Electrocardiographic QT interval and mortality: a meta-analysis

Association of same-day urinary phenol levels and cardiac electrical alterations: analysis of the Fernald Community Cohort

Background

Exposure to phenols has been linked in animal models and human populations to cardiac function alterations and cardiovascular diseases, although their effects on cardiac electrical properties in humans remains to be established. This study aimed to identify changes in electrocardiographic (ECG) parameters associated with environmental phenol exposure in adults of a midwestern large cohort known as the Fernald Community Cohort (FCC).

Methods

During the day of the first comprehensive medical examination, urine samples were obtained, and electrocardiograms were recorded. Cross-sectional linear regression analyses were performed.

Results

Bisphenol A (BPA) and bisphenol F (BPF) were both associated with a longer PR interval, an indication of delayed atrial-to-ventricle conduction, in females (p < 0.05) but not males. BPA combined with BPF was associated with an increase QRS duration, an indication of delayed ventricular activation, in females (P < 0.05) but not males. Higher triclocarban (TCC) level was associated with longer QTc interval, an indication of delayed ventricular repolarization, in males (P < 0.01) but not females. Body mass index (BMI) was associated with a significant increase in PR and QTc intervals and ventricular rate in females and in ventricular rate in males. In females, the combined effect of being in the top tertile for both BPA urinary concentration and BMI was an estimate of a 10% increase in PR interval. No associations were found with the other phenols.

Conclusion

Higher exposure to some phenols was associated with alterations of cardiac electrical properties in a sex specific manner in the Fernald cohort. Our population-based findings correlate directly with clinically relevant parameters that are associated with known pathophysiologic cardiac conditions in humans.

New Insights on Cardiac Arrhythmias in Patients With Kidney Disease

The risk of arrhythmia and its management become increasingly complex as kidney disease progresses. This presents a multifaceted clinical challenge. Our discussion addresses these specific challenges relevant to patients as their kidney disease advances. We highlight numerous opportunities for enhancing the current standard of care within this realm. Additionally, this review delves into research concerning early detection, prevention, diagnosis, and treatment of various arrhythmias spanning the spectrum of kidney disease.

Beat-to-beat cardiac repolarization lability increases during hypoxemia and arousals in obstructive sleep apnea patients

Obstructive sleep apnea (OSA) is associated with the progression of cardiovascular diseases, arrhythmias, and sudden cardiac death (SCD). However, the acute impacts of OSA and its consequences on heart function are not yet fully elucidated. We hypothesized that desaturation events acutely destabilize ventricular repolarization, and the presence of accompanying arousals magnifies this destabilization. Ventricular repolarization lability measures, comprising heart rate corrected QT (QTc), short-time-variability of QT (STVQT), and QT variability index (QTVI), were calculated before, during, and after 20,955 desaturations from lead II electrocardiography signals of 492 patients with suspected OSA (52% men). Variations in repolarization parameters were assessed during and after desaturations, both with and without accompanying arousals, and groupwise comparisons were performed based on desaturation duration and depth. Regression analyses were used to investigate the influence of confounding factors, comorbidities, and medications. The standard deviation (SD) of QT, mean QTc, SDQTc, and STVQT increased significantly (P < 0.01), whereas QTVI decreased (P < 0.01) during and after desaturations. The changes in SDQT, mean QTc, SDQTc, and QTVI were significantly amplified (P < 0.01) in the presence of accompanying arousals. Desaturation depth was an independent predictor of increased SDQTc (β = 0.405, P < 0.01), STVQT (β = 0.151, P < 0.01), and QTVI (β = 0.009, P < 0.01) during desaturation. Desaturations cause acute changes in ventricular repolarization, with deeper desaturations and accompanying arousals independently contributing to increased ventricular repolarization lability. This may partially explain the increased risk of arrhythmias and SCD in patients with OSA, especially when the OSA phenotype includes high hypoxic load and fragmented sleep.NEW & NOTEWORTHY Nocturnal desaturations are associated with increased ventricular repolarization lability. Deeper desaturations with accompanying arousals increase the magnitude of alterations, independent of confounding factors, comorbidities, and medications. Changes associated with desaturations can partially explain the increased risk of arrhythmias and sudden cardiac death in patients with OSA, especially in patients with high hypoxic load and fragmented sleep. This highlights the importance of detailed electrocardiogram analytics for patients with OSA.

Prevalence and prognostic value of electrocardiographic abnormalities in hypokalemia: A multicenter cohort study

BACKGROUND

Hypokalemia is common in hospitalized patients and associated with ECG abnormalities. The prevalence and prognostic value of ECG abnormalities in hypokalemic patients are, however, not well established.

