Comparative reproducibility of QT, QT peak, and T peak-T end intervals and dispersion in normal subjects, patients with myocardial infarction, and patients with hypertrophic cardiomyopathy

The Effect of Low-Flow and Normal-Flow Desflurane Anesthesia on the Frontal QRS-T Angle in Patients Undergoing Rhinoplasty Operation: A Randomized Prospective Study

Introduction: Low-flow anesthesia (LFA) has gained more interest worldwide owing to its economic and ecological advantages compared to normal-flow anesthesia (NFA). Desflurane is one of the commonly used anesthetic agents for LFA, but it may prolong myocardial repolarization. Frontal QRS-T angle (f[QRS-T]a) is a novel marker of myocardial repolarization. To our knowledge, no study has compared the effect of LFA and NFA on f(QRS-T)a. In this study, we aimed to compare the effect of the LFA and NFA with desflurane on f(QRS-T)a in patients undergoing rhinoplasty operation.

Methods: A total of 80 patients undergoing rhinoplasty operations were included in this prospective study. The patients were randomized into two groups as follows: LFA (n = 40) and NFA (n = 40). The frontal QRS-T angle was calculated from the automatic report of the electrocardiography device (Nihon Kohden, Tokyo, Japan). It was recorded at the following time points: T1: preoperative (basal), T2: immediately after anesthesia induction, T3: immediately after endotracheal intubation, T4: 5 min after endotracheal intubation, T5: 15 min after endotracheal intubation, T6: 30 min after endotracheal intubation, T7: 60 min after endotracheal intubation, T8: end of the operation, T9: 15 min after the end of the operation.

Results: Baseline clinical characteristics and laboratory parameters were similar between the two groups. In the LFA group, f(QRS-T)a was significantly increased at only the T3 time point when compared to T1 (P = 0.003). However, in the NFA group, f(QRS-T)a was significantly increased at T3, T4, T5, T6, T7, T8, and T9 time points when compared to the T1 value (P < 0.05, for all). On the other hand, fQRS-Ta was significantly higher in the NFA group than in the LFA group at T4, T5, and T6 time points. 

Conclusion: In our study, we have shown for the first time that NFA significantly increased the f(QRS-T)a, whereas LFA did not significantly increase the f(QRS-T)a except for immediately after the endotracheal intubation. It was also detected that f(QRS-T)a was significantly higher in the NFA group compared to that in the LFA group. Therefore, it can be concluded that LFA has more protective effects on myocardial repolarization than NFA.

Can QT dispersion improve the accuracy of stress ECG TMT in detecting myocardial ischemia in chronic stable CAD patients? A stress myocardial perfusion imaging study

BACKGROUND

QT dispersion (QTd) is related to regional variations in myocardial repolarization. Our study aims to assess the value of QTd in prediction of myocardial ischemia and its severity during stress imaging. We enrolled one hundred patients having stable coronary artery disease (CAD) and fulfilling the "Appropriateness criteria for cardiac radionuclide imaging" (MPI). They were divided into group I including patients with MPI-detected ischemia (50 patients) and group II including patients with normal perfusion scan (50 patients). We excluded unstable CAD and all other causes affecting QTd. During isotope scan, ECGs were taken and QTd was calculated at rest and at maximum heart rate.

RESULTS

QTd was significantly higher in the ischemic group both at rest and exercise (P = 0.000). QTd difference, the difference between QTd at rest and stress, was calculated. QTd difference was significantly lower in normal than in ischemic group (P = 0.003). There was a significant positive correlation between QTd difference and defect size (P = 0.04).

CONCLUSION

QTd increases in ischemia and the QTd difference (between rest and stress) correlates positively with severity of ischemia. QTd and QTd difference could be used to improve the accuracy of stress imaging test.

Reproducibility and Reliability Of QTc and QTcd Measurements and Their Relationships with Left Ventricular Hypertrophy in Hemodialysis Patients

Background

Left ventricular hypertrophy (LVH) is very common in hemodialysis patients and an independent risk factor for mortality in this population. The myocardial remodeling underlying the LVH can affect ventricular repolarization causing abnormalities in QT interval.

Objective

to evaluate the reproducibility and reliability of measurements of corrected QT interval (QTc) and its dispersion (QTcd) and correlate these parameters with LVH in hemodialysis patients.

Methods

Case-control study involving hemodialysis patients and a control group. Clinical examination, blood sampling, transthoracic echocardiogram, and electrocardiogram were performed. Intra- and interobserver correlation and concordance tests were performed by Pearson´s correlation, Cohen’s Kappa coefficient and Bland Altman diagram. Linear regression was used to analyze association of QTc or QTcd with HVE.

Results

Forty-one HD patients and 37 controls concluded the study. Hemodialysis patients tended to have higher values of QTc, QTcd and left ventricular mass index (LVMi) than controls but statistical significance was not found. Correlation and concordance tests depicted better results for QTc than for QTcd. In HD patients, a poor but significant correlation was found between QTc and LVMi (R² = 0.12; p = 0.03). No correlation was found between values of QTcd and LVMi (R²= 0.00; p=0.940). For the control group, the correspondent values were R²= 0.00; p = 0.67 and R²= 0.00; p = 0.94, respectively.

Conclusion

We found that QTc interval, in contrast to QTcd, is a reproducible and reliable measure and had a weak but positive correlation with LVMi in HD patients.

Evaluating ECG and carboxyhemoglobin changes due to smoking narghile

PURPOSE

This study aimed to investigate whether increased carboxyhemoglobin (COHB) levels and ECG changes, which associated with fatal ventricular dysrhythmias, including increased QT, P-wave and T peak (Tp)-Tend (Te) dispersion, can be detected after smoking narghile, which is a traditional method of smoking tobacco that is smoked from hookah device.

