Repolarization Indices Research Articles

Evaluation of Tp-e interval and Tp-e/QT ratio in patients with rheumatoid arthritis

Several studies have suggested that the interval from the peak to the end of the electrocardiographic T wave (Tp-e) may correspond to the transmural dispersion of repolarization and that increased Tp-e interval and Tp-e/QT ratio are associated with malignant ventricular arrhythmias. The aim of this study was to evaluate ventricular repolarization by using the Tp-e interval and Tp-e/QT ratio in patients with rheumatoid arthritis (RA), and to assess the relation with inflammation. Ninety-six patients (72 females, 24 males; mean age 43.8±11.8 years) with RA and 50 controls (35 females, 15 males; mean age 44.2±11.1 years) were included. From the 12-lead electrocardiogram, Tp-e interval and Tp-e/QT ratio were measured. Blood samples were taken for erythrocyte sedimentation rate (ESR) and plasma levels of C-reactive protein (CRP). These parameters were compared between groups. The relationship between ventricular repolarization and inflammation was assessed by Pearson correlation coefficients. Tp-e interval and Tp-e/QT ratio were increased in RA patients compared to the controls (72.6±8.2 vs 66.4±8.5 ms, 0.20±0.02 vs 0.18±0.02; p<0.001 and p<0.001, respectively). The Tp-e interval was significantly correlated with CRP, ESR, and disease activity score (DAS-28) (r=0.56, p<0.001, r=0.57, p<0.001, and r=0.29, p=0.02, respectively). The Tp-e/QT ratio was also correlated with CRP, ESR, and DAS-28 score (r=0.43, p<0.001, r=0.53, p<0.001, and r=0.25, p=0.03, respectively). In RA patients, the increased frequency of ventricular arrhythmias may be explained by increased indexes of ventricular repolarization and their relationship with inflammation.

No association between high-density lipoprotein levels and ventricular repolarization indexes in subjects with primary hypercholesterolemia

Objective. Data regarding the effect of lipid parameters on repolarization are sparse. Recent data indicate that reconstituted HDL administration shortens repolarization in cardiomyocytes as well as the corrected QT (QTc) interval in human subjects. We investigated the potential association of high-density lipoprotein cholesterol (HDL-C) levels with conventional and novel electrocardiographic markers of ventricular repolarization in patients with hypercholesterolemia. Methods. Consecutive subjects with primary hypercholesterolemia were recruited. We recorded clinical and laboratory parameters as well as electrocardiographic indexes. With regard to ventricular repolarization, we calculated the QTc interval, the T peak-to-end (Tpe) interval, and the Tpe/QT ratio. Results. The study population consisted of 440 patients (199 men) with a median age of 56 [48–65] years. The correlation analysis (Spearman's) failed to show any association between HDL-C and any of the studied electrocardiographic parameter. Moreover, no correlation between other lipid parameters and the electrocardiograhic indexes was evident. Also, a comparison of the ventricular repolarization parameters between different HDL-C quartile groups (HDL-Q1: ≤ 1.11 mmol/L; HDL-Q2: 1.12–1.29 mmol/L; HDL-Q3: 1.30–1.53 mmol/L; HDL-Q4: ≥ 1.54 mmol/L) was performed. Specifically, the differences in QTc (p: 0.372), Tpe in leads II (p: 0.356), V2 (p: 0.372), V5 (p: 0.112), and Tpe/QT in leads II (p: 0.348), V2 (p: 0.162), V5 (p: 0.122) were not significant. Conclusion. HDL-C levels are not associated with the QTc interval or indexes of repolarization dispersion in patients with primary hypercholesterolemia. The potential antiarrhythmic efficacy of HDL should be further evaluated in the setting of myocardial ischemia where dynamic changes in the heterogeneity of ventricular repolarization ensue.