METHODS

The study was a multicentered cohort study, including all ault patients with an ECG and potassium level <4.4 mmol/L recorded at arrival to four emergency departments in Denmark and Sweden. Using computerized measurements from ECGs, we investigated the relationship between potassium levels and heart rate, QRS duration, corrected QT (QTc) interval, ST-segment depressions, T-wave flattening, and T-wave inversion using cubic splines. Within strata of potassium levels, we further estimated the hazard ratio (HR) for 7-day mortality, admission to the intensive care unit (ICU), and diagnosis of ventricular arrhythmia or cardiac arrest, comparing patients with and without specific ECG abnormalities matched 1:2 on propensity scores.

RESULTS

Among 79,599 included patients, decreasing potassium levels were associated with a concentration-dependent increase in all investigated ECG variables. ECG abnormalities were present in 40% of hypokalemic patients ([K+ ] <3.5 mmol/L), with T-wave flattening, ST-segment depression, and QTc prolongation occurring in 27%, 16%, and 14%. In patients with mild hypokalemia ([K+ ] 3.0-3.4 mmol/L), a heart rate >100 bpm, ST-depressions, and T-wave inversion were associated with increased HRs for 7-day mortality and ICU admission, whereas only a heart rate >100 bpm predicted both mortality and ICU admission among patients with [K+ ] <3.0 mmol/L. HR estimates were, however, similar to those in eukalemic patients. The low number of events with ventricular arrhythmia limited evaluation for this outcome.

CONCLUSIONS

ECG abnormalities were common in hypokalemic patients, but they are poor prognostic markers for short-term adverse events under the current standard of care.

Relationship between Alzheimer dementia and QT interval: A meta-analysis

While the link between aging and mortality from dementia is widely appreciated, the mechanism is not clear. The objective of this study was to determine whether there is a direct relationship between Alzheimer dementia (AD) and the QT interval, because the latter has been related to cardiac mortality. A systematic review and meta-analysis were conducted after a Medline and EMBASE search using terms "Alzheimer disease or Dementia AND QT interval, QT dispersion or cardiac repolarization." Four studies with control groups were identified. There were significant differences in QT interval between individuals with AD vs individuals without dementia (controls) (odds ratio (OR)1.665 [random effects model] and 1.879 [fixed effect model]) (p < 0.001). There were significant differences in QT interval between individuals with AD vs individuals with mild cognitive impairment (MCI) (OR 1.760 [random effects] and 1.810 [fixed effect]) (p < 0.001). A significant (p <0.001) correlation exists between the QTc and the Mini-Mental State Exam (MMSE), a test of cognitive function. Two studies examined QT variability (the difference between the longest and shortest QT interval on a 12 lead ECG); the OR for QT variability AD vs MCI was 3.858 [random effects model] and 3.712 [fixed effects model] (p < 0.001). When compared to the control group, the OR for QT dispersion in AD was 6.358 [random effects model] or 5.143 ( P< 0.001) [fixed effects model]. A qualitative analysis of the data raised questions about paucity of data defining the nature of the control groups, the pathophysiologic mechanism, and the uniform use of a poor QT heart rate correction factor. The longer QT in AD, greater QT variability in AD, and the direct relationship between QT interval and AD severity supports a brain-heart connection in AD that might be fundamental to aging-induced AD and mortality. Issues with defining the control group, limited number of studies, conflicting data in population studies, and the lack of a strong electrophysiological basis underscore the need for additional research in this field.

Dapagliflozin Pretreatment Prevents Cardiac Electrophysiological Changes in a Diet and Streptozotocin Induction of Type 2 Diabetes in Rats: A Potential New First-Line?

Purpose

Dapagliflozin exerts cardioprotective effects in Type 2 Diabetes Mellitus (T2DM). However, whether these effects prevent electrocardiographic changes associated with T2DM altogether remain unknown. Our aim was to investigate the prophylactic effect of dapagliflozin pretreatment on the rat ECG using a high-fat, high-fructose (HFHf) diet and a low dose streptozotocin (STZ) model of T2DM.

Methods

Twenty-five (25) rats were randomized into five (5) groups: normal control receiving a normal diet while the other groups received an 8-week HFHf and 40mg/kg STZ on day 42, and either: saline for the diabetic control (1 mg/kg/d), low dose (1.0 mg/kg/d) and high dose dapagliflozin (1.6 mg/kg/d), or metformin (250 mg/kg/d). Oral glucose tolerance (OGT), electrocardiograms (ECGs), paracardial adipose mass, and left ventricular fibrosis were determined. Data were analyzed using GraphPad version 9.0.0.121, with the level of significance at p < 0.05.

