐II, ‐aVF, ‐III, aVL. and: V₁, V₂, V₃, V₄, V₅, V₆, ‐V₁ ‐V₂, ‐V₃, ‐V₄, ‐V₅, ‐V₆. The T‐wave amplitudes and QT were categorized according to QT into four groups with increasing mean QT. Results: Kruskal‐Wallis nonparametric test showed that the shortest and longest QT values are measured on the T wave with the smallest amplitudes (P < 0.001). Inspection of plots of QT and T waves reveals that the shortest and longest QT values are usually measured in leads with a small difference in orientation (neighbor leads). The mechanism behind these characteristics is mainly that the shortest and longest QT values are measured on T waves that are close to a lead orientation, whereas the T waves are flat or biphasic. We also observed an almost significant (P = 0.057) decrease in the T‐wave amplitude with increasing dispersion. Conclusion: The relation between T‐wave morphology and QT in the same cardiac plane is highly organized. The shortest and longest QT values are measured on the T wave with the smallest amplitudes (P < 0.001).     

Circadian Pattern of the QT Dispersion Using Three Orthogonal Leads of a Holter ECG in Patients with Heart Failure

This study evaluated: (1) if three orthogonal leads (3-OL) can provide the same information about QT dispersion (QT-D) as 12-lead ECG; (2) the circadian pattern of QT-D adopting 3-OL during 24-hour Holter monitoring; (3) if the QT-D circadian pattern is influenced by therapy. In the first part of the study, we evidenced a significant direct correlation (r = 0.91; P < 0.0005) between QT-D values of 12 ECG leads and of 3-OL simultaneously recorded in 15 normal subjects and 11 patients with myocardial infarction. The second part of the study evaluated the circadian pattern of QT-D adopting 3-OL during Holter (ELA Medical, Mod. Synesis) monitoring in 15 patients with congestive heart failure (CHF: aged 73 ± 8 yrs. III NYHA) in pharmacological washout and after 10 days of therapy (furosemide, digoxin, captopril) and in 15 age-matched normal subjects (N: aged 70 ± J yrs). Mean QT-D values of CHF before therapy were significantly higher at each hour than those of N (always P < 0.001). Mean hourly QT-D values after therapy were significantly lower than those before therapy (P < 0.03 up to P < 0.001), except for the value at 9:00 A.M. Our results suggest that: (1) 3-OL can evaluate QT-D as much as the usual 12-lead ECG; (2) the use of 3-OL during Holter monitoring allows the evaluation of the QT dispersion circadian pattern both in N and in CHF; and (3) therapy is able to modify the circadian pattern of QT-D.     

Assessment of Physiological Amplitude,Duration, and Magnitude of ECG T‐Wave Alternans

Background: An association between T‐wave alternans (TWA) and malignant ventricular arrhythmias is generally recognized. Because relatively low levels of TWA have also been observed in healthy (H) subjects, the question arises as to whether these are ascribable to noise and artifacts, or can be given the relevance of a physiological phenomenon characterizing a preclinical condition. Methods: To answer this question, in the present study 20‐minute not noisy, sinus ECG recordings, from 138 H‐subjects and 148 coronary artery diseased (CAD) patients, were submitted to our adaptive match filter (AMF) procedure to identify and parameterize TWA in terms of duration (TWAD), amplitude (TWAA), and magnitude (TWAM, defined as the product of TWAD times TWAA). The 99.5th percentiles of mean values of TWAA, TWAD, and TWAM over 20‐minute ECGs were used to define three threshold levels (THRD, THRA, and THRM), which allow discrimination of abnormal TWA levels. Results: Nonstationary TWA was found in all our H‐subjects and CAD‐patients. TWAD, TWAA, and TWAM levels were classified as being physiological in 99% of H‐subjects and 87% of CAD‐patients. A linear correlation (r =?0.52, P < 0.001) was found between TWAA and RR interval in the H‐population. Conclusions: Our results support the hypothesis of the existence of physiological TWA levels, which are to be considered in the effort to improve reliability of nonphysiological TWA levels discrimination.     

Impact of Left Ventricular Remodeling on Ventricular Repolarization and Heart Rate Variability in Patients after Myocardial Infarction Treated with Primary PCI: Prospective 6 Months Follow‐up

Background: The relation between postinfarction left ventricle remodeling (LVR), autonomic nervous system and repolarization process is unclear. Purpose of the study was to assess the influence of LVR on the early (QTpeak) and late (TpeakTend) repolarization periods in patients after myocardial infarction (MI) treated with primary PCI. The day‐to‐night differences of repolarization parameters and the relation between QT and heart rate variability (HRV) indices, as well left ventricle function were also assessed. Methods: The study cohort of 104 pts was examined 6 months after acute MI. HRV and QT indices (corrected to the heart rate) were obtained from the entire 24‐hour Holter recording, daytime and nighttime periods. Results: LVR was found in 33 patients (31.7%). The study groups (LVR+ vs LVR?) did not differ in age, the extent of coronary artery lesions and treatment. Left ventricle ejection fraction (LVEF) was lower (38%± 11% vs 55%± 11%, P < 0.001), both QTc (443 ± 26 ms vs 420 ± 20 ms, P < 0.001) and TpeakTendc (98 ± 11 ms vs 84 ± 12 ms, P < 0.005) were longer in LVR + patients, with no differences for QTpeakc. Trends toward lower values of time‐domain (SDRR, rMSSD) HRV parameters were found in LVR+ pts. Day‐to‐night difference was observed only for SDRR, more marked in LVR‐group. Remarkable relations between delta LVEF (6 months minus baseline), delta LVEDV and TpeakTendc were found, with no such relationships for QTpeakc. Conclusions: The patients with LVR have longer repolarization time, especially the late phase‐ TpeakTend, which represents transmural dispersion of repolarization. Its prolongation seems to be related to local attributes of myocardium and global function of the left ventricle but unrelated to the autonomic nervous influences. Remodeling with moderate LV systolic dysfunction is associated with insignificant decrease in HRV indices and preserved circadian variability.     

