Gender differences in ventricular repolarization: terminal T wave interval was shorter in women than in men

Time-Warping Analysis of the T-Wave Peak-to-End Interval to Quantify Ventricular Repolarization Dispersion During Ischemia

Variations in the dispersion of ventricular repolarization can be quantified by T-wave time-warping based index, dw. However, the early phase of the T-wave can be affected by ST-segment changes during ischemia. We hypothesized that restricting dw to the T-wave peak-to-end ( Tpe) would circumvent this limitation while still quantifying variations in repolarization dispersion. A total of 101 ECG recordings from patients undergoing coronary occlusion, together with their control recordings, were analyzed. A series of dw values was calculated by quantifying the Tpe morphological variations between the T-waves at different occlusion stages and a baseline T-wave. We introduced a normalized version of dw, Rd, reflecting variations of dw during occlusion relative to control recordings ( Rd = 1 corresponds to the same level of variation). The dw series followed a gradually increasing trend with occlusion time, reaching median [range] Rd values of 9.44 [1.01, 80.74] at the occlusion end. Rd at occlusion end was significantly higher than threshold values of 1, 2, 5, and 10 in 94.1%, 85.11%, 64.4% and 48.5% of patients, respectively. The spatial lead-wise analysis of dw showed distinct distributions depending on the occluded artery, suggesting a relation with the ischemia location. The relative variation R with ischemia of index dw (9.4) is greater than that of the T-wave amplitude (7.7), Tpe interval (2.7) and T-wave width (3.0). In conclusion, dw tracks ischemic-induced variations in repolarization dispersion in a more robust manner than classical indexes, avoiding the impact of ST segment elevation/depression or early T-wave distortions, thus warranting further clinical studies.

Usefulness of Heat Map Explanations for Deep-Learning-Based Electrocardiogram Analysis

Deep neural networks are complex machine learning models that have shown promising results in analyzing high-dimensional data such as those collected from medical examinations. Such models have the potential to provide fast and accurate medical diagnoses. However, the high complexity makes deep neural networks and their predictions difficult to understand. Providing model explanations can be a way of increasing the understanding of "black box" models and building trust. In this work, we applied transfer learning to develop a deep neural network to predict sex from electrocardiograms. Using the visual explanation method Grad-CAM, heat maps were generated from the model in order to understand how it makes predictions. To evaluate the usefulness of the heat maps and determine if the heat maps identified electrocardiogram features that could be recognized to discriminate sex, medical doctors provided feedback. Based on the feedback, we concluded that, in our setting, this mode of explainable artificial intelligence does not provide meaningful information to medical doctors and is not useful in the clinic. Our results indicate that improved explanation techniques that are tailored to medical data should be developed before deep neural networks can be applied in the clinic for diagnostic purposes.

Ventricular arrhythmias in acute myocardial ischaemia-Focus on the ageing and sex

Annually, approximately 17 million people die from cardiovascular diseases worldwide, half of them suddenly. The most common direct cause of sudden cardiac death is ventricular arrhythmia triggered by an acute coronary syndrome (ACS). The study summarizes the knowledge of the mechanisms of arrhythmia onset during ACS in humans and in animal models and factors that may influence the susceptibility to life-threatening arrhythmias during ACS with particular focus on the age and sex. The real impact of age and sex on the arrhythmic susceptibility within the setting of acute ischaemia is masked by the fact that ACSs result from coronary artery disease appearing with age much earlier among men than among women. However, results of researches show that in ageing process changes with potential pro-arrhythmic significance, such as increased fibrosis, cardiomyocyte hypertrophy, decrease number of gap junction channels, disturbances of the intracellular Ca²⁺ signalling or changes in electrophysiological parameters, occur independently of the development of cardiovascular diseases and are more severe in male individuals. A review of the literature also indicates a marked paucity of research in this area in female and elderly individuals. Greater awareness of sex differences in the aging process could help in the development of personalized prevention methods targeting potential pro-arrhythmic factors in patients of both sexes to reduce mortality during the acute phase of myocardial infarction. This is especially important in an era of aging populations in which women will predominate due to their longer lifespan.