Results

Compared to the diabetic control group, a high dose of dapagliflozin preserved the OGT (p = 0.0001), QRS-duration (p = 0.0263), QT-interval (p = 0.0399), and QTc intervals (p = 0.0463). Furthermore, the high dose dapagliflozin group had the lowest paracardial adipose mass (p = 0.0104) and fibrotic area (p = 0.0001). In contrast, while metformin showed favorable effects on OGT (p = 0.0025), paracardial adiposity (p = 0.0153) and ventricular fibrosis (p = 0.0291), it did not demonstrate significant antiarrhythmic effects.

Conclusion

Pretreatment with higher doses of Dapagliflozin exhibits prophylactic cardioprotective characteristics against diabetic cardiomyopathy that include antifibrotic and antiarrhythmic qualities. This suggests that higher doses of dapagliflozin could be a more effective initial therapeutic option in T2DM.

QTc intervals at rest and during exercise assessed by group correction formulas in survivors of childhood acute lymphoblastic leukemia

INTRODUCTION

Early signs of subclinical cardiac damage must be identified before they turn into clinical manifestations. Tailoring a formula is relevant for precise QTc evaluation in childhood acute lymphoblastic leukemia (ALL) survivors considering they are at risk of long-term cardiac problems. Therefore, we aim to develop group heart rate correction formulas for QT intervals in childhood ALL survivors at rest and during exercise, and to assess the applicability of these methods across a variety of risk groups exposed to diverse chemotherapy dosages.

METHODS

Two hundred and fifty childhood ALL survivors in the PETALE study were classified into 3 groups depending on their prognostic risk group. ECG measurements (QT and RR intervals) were made at rest and during a cardiopulmonary exercise test. QT correction for heart rate was applied using 5 different formulas, which included 2 previously published formulas and 3 group-specific formulas for each sex.

RESULTS

The QT/RR relation showed 2 different curves between rest and during exercise, which was worse for females. Group-specific QTc formulas allowed adequate heart rate-corrected QT interval, independently of the cumulative dose of doxorubicin received during treatment. Group-specific formulas showed significantly shorter QTc intervals than QTc from Bazett's formula. QTc (Bazett's formula) values surpassed the established clinical norm in 22 males (11%) and 22 females (11%), with a majority occurring during exercise, affecting 15 males (7.5%) and 10 females (5%).

CONCLUSION

This study shows the applicability of personalized group correction of QT/RR data in childhood ALL survivors. Our comprehensive assessments (spanning rest, exercise, and recovery) is an effective approach for risk stratification of cardiac complications in childhood ALL survivors.

QT prolongation predicts all-cause mortality above and beyond a validated risk score

INTRODUCTION

QT prolongation is a risk factor for life-threatening arrhythmias and sudden cardiac death. In large cohorts, QT interval was associated with all-cause mortality, but these analyses may contain residual confounding. Whether the QT interval provides prognostic information above and beyond a validated mortality risk score is unknown. We hypothesized that QT interval on ECG will independently predict mortality after adjustment for the Care Assessment Needs (CAN) score, which was validated to predict mortality nationwide at the Veterans Administration (VA) (c-index 0.86).

METHODS

Outpatients with an ECG at the Minneapolis VA from 2012 to 2016 were included in this retrospective cohort study. ECGs with ventricular rate < 50 or > 100 beats/min and those with QRS > 120 ms were excluded. QT intervals were corrected (QTc) using the Bazett's formula. CAN score, calculated within 1-week of the ECG, was obtained from the VA Corporate Data Warehouse.

RESULTS

Of the 31,201 patients, 427 (1.4%) had QTc ≥ 500 ms, 1799 (5.8%) had QTc 470-500 ms and 28,975 (92.9%) had QTc < 470 ms. Compared to those with QTc < 470 ms, CAN-adjusted odds ratios (OR) for 1-year mortality (1.76 for QTc 470-500 and 2.70 for QTc > 500 ms; p < 0.0001 for both) and for 5-year mortality (1.75 for QTc 470-500 and 2.48 for QTc > 500 ms; p < 0.0001 for both) were significantly higher in those with longer QTc. C-index for CAN score and QTc predicting 1-year mortality was 0.837.

CONCLUSIONS

QT prolongation predicts all-cause mortality independently of a validated mortality risk prediction score.

Obstructive sleep apnea and temporal changes in cardiac repolarization in patients undergoing coronary artery bypass grafting

STUDY OBJECTIVES

In coronary artery bypass grafting (CABG), abnormal cardiac repolarization is associated with adverse cardiovascular events that can be measured via the QTc interval. We investigated the impact of obstructive sleep apnea on the change in repolarization after CABG and the association of change in repolarization with the occurrence of major adverse cardiac and cerebrovascular events.