Comparison of Five QT Correction Methods in Patients with Hypoxic Brain Injury

PP-182 There has been increasing interest in developing non-invasive methods to assess ventricular arythmias and the risk of sudden cardiac arrest. Certain electrocardiographic repolarization indexes are valuable in determining prognosis of healthy individuals. Increases in the heart rate shortens

Ventricular repolarization indices as predictors of fatal arrhythmias in ischemia/reperfusion model

Ventricular repolarization indices as predictors of fatal arrhythmias in ischemia/reperfusion model

FRI0154 Increased risk of qt interval prolongation in rheumatoid arthritis patients compared to the general population: a population-based study

BackgroundPatients with rheumatoid arthritis (RA) have increased risk of sudden cardiac death (SCD), not entirely explained by RA disease characteristics. The 12-lead electrocardiogram (ECG) derived heart- rate corrected QT interval...

Antiarrhythmic effect of cardiac resynchronization therapy with triple-site biventricular stimulation

The antiarrhythmic effect of triple-site biventricular stimulation (Tri-V) is poorly understood. This study aims to evaluate the effect of cardiac resynchronization therapy (CRT) on ventricular arrhythmia (VA) with Tri-V using a single right ventricular (RV) and double left ventricular (LV) lead. Over a period of 3.5 years, 58 consecutive patients with New York Heart Association class II-IV heart failure, an LV ejection fraction of ≤ 0.35, and a QRS interval of ≥ 120 ms were enrolled. Acute haemodynamic responses to dual-site biventricular stimulation (Bi-V) and Tri-V were evaluated by assigning patients to a Bi-V or Tri-V group. Electrocardiogram parameters [QT interval, JT interval, and transmural dispersion of repolarization (TDR)] were measured over time after CRT. Spontaneous VA detected by telemetry was reviewed and confirmed. During a mean follow-up of 481 days after implantation, VA occurred in 2 of 22 patients in the Tri-V group and 14 of 36 patients in Bi-V group. Triple-site biventricular stimulation was thus associated with a decreased VA risk (P = 0.044). Multivariate Cox analysis showed that Tri-V pacing prevented arrhythmic events as compared with Bi-V pacing (hazard ratio, 0.13; 95% confidence interval, 0.029-0.610; P = 0.009). Ventricular repolarization indices at 6 months were significantly shortened in Tri-V compared with Bi-V (QTc, -23.6 vs. -14.1%, P = 0.008; JTc, -21.4 vs. -7.7%, P = 0.005; TDRc, -39.9 vs. -17.0%, P < 0.001). Compared with Bi-V, Tri-V reduced VA during long-term follow-up. Improvements in repolarization parameters may result in antiarrhythmic effects.

Long-term high-intensity interval training associated with lifestyle modifications improves QT dispersion parameters in metabolic syndrome patients

QT dispersion (QTd) is a marker of myocardial electrical instability, and is increased in metabolic syndrome (MetS). Moderate intensity continuous exercise (MICE) training was shown to improve QTd in MetS patients. To describe long-term effects of MICE and high-intensity interval exercise training (HIIT) on QTd parameters in MetS. Sixty-five MetS patients (53 ± 9 years) were assigned to either a MICE (60% of peak power output [PPO]), or a HIIT program (alternating phases of 15-30 s at 80% of PPO interspersed by passive recovery phases of equal duration), twice weekly during 9 months. Ventricular repolarization indices (QT dispersion=QTd, standard deviation of QT = sdQT, relative dispersion of QT = rdQT, QT corrected dispersion = QTcd), metabolic, anthropometric and exercise parameters were measured before and after the intervention. No adverse events were noted during exercise. QTd decreased significantly in both groups (51 vs 56 ms in MICE, P < 0.05; 34 vs 38 ms in HIIT, P < 0.05). Changes in QTd were correlated with changes in maximal heart rate (r = -0.69, P < 0.0001) and in heart rate recovery (r = -0.49, P < 0.01) in the HIIT group only. When compared to MICE, HIIT training induced a greater decrease in weight, BMI and waist circumference. Exercise capacity significantly improved by 0.82 and 1.25 METs in MICE and HIIT groups respectively (P < 0.0001). Lipid parameters also improved to the same degree in both groups. In MetS, long-term HIIT and MICE training led to comparable effects on ventricular repolarization indices, and HIIT might be associated with greater improvements in certain cardiometabolic risk factors.

Evaluation of Tp-e interval and Tp-e/QT ratio in patients with ankylosing spondylitis.