Prolongation of QTc interval due to increased parity and great grand multiparity

Women are more prone to cardiac arrhythmias. Increased exposure to sex hormones may alter the ventricular repolarisation of the heart as the parity number increases. In this study, we aim to investigate the effect of parity number to electrocardiographic parameters. A total of 205 adult women were included for the study. Nulliparous (NP), primiparous (PP), multiparous (MP), grand multiparous (GMP) and great grand multiparous (GGMP) women constituted the study population. Increased parity has positive correlation with QTc interval (p=.000, r = 0.303). GGMP has significantly higher QTc compared to NP, PP, MP and GMP (p=.001, p=.000, p=.004 and p=.007, respectively). GGMP and parity have explanatory power on QTc (p=.019 and p=.020, respectively). Parity and GGMP affect cardiac repolarisation and prolong the QTc interval most probably due to repeated exposure to sex hormones. This study showed that GGMP and parity are independent risk factors for QTc interval prolongation.Impact StatementWhat is already known on this subject? Increased exposure to sex hormones may alter the ventricular repolarisation of the heart as the parity number increases. Previous studies showed that increased parity (up to 7) deteriorates ventricular diastolic functions, prolongs QTc interval and these conditions cause cardiovascular diseases.What do the results of this study add? In this study, we added great grand multiparity (10 or more parity) (GGMP) group that have never been studied before. We found that GGMP has much more impact on QTc prolongation than fewer parity groups and this result shows us that GGMP deteriorates ventricular functions more.What are the implications of these findings for clinical practice and/or further research? These results show us that women should be discouraged from having more delivery. Also, women with a pregnancy history of five and more (grand multiparity) should be evaluated with an electrocardiography and a cardiology consultation should be performed before re-conception. In the future, larger prospective studies are needed on this subject. In addition, other electrocardiographic parameters (QRS-T angle and Tpe/QTc in electrocardiography, etc.) that related with diastolic functions should be evaluated for comparison of GGMP and non-GGMP populations in future studies.

Effect of age and sex on the incidence of ventricular arrhythmia in a rat model of acute ischemia

BACKGROUND

The impact of sex and age on the arrhythmic susceptibility within the setting of acute ischemia is masked by the fact that acute coronary events result from coronary artery disease appearing with age much earlier among men than among women.

METHODS AND RESULTS

LAD ligation or sham operations were performed in rats of both sexes at the age 3 and 24 months. An ECG was recorded continuously for 6 h after the operation. The number of early and late premature ventricular beats (PVBs), episodes of ventricular tachycardia (VT) and fibrillation (VF), heart rate, QRS, QT and Tpeak-Tend duration were analysed. Epicardial action potentials were recorded in vivo, Ca²⁺ signaling was evaluated in isolated cardiomyocytes, fibrosis and connexin-43 expression and localization were measured in the septum. PVBs, VT and VF episodes are much more common in older males than in young males and females independently from their age. Fibrosis with varying intensity in different muscle layers, hypertrophy of cardiomyocytes, reduced number of gap junctions and their appearance on the lateral myocyte membrane, QT prolongation, increase transmural dispersion of repolarisation and a decreased function of SERCA2a may increase the propensity to arrhythmia within the setting of acute ischemia.

CONCLUSION

We show that the male sex, especially in case of older individuals is a strong predictor of increased arrhythmic susceptibility within the acute ischemia setting regardless of its impact on the occurrence of cardiovascular diseases. A personalized sex-dependent prevention treatment is needed to reduce the mortality in acute phases of myocardial infarction.

Importance of electrocardiographic markers in predicting cardiac events in children

ECG is a common diagnostic tool in medical practice. Sudden cardiac death (SCD) is a rare but devastating event. The most common cause of SCD in the young is a primary arrhythmic event, which is often produced by malignant ventricular arrhythmia. Several electrocardiographic markers for ventricular repolarization and depolarization have been proposed to predict this arrhythmic risk and SCD in children. Although many of these parameters can easily be used in clinical practice, some of them need specific techniques for interpretation. In this review, we summarized the current knowledge regarding the clinical importance and the ability of these ECG parameters to predict adverse cardiac events in the pediatric population.

Testosterone-mediated upregulation of delayed rectifier potassium channel in cardiomyocytes causes abbreviation of QT intervals in rats

Men have shorter rate-corrected QT intervals (QTc) than women, especially at the period of adolescence or later. The aim of this study was to elucidate the long-term effects of testosterone on cardiac excitability parameters including electrocardiogram (ECG) and potassium channel current. Testosterone shortened QT intervals in ECG in castrated male rats, not immediately after, but on day 2 or later. Expression of Kv7.1 (KCNQ1) mRNA was significantly upregulated by testosterone in cardiomyocytes of male and female rats. Short-term application of testosterone was without effect on delayed rectifier potassium channel current (IKs), whereas IKs was significantly increased in cardiomyocytes treated with dihydrotestosterone for 24 h, which was mimicked by isoproterenol (24 h). Gene-selective inhibitors of a transcription factor SP1, mithramycin, abolished the effects of testosterone on Kv7.1. Testosterone increases Kv7.1-IKs possibly through a pathway related to a transcription factor SP1, suggesting a genomic effect of testosterone as an active factor for cardiac excitability.

Incidence of Idiopathic Ventricular Arrhythmias: A Population-Based Study

BACKGROUND

Ventricular tachycardia and premature ventricular complexes (PVCs) most frequently occur in the context of structural heart disease. However, the burden of idiopathic ventricular arrhythmias (IVA) in the general population is unknown.