METHODS

A total of 1,007 patients from 4 hospitals underwent an overnight sleep study prior to a nonemergent CABG. Electrocardiograms of 954 patients (median age: 62 years; male: 86%; mean follow-up: 2.1 years) were acquired prospectively within 48 hours before CABG (T1) and within 24 hours after CABG (T2). QTc intervals were measured using the BRAVO algorithm by Analyzing Medical Parameters for Solutions LLC. The change in T2 from T1 for QTc (ΔQTc) was derived, and Cox regression was performed.

RESULTS

Compared with those without, patients who developed major adverse cardiac and cerebrovascular events (n = 115) were older and had (1) a higher prevalence of smoking, hypertension, diabetes mellitus, and chronic kidney disease; (2) a higher apnea-hypopnea index and oxygen desaturation index; and (3) a smaller ΔQTc. Cox regression analysis demonstrated a smaller ΔQTc to be an independent risk factor for major adverse cardiac and cerebrovascular events (hazard ratio: 0.997; P = .032). In the multivariable regression model, a higher oxygen desaturation index was independently associated with a smaller ΔQTc (correlation coefficient: -0.58; P < .001).

CONCLUSIONS

A higher preoperative oxygen desaturation index was an independent predictor of a smaller ΔQTc. ΔQTc within 24 hours after CABG could be a novel predictor of occurrence of major adverse cardiac and cerebrovascular events at medium-term follow-up.

CLINICAL TRIAL REGISTRATION

Registry: ClinicalTrials.gov; Name: Undiagnosed Sleep Apnea and Bypass OperaTion (SABOT); URL: https://classic.clinicaltrials.gov/ct2/show/NCT02701504; Identifier: NCT02701504.

CITATION

Teo YH, Yong CL, Ou YH, et al. Obstructive sleep apnea and temporal changes in cardiac repolarization in patients undergoing coronary artery bypass grafting. J Clin Sleep Med. 2024;20(1):49-55.

Genetic QT Score and Sleep Apnea as Predictors of Sudden Cardiac Death in the UK Biobank

Introduction

The goal of this study was to evaluate the association between a polygenic risk score (PRS) for QT prolongation (QTc-PRS), QTc intervals and mortality in patients enrolled in the UK Biobank with and without sleep apnea.

Methods

The QTc-PRS was calculated using allele copy number and previously reported effect estimates for each single nuclear polymorphism SNP. Competing-risk regression models adjusting for age, sex, BMI, QT prolonging medication, race, and comorbid cardiovascular conditions were used for sudden cardiac death (SCD) analyses.

Results

500,584 participants were evaluated (56.5 ±8 years, 54% women, 1.4% diagnosed with sleep apnea). A higher QTc-PRS was independently associated with the increased QTc interval duration (p<0.0001). The mean QTc for the top QTc-PRS quintile was 15 msec longer than the bottom quintile (p<0.001). Sleep apnea was found to be an effect modifier in the relationship between QTc-PRS and SCD. The adjusted HR per 5-unit change in QTc-PRS for SCD was 1.64 (95% CI 1.16 - 2.31, p=0.005) among those with sleep apnea and 1.04 (95% CI 0.95 - 1.14, p=0.44) among those without sleep apnea (p for interaction =0.01). Black participants with sleep apnea had significantly elevated adjusted risk of SCD compared to White participants (HR=9.6, 95% CI 1.24 - 74, p=0.03).

Conclusion

In the UK Biobank population, the QTc-PRS was associated with SCD among participants with sleep apnea but not among those without sleep apnea, indicating that sleep apnea is a significant modifier of the genetic risk. Black participants with sleep apnea had a particularly high risk of SCD.

Corrected QTc interval combined with troponin value and mortality in acute ischemic stroke

Background and Purpose

Cardiac biomarkers including, elevated troponin (ET) and prolonged heart rate-corrected QT (PQTc) interval on electrocardiography are known to frequent and have a prognostic significance in patients with acute ischemic stroke (AIS). However, it is still challenging to practically apply the results for appropriate risk stratification. This study evaluate whether combining ET and PQTc interval can better assess the long-term prognosis in AIS patients.

Methods

In this prospectively registered observational study between May 2007 and December 2011, ET was defined as serum troponin-I ≥ 0.04 ng/ml and PQTc interval was defined as the highest tertile of sex-specific QTc interval (men ≥ 469 ms or women ≥ 487 ms).

Results

Among the 1,668 patients [1018 (61.0%) men; mean age 66.0 ± 12.4 years], patients were stratified into four groups according to the combination of ET and PQTc intervals. During a median follow-up of 33 months, ET (hazard ratio [HR]: 4.38, 95% confidence interval [CI]: 2.94-6.53) or PQTc interval (HR: 1.53, 95% CI: 1.16-2.01) alone or both (HR: 1.77, 95% CI: 1.16-2.71) was associated with increased all-cause mortality. Furthermore, ET, PQTc interval alone or both was associated with vascular death, whereas only ET alone was associated with non-vascular death. Comorbidity burden, especially atrial fibrillation and congestive heart failure, and stroke severity gradually increased both with troponin value and QTc-interval.