MATERIALS AND METHODS

After local ethics committee approval, this prospective study was conducted using healthy volunteer subjects at a "narghile café," which is used by people smoking narghile in an open area. Before beginning to smoke narghile, all subjects' 12-lead electrocardiographs (ECG), measurements of COHB levels, and vital signs were recorded. After smoking narghile for 30 min, the recording of the 12-lead ECGs and the measurements of COHB level and all vital signs were repeated.

RESULTS

The mean age of subjects was 26.8 ± 6.2 years (min-max: 18-40), and 28 subjects (84.8%) were male. Before smoking narghile, the median value of subjects' COHB levels was 1.3% (min-max: 0-6), whereas after smoking, the median value of COHB was 23.7% (min-max: 6-44), a statistically significant increase (p < 0.001). Analysis of the subjects' ECG changes after smoking narghile showed that dispersions of QT, QTc, P-wave and Tp-Te were increased, and all changes were statistically significant (p < 0.001 for all parameters).

CONCLUSION

Although, especially among young people, it is commonly thought that smoking narghile has less harmful or toxic effects than other tobacco products. The results of this study and past studies clearly demonstrated that smoking narghile can cause several ECG changes - including increased QT, P-wave and Tp-Te dispersion - which can be associated with ventricular dysrhythmias.

Cardiomyopathy confers susceptibility to particulate matter-induced oxidative stress, vagal dominance, arrhythmia and pulmonary inflammation in heart failure-prone rats

Acute exposure to ambient fine particulate matter (PM2.5) is tied to cardiovascular morbidity and mortality, especially among those with prior cardiac injury. The mechanisms and pathophysiological events precipitating these outcomes remain poorly understood but may involve inflammation, oxidative stress, arrhythmia and autonomic nervous system imbalance. Cardiomyopathy results from cardiac injury, is the leading cause of heart failure, and can be induced in heart failure-prone rats through sub-chronic infusion of isoproterenol (ISO). To test whether cardiomyopathy confers susceptibility to inhaled PM2.5 and can elucidate potential mechanisms, we investigated the cardiophysiologic, ventilatory, inflammatory and oxidative effects of a single nose-only inhalation of a metal-rich PM2.5 (580 µg/m(3), 4 h) in ISO-pretreated (35 days × 1.0 mg/kg/day sc) rats. During the 5 days post-treatment, ISO-treated rats had decreased HR and BP and increased pre-ejection period (PEP, an inverse correlate of contractility) relative to saline-treated rats. Before inhalation exposure, ISO-pretreated rats had increased PR and ventricular repolarization time (QT) and heterogeneity (Tp-Te). Relative to clean air, PM2.5 further prolonged PR-interval and decreased systolic BP during inhalation exposure; increased tidal volume, expiratory time, heart rate variability (HRV) parameters of parasympathetic tone and atrioventricular block arrhythmias over the hours post-exposure; increased pulmonary neutrophils, macrophages and total antioxidant status one day post-exposure; and decreased pulmonary glutathione peroxidase 8 weeks after exposure, with all effects occurring exclusively in ISO-pretreated rats but not saline-pretreated rats. Ultimately, our findings indicate that cardiomyopathy confers susceptibility to the oxidative, inflammatory, ventilatory, autonomic and arrhythmogenic effects of acute PM2.5 inhalation.

Negative effects of acute sleep deprivation on left ventricular functions and cardiac repolarization in healthy young adults

BACKGROUND

Sleep deprivation (SD) is associated with an increased incidence of adverse cardiovascular events, we aimed to determine the impact of acute SD on structural and functional alterations of the left ventricle (LV) and on electrocardiogram (ECG) markers including T wave peak-to-end interval (TpTe), QT interval, and TpTe/QT ratio in healthy subjects after a night of SD.

METHODS

The study population consisted of 40 healthy young adults (19 males, 21 females; mean age: 28.2 ± 3.86 years). Echocardiographic images and ECGs were obtained from the participants after a night of regular sleep (RS) and SD. The average sleep time of the subjects was 6.67 ± 1.76 hours during RS and 1.25 ± 0.74 hours during a night of SD.

RESULTS

The myocardial performance index, isovolumic relaxation time, and deceleration time values were significantly higher after SD. In addition, the corrected TpTe interval, corrected QT interval (QTc) max, and TpTe/QT ratio were significantly increased after a night of SD when compared with a night of RS (78.5 ± 6.8 ms vs 70.7 ± 7.6 ms, P < 0.001; 407.5 ± 18.6 ms vs 395.07 ± 21.3 ms, P = 0.001; and 0.189 ± 0.014 ms vs 0. 0.179 ± 0.016 ms, P < 0.001, respectively). However, subjects had similar QTp interval values (defined as beginning of the QRS complex to peak of the T wave) after a night of SD as a night of RS (294.6 ± 19.0 vs 291.9 ± 18.5, P = 233).

CONCLUSION

Our crossover study revealed the presence of subclinical LV diastolic functional changes and increased QT intervals, TpTe intervals, and TpTe/QT ratios in healthy young adults after one night SD. Therefore, the increased QT interval occurred secondary to the increased TpTe interval in this population.

New markers for ventricular repolarization in coronary slow flow: Tp-e interval, Tp-e/QT ratio, and Tp-e/QTc ratio

BACKGROUND

Coronary slow flow (CSF) is characterized by normal or near-normal coronary arteries with delayed opacification of the distal vasculature that it may cause angina pectoris, acute myocardial infarction, life-threatening arrhythmias, and sudden cardiac death. The Tp-e interval, Tp-e/QT ratio, and Tp-e/QTc ratio are also known as predictors of ventricular arrhythmogenesis. The aim of this study was to assess ventricular repolarization in patients with CSF by using Tp-e interval, Tp-e/QT ratio, and Tp-e/QTc ratio.

METHODS

This study included 50 patients with CSF and 51 control subjects. Coronary flow rates of all subjects were documented by thrombolysis in myocardial infarction (TIMI) frame count (TFC). Tp-e interval, Tp-e/QT ratio, and Tp-e/QTc ratio were measured from the 12-lead electrocardiogram. These parameters were compared between groups.