METHODS AND RESULTS

We identified incident cases of IVA between 2005 and 2013 from Olmsted County, Minnesota, using the Rochester Epidemiology Project database. For PVC cohorts, we included those with frequent (defined as ≥100 PVC/24 hours) symptomatic PVCs. We defined IVA-associated cardiomyopathy as a drop in ejection fraction of ≥10% from baseline. Between 2005 and 2013, we identified 614 individuals with incident IVA (229 [37.3%] were male; average age was 52.1±17.2 years). Of these, 177 (28.8%) had idiopathic ventricular tachycardia, 408 (66.5%) had symptomatic PVCs, and 29 (4.7%) had IVA-associated cardiomyopathy. The age- and sex-adjusted incidence rates in 2005 to 2007, 2008 to 2010, and 2011 to 2013 were 44.9 per 100 000 (95% confidence interval [CI], 38.0-51.8), 47.6 per 100 000 (95% CI, 40.8-54.5), and 62.0 per 100 000 (95% CI, 54.4-69.6), respectively. In idiopathic ventricular tachycardia, there was an increase in incidence rate with ages (P<0.001) but not between sexes (P=0.12). The age-adjusted incidence of symptomatic PVC was higher in females than in males (46.2 per 100 000 [95% CI, 40.9-51.6] versus 20.5 per 100 000 [95% CI, 16.8-24.3]; P<0.001). The small number of individuals with IVA-associated cardiomyopathy precluded any formal testing.

CONCLUSIONS

The incidence of IVA is increasing. Furthermore, overall incidence increases with age. Although the rate of idiopathic ventricular tachycardia is similar across sexes, women have a higher incidence of symptomatic PVC.

Mechanisms of sex and age differences in ventricular repolarization in humans

INTRODUCTION

Corrected QT interval (QTc) is shorter in postpubertal men than in women; however, QTc lengthens as men age and testosterone levels decrease. Animal studies have demonstrated that testosterone decreases L-type calcium current and increases slow delayed rectifier potassium current; however, it is not known how these contribute to QTc differences by sex and age in humans. We separately analyzed early versus late repolarization duration and performed simulations of the effect of testosterone on the electrocardiogram (ECG) to examine the mechanism of sex and age differences in QTc in humans.

METHODS

Twelve-lead ECGs from 2,235 healthy subjects (41% women) in Thorough QT studies were analyzed to characterize sex- and age-dependent differences in depolarization (QRS), early repolarization (J-T(peak)), and late repolarization (T(peak)-T(end)). In addition, we simulated the effects of testosterone on calcium current, slow delayed rectifier potassium current, and surface ECG intervals.

RESULTS

QTc was shorter in men than in women (394 ± 16 vs 408 ± 15 milliseconds, P < .001), which was due to shorter early repolarization (213 ± 16 vs 242 ± 16 milliseconds, P < .001), as men had longer depolarization (94 ± 7 vs 89 ± 7 milliseconds, P < .001) and longer late repolarization (87 ± 10 vs 78 ± 9 milliseconds, P < .001). Sex difference in QTc decreased with age and was due to changes in early repolarization. Simulations showed that the early repolarization changes were most influenced by testosterone's effect on calcium current.

CONCLUSION

Shorter QTc in men compared to women is explained by shorter early repolarization, and this difference decreases with age. These sex and age differences in repolarization appear to be caused by testosterone effects on calcium current.

Use of QT intervals for a more accurate diagnose of syncope and evaluation of syncope severity

BACKGROUND

This study aimed to evaluate the use of QT intervals, their diagnostic predictive value in patients with syncope and their relationship with syncope severity.

METHODS

One hundred and forty nine patients with a diagnosis of syncope were admitted to Internal Medicine departments at the University of Palermo, Italy, between 2006 and 2012, and 140 control subjects hospitalised for other causes were enrolled. QT maximum, QT minimum, QTpeak, QT corrected, QT dispersion and Tpeak-to-Tend interval were compared between two groups. The paper medical records were used for scoring with San Francisco Syncope Rule (SFSR), Evaluation of Guidelines in SYncope Study (EGSYS) score and Osservatorio Epidemiologico sulla Sincope nel Lazio (OESIL) risk score.

RESULTS

Mean QTc (p < 0.0005), mean QTmax (p < 0.0005), mean QTdisp (p < 0.0005), mean QTpeak (p = 0.005) and mean TpTe (p = 0.018) were significantly longer in patients with syncope compared with control subjects. A QTc > 424.8 ms (sensibility: 81.88 - specificity: 57.86) showed the greatest predictive value for diagnosis of syncope. On the EGSYS score and on the OESIL score, QTc was significantly prolonged in high-risk patients compared with low-risk patients. On the San Francisco Syncope Rule, QTc and QTdisp were significantly prolonged in high-risk patients compared with low-risk patients.