Conclusions

In patients with AIS, combining ET and PQTc interval on ECG enhances risk stratification for long-term mortality while facilitating the discerning ability for the burden of comorbidities and stroke severity.

Prolongation of the QTc interval is associated with an increased risk of cardiovascular diseases: The Hoorn study

BACKGROUND/OBJECTIVE

Prolonged heart rate-corrected QT interval (QTc) on the electrocardiogram (ECG) is maybe associated with the occurrence of cardiovascular diseases (CVD), but the evidence is inconsistent. Therefore, we investigated whether baseline prolongation of the QTc interval is associated with CVD morbidity and mortality and its subtypes and whether glucose tolerance modifies this association in a population-based cohort study with a mean follow-up of 10.8 years.

METHODS

We analyzed a glucose tolerance stratified sample (N = 487) from the longitudinal population-based Hoorn Study cohort (age 64 ± 7 years, 48% female). Cox regression was used to investigate the association between sex-specific baseline QTc quartiles and CVD morbidity and mortality. The risk was also estimated per 10 ms increase in QTc. All analyses were adjusted for age, sex, smoking status, systolic blood pressure, prevalent CVD, glucose tolerance status, hypertension and total cholesterol. In addition, stratified analyses were conducted for glucose tolerance status.

RESULTS

During a mean follow-up of 10.8 years, 351 CVD events were observed. The adjusted hazard ratios (95% CI) for each 10 ms increase in QTc interval were 1.06 (95% CI: 1.02-1.10) for CVD, 1.06 (95% CI: 0.97-1.15) for acute myocardial infarction, 1.07 (95% CI: 1.01-1.13) for stroke, 1.12 (95% CI: 1.06-1.19) for heart failure, 1.04 (95% CI: 0.96-1.12) for peripheral arterial disease and 1.01 (95% CI:0.95-1.08) for coronary heart disease. Glucose tolerance status did not modify the association (P > 0.2).

CONCLUSION/INTERPRETATION

Prolongation of the QTc interval is associated with morbidity and mortality due to general CVD. Glucose tolerance status did not modify these associations.

The association between serum uric acid and creatine phosphokinase in the general population: NHANES 2015-2018

BACKGROUND

The association between serum creatine phosphokinase (CPK), a standard biochemical measure of acute myocardial infarction, and serum uric acid (sUA) has not been studied. This study aimed to determine the association between sUA and CPK in the general population of the US.

METHODS

Data from the National Health and Nutrition Examination Survey (NHANES) 2015-2018 were used, including a total of 8,431 subjects aged ≥ 30 years. Weighted multiple regression analysis was used to estimate the independent relationship between sUA and CPK. Fitted smoothing curves and weighted generalized additive models were also performed.

RESULTS

We found a positive relationship between sUA and CPK after adjusting for potential confounders. In subgroup analyses stratified by sex and race/ethnicity, sUA was positively correlated with CPK in each subgroup. The association between sUA and CPK followed an inverted U-shaped curve in females (turning point: sUA = 428.3 μmol/L).

CONCLUSIONS

Our study suggested that sUA level was positively correlated with CPK in the general population of the US. However, CPK increased with sUA until the turning point (sUA = 428.3 μmol/L) in females. Fundamental research and large sample prospective studies are needed to determine the exact mechanism of the association between sUA and CPK.

Added value of patient- and drug-related factors to stratify drug-drug interaction alerts for risk of QT prolongation: Development and validation of a risk prediction model

AIMS

Many clinical decision support systems trigger warning alerts for drug-drug interactions potentially leading to QT prolongation and torsades de pointes (QT-DDIs). Unfortunately, there is overalerting and underalerting because stratification is only based on a fixed QT-DDI severity level. We aimed to improve QT-DDI alerting by developing and validating a risk prediction model considering patient- and drug-related factors.

METHODS

We fitted 31 predictor candidates to a stepwise linear regression for 1000 bootstrap samples and selected the predictors present in 95% of the 1000 models. A final linear regression model with those variables was fitted on the original development sample (350 QT-DDIs). This model was validated on an external dataset (143 QT-DDIs). Both true QTc and predicted QTc were stratified into three risk levels (low, moderate and high). Stratification of QT-DDIs could be appropriate (predicted risk = true risk), acceptable (one risk level difference) or inappropriate (two risk levels difference).