RESULTS

In electrocardiographic parameters analysis, QT, QTc, QTd, and QTcd were significantly increased in CSF patients compared with the control subjects (P < 0.001, P = 0.019, P < 0.001, P < 0.001, respectively). The Tp-e interval, Tp-e/QT ratio, and Tp-e/QTc ratio in the CSF patients were significantly higher than those in the control subjects (Tp-e: 117 ± 21 milliseconds [ms] vs 96 ± 16 ms, P < 0.001; Tp-e/QT: 0.30 ± 0.06 vs 0.27 ± 0.06, P = 0.005; Tp-e/QTc: 0.27 ± 0.06 vs 0.24 ± 0.05, P < 0.001). In the multivariate analysis, increased Tp-e and Tp-e/QT ratio were associated with CSF.

CONCLUSIONS

Our study revealed that when compared to the control subjects, Tp-e interval, Tp-e/QT ratio, and Tp-e/QTc were significantly increased in the CSF patients.

Evaluation of ventricular repolarization dispersion during acute myocardial ischemia: spatial and temporal ECG indices

In this work, we studied the evolution of different electrocardiogram (ECG) indices of ventricular repolarization dispersion (VRD) during acute transmural myocardial ischemia in 95 patients undergoing percutaneous coronary intervention (PCI). We studied both temporal indices of VRD (T-VRD), based on the time intervals of the ECG wave, and spatial indices of VRD (S-VRD), based on the eigenvalues of the spatial correlation matrix of the ECG. The T-wave peak-to-end interval I(TPE) index showed statistically significant differences during left anterior descending artery and right coronary artery (RCA) occlusion for almost the complete time course of the PCI procedure with respect to the control recording. Regarding S-VRD indices, we observed statistically significant increases in the ratio of second to the first eigenvalue I(T21), the ratio of the third to the first eigenvalue I(T31) and the T-wave residuum I(TWR) during RCA occlusions. We also found a statistically significant increase in the I(T31) during left circumflex artery occlusions. To evaluate the evolution of VRD indices during acute ischemia, we calculated the relative change parameter R(I) for each index I. Maximal relative changes (R(I)) during acute ischemia were found for the S-VRD indices I(T21), the first eigenvalue I(λ1) and the second eigenvalue I(λ2), with changes 64, 57 and 52 times their baseline range of variation during the control recording, respectively. Also, we found that relative changes with respect to the baseline were higher in patients with T-wave alternans (TWA) than in those without TWA. In conclusion, results suggest that I(TPE) as well as I(T21), I(T31) and I(TWR) are very responsive to dispersion changes induced by ischemia, but with a behavior which very much depends on the occluded artery.

Sex differences in cardiac autonomic regulation and in repolarisation electrocardiography

The review summarises the present knowledge on the sex differences in cardiac autonomic regulations and in related aspects of electrocardiography with particular attention to myocardial repolarisation. Although some of the sex differences are far from fully established, multitude of observations show consistent differences between women and men. Despite more pronounced parasympathetic cardiac regulation, women have higher resting heart rate and lower baroreflex sensitivity. Of the electrocardiographic phenomena, women have longer QT interval duration, repolarisation sequence more synchronised with the inverse of the depolarisation sequence, and likely increased regional heterogeneity of myocardial repolarisation. Studies investigating the relationship of these sex disparities to hormonal differences led frequently to conflicting results. Although sex hormones seem to play a key role by influencing both autonomic tone and electrophysiological properties at the cellular level, neither the truly relevant hormones nor their detailed actions are known. Physiologic usefulness of the described sex differences is also unknown. The review suggests that new studies are needed to advance the understanding of the physiologic mechanisms responsible for these inequalities between women and men and provides key methodological suggestions that need to be followed in future research.

Enhanced transmural dispersion of repolarization in patients with J wave syndromes

INTRODUCTION

Recently, great attention has been paid to the risk stratification of asymptomatic patients with an electrocardiographic early repolarization (ER) pattern. We investigated several repolarization parameters including the Tpeak-Tend interval and Tpeak-Tend/QT ratio in healthy individuals and patients with J wave syndrome who were aborted from sudden cardiac death.

METHODS AND RESULTS

Ninety-two subjects were enrolled: 12 patients with ventricular fibrillation associated with J waves, 40 healthy subjects with an uneventful ER pattern and 40 healthy control subjects (C) without any evident J waves. Using ambulatory electrocardiogram recordings, the average QT interval, corrected QT interval (QTc), Tpeak-Tend (Tp-e) interval, which is the interval from the peak to the end of the T wave, and Tp-e/QT ratio were calculated. Using ANOVA and post hoc analysis, there was no significant difference in the average QT and QTc in all 3 groups (QT; 396 ± 27 vs 405 ± 27 vs 403 ± 27 m, QTc; 420 ± 26 vs 421 ± 21 vs 403 ± 19 milliseconds in the C, ER pattern and J groups, respectively). The Tp-e interval and Tp-e/QT ratio were significantly more increased in the J wave group than the ER Pattern group (Tp-e: 86.7 ± 14 milliseconds vs 68 ± 13.2 milliseconds, P < 0.001, Tp-e/QT; 0.209 ± 0.04 vs 0.171 ± 0.03, P < 0.001), but they did not significantly differ between the C and ER pattern groups (Tp-e: 68.6 ± 7.5 vs 68 ± 13.2, P = 0.97, Tp-e/QT 0.174 ± 0.02 vs 0.171 ± 0.03, P = 0.4).

CONCLUSION

As novel markers of heterogeneity of ventricular repolarization, Tpeak-Tend interval and Tp-Te/QT ratio are significantly increased in patients with J wave syndromes compared to age and sex-matched uneventful ER.