OBJECTIVES: Ankylosing spondylitis (AS) is a chronic multi-systemic inflammatory rheumatic disorder. Several studies have suggested that the interval from the peak to the end of the electrocardiographic T wave (Tp-e) may correspond to the transmural dispersion of repolarization and that increased Tp-e interval and Tp-e/QT ratio are associated with malignant ventricular arrhythmias. The aim of this study was to evaluate ventricular repolarization by using Tp-e interval and Tp-e/QT ratio in patients with AS, and to assess the relation with inflammation. METHODS: Sixty-two patients with AS and 50 controls were included. Tp-e interval and Tp-e/QT ratio were measured from a 12-lead electrocardiogram, and the Tp-e interval corrected for heart rate. The plasma level of high sensitive C-reactive protein (hsCRP) was measured. These parameters were compared between groups. RESULTS: In electrocardiographic parameters analysis, QT dispersion (QTd) and corrected QTd were significantly increased in AS patients compared to the controls (31.7±9.6 vs 28.2±7.4 and 35.8±11.5 vs 30.6±7.9ms, P=0.03 and P=0.007, respectively). cTp-e interval and Tp-e/QT ratio were also significantly higher in AS patients (92.1±10.2 vs 75.8±8.4 and 0.22±0.02 vs 0.19±0.02ms, all P values <0.001). cTp-e interval and Tp-e/QT ratio were significantly correlated with hsCRP (r=0.63, P<0.001 and r=0.49, P<0.001, respectively). CONCLUSIONS: Our study revealed that Tp-e interval and Tp-e/QT ratio were increased in AS patients. These electrocardiographic ventricular repolarization indexes were significantly correlated with the plasma level of hsCRP.

SNPs Identified as Modulators of ECG Traits in the General Population Do Not Markedly Affect ECG Traits during Acute Myocardial Infarction nor Ventricular Fibrillation Risk in This Condition

BackgroundVentricular fibrillation (VF) in the setting of acute ST elevation myocardial infarction (STEMI) is a leading cause of mortality. Although the risk of VF has a genetic component, the underlying genetic factors are largely unknown. Since heart rate and ECG intervals of conduction and repolarization during acute STEMI differ between patients who do and patients who do not develop VF, we investigated whether SNPs known to modulate these ECG indices in the general population also impact on the respective ECG indices during STEMI and on the risk of VF.Methods and ResultsThe study population consisted of participants of the Arrhythmia Genetics in the NEtherlandS (AGNES) study, which enrols patients with a first STEMI that develop VF (cases) and patients that do not develop VF (controls). SNPs known to impact on RR interval, PR interval, QRS duration or QTc interval in the general population were tested for effects on the respective STEMI ECG indices (stage 1). Only those showing a (suggestive) significant association were tested for association with VF (stage 2). On average, VF cases had a shorter RR and a longer QTc interval compared to non-VF controls. Eight SNPs showed a trend for association with the respective STEMI ECG indices. Of these, three were also suggestively associated with VF.ConclusionsRR interval and ECG indices of conduction and repolarization during acute STEMI differ between patients who develop VF and patients who do not. Although the effects of the SNPs on ECG indices during an acute STEMI seem to be similar in magnitude and direction as those found in the general population, the effects, at least in isolation, are too small to explain the differences in ECGs between cases and controls and to determine risk of VF.

Impaired Ventricular Repolarization Dynamics in Patients with Early Repolarization Syndrome