RESULTS

The final model included 11 predictors with the three most important being use of antiarrhythmics, age and baseline QTc. Comparing current practice to the prediction model, appropriate stratification increased significantly from 37% to 54% appropriate QT-DDIs (increase of 17.5% on average [95% CI +5.4% to +29.6%], p_adj  = 0.006) and inappropriate stratification decreased significantly from 13% to 1% inappropriate QT-DDIs (decrease of 11.2% on average [95% CI -17.7% to -4.7%], p_adj  ≤ 0.001).

CONCLUSION

The prediction model including patient- and drug-related factors outperformed QT alerting based on QT-DDI severity alone and therefore is a promising strategy to improve DDI alerting.

Effect of polypharmacy on plasma bepridil concentration in patients with heart failure: a multicenter retrospective study

BACKGROUND

Polypharmacy, defined as the concurrent use of over six drugs, is common in the treatment of heart failure (HF); however, unpredictable drug interactions with bepridil may occur. In this study, we have elucidated the influence of polypharmacy on plasma bepridil concentrations in patients with HF.

METHODS

We conducted a multicenter retrospective study involving 359 adult patients with HF who received oral bepridil. Because QT prolongation is an adverse effect following plasma bepridil concentrations ≥800 ng/mL, the risk factors for patients achieving these concentrations at steady state were elucidated via multivariate logistic regression. The correlation between bepridil dose and plasma concentration was examined. The effect of polypharmacy on the value of the concentration-to-dose (C/D) ratio was investigated.

RESULTS

A significant relationship was observed between bepridil dose and plasma concentration (p <  0.001), and the intensity of the correlation was moderate (r = 0.503). Based on multivariate logistic regression, the adjusted odds ratios for a daily dose of bepridil ≥1.6 mg/kg, polypharmacy, and concomitant of aprindine, a cytochrome P450 2D6 inhibitor, were 6.82 (95% coefficient interval: 2.104-22.132, p = 0.001), 2.96 (95% coefficient interval: 1.014-8.643, p = 0.047), and 8.63 (95% coefficient interval: 1.684-44.215, p = 0.010), respectively. Despite the moderate correlation in non-polypharmacy, the correlation was not observed in polypharmacy. Therefore, inhibiting metabolism, along with other mechanisms, may contribute to the polypharmacy-induced increase in plasma bepridil concentrations. Moreover, the C/D ratios in the groups receiving 6-9 and 10≤ concomitant drugs were 1.28- and 1.70-fold higher than in those receiving <6 drugs, respectively.

CONCLUSIONS

Plasma bepridil concentrations may be influenced by polypharmacy. Moreover, the plasma bepridil concentration increased in correlation with the number of concomitant drugs used. Although the mechanism of this increase could not be determined, plasma bepridil concentrations should be periodically monitored for safe use in patients with HF.

TRIAL REGISTRATION

Retrospectively registered.

A QTc risk score in patients with obstructive sleep apnea

INTRODUCTION

Patients with obstructive sleep apnea (OSA) are at risk for QTc prolongation, a known risk factor for increased mortality. The pro-QTc score can help identify individuals at increased risk for mortality associated with increased QTc however, it has not been evaluated in patients with OSA. The goal of this study was to evaluate the pro-QTc score in patients with OSA.

METHODS

Medical records of patients undergoing a sleep study at our sleep center from February 2012 to August 2020 were analyzed. Presence or absence of OSA was determined by polysomnography. The pro-QTc score was calculated with 1 point assigned for each of the following: female sex, QT-prolonging diagnoses and conditions, QT-prolonging electrolyte abnormalities, and medications with known risk for QT-prolongation. Mortality was determined from the electronic medical record of an integrated healthcare system.

RESULTS

There were 2246 patients (age 58 ± 15 years, 54% male, 82 dead) with OSA and 421 patients (age 54 ± 18 years, 43% male, 18 dead) without OSA. Of those with OSA, 1628 (72.5%) had at least one risk factor for QTc prolongation. A higher pro-QTc score was associated with greater mortality in patients with OSA (HR 1.48 per pro-QTc score, p < 0.001, 95% CI 1.3-1.7) but not in patients without OSA (HR 1.25 per pro-QTc score, p = 0.30, 95% CI 0.82-1.9), after adjusting for age, body mass index (BMI), and smoking status.

CONCLUSION

In patients with OSA, a higher pro-QTc score was associated with greater mortality.

Relationship between a risk score for QT interval prolongation and mortality across rural and urban inpatient facilities

OBJECTIVES

To evaluate the relationship between a modified Tisdale QTc-risk score (QTc-RS) and inpatient mortality and length of stay in a broad inpatient population with an order for a medication with a known risk of torsades de pointes (TdP).

BACKGROUND

Managing the risk of TdP is challenging due to the number of medications with known risk of TdP and the complexity of precipitating factors. A model to predict risk of mortality may be useful to guide treatment decisions.