The Association between Myocardial Iron Load and Ventricular Repolarization Parameters in Asymptomatic Beta-Thalassemia Patients

Previous studies have demonstrated impaired ventricular repolarization in patients with β-TM. However, the effect of iron overload with cardiac T2* magnetic resonance imaging (MRI) on cardiac repolarization remains unclear yet. We aimed to examine relationship between repolarization parameters and iron loading using cardiac T2* MRI in asymptomatic β-TM patients. Twenty-two β-TM patients and 22 age- and gender-matched healthy controls were enrolled to the study. From the 12-lead surface electrocardiography, regional and transmyocardial repolarization parameters were evaluated manually by two experienced cardiologists. All patients were also undergone MRI for cardiac T2* evaluation. Cardiac T2* score <20 msec was considered as iron overload status. Of the QT parameters, QT duration, corrected QT interval, and QT peak duration were significantly longer in the β-TM group compared to the healthy controls. T_p − T_e and T_p − T_e dispersions were also significantly prolonged in β-TM group compared to healthy controls. (T_p − T_e)/QT was similar between groups. There was no correlation between repolarization parameters and cardiac T2* MRI values. In conclusion, although repolarization parameters were prolonged in asymptomatic β-TM patients compared with control, we could not find any relation between ECG findings and cardiac iron load.

Electrocardiographic findings in patients with polycythemia vera

BACKGROUND

The 12-lead surface electrocardiogram (ECG) is a useful tool to predict both atrial and ventricular arrhythmias via P-wave and QT measurements and its derivatives. Polycythemia vera (PV) is a chronic myeloproliferative disorder associated with cardiovascular events. The aim of this study was to assess ECG findings of patients with PV.

METHOD AND MATERIALS

Sixty patients with PV (34 male, mean age 58±11 years) and 60 age and gender-matched healthy volunteers were enrolled into the study. From the 12-lead surface ECG, P-wave and both conventional QT measurements and transmyocardial repolarization parameters (T(peak)-T(end) interval (T(p)-T(e)) and derivatives) were evaluated digitally by two experienced cardiologists. In addition, a novel parameter, Pi was calculated digitally as the standard deviation of the P-wave duration across the 12 ECG leads.

RESULTS

QT duration and corrected QT interval were significantly longer in the PV group compared to healthy controls (p<0.01 and p<0.01, respectively). The T(p)-T(e) was longer and the T(p)-T(e)/QT ratio was significantly higher in the PV group compared to the controls. P-wave analyses showed that all P-wave parameters including Pmax, Pmin, P dispersion, and Pi were significantly prolonged in PV patients compared to the controls. The increase of both T(p)-T(e )and P max in the PV group was independent of age, BMI, diabetes and hypertension, gender, systolic blood pressure, hemoglobin, hematocrit, left atrial dimension, left ventricular end-diastolic diameter and early deceleration time in a univariate analysis of co-variance model (F=11.097, p=0.001 and F=31.537, p=0.0001, respectively).

CONCLUSION

The present study demonstrated that PV may be associated with electrocardiographic abnormalities of both atrium and ventricle.

Assessment of repolarization heterogeneity for prediction of mortality in cardiovascular disease: peak to the end of the T wave interval and nondipolar repolarization components

BACKGROUND

In the canine wedge preparation, the interval from the peak to the end of the T wave (TpTe) reflects transwedge heterogeneities. Increase of ventricular dispersion of action potential durations has been repeatedly shown to be arrhythmogenic; thus, prolonged TpTe intervals were assumed to reflect increased risk. However, despite attempted extrapolation to clinical electrocardiograms, the appropriateness of this assumption has not been investigated in a large population. In another animal model, nondipolar components of the descending T-wave limb (TWRd) have been shown to correlate with TpTe interval. Although total T-wave nondipolar components (TWRt), believed to reflect heterogeneities during total repolarization, were shown associated with worse outcome of cardiac patients, this has not been investigated for TWRd.

METHODS AND RESULTS

Male cardiovascular patients (n = 813) had digital 12-lead electrocardiograms recorded between 1984 and 1991 and were followed until 2000. Using commercial and previously validated technology, QT intervals, TpTe intervals, TWRd, and TWRt were calculated, heart rate corrected, and compared between survivors and nonsurvivors. Their predictive power was also compared with established markers of mortality risk. In contrast to former reports, TpTe(c) intervals were significantly shorter in nonsurvivors (98.76 ± 20.63 milliseconds vs 103.14 ± 20.87 milliseconds, P = .016) and not predictive of outcome. Although TWRd(c) was significantly higher in nonsurvivors (0.007% ± 0.02% vs 0.005% ± 0.08%, P = .03), it was also not predictive of outcome. Only increased TWRt(c), increased heart rate, and increased age were predictive of death.

CONCLUSIONS

The findings challenge the concept that prolongation of TpTe corresponds to higher risk of death from any cause in every population. Further investigations are needed to confirm that clinically measured TpTe reflects transmural repolarization heterogeneity in all clinical populations and indeed is a useful risk marker.

Clinical determinants of electrocardiographic and spatial vectorcardiographic descriptors of ventricular repolarization in healthy children

BACKGROUND

Although the association of repolarization alterations to the development of life-threatening ventricular arrhythmias has received considerable research attention, there is paucity of data regarding what may be considered as normal, especially in children.

METHODS

To define electrocardiographic (ECG) and vectorcardiographic (VCG) descriptors of ventricular repolarization in healthy school-age children, 12-lead digital ECGs were obtained from 646 children (348 males/298 females, mean age 8.54 ± 1.86 years). All QT intervals were measured manually using the digitally stored ECGs. Orthogonal X, Y, and Z leads were reconstructed from the standard 12-lead ECGs and the maximal amplitudes of the spatial QRS and T vectors were calculated, as well as the spatial QRS-T angle.