Almost all current investigations on early repolarization syndrome (ERS) have focused on the J-wave characteristics and ST-segment configuration; however, few have reported on ventricular repolarization indexes in ERS. A total of 145 subjects were enrolled: 10 ERS patients, 45 uneventful ER pattern (ERP) subjects, and 90 healthy controls without J waves or ST-segment elevation. Ambulatory ECG-derived parameters (QT, QTc(B), QTc(F), T peak-Tend(Tpe), and QT/RR slope) were measured and statistically compared. Among the groups, there was no significant difference in the average QT and QTc(B); however, ERS patients had the shortest QTc(F) and longest Tpe (QTc(F): 396.2 ± 19 vs 410.4 ± 20 vs 419.2 ± 19 milliseconds, P = 0.036, Tpe: 84.9 ± 12 vs 70.4 ± 11 vs 66.9 ± 15 milliseconds, P < 0.001, for the ERS, ERP, and control groups, respectively). Importantly, the 24-hour QT/RR slope was significantly smaller in the ERS than ERP and control groups (QT/RR: 0.105 ± 0.01 vs 0.154 ± 0.02 vs 0.161 ± 0.03, respectively; P < 0.001). When analyzing the diurnal and nocturnal QT/RR slopes, ERS patients had small diurnal and nocturnal QT/RR slopes while the ERP and control groups had large diurnal and small nocturnal QT/RR slopes (diurnal QT/RR: 0. 077 ± 0.01 vs 0.132 ± 0.03 vs 0.143 ± 0.03, P < 0.001; nocturnal QT/RR: 0.093 ± 0.02 vs 0.129 ± 0.03 vs 0.130 ± 0.04, P = 0.02 in the ERS, ERP, and control groups, respectively). ERS patients had a continuously depressed diurnal and nocturnal adaptation of the QT interval to the heart rate. Such abnormal repolarization dynamics might provide a substrate for reentry and be an important element for developing ventricular fibrillation in the ERS cohort.

The Impact of Hemodialysis on the Dispersion of Ventricular Repolarization

Sudden cardiac death is prevalent in chronic hemodialysis (HD) patients while the dialysis process may have arrhythmogenic potential. We sought to examine the effect of HD on conventional electrocardiographic parameters as well as on novel indexes of repolarization, given that increased spatial dispersion of repolarization is related to ventricular arrhythmias. We recorded clinical, echocardiographic, and laboratory parameters as well as electrocardiographic indexes before and after a single HD session. Specifically, we calculated the QTc interval, the QRS duration, the T peak-to-end (Tpe) interval, and the Tpe/QT ratio. The study population consisted of 66 chronic HD patients (mean age: 68.9 ± 11.8 years, 40 males). Heart rate, blood pressure, QRS duration, QTc interval, and QT dispersion did not change significantly after the HD session. However, the Tpe interval and the Tpe/QT ratio increased significantly (80 [65-90] ms vs 85 [77.5-100] ms; P = 0.04, and 0.21 [0.18-0.24] vs 0.25 [0.21-0.28]; P = 0.05, respectively). Correlation analysis and multiple regression analysis failed to show significant associations between the baseline parameters and the baseline values of Tpe and Tpe/QT or between the change of the laboratory parameters during HD and the corresponding change of the Tpe and the Tpe/QT values. No significant arrhythmias were observed during the HD sessions. HD induces an increase in novel markers of spatial dispersion of ventricular repolarization. Whether the assessment of these indexes of heterogeneity of repolarization at baseline or their change during HD has a prognostic value with regard to future untoward events, remains to be elucidated.

Ibutilide and novel indexes of ventricular repolarization in persistent atrial fibrillation patients

To examine the effect of ibutilide on novel indexes of repolarization in patients with persistent atrial fibrillation (AF). We studied consecutive patients scheduled for elective electrical cardioversion. Intravenous ibutilide (1 + 1 mg) was administered before the electrical cardioversion while close electrocardiographic (ECG) monitoring was performed. ECG indexes such as corrected QT interval (QTc), the interval from the peak until the end of T wave (Tpe), and the Tpe/QT ratio were measured before ibutilide infusion and 10 min after the end of infusion. The final study population consisted of 20 patients (mean age: 67.1 ± 9.9 years, 10 men). Six patients were cardioverted pharmacologically and did not proceed to electrical cardioversion. Two patients developed short non-sustained episodes of torsades de pointes ventricular tachycardia. All but one of the aforementioned ECG indexes increased significantly after ibutilide administration. In specific, the QTc interval increased from 442 ± 29 to 471 ± 37 ms (P = 0.037), the Tpe interval in precordial leads from 96 ms (range 80-108 ms) to 101 ms (range 91-119 ms) (P = 0.021), the Tpe interval in lead II from 79 ms (range 70-88 ms) to 100 ms (range 87-104 ms) (P < 0.001), the Tpe/QT ratio in precordial leads from 0.23 ms (range 0.18-0.26 ms) to 0.26 ms (range 0.23-0.28 ms) (P = 0.028), and the Tpe interval dispersion from 25 ms (range 23-30 ms) to 35 ms (range 27-39 ms) (P = 0.012). However, the Tpe/QT ratio in lead II did not change significantly. Ibutilide increases the duration and dispersion of ventricular repolarization. The prognostic value of Tpe and Tpe/QT in the setting of drug-induced proarrhythmia needs further study.