CONCLUSION

Mean QTc, mean QTdisp, mean TpTe, mean QTmax and mean QTpeak were significantly longer in patients with syncope compared with control subjects. Furthermore, prolonged QTc and QTdisp were associated with major severe syncope according to San Francisco Syncope Rule, EGSYS and OESIL risk scores.

Transcatheter mapping and ablation of arrhythmias in the coronary sinus

The coronary sinus (CS) is a complex structure of particular interest to cardiac electrophysiologists. It is exploited as an anatomical reference, a site to record left-sided atrial and ventricular signals and for cardiac resynchronization therapy. Perhaps less appreciated, it may itself serve as a substrate for arrhythmias. It is now increasingly recognized that arrhythmias may be targeted by transcatheter ablation within the CS. This review summarizes pertinent anatomic considerations, explores the relationship between the CS and various arrhythmia substrates, elaborates on current indications for intra CS ablation and addresses efficacy and safety concerns associated with transcatheter ablation.

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.

Sex and gender aspects in antiarrhythmic therapy

Although cardiac arrhythmia had long been considered a predominantly male syndrome, it is now clear that arrhythmia is also a primary cause of mortality in women. Notably, the manifestation of specific arrhythmia syndromes appears to be gender specific. In particular, female sex is an independent risk factor for development of torsade de pointes (TdP) arrhythmias not only in congenital long QT syndromes but also in acquired long QT syndromes which occur as adverse effects of existing drugs. Males, on the other hand, are more likely to develop Brugada syndrome. Recent clinical and experimental studies suggest that these differences may stem from intrinsic sex differences in cardiac tissue. These include fundamental electrical differences resulting from variable ion channel expression and diverse sex hormonal regulation via long-term genomic and acute nongenomic pathways, and sex differences in drug responses and metabolisms. Undoubtedly, determining the effect of gender on cardiac function will be difficult and require sophisticated methodologies. However, gender differences underlying predilection to distinct arrhythmia syndromes must be revealed so that new therapeutic strategies that take gender into account can be applied to at-risk patients.

The allometric model in chronic myocardial infarction

Background

An allometric relationship between different electrocardiogram (ECG) parameters and infarcted ventricular mass was assessed in a myocardial infarction (MI) model in New Zealand rabbits.

Methods

A total of fifteen animals were used, out of which ten underwent left anterior descending coronary artery ligation to induce infarction (7–35% area). Myocardial infarction (MI) evolved and stabilized during a three month-period, after which, rabbits were sacrificed and the injured area was histologically confirmed. Right before sacrifice, ECGs were obtained to correlate several of its parameters to the infarcted mass. The latter was normalized after combining data from planimetry measurements and heart weight. The following ECG parameters were studied: RR and PR intervals, P-wave duration (P_D), QRS duration (QRS_D) and amplitude (QRS_A), Q-wave (Q_A), R-wave (R_A) and S-wave (S_A) amplitudes, T-wave peak amplitude (T_A), the interval from the peak to the end of the T-wave (T_PE), ST-segment deviation (ST_A), QT interval (QT), corrected QT and JT intervals. Corrected QT was analyzed with different correction formulae, i.e., Bazett (QT_B), Framingham (QT_FRA), Fridericia (QT_FRI), Hodge (QT_HO) and Matsunaga (QT_MA) and compared thereafter. The former variables and infarcted ventricular mass were then fitted to the allometric equation in terms of deviation from normality, in turn derived after ECGs in 5 healthy rabbits.

Results

Six variables (JT, QT_B, Q_A, S_A, T_A and ST_A) presented statistical differences among leads. QT showed the best allometric fit (r = 0.78), followed by T_A (r = 0.77), ST_A (r = 0.75), QT_FRA (r = 0.72), T_PE (r = 0.69), QT_FRI (r = 0.68) and QT_MA (r = 0.68). Corrected QT’s (QT_FRA, QT_FRI and QT_MA) performed worse than the uncorrected counterpart (QT), the former scaling allometrically with similar goodness of fits.

Conclusions

QT, T_A, ST_A and T_PE could possibly be used to assess infarction extent in an old MI event through the allometric model as a first approach. Moreover, the T_PE also produced a good allometric scaling, leading to the potential existence of promising allometric indexes to diagnose malignant arrhythmias.

Behavior of the electrocardiographic T peak to end interval in childhood

BACKGROUND

The T-wave peak to T-wave end (TpTe) interval reflects spatial and transmural dispersion in repolarization and serves as an arrhythmogenic index. Normal TpTe interval data in children are lacking. We evaluated the effects of age, gender, heart rate, leads (II and V(5)) on TpTe and T-wave voltage.

METHODS

Four hundred healthy children (age 4 days to 16.7 years) were enrolled. From a resting 12-lead digital ECG, TpTe, RR, QT, JT intervals, and T amplitude were measured (leads II and V(5)). Bazett and Fridericia formulas were applied to TpTe for heart rate correction and TpTe/QT and TpTe/JT were calculated. Descriptive and analytical statistics were applied, significance level set at P < or = 0.05.