METHODS

This was a retrospective observational study using inpatient data from 28 healthcare facilities in the western United States. This risk score ranges from zero to 23 with weights applied to each risk factor based on a previous validation study. Logistic regression and a generalized linear model were performed to assess the relationship between QTc-RS and mortality and length of stay.

RESULTS

Between April and December 2020, a QTc-RS was calculated for 92,383 hospitalized patients. Common risk factors were female (55.0%); age > 67 years (32.1%); and receiving a medication with known risk of TdP (24.5%). A total of 2770 (3%) patients died during their hospitalization. Relative to patients with QTc-RS < 7, the odds ratio for mortality was 4.80 (95%CI:4.42-5.21) for patients with QTc-RS = 7-10 and 11.51 (95%CI:10.23-12.94) for those with QTc-RS ≥ 11. Length of hospital stay increased by 0.7 day for every unit increase in the risk score (p < 0.0001).

CONCLUSION

There is a strong relationship between increased mortality as well as longer duration of hospitalization with an increasing QTc-RS.

Why and How Should We Assess the Cardiovascular Risk in Patients with Juvenile Idiopathic Arthritis? A Single-Centre Experience with Carotid Intima-Media Measurements

Background: Children diagnosed with juvenile idiopathic arthritis (JIA) are thought to be more likely to develop cardiovascular disease in adulthood. The factors modulating the cardiovascular risk, involving exposure to secondhand smoking, sedentary lifestyle and abnormal body mass index, might have had a stronger impact during the COVID-19 pandemic. The lack of reliable prognostic markers for a higher probability of cardiovascular events might be solved by carotid intima-media thickness (cIMT) measurement. The paramount goal of the study was to assess its usefulness in JIA patients. Materials and Methods: The results of cIMT measured by a single physician in 45 children diagnosed with JIA were compared to 37 age- and sex-matched healthy counterparts. The analysis also involved anthropometric parameters, laboratory tests, and a survey regarding lifestyle-related factors. Results: Four JIA patients appeared to have cIMT above the 94th percentile. A positive correlation between erythrocytes sedimentation rate (ESR) and right carotid artery percentiles was found. Passive smoking increased the cardiovascular risk regardless of JIA. Doubling the daily screen time during the pandemic led to a significant reduction in children’s physical activity. However, the number of enrolled subjects was not enough to make significant recommendations. Conclusions: cIMT measurements remain an interesting perspective for future cardiovascular screening of children with JIA. It has yet to be determined whether it should be considered in all JIA patients on a reliable basis.

Prolongation of the heart rate-corrected QT interval is associated with cardiovascular diseases: Systematic review and meta-analysis

BACKGROUND

Conflicting findings have described the association between prolonged heart rate-corrected QT interval (QTc) and cardiovascular disease.

AIMS

To identify articles investigating the association between QTc and cardiovascular disease morbidity and mortality, and to summarize the available evidence for the general and type 2 diabetes populations.

METHODS

A systematic search was performed in PubMed and Embase in May 2022 to identify studies that investigated the association between QTc prolongation and cardiovascular disease in both the general and type 2 diabetes populations. Screening, full-text assessment, data extraction and risk of bias assessment were performed independently by two reviewers. Effect estimates were pooled across studies using random-effect models.

RESULTS

Of the 59 studies included, 36 qualified for meta-analysis. Meta-analysis of the general population studies showed a significant association for: overall cardiovascular disease (fatal and non-fatal) (hazard ratio [HR] 1.68, 95% confidence interval [CI] 1.33-2.12; I²=69%); coronary heart disease (fatal and non-fatal) in women (HR 1.27, 95% CI 1.08-1.50; I²=38%; coronary heart disease (fatal and non-fatal) in men (HR 2.07, 95% CI 1.26-3.39; I²=78%); stroke (HR 1.59, 95% CI 1.29-1.96; I²=45%); sudden cardiac death (HR 1.60, 95% CI 1.14-2.25; I²=68%); and atrial fibrillation (HR 1.55, 95% CI 1.31-1.83; I²=0.0%). No significant association was found for cardiovascular disease in the type 2 diabetes population.

CONCLUSION

QTc prolongation was associated with risk of cardiovascular disease in the general population, but not in the type 2 diabetes population.

Prognostic value of index of cardiac electrophysiological balance among US middle-aged adults

Background

Index of cardiac electrophysiological balance (iCEB) has been widely used in clinical practice but no studies investigated the association between iCEB and prognosis in the general population.

Objective

To assess the correlation between the iCEB and the prognosis in the general population.