Beat‐to‐Beat QT Interval Variability Is Primarily Affected by the Autonomic Nervous System

Background : Beat‐to‐beat QT interval variability is associated with life‐threatening arrhythmias and sudden death, however, its precious mechanism and the autonomic modulation on it remains unclear. The purpose of this study was to determine the effect of drugs that modulate the autonomic nervous system on beat‐to‐beat QT interval. Method : RR and QT intervals were determined for 512 consecutive beats during fixed atrial pacing with and without propranolol and automatic blockade (propranolol plus atropine) in 11 patients without structural heart disease. Studied parameters included: RR, QTpeak (QRS onset to the peak of T wave), QTend (QRS onset to the end of T wave) interval, standard deviation (SD) of the RR, QTpeak, and QTend (RR‐SD, QTpeak‐SD, and QTend‐SD), coefficients of variation (RR‐ CV, QTpeak‐CV, and QTend‐CV) from time domain analysis, total power (TP; RR‐TP, QTpeak‐TP, and QTend‐TP), and power spectral density of the low‐frequency band (LF; RR‐LF, QTpeak‐LF, and QTend‐LF) and the high‐frequency band (HF; RR‐HF, QTpeak‐HF and QTend‐HF). Results : Administration of propranolol and infusion of atropine resulted in the reduction of SD, CV, TP, and HF of the QTend interval when compared to controlled atrial pacing (3.7 ± 0.6 and 3.5 ± 0.5 vs 4.8 ± 1.4 ms, 0.9 ± 0.1 and 0.9 ± 0.1 vs 1.2 ± 0.3%, 7.0 ± 2.2 and 7.0 ± 2.2 vs 13.4 ± 8.1 ms², 4.2 ± 1.4 and 4.2 ± 1.2 vs 8.4 ± 4.9 ms², respectively). Administration of propranolol and atropine did not affect RR interval or QTpeak interval indices during controlled atrial pacing. Conclusions : Beat‐to‐beat QT interval variability is affected by drugs that modulate the autonomic nervous system.     

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.     

Postmyocardial Infarction Patients Susceptible to Ventricular Tachycardia Show Increased T Wave Dispersion Independent of Delayed Ventricular Conduction

Arrhythmia Markers After Myocardial Infarction. Introduction: Experimentally, both delayed ventricular conduction and nonhomogeneous ventricular repolarization contribute to reentrant arrhythmias. We tested the hypothesis that increased T wave dispersion is independent of delayed ventricular conduction associated with arrhythmia vulnerability in postmyocardial infarction (post-MI) patients.
Methods and Results: We studied 32 post-MI patients with clinical or inducible monomorphic ventricular tachycardia (VT group), 28 post-MI patients without arrhythmias (MI group), and 13 healthy controls, using magnetocardiographic (MCG) mapping with signal averaging. Twelve-lead ECG was the reference. Filtered QRS duration (fQRS) and T wave peak to T wave end interval (TPE) were used as measures of ventricular conduction and nonhomogeneity in ventricular repolarization, respectively. In MCG, the VT group showed the longest fQRS (  135 ± 34  msec vs  114 ± 22  msec in the MI group;  P = 0.012  ). Mean TPE and maximum TPE in VT versus MI groups were  78 ± 9  msec versus  70 ± 6  msec (  P < 0.001  ) and  117 ± 23  msec versus  104 ± 19  msec (  P = 0.020  ), respectively. Maximum TPE did not correlate with fQRS in the VT group (  r = 0.063; P = NS  ) but did correlate in the MI group (  r = 0.396; P = 0.037  ). For identification of post-MI patients prone to VT, selection of cutoff values for fQRS > 140 msec and mean TPE > 81 msec gave sensitivity and specificity of 41% and 89%, and 31% and 96%, respectively. Their combination increased sensitivity to 63% while maintaining 89% specificity.
Conclusion: Post-MI patients susceptible to VT show increased T wave dispersion independent of delayed ventricular conduction.     

Evaluation of QT Interval Dispersion in a Multiple Electrodes Recording System versus 12‐Lead Standard ECG in an In Vitro Model

Background: QT interval dispersion (QTID) as assessed on conventional surface electrocardiogram (ECG) has been used as a clinical tool to identify patients at high risk of ventricular arrhythmia. However, the results obtained have been controversial. The main purpose of this study was to compare QTID measured from an array of 5 × 6 electrodes homogeneously distributed against the values found when the 12‐lead standard ECG was used. Methods: QTID was calculated in a modified Langendorff‐perfused rabbit heart model immersed in a cylindrical chamber. Dispersion in ventricular repolarization was artificially increased by d‐sotalol (60 μ;m) perfusion. Results: All the duration variables measured from any of the lead systems used were significantly increased after d‐sotalol perfusion. The most commonly used variables in clinical studies, such as QTID (maximum ‐ minimum), do not reach a level of statistical significance, except when measured from the 30‐electrodes array or 15 electrodes covering the left or right side of the heart. The standard deviation of the QT interval (QTI) hardly reached a significant level (P = 0.0499) when calculated from the 12‐lead standard ECG. QTID measured at the peak of the T wave exhibited the highest level of significance when calculated from any of the lead systems used. Conclusion: Thirty electrodes homogeneously distributed on the body surface can better discriminate changes in heterogeneity of repolarization. These data further support the importance of multiple recording systems for the evaluation of QTID and may help to provide an understanding of the discrepancies found in clinical applications.