RESULTS

TpTe in leads II and V(5) correlate well. Contrary to adults, no gender differences in TpTe were observed in childhood. TpTe lengthens with increasing age, and is inversely related to heart rate. TpTe 98th percentile is 85 msec in first 5 years, increasing to 92 msec in adolescence. TpTe Fridericia is a good correction formula in childhood; TpTe Bazett overcorrects in the younger age. TpTe/QT and TpTe/JT are longer in younger subjects due to greater QT shortening than the TpTe interval at higher heart rates.

CONCLUSIONS

In children, TpTe in lead II and V(5) correlate well. The TpTe interval lengthens with advancing age as heart rate diminishes. TpTe Fridericia is a good correction formula in children. Younger subjects have higher TpTe/QT and TpTe/JT indices compared to older children. T-wave voltage increases with age, tallest in the 5-10-year-age group particularly in V(5).

Reference values of electrocardiogram repolarization variables in a healthy population

INTRODUCTION

Reference values for T-wave morphology analysis and evaluation of the relationship with age, sex, and heart rate are lacking in the literature. In this study, we characterized T-wave morphology in a large sample of healthy individuals.

METHOD

A total of 1081 healthy subjects (83% men; range, 17-81 years) were included. T-wave morphology variables describing the duration, area, slopes, amplitude, and distribution were calculated using 10-second digital electrocardiogram recordings. Multivariate regression was used to test for dependence of T-wave variables with the subject age, sex, and heart rate.

RESULTS

Lead V5 (men vs women) T-wave variables were as follows: amplitude, 444 versus 317 muV; area, 48.4 versus 33.2 ms mV; Tpeak-Tend interval, 94 versus 92 milliseconds; maximal descending slope, -5.15 versus -3.69 muV/ms; skewness, -0.24 versus -0.22; and kurtosis, -0.36 versus -0.35. Tpeak-Tend interval, skewness, and kurtosis were independent of age, sex, and heart rate (r(2) < 0.05), whereas Bazett-corrected QT-interval was more dependent (r(2) = 0.40).

CONCLUSION

A selection of T-wave morphology variables is found to be clinically independent of age, sex, and heart rate, including Tpeak-Tend interval, skewness, and kurtosis.

Initial Experience Using a Forward Directed, High-Intensity Focused Ultrasound Balloon Catheter for Pulmonary Vein Antrum Isolation in Patients with Atrial Fibrillation

BACKGROUND

A high-intensity-focused ultrasound balloon catheter (HIFU-BC) is designed to isolate pulmonary veins (PV) outside the ostia (PV antrum). This catheter uses a parabolic CO2 balloon (behind water balloon) to focus a 20-, 25-, or 30-mm diameter ring of ultrasound forward of the balloon (parallel to catheter shaft). The purpose of this study is to test the safety and efficacy of the HIFU-BC for PV antrum isolation in patients with atrial fibrillation (AF).

METHODS AND RESULTS

Twenty-seven patients with paroxysmal (19 patients) or persistent (8 patients) AF were studied. Double transseptal puncture was performed for left atrial deployment of a Lasso catheter (for PV mapping) and the 14 Fr HIFU-BC. The HIFU-BC was positioned outside the PV orifice over a guidewire. HIFU energy (acoustic power 45 watts) was applied for 40 seconds with a 20-mm sonicating ring and 40 or 60 seconds with a 25-mm or 30-mm sonicating ring. No other ablation system was utilized. PV antrum isolation was attempted using HIFU-BC in 78 of 104 PVs (25/27 RSPVs, all 23 LSPVs, all 23 LIPVs, all four left common trunks and 3/27 RIPVs). HIFU-BC successfully isolated 68 (87%) of the 78PV antra with 1-26 (median 3) HIFU applications. The complications include transient bleeding from a distal branch of the left superior PV resulting from guidewire manipulation in one patient and right phrenic nerve injury in another patient. No PV stenosis (>50% narrowing) and no LA-esophageal fistula occurred. At the 12-month follow-up, 16 (59%) of the 27 patients were free of symptomatic episodes of AF (only 3 of the 16 patients were receiving antiarrhythmic medications).

CONCLUSIONS

Forward-focused HIFU applications isolated PVs outside the PV ostium with elimination of AF in 16 (59%) of the 27 patients at 12 months following the single ablation procedure.

Tpeak-Tend interval as an index of global dispersion of ventricular repolarization: evaluations using monophasic action potential mapping of the epi- and endocardium in swine

The ECG interval from the peak to the end of the T wave (Tpeak-Tend) has been used as an index of transmural dispersion of ventricular repolarization (DVR). The correlation between the Tpeak-Tend interval and the global DVR, however, has not been well-evaluated.