Detection of Peripartum Myocardial Burden by Vector-Projected 187 Channel Electrocardiography and Serum NT-proBNP

There is no reliable method of screening for pregnant women at high risk of developing severe myocardial disorders. In this study, we used vector-projected 187 channel electrocardiography (DREAM-ECG) and serum biochemical markers to evaluate peripartum myocardial burden in pregnant women. Forty-one pregnant women were examined at 36-37 weeks gestation (GW36), 7 days postpartum (PPD7), and 1 month postpartum (PPM1). Ten non-pregnant control women were assessed at a single time point. Heart rate, sympathetic index, and repolarization index (RTc dispersion) were quantified using the DREAM-ECG system, and serum levels of NT-proBNP, cardiac troponin T, estrogen, and progesterone were determined. Heart rate and the sympathetic index decreased from GW36 to PPM1 (P = 0.0031). The repolarization index decreased over time and was greater than in non-pregnant controls (31 ± 13 ms). Estrogen and progesterone at PPD7 and PPM1 were significantly lower than those at GW36 (P < 0.0001, P < 0.001). NT-proBNP at PPD7 was greater than at GW36 (median 29 pg/mL at GW36, 86 pg/mL at PPD7), and decreased at PPM1 in comparison to PPD7 (median 18.5 pg/mL). Troponin T was in the normal range during the whole period (< 0.003 ng/mL). In conclusion, these results indicate that the peripartum myocardial burden in pregnant women does not return to normal nonpregnant levels by PPM1. We propose that both repolarization indexes such as RTc dispersion by DREAM-ECG and serum biochemical markers may identify pregnant women at high risk of developing severe myocardial damage in the peripartum period.

Characterization of ventricular depolarization and repolarization changes in a porcine model of myocardial infarction

In this study, several electrocardiogram (ECG)-derived indices corresponding to both ventricular depolarization and repolarization were evaluated during acute myocardial ischemia in an experimental model of myocardial infarction produced by 40 min coronary balloon inflation in 13 pigs. Significant changes were rapidly observed from minute 4 after the start of coronary occlusion, achieving their maximum values between 11 and 22 min for depolarization and between 9 and 12 min for repolarization indices, respectively. Subsequently, these maximum changes started to decrease during the latter part of the occlusion. Depolarization changes associated with the second half of the QRS complex showed a significant but inverse correlation with the myocardium at risk (MaR) estimated by scintigraphic images. The correlation between MaR and changes of the downward slope of the QRS complex, , evaluated at the two more relevant peaks observed during the occlusion, was r = −0.75, p < 0.01 and r = −0.79, p < 0.01 for the positive and negative deflections observed in temporal evolution, respectively. Repolarization changes, analyzed by evaluation of ST segment elevation at the main observed positive peak, also showed negative, however non-significant correlation with MaR: r = −0.34, p = 0.28. Our results suggest that changes evaluated in the latter part of the depolarization, such as those described by , which are influenced by R-wave amplitude, QRS width and ST level variations simultaneously, correlate better with the amount of ischemia than other indices evaluated in the earlier part of depolarization or during the ST segment.

1663 Early Coronary Flow and ECG Changes Following Cardiopulmonary Bypass Surgery in Children with Congenital Heart Disease

BackgroundSurgery with cardiopulmonary bypass (CPB) remains the mainstay of therapy in children with congenital heart defects but little is known about its pathophysiologic consequences. We have recently demonstrated that CPB...