RESULTS

The mean heart rate was 95.3 ± 15.8 bpm and the QRS duration was 83.4 ± 9.3 ms. Mean QT interval was 334.1 ± 24.2 ms and the corrected QT interval was 436.5 ± 23.8 ms (Bazzet) and 404.3 ± 19.4 ms (Fridericia). Although the uncorrected maximum and mean QT intervals were significantly higher in boys (P values 0.011 and 0.009, respectively), there was no difference in the rate-corrected QT interval. The spatial QRS and T-vector amplitudes were 1512.0 ± 365.7 μV and 478.8 ± 149.3 μV, respectively. The spatial QRS-T angle was 14.1 ± 8.0 degrees. Although the mean QT interval showed significant increase with age (P = 0.014), all VCG parameters did not show significant variance with age.

CONCLUSIONS

A range of ECG and VCG descriptors of ventricular repolarization was determined in a large sample of healthy school-age children to provide a data basis of normal values for future reference.

The effect of sertindole on QTD and TPTE

OBJECTIVE

Recent research suggests that other surrogate markers than QTc, including QTc dispersion and Tpeak-Tend, may better correlate with cardiac arrhythmia risk. While sertindole significantly prolongs the QTc interval, the effects on other markers of arrhythmia risk, such as QTc dispersion and Tpeak-Tend are unknown.

METHOD

Digital 12-lead ECG was recorded at baseline and at steady-state in 37 patients switched to sertindole. ECG was analysed for Fridericia-corrected QT duration (QTcF), QT dispersion and Tpeak-Tend.

RESULTS

From a baseline QTcF of 407 +/- 22 ms, mean QTcF prolongation during sertindole treatment was 20 +/- 23 ms, P < 0.01. No effect on QTc dispersion was found (-1 +/- 11 ms; P = 0.41). No increased duration of the Tpeak-Tend interval from baseline was found (+7 +/- 21 ms; P = 0.05).

CONCLUSION

These findings might be related to the absence of confirmed Torsade de Pointes (TdP) cases related to sertindole exposure, despite sertindole's QTc prolonging effects.

The prognostic value of the Tpeak-Tend interval in patients undergoing primary percutaneous coronary intervention for ST-segment elevation myocardial infarction

INTRODUCTION

The Tpeak-Tend interval (TpTe) has been linked to increased arrhythmic risk. TpTe was investigated before and after primary percutaneous coronary intervention (pPCI) in patients with ST-segment elevation myocardial infarction (STEMI).

METHOD

Patients with first-time STEMI treated with pPCI were included (n = 101; mean age 62 years; range 39-89 years; 74% men). Digital electrocardiograms were taken pre- and post-PCI, respectively. Tpeak-Tend interval was measured in leads with limited ST-segment deviation. The primary end point was all-cause mortality during 22 +/- 7 months (mean +/- SD) of follow-up.

RESULTS

Pre- and post-PCI TpTe were 104 milliseconds [98-109 milliseconds] and 106 milliseconds [99-112 milliseconds], respectively (mean [95% confidence interval], P = .59). A prolonged pre-PCI TpTe was associated with increased mortality (hazard ratio, 10.5 [1.7-20.4] for a cutoff value of 100 milliseconds). Uncorrected QT and heart rate-corrected QT intervals (Fridericia-corrected QT) were prolonged after PCI (QT: 401 vs 410 milliseconds, P = .022, and Fridericia-corrected QT: 430 vs 448 milliseconds, P < .0001).

CONCLUSION

In patients with STEMI undergoing pPCI, pre-PCI TpTe predicted subsequent all-cause mortality, and the QT interval was increased after the procedure.

Robust QT interval estimation--from algorithm to validation

BACKGROUND

This article presents an effort of measuring QT interval with automatic computerized algorithms. The aims of the algorithms are consistency as well as accuracy. Multilead and multibeat information from a given segment of ECG are used for more consistent QT interval measurement.

METHODS

A representative beat is generated from selected segment of each lead, and then a composite beat is formed by the representative beats of all independent leads. The end result of the QT measure is so-called global QT measurement, which usually correlates with the longest QT interval in multiple leads. Individual lead QT interval was estimated by using the global measurement as a starting point, and then adapted to the signal of the particular lead and beat. In general, beat-by-beat QT measurement is more prone to noise, therefore less reliable than the global estimation. It is usually difficult to know if difference of beat-by-beat QT interval is due to true physiological change or noise fluctuation.

RESULTS

The algorithm was tested independently by a clinical database. It is also tested against action potential duration (APD) generated by a Cell-to-ECG forward-modeling based simulation signals. The modeling approach provided an objective test for the QT estimation. The modeling approach allowed us to evaluate the QT measurement versus APD. The mean error between the algorithm and cardiologist QT intervals is 3.95 +/- 5.5 ms, based on the large clinical trial database consisting of 15,910 ECGs. The mean error between QT intervals and maximum APD is 17 +/- 2.4, and the correlation coefficient is 0.99.

CONCLUSIONS

The global QT interval measurement method presented in this study shows very satisfactory results against the CSE database and a large clinical trial database. The modeling test approach used in this study provides an alternative "gold standard" for QT interval measurement.

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.

Clinical implications of QRS duration and QT peak prolongation in patients with suspected coronary disease referred for elective cardiac catheterization

BACKGROUND

The electrocardiogram (ECG) remains a simple, universally available, and prognostically powerful investigation in heart failure, and acute coronary syndromes. We sought to assess the prognostic utility of clinical, angiographic, and simple ECG parameters in a large cohort of patients undergoing elective cardiac catheterization (CC) for known or suspected coronary artery disease.

METHODS

Consecutive consenting patients undergoing CC for coronary disease were enrolled at a single tertiary center. Patient data, drug therapy, catheter reports, and ECG recordings were prospectively recorded in a validated electronic archive. The primary outcome measure was death or nonfatal myocardial infarction (MI) over 1 year or until percutaneous or cardiac surgical intervention. Independent prognostic markers were identified using the Cox proportional hazard model.