METHODS

Monophasic action potentials (MAPs) were recorded from 51+/-10 epicardial and 64 +/- 9 endocardial sites in the left ventricles of 10 pigs, and from 41+/-4 epicardial and 53+/-2 endocardial sites in the right ventricles of 2 of the 10 pigs using the CARTO mapping system. The end of repolarization times over the epi- and endocardium were measured, and the end of repolarization dispersions over the epicardium (DVR-epi), over the endocardium (DVR-endo) and over both (DVR-total) were calculated. The QTpeak, QTend and Tpeak-Tend intervals as well as the QTpeak and QTend dispersions were obtained from the simultaneously recorded 12-lead ECG.

RESULTS

The maximal Tpeak-Tend intervals (57+/-7 ms) were consistent with the DVR-total (58+/-11 ms, p>0.05), and significantly correlated with the DVR-total (r=0.64, p<0.05). However, the mean Tpeak-Tend intervals (44+/-5 ms), and Tpeak-Tend intervals from lead II (41+/-6 ms) and V5 (43+/-5 ms) were all significantly smaller than and poorly correlated with the DVR-total, as were the QTpeak and QTend dispersions (15+/-2 ms vs. 21+/-4 ms).

CONCLUSION

The maximal Tpeak-Tend interval may be used as a noninvasive estimate for the global DVR, but not the QTpeak and QTend dispersions, nor the mean Tpeak-Tend interval and that from a single lead.

Gender and age effects on ventricular repolarization abnormality in Japanese general carriers of a G643S common single nucleotide polymorphism for the KCNQ1 gene

BACKGROUND

The KCNQ1 single nucleotide polymorphism (SNP), G643S, is known to be associated with secondary long QT syndrome (LQTS) and to cause a mild reduction in KCNQ1 current. However, the precise incidence and its association with QT intervals remain unknown in the greater cohort of the population in Japan.

METHODS AND RESULTS

The genotype was screened at codon 643 of KCNQ1 in 992 residents of a farming community. Eighty-eight individuals (female/male =52/36, 8.9%) were found to have a heterozygous G643S SNP. Matching both gender and age, we randomly selected 243 control (G643G) cases and compared the electrocardiogram parameters in both groups; QT, QTf (QT corrected by Fridericia's formula) intervals, the peak and the end of the T wave (Tpe) interval, and the Tpe/QT ratio. The latter 2 reflect the transmural dispersion of ventricular repolarization (TDR). In G643S carriers, both Tpe and Tpe/QT were significantly longer than in non-carriers, without significant QT prolongation. Both genders showed a tendency for an increase in QTf with aging. In females, both Tpe and Tpe/QT showed a similar significant increase with age, which was not observed in males.

CONCLUSIONS

In elderly females, G643S might be an independent risk factor for secondary LQTS by causing a greater TDR.

Influence of Menstrual Cycle on QT Interval Dynamics

OBJECTIVES

The aim of this study was to investigate the effects of the menstrual cycle on QT interval dynamics and the autonomic tone in healthy women.

METHODS

Holter ECGs were recorded in 11 healthy women aged 18-32 years during the follicular and luteal phases of their regular menstrual cycle. The interval from QRS onset to the apex (QaT) and to the end of the T-wave (QeT), the interval between the apex and the end of the T-wave (Ta-e), and RR intervals were measured automatically in the course of 24 hours by Holter ECGs. The QeT/RR, QaT/RR, and Ta-e/RR relationships were evaluated in each subject. The autonomic tone was assessed by the serum catecholamine level at rest and heart rate variability was measured by Holter ECGs.

RESULTS

(1) The follicular and luteal phases did not differ significantly with respect to the slopes of the QeT/RR, QaT/RR, and Ta-e/RR relationships. However, QeT and QaT intervals were significantly shorter for all RR intervals in the luteal than in the follicular phase (P < 0.0001). (2) The serum progesterone concentration was significantly higher in the luteal than in the follicular phase (P < 0.001). (3) Noradrenaline was significantly higher in the luteal than in the follicular phase (P < 0.05). There was no significant difference in the follicular and luteal phases with respect to heart rate variability measurements.

CONCLUSIONS

Our results suggest that the menstrual cycle affects the QT intervals. The observed shorter QT interval during the luteal than the follicular phase may be attributable to the increase in serum progesterone and sympathetic tone.