Apicobasal gradient of left ventricular myocardial edema underlies transient T-wave inversion and QT interval prolongation (Wellens’ ECG pattern) in Tako-Tsubo cardiomyopathy

Tako-Tsubo cardiomyopathy (TTC) presents with chest pain, ST-segment elevation followed by T-wave inversion and QT interval prolongation (Wellens' electrocardiographic [ECG] pattern), and left ventricular dysfunction, which may mimic an acute coronary syndrome. To assess the pathophysiologic basis of the Wellens' ECG pattern in TTC by characterization of underlying myocardial changes by using cardiac magnetic resonance (CMR). The study population included 20 consecutive patients with TTC (95% women; mean age 65.3 ± 10.4 years) who underwent CMR studies both in the initial phase and after 3-month follow-up by using a protocol that included cine images, T2-weighted sequences for myocardial edema, and post-contrast sequences for late gadolinium enhancement. Quantitative ECG indices of repolarization, such as maximal amplitude of negative T waves, sum of the amplitudes of negative T waves, and maximum corrected QT interval (QTc max), were correlated to CMR findings. At the time of initial CMR study, there was a significant linear correlation between the apicobasal ratio of T2-weighted signal intensity for myocardial edema and the maximal amplitude of negative T waves (ρ = 0.498; P = .02), sum of the amplitudes of negative T waves (ρ = 0.483; P = .03), and maximum corrected QT interval (ρ = 0.520; P = .02). Repolarization indices were unrelated to either late gadolinium enhancement or quantitative cine parameters. Wellens' ECG abnormalities and myocardial edema showed a parallel time course of development and resolution on initial and follow-up CMR studies. Our study results show that the ischemic-like Wellens' ECG pattern in TTC coincides and quantitatively correlates with the apicobasal gradient of myocardial edema as evidenced by using CMR. Dynamic negative T waves and QTc prolongation are likely to reflect the edema-induced transient inhomogeneity and dispersion of repolarization between apical and basal left ventricular regions.

Repolarization Perturbation and Hypomagnesemia after Extreme Exercise

Strenuous exercise induces significant increases in inflammatory and cardiac biomarkers and transient dysfunction of the left ventricle. It is still unclear whether the electrophysiological correlate of these alterations can also be observed in ECG recordings, which indicate increased vulnerability for arrhythmias. ECG parameters were measured and compared with inflammatory and electrolyte statuses in 198 healthy men (42 ± 9 yr) 1 wk before (baseline) and at 0, 24, and 72 h after participating in a marathon. HR-corrected QT interval (QTc) duration increased significantly immediately after the race (442.4 ± 23.0 ms) compared with baseline (415.3 ± 22.5 ms, P < 0.001) and returned to baseline values within 72 h (415.8 ± 24.7 ms). Other indices of ventricular repolarization (Sagie-Framingham-corrected QTcF, T(peak)-Tend (T(pe)) duration, T(pe)/QT ratio) showed similar results.Compared with baseline, significant decreases in serum concentrations of magnesium and potassium were shown immediately after the race (median (interquartile range): [Mg(2+)] = 0.85 (0.79-0.92) vs 0.77 (0.70-0.82) mmol · L(-1), P < 0.001; [K+] = 4.27 (4.02-4.58) vs 4.14 (3.81-4.57) mmol · L(-1), P < 0.05). Interleukin 6 values were significantly augmented immediately after the race compared with baseline (interleukin 6 = 2.08 (1.96-2.20) vs 30.56 (19.83-43.63) ng · L, P < 0.001) and returned to baseline values within 72 h.Significant associations were not observed between ECG alterations and inflammatory or electrolyte concentrations (all P > 0.05). Cardiac repolarization was significantly altered immediately after a marathon, coincident with hypomagnesemia and hypokalemia. Inflammatory and electrolyte statuses returned to baseline values within 72 h. The current data do not support that ECG alterations after marathon running represent an increased risk for arrhythmic events. However, further investigation is warranted to describe these relationships in more detail.

P-wave parameters and cardiac repolarization indices: Does menopausal status matter?