RESULTS

A total of 682 individuals were recruited of whom 17(2.5%) died or suffered a nonfatal MI in 1 year. In multivariate analysis QRS duration (ms) (HR 1.03 95% CI 1.01-1.05, P = 0.003), extent of coronary disease (HR 2.01 95% CI 1.24-3.58, P = 0.006), and prolonged corrected QT peak interval in lead I (HR 1.02 95% CI 1.00-1.03, P = 0.044) were independently associated with death or nonfatal MI. Receiver-operator characteristic (ROC) analysis for the multivariate model against the primary end point yielded an area under the curve of 0.759 (95% CI 0.660-0.858), P < 0.001.

CONCLUSIONS

QRS duration and QT peak are independently associated with increased risk of death or nonfatal MI in stable patients attending for coronary angiography.

Effects of atorvastatin on ventricular late potentials and repolarization dispersion in patients with hypercholesterolemia

Emerging evidence suggests that statins have a favorable impact on the reduction of arrhythmia events and sudden cardiac death in patients with structural heart disease. We aimed to investigate the possibly and directly favorable effects of statins on ventricular late potentials, QT dispersion, and transmural dispersion of repolarization attained by analyzing clinical electrocardiography (ECG) risk stratification parameters in patients with hypercholesterolemia without structural heart disease. In total, 82 patients (45 females; mean age, 62 +/- 10 years) with hypercholesterolemia were enrolled in this prospective study to examine the effects of statin therapy (atorvastatin 10 mg/day for 3 months) on ECG risk stratification parameters. Surface 12-lead ECG and signal-average ECG (SAECG) were recorded before and after statin treatment. The SAECG parameters, QT dispersion, Bazett-corrected QT (QTc) dispersion, T wave peak-to-end interval (Tpe), and percentage of Tpe/QT interval were calculated and compared before and after statin therapy. Twelve-lead ambulatory 24-hour ECGs were recorded in 12 patients. The results demonstrated that after statin therapy for 3 months, serum levels of total cholesterol and low-density lipoprotein cholesterol were significantly reduced (both p values < 0.001). However, neither significant changes of each SAECG parameter nor the frequency of late potentials were demonstrated after atorvastatin therapy. In addition, no significant changes in QT dispersion, QTc dispersion, Tpe, or Tpe/QT were found. However, 24-hour ambulatory ECG revealed a flattening effect of circadian variation of QTc dispersion after atorvastatin therapy. In conclusion, the favorable antiarrhythmia effect of atorvastatin (10 mg/day) therapy cannot be directly reflected by analyzing these noninvasive ECG risk stratification parameters in low-risk patients with hypercholesterolemia.

Novel indices of ventricular repolarization to screen post myocardial infarction patients

We propose novel indices of ventricular repolarization intervals, the JTp/JT, Tpe/JTp and Tpe/JT ratios. These indices have been compared with the duration of the ventricular repolarization intervals and other ratios in 17 normal subjects and 17 patients with old myocardial infarction. In the intervals and other ratios, the best separation between groups is obtained with the Tpe/QTp and Tpe/QT ratios with 94% sensitivity and 82% specificity, the proposed ratios increased sensitivity to 100% and specificity to 94%. These indices should be further tested to determine their usefulness in discriminating between OMI patients with and without susceptibility to ventricular arrhythmias.

QT peak dispersion, not QT dispersion, is a more useful diagnostic marker for detecting exercise-induced myocardial ischemia

BACKGROUND

The electrocardiographic indices of QT dispersion (QTd), QT peak dispersion (QTpd), and the principal component analysis ratio (PCAr) are related to the occurrence of fatal arrhythmia and are influenced by physical exercise.

OBJECTIVE

The purpose of this study was to investigate whether or not the QT parameters can be used as markers for exercise-induced myocardial ischemia.

METHODS

We measured these QT parameters at rest and at 3 minutes after exercise using exercise-stress thallium-201 scintigraphy (SPECT), compared with conventional ST segment changes in 161 patients with suspected or known coronary artery disease. The patients were classified into four groups (normal, redistribution, fixed defect, and redistribution with fixed defect) according to SPECT.

RESULTS

At rest, QTd and PCAr were greater in the fixed defect and redistribution with fixed defect groups. PCAr, however, increased after exercise in the redistribution and redistribution with fixed defect groups. Although QTpd at rest was not significantly different among the four groups, it increased in the redistribution and redistribution with fixed defect groups after exercise (QTpd after exercise: normal, 36 +/- 16 ms vs. redistribution, 51 +/- 23 ms, redistribution with fixed defect, 53 +/- 19 ms; P<.05). For myocardial infarction reflected by fixed defect, QTd at rest was the most useful indicator, while QTpd after exercise was the most useful indicator for exercise-induced myocardial ischemia according to multiple logistic regression analysis with receiver operating characteristic curves. In addition, the change in PCAr by exercise was an independent predictor for exercise-induced ischemia.

CONCLUSIONS

QTpd and PCAr could be useful indices for exercise-induced myocardial ischemia. Determining the QTpd of a patient after exercising can improve the diagnostic accuracy of ischemia in a routine clinical setting.

Prevention of ventricular extrasystole by mexiletine in patients with normal QT intervals is associated with a reduction of transmural dispersion of repolarization

BACKGROUND

Antiarrhythmic potential of mexiletine in patients with congenital and acquired long-QT syndrome (LQTS) has been attributed to a reduction of transmural dispersion of repolarization (TDR). A similar mechanism could be involved in the antiarrhythmic activity of the drug in patients with normal QT intervals, but the issue remains to be investigated.