Evidences of the gender-related differences in cardiac repolarization and the underlying mechanisms in different animal species and human

Clinical and experimental studies have shown that gender differences exist in cardiac repolarization in various animal species and human, as is evidenced by significantly longer QT, JT intervals and action potential duration in females than in males due to a reduced repolarization reserve in females. The latter is shown by the relatively greater increase in ventricular repolarization and higher incidence of torsades de pointes (TdP) in preparations from females by drugs blocking repolarizing K(+) currents. These results can be modulated by gonadectomy, suggesting that gonadal steroids are important determinants of gender difference in repolarization. In human subjects, QT and JT intervals are longer in women, whereas QT dispersion and Tp-e interval (the interval from the peak to the end of T wave) are longer in men. At slow heart rates greater prolongation in QT and increase in transmural repolarization heterogeneity (i.e. increase in Tp-e) may predispose to TdP tachycardias in women. In healthy postmenopausal women, hormone replacement therapy with estrogen alone usually produced a prolongation of QT interval, while estrogen plus progesterone had no significant effects on QT interval but reduced QT dispersion. Along with these, there are still conflicting data reported. Further work is needed before the elucidation of the basis of gender differences in ventricular repolarization.

Clinical implication of T-wave morphology analysis as a new repolarization descriptor

BACKGROUND

T-wave morphology analysis (TMA) quantifies irregularities of ventricular repolarization based on singular value decomposition of the 12-lead electrocardiogram (ECG). Furthermore, TMA is useful for risk stratification of patients with myocardial infarction (MI), although gender differences in TMA and the relationship between TMA and heart diseases are unknown. The aim of this study was to evaluate the significance of TMA in healthy individuals and patients with heart diseases.

METHODS AND RESULTS

Patients with heart disease and either with or without an implanted cardioverter defibrillator (ICD, n = 33, 57+/-16 years; non-ICD, n = 50, 67+/-10 years) were studied. Normal control ECGs (n = 114) were selected from Marquette's database (NC, 33+/-13 years) and the TMA descriptors, including T-wave morphology dispersion (TMD) and percentage of the loop area (PL), were calculated. TMD was significantly lower in group NC males than in the group NC females (11+/-5.9 vs 22+/-16, p < 0.0001). PL was significantly higher in group NC than in the ICD and non-ICD groups (0.63+/-0.12 vs 0.53+/-0.15, p < 0.0001). TMD of group NC was significantly lower than that of the ICD and non-ICD groups (14+/-11 vs 47+/-27, p < 0.0001).

CONCLUSION

There are gender differences in TMD. Abnormal values for TMA could reflect abnormalities of ventricular repolarization.

Gender differences in autonomic modulation of ventricular repolarization in humans

BACKGROUND

Gender differences in the incidence of ventricular arrhythmias have been reported and torsades de pointes associated with long QT syndrome are more common in women than men. Although increased sympathetic tone has an important role in vulnerability to arrhythmia, little is currently known regarding gender differences in the dynamic electrophysiological response to sympathetic stimulation. Therefore, we investigated whether there is a gender difference in humans with respect to the dynamic response of ventricular repolarization to beta-adrenergic stimulation and to autonomic blockade.

METHODS

Twelve-lead ECGs were continuously recorded during isoproterenol infusion (protocol 1) and autonomic blockade with propranolol and atropine infusion (protocol 2) in 24 healthy volunteers (12 men, 23 +/- 2 years; 12 women, 23 +/- 5 years). QT (QTc) intervals were measured at the baseline and at a heart rate of 75, 100, and 120 beats/min.

RESULTS

(1) The morphology of the T wave dynamically and transiently changed to bifid or biphasic during the acute phase of isoproterenol infusion. The incidence of these morphologic changes was higher in women than men (P < 0.05). (2) The QTc interval was initially prolonged and then shortened in both men and women during isoproterenol administration. However, QTc prolongation was significantly greater in women (0.44 +/- 0.02 to 0.55 +/- 0.03 sec) than men (0.42 +/- 0.03 to 0.51 +/- 0.04 sec; P < 0.05). (3) The QTc interval was significantly prolonged under autonomic blockade and the intrinsic QTc interval was longer in women than men (P < 0.05).

CONCLUSION

While sympathetic stimulation and autonomic blockade modulated the dynamics of ventricular repolarization in both sexes, it was more pronounced in women. This gender difference may partially account for the susceptibility of women to arrhythmogenesis.

Recent advances in understanding sex differences in cardiac repolarization

A number of gender differences exist in the human electrocardiogram (ECG): the P-wave and P-R intervals are slightly longer in men than in women, whilst women have higher resting heart rates than do men, but a longer rate-corrected QT (QT(C)) interval. Women with the LQT1 and LQT2 variants of congenital long-QT syndrome (LQTS) are at greater risk of adverse cardiac events. Similarly, many drugs associated with acquired LQTS have a greater risk of inducing torsades de pointes (TdP) arrhythmia in women than in men. There are also male:female differences in Brugada syndrome, early repolarisation syndrome and sudden cardiac death. The differences in the ECG between men and women, and in particular those relating to the QT interval, have been explored experimentally and provide evidence of differences in the processes underlying ventricular repolarization. The data available from rabbit, canine, rat, mouse and guinea pig models are reviewed and highlight involvement of male:female differences in Ca and K currents, although the possible involvement of rapid and persistent Na current and Na-Ca exchange currents cannot yet be excluded. The mechanisms underlying observed differences remain to be elucidated fully, but are likely to involve the influence of gonadal steroids. With respect to the QT interval and risk of TdP, a range of evidence implicates a protective role of testosterone in male hearts, possibly by both genomic and non-genomic pathways. Evidence regarding oestrogen and progesterone is less unequivocal, although the interplay between these two hormones may influence both repolarization and pro-arrhythmic risk.