Background and purposeData regarding electrocardiographic characteristics of postmenopausal women are lacking. In this prospective, cross-sectional study, electrocardiographic P-wave parameters and cardiac repolarization indices of age-matched pre- and postmenopausal healthy women were compared. We hypothesized that menopausal status would have a significant effect on cardiac electrical activity and hence electrocardiography (ECG) recordings. Materials and methodsTwelve-lead ECG recordings were obtained from 125 consecutively recruited postmenopausal healthy women aged between 44 and 54years. The control group consisted of 125 age-matched premenopausal women. P-wave parameters and cardiac repolarization indices were measured and compared with respect to menopausal status. ResultsDemographic features of premenopausal and postmenopausal women were comparable. There were no significant differences between two groups regarding mean values of heart rate, maximum and minimum P-wave duration, P-wave dispersion, maximum and minimum QT interval, and QT dispersion. Mean values of QT interval obtained from lead V5 were also similar. Corrected values which were calculated according to Bazett and Fridericia formulas also did not differ between the groups. Mean values of Tpeak to Tend (TpTe) (p<0.001) and corrected TpTe (p=0.001) intervals obtained from lead V5 were significantly shorter in postmenopausal women when compared to those without menopause. ConclusionTpeak to Tend interval decreased significantly while QT intervals and P-wave parameters did not change in postmenopausal women when compared to premenopausal women. Association of these findings with changes in levels of sex steroids and their prognostic implications need to be elucidated with further studies.

The effects of continuous positive airway pressure therapy withdrawal on cardiac repolarization: data from a randomized controlled trial

The preliminary evidence supports an association between obstructive sleep apnoea (OSA), disturbed cardiac repolarization, and consequent cardiac dysrhythmias. The aim of the current trial was to assess the effects of continuous positive airway pressure (CPAP) therapy withdrawal on the measures of cardiac repolarization in patients with OSA. Forty-one OSA patients established on CPAP treatment were randomized to either CPAP withdrawal (subtherapeutic CPAP) or continue therapeutic CPAP for 2 weeks. Polysomnography was performed, and indices of cardiac repolarization (QT(c), TpTe(c) intervals) and dispersion of repolarization (TpTe/QT ratio) were derived from 12-lead electrocardiography (ECG) at baseline and 2 weeks. Continuous positive airway pressure withdrawal led to a recurrence of OSA. Compared with therapeutic CPAP, subtherapeutic CPAP for 2 weeks was associated with a significant increase in the length of the QT(c) and TpTe(c) intervals (mean difference between groups 21.4 ms, 95% CI 11.3-1.6 ms, P < 0.001 and 14.4 ms, 95% CI 7.2-21.5 ms, P < 0.001, respectively) and in the TpTe/QT ratio (mean difference between groups 0.02, 95% CI 0.00-0.03, P = 0.020). There was a statistically significant correlation between the change in apnoea/hypopnoea index (AHI) from baseline, and both the change in the QT(c) interval and the TpTe(c) interval (r = 0.60, 95% CI 0.36-0.77, P < 0.001 and r = 0.45, 95% CI 0.17-0.67, P = 0.003, n = 41, respectively). Continuous positive airway pressure withdrawal is associated with the prolongation of the QT(c) and TpTe(c) intervals and TpTe/QT ratio, which may provide a possible mechanistic link between OSA, cardiac dysrhythmias, and thus sudden cardiac death.

Circadian rhythms govern cardiac repolarization and arrhythmogenesis.

Sudden cardiac death exhibits diurnal variation in both acquired and hereditary forms of heart disease 1, 2, but the molecular basis is unknown. A common mechanism that underlies susceptibility to ventricular arrhythmias is abnormalities in the duration (e.g. short or long QT syndromes, heart failure) 3-5 or pattern (e.g. Brugada syndrome) 6 of myocardial repolarization. Here we provide the first molecular evidence that links circadian rhythms to vulnerability in ventricular arrhythmias in mice. Specifically, we show that cardiac ion channel expression and QT interval duration (an index of myocardial repolarization) exhibit endogenous circadian rhythmicity under the control of a novel clock-dependent oscillator, Krüppel-like factor 15 (Klf15). Klf15 transcriptionally controls rhythmic expression of KChIP2, a critical subunit required for generating the transient outward potassium current (Ito). 7 Deficiency or excess of Klf15 causes loss of rhythmic QT variation, abnormal repolarization and enhanced susceptibility to ventricular arrhythmias. In sum, these findings identify circadian transcription of ion channels as a novel mechanism for cardiac arrhythmogenesis.