METHODS AND RESULTS

We analyzed 24-h Holter ECG recordings from 17 patients in sinus rhythm showing premature ventricular complexes (PVCs) with normal QT intervals (age, 62+/-10 years, mean+/-S.D.). Treatment of the patients with oral mexiletine (300 mg/day for 21-40 days) resulted in a significant reduction of PVCs (from 13899+/-18887 to 6949+/-12822 beats/24 h, p<0.01). Rate-dependent behavior of ventricular repolarization was analyzed by plotting QT intervals (QT(peak), QT(end)), and the interval from T-wave peak to T-wave end (TPE) against preceding respective RR intervals of sinus beats. Both the QT(peak) and QT(end) tended to be shortened by mexiletine at RR intervals from 600 ms to 1000 ms, although the changes did not reach statistical significances. TPE, which reflects TDR, was shortened significantly at relatively long RR intervals (by 14+/-9% at RR of 900 ms, p<0.05). There was a linear relationship between the percentage shortening of TPE and the percentage reduction of PVCs (r=0.86, p<0.04). TPE> or =70 ms was significantly associated with PVC suppression >75% with an odds ratio of 0.60 (95% confidence interval 0.36-0.98, per 1 ms increment).

CONCLUSION

Inhibitory effect of mexiletine against PVCs in patients with normal QT intervals is mediated at least in part by a reduction of TDR. Mexiletine may be effective in patients exhibiting longer baseline TPE.

Lithium concentration correlates with QTc in patients with psychosis

QT prolongation induced by antipsychotics has been reported to be a determinant for the development of torsade de pointes and sudden death. However, the effect of lithium on QT interval has not been fully clarified. The aim of the present study was to elucidate the relationship between serum lithium concentration and QT interval in patients treated with lithium. We examined serum lithium concentrations and electrocardiographic features in 39 inpatients with bipolar affective disorder or schizophrenia. The longest QT interval in the 12 electrocardiographic leads was measured using GE Marquette QT guard System Software, and Bazett formula was used for heart rate correction. The longest QTc was positively correlated with lithium concentration ( r = 0.46, P = .003). Multiple regression analysis revealed that sex (female, P = .037), lower serum K + concentration ( P = .029), and especially, higher serum lithium concentration ( P = .009) were determinants for the prolongation of the QTc.

Short-term repeatability of electrocardiographic spatial T-wave axis and QT interval

Although ventricular repolarization abnormalities reflect arrhythmic susceptibility, few reliable tools exist to identify their presence. We investigated the repeatability of the spatial T-wave axis and QT interval from standard 12-lead electrocardiograms in 63 asymptomatic volunteers. Certified technicians used a standardized protocol to digitally record 2 electrocardiograms per participant at each of 2 visits separated by 1 to 2 weeks. Absolute paired differences within and between visits were 0.19 degrees and 0.90 degrees for the T-wave axis and 1.08 and 1.55 milliseconds for the QT interval, respectively. The intraclass correlation coefficients for the T-wave axis and QT interval were 0.87 and 0.86, respectively. The impact of repeated measurements on the precision of the QT-interval measurements was evaluated for a hypothetical clinical trial aimed at detecting a drug-induced QT prolongation. We conclude that the spatial T-wave axis is as repeatable a measure of ventricular repolarization as the QT interval.

T vector and loop characteristics in coronary artery disease and during acute ischemia

OBJECTIVE

Three-dimensional characterization of the ventricular repolarization by the T vector and T vector loop morphology in coronary artery disease (CAD), and their response to short-term (no flow) ischemia induced by coronary occlusion during a percutaneous intervention (PCI).

BACKGROUND

The risk for sudden cardiac death is increased in conditions of acute or permanently heterogeneous ventricular repolarization, for which ischemia is a risk factor.

METHODS

Fifty-six CAD patients without visible collateral circulation were studied during an elective single-vessel PCI, and 10 healthy controls twice at rest. T vector parameters (Televation, Tazimuth, and QRS-T angle), and T loop parameters (Tarea, Tavplan, and Teigenv) were measured by vectorcardiography. ST vector magnitude (ST-VM) and its change (STC-VM) were used for reference.

RESULTS

At rest, T vector loop morphology (Tarea, Teigenv) was significantly different in CAD patients and controls, while T vector angles did not separate the groups. Ischemia induced significant changes in T loop parameters in the entire CAD group, whereas in the LAD subgroup significant changes were seen also in T vector angle. The T loop morphology was significantly different at baseline and a more pronounced response to ischemia (Tarea) was seen in patients with, than in those without, a history of hypertension.

CONCLUSION

T loop morphology, rather than the T vector angle, separated CAD patients from healthy controls. Coronary occlusion had significant impact on ventricular repolarization, as assessed by T vector and morphology analysis, and most prominently in the LAD group. Hypertensive patients appeared especially vulnerable to ischemia.

Development of a new QT algorithm with heterogenous ECG databases

An algorithm for automated QT interval assessments has been developed and evaluated using the PhysioNet QT database and the electrocardiogram multilead database (2 collections of electrocardiograms with different characteristics, eg, numbers of leads and expert annotations). QRS onset and coarse T offset detection was based on the definition of a short time window, within which the range of signal amplitudes was calculated and compared to given threshold values. The final position of T offset was based on a combination of 3 methods: decreasing thresholds, multiple tangents, and a model based approach. The evaluation was based on the comparison of a waveform marker as computed automatically, and those of the human experts. Mean and standard deviation of those differences compared well to other algorithms and to inter-expert variations. Waveform marker detection was successful in at least 98% of the annotated beats in both databases, thus, indicating the robustness of the proposed method.

Effect of amiodarone on the descending limb of the T wave

Comparing patients treated after myocardial infarction with amiodarone or with placebo, we found a significant rate-dependent prolongation of TpTe interval in patients who received amiodarone. Patients who had arrhythmic death had significantly longer TpTe intervals than others on placebo but not on amiodarone. Assuming that TpTe reflects transmural repolarization heterogeneity, our findings suggest that heterogeneity and arrhythmic risk are increased by amiodarone. This contradicts the finding of decreased transmural repolarization heterogeneity by amiodarone and the appreciated antiarrhythmic efficacy of this drug.

Beta blockers normalize QT hysteresis in long QT syndrome

OBJECTIVES

This study was performed to evaluate the impact of beta blockers on QT adaptation to heart rate during the exercise and recovery phases of exercise testing in long QT syndrome.