Regulation of QT indices mediated by autonomic nervous function in patients with type 2 diabetes

Both the QT interval and QT dispersion in diabetic patients have been reported to increase with the progression of cardiac autonomic neuropathy and to have a prognostic value. We assessed the cardiac autonomic influences on QT indices using the measurements of baroreflex sensitivity, heart rate variability, and cardiac (123)I-metaiodobenzylguanidine scintigraphic findings in patients with type 2 diabetes mellitus. Forty-two consecutive patients with type 2 diabetes (mean+/-SD: 54+/-10 years, 22 women and 20 men) were studied. Baroreflex sensitivity negatively correlated with the maximum and minimum QTc intervals as well as QT/QTc dispersion. However, the high-frequency power and the ratio of low-frequency power to high-frequency power of heart rate variability did not correlate with any QT indices. The percent washout rate of (123)I-metaiodobenzylguanidine positively correlated with QT/QTc dispersion, but not with maximum and minimum QTc intervals. Our findings suggest that cardiac vagal dysfunction is related to QT interval prolongation while both sympathetic and vagal dysfunctions are related to increased QT dispersion in type 2 diabetic patients. Baroreflex sensitivity and percent washout rate of (123)I-metaiodobenzylguanidine may be useful parameters indicating the abnormalities of the cardiac ventricular repolarization in this population.

Gender Differences in the Dynamics of Terminal T Wave Intervals

This study was designed to investigate gender differences in the dynamic changes of the terminal T wave (Ta-e interval) of healthy subjects. Holter ECGs were recorded in 24 healthy volunteers (12 men aged 23 +/- 2 years). The intervals from QRS onset to the apex (QaT) and to the end of the T wave (QeT), and the interval between the apex and the end of the T wave (Ta-e) were measured. Then, the QeT/RR, QaT/RR, and Ta-e/RR relationship was evaluated by linear regression analysis in each subject. The QeT and QaT intervals were significantly longer in women than men and the slope of the QeT/RR and QaT/RR relationship was steeper in women than men. The Ta-e intervals showed a significant but weaker positive correlation with the preceding RR intervals in 7 (58.3%) men and 9 (75.0%) women. The average values of the slope and the correlation coefficient of the Ta-e/RR relationship were significantly smaller compared to those of QeT and QaT in both men and women (P < 0.0001). The slope of the Ta-e/RR relationship was significantly greater in women than men (0.025 +/- 0.009 vs 0.011 +/- 0.012, P < 0.005). However, the Ta-e intervals were significantly longer over the entire range of RR intervals in men than women (P < 0.0001). The rate-correcting formulas of Bazett and Framingham overcorrected the Ta-e intervals. The observed gender difference in the measurement and dynamics of the Ta-e interval may help to understand the mechanisms underlying the gender difference in the incidence of ventricular arrhythmias.

Role of Dipolar and Nondipolar Components of the T Wave in Determining the T Wave Residuum in an Isolated Rabbit Heart Model

INTRODUCTION

Repolarization heterogeneity has been shown to constitute a substrate for malignant ventricular arrhythmias. Noninvasive measurement of abnormal repolarization through assessment of QT interval dispersion from the resting standard 12-lead ECG initially had shown promise in assessing arrhythmia risk but was challenged recently. The relative T wave residuum (TWR) has been proposed recently to reflect regional repolarization dispersion more accurately. We analyzed the role played by the dipolar and nondipolar components in determining TWR.

METHODS AND RESULTS

Singular value decomposition was applied to the repolarization signals obtained from isolated rabbit hearts using a 5 x 8 array multielectrode recording system during premature beats (N = 11) and after d-sotalol (N = 9) exposure. Both the dipolar and nondipolar components of the T wave increased significantly during premature stimulation and after d-sotalol exposure. The relative TWR decreased significantly during premature stimulation but did not change after d-sotalol. Changes in the dipolar and nondipolar components of the second half of the T wave were significantly greater than those corresponding to the first half during premature stimulation, and a significant correlation was observed between the nondipolar components of the second half of the T wave and the T(peak-end) interval.

CONCLUSION

Conditions exist during which both the dipolar and nondipolar components can change simultaneously. Under these conditions, the relative TWR may not reflect regional heterogeneity of repolarization with accuracy. The nondipolar components of the second half of the T wave can be linked to assessment of the transmural dispersion of repolarization.