BACKGROUND

Long QT syndrome is characterized by familial syncope and sudden death in the context of sudden heart rate changes. QT hysteresis has been proposed as a phenotypic marker of long QT syndrome, suggesting altered QT adaptation to changes in heart rate.

METHODS

Fourteen patients with long QT syndrome (aged 26 +/- 16 years, 6 male) and 10 healthy volunteers (aged 37 +/- 11 years, 9 male) underwent graded exercise testing with continuous lead II electrocardiographic monitoring. Long QT patients underwent repeat assessment after 1 month of beta blockade. QT intervals at matching heart rates were compared during exercise and recovery to determine the effect of beta blockade on QT hysteresis, defined as the recovery QT peak interval subtracted from the exercise QT peak interval.

RESULTS

In the 14 long QT syndrome patients, beta blockers slowed the resting heart rate without affecting the corrected QT interval (502 +/- 52 ms baseline vs 481 +/- 40 ms beta blocker, P =.17). The increase in heart rate with exercise was similar in the 3 groups (P =.73). Exaggerated hysteresis of the QT interval was seen in the patients with long QT syndrome at baseline compared with controls (46 +/-19 ms vs 19 +/- 11 ms 1 minute into recovery, P =.006). Beta blockers had minimal effect on the QT interval but markedly reduced hysteresis with minimal separation of the exercise and recovery QT/RR curves (25 +/- 35 ms 1 minute into recovery, P =.027). The combined curve separation at all 6 time points analyzed was 165 +/- 95 ms in patients with long QT syndrome at baseline, 40 +/- 131 ms after beta blockade, and 29 +/- 30 ms in control subjects (P =.002). Comparison of the beta blocker effect on hysteresis in the 2 genotypes suggested a greater reduction in hysteresis in the 3 patients with long QT syndrome 1 compared with the 11 patients with long QT syndrome 2.

CONCLUSIONS

Beta blockers reduce QT hysteresis in patients with long QT syndrome to values seen in normal patients. This improved QT adaptation to changes in heart rate may explain the clinical benefit of beta blockers in long QT syndrome.

The effects of cigarette smoking on the heterogeneity of ventricular repolarization

BACKGROUND

Although the circulatory effects of cigarette smoking have been studied extensively, its impact on ventricular repolarization has not been adequately evaluated.

METHODS

The goal of our study was to determine whether cigarette smoking influences the spatial and temporal heterogeneity of ventricular repolarization in a population of young, healthy, male subjects. A digital 12-lead surface electrocardiogram was obtained from 1394 men recruited from the Hellenic Air Force and classified as smokers and nonsmokers. The maximum, minimum, and median QT intervals, QT dispersion (QT maximum - QT minimum), the rate-corrected maximum and median QT intervals, the slopes of the QT maximum/RR and QT median/RR regression equations, and the vectorcardiographic markers spatial T amplitude and spatial QRS-T angle were evaluated in the 2 groups.

RESULTS

Heart rate was significantly higher (P <.001) in smokers (n =691) compared with nonsmokers (n = 703). QT maximum, QT minimum, and QT median were significantly lower (P <.001), whereas the rate-corrected QT maximum (P =.04) and QT median (P =.06) were marginally higher in smokers than in nonsmokers. The spatial T amplitude was lower (P =.002), whereas the spatial QRS-T angle was higher (P =.01) in smokers compared with nonsmokers. Neither QT dispersion nor the slopes of the QT/RR and the spatial descriptors/RR regression equations differed between smokers and nonsmokers.

CONCLUSIONS

Ventricular repolarization is altered in young male cigarette smokers. The differences in the heterogeneity of ventricular repolarization between smokers and nonsmokers are mainly due to heart rate differences between the 2 study groups.

Association between heart rate-corrected QT interval and coronary risk factors in 2,894 healthy subjects (the DESIR Study). Data from an Epidemiological Study on the Insulin Resistance syndrome

In the prospective Data from an Epidemiological Study on the Insulin Resistance Syndrome, 2,894 healthy subjects aged 30 to 64 years had determinations of fasting glucose, insulin, serum lipid and fibrinogen concentrations, blood pressures, body mass index, and waist-hip ratio, as well as tobacco and alcohol consumptions and physical activity. A 12-lead electrocardiogram with automatic measurement of the QT interval was recorded and the formula used for heart rate correction was based on the best-fit regression between QT and heart rate. The QT duration was influenced by glucose homeostasis in both sexes, and increased in men with physical activity; there was a dose-effect relation for men who smoked.

Measurement and interpretation of QT dispersion

QT dispersion was proposed as an index of the spatial inhomogeneity of ventricular recovery times. The results of studies that found significant correlation between dispersion of ventricular recovery times measured with monophasic action potentials and QT dispersion were interpreted as proof of the direct link between QT dispersion and the dispersion of ventricular recovery times. Later it was shown that QT dispersion is not a direct reflection of the spatial variation of the recovery times and cannot be used for quantification of this variation. The interlead variability of the QT intervals is a result of different projections of the spatial T-wave loop into the various electrocardiographic leads. The reliability of both manual and automatic measurement of QT dispersion is low and is often of the order of the differences of Qt dispersion between different patient groups. The measurement reliability is influenced by intrinsic factors (e.g., amplitude of the T wave) and extrinsic factors (e.g., noise, paper speed of recording, instruments for manual measurements, and type of algorithm and interalgorithmic settings for automatic measurement). There is very little to choose between the different indices of expression of QT dispersion, as well as between the different lead configurations used for its measurement. QT dispersion is not simply a result of measurement error, but a crude measure of abnormalities during the whole course of repolarization. Only grossly prolonged QT dispersion (e.g., > or =100 ms), must be interpreted simply as a sign of the abnormal course of the repolarization, and inferences about the actual dispersion of the ventricular recovery times should not be made. Newer concepts of assessment of the morphology of the T wave are already emerging and will probably be of higher clinical value.