Methods

This retrospective cohort study involved adults aged 40-65 years who participated in the Third National Health and Nutrition Examination Survey (NHANES-III) and whose electrocardiograms were in sinus rhythm. The corrected iCEB (iCEBc) was the ratio of corrected QT interval (QTc) to QRS duration, and outcomes were cardiac and all-cause mortality. Cox proportional hazards regression model was used to identify the associations of iCEBc with end point. The value of iCEBc for predicting adverse events was evaluated by reclassification and discrimination analyses.

Results

Among 5,010 participants (mean age 51.10 ± 7.67 years, 52.5% female), 3,454 (68.9%) were Non-Hispanic White. The mean iCEBc was 4.45 ± 0.56. A total of 2,147 deaths were recorded during a median follow-up of 319 months. The adjusted model shown iCEBc was an independent risk factor for all-cause death. The iCEBc was linearly correlated with all-cause mortality and the optimal cutoff value was 4.57 in males and 4.98 in females. In the resultant model, prolonged iCEBc remained independently associated with a higher rate of mortality (HR: 1.25; 95% CI: 1.11-1.42) and cardiac death (HR: 1.34; 95% CI: 1.04-1.71). Among the complete study population or the group with normal QTc interval, the performance of the predictive model after addition of iCEBc was not weaker than the model after the addition of prolonged QTc.

Conclusion

Elevated iCEBc (male ≥4.57 and female ≥4.98) is an independent risk factor for cardiac or all-cause death among the middle-age adults. The clinical application value of iCEBc is firmly based on basic physiological principles and its application deserves further attention.

Electrophysiological heterogeneity in large populations of rabbit ventricular cardiomyocytes

AIMS

Cardiac electrophysiological heterogeneity includes: (i) regional differences in action potential (AP) waveform, (ii) AP waveform differences in cells isolated from a single region, (iii) variability of the contribution of individual ion currents in cells with similar AP durations (APDs). The aim of this study is to assess intra-regional AP waveform differences, to quantify the contribution of specific ion channels to the APD via drug responses and to generate a population of mathematical models to investigate the mechanisms underlying heterogeneity in rabbit ventricular cells.

METHODS AND RESULTS

APD in ∼50 isolated cells from subregions of the LV free wall of rabbit hearts were measured using a voltage-sensitive dye. When stimulated at 2 Hz, average APD90 value in cells from the basal epicardial region was 254 ± 25 ms (mean ± standard deviation) in 17 hearts with a mean interquartile range (IQR) of 53 ± 17 ms. Endo-epicardial and apical-basal APD90 differences accounted for ∼10% of the IQR value. Highly variable changes in APD occurred after IK(r) or ICa(L) block that included a sub-population of cells (HR) with an exaggerated (hyper) response to IK(r) inhibition. A set of 4471 AP models matching the experimental APD90 distribution was generated from a larger population of models created by random variation of the maximum conductances (Gmax) of 8 key ion channels/exchangers/pumps. This set reproduced the pattern of cell-specific responses to ICa(L) and IK(r) block, including the HR sub-population. The models exhibited a wide range of Gmax values with constrained relationships linking ICa(L) with IK(r), ICl, INCX, and INaK.

CONCLUSION

Modelling the measured range of inter-cell APDs required a larger range of key Gmax values indicating that ventricular tissue has considerable inter-cell variation in channel/pump/exchanger activity. AP morphology is retained by relationships linking specific ionic conductances. These interrelationships are necessary for stable repolarization despite large inter-cell variation of individual conductances and this explains the variable sensitivity to ion channel block.

Inter-sleep stage variations in corrected QT interval differ between obstructive sleep apnea patients with and without stroke history

Obstructive sleep apnea (OSA) is related to the progression of cardiovascular diseases (CVD); it is an independent risk factor for stroke and is also prevalent post-stroke. Furthermore, heart rate corrected QT (QTc) is an important predictor of the risk of arrhythmia and CVD. Thus, we aimed to investigate QTc interval variations in different sleep stages in OSA patients and whether nocturnal QTc intervals differ between OSA patients with and without stroke history. 18 OSA patients (apnea-hypopnea index (AHI)≥15) with previously diagnosed stroke and 18 OSA patients (AHI≥15) without stroke history were studied. Subjects underwent full polysomnography including an electrocardiogram measured by modified lead II configuration. RR, QT, and QTc intervals were calculated in all sleep stages. Regression analysis was utilized to investigate possible confounding effects of sleep stages and stroke history on QTc intervals. Compared to patients without previous stroke history, QTc intervals were significantly higher (β = 34, p<0.01) in patients with stroke history independent of age, sex, body mass index, and OSA severity. N3 sleep (β = 5.8, p<0.01) and REM sleep (β = 2.8, p<0.01) increased QTc intervals in both patient groups. In addition, QTc intervals increased progressively (p<0.05) towards deeper sleep in both groups; however, the magnitude of changes compared to the wake stage was significantly higher (p<0.05) in patients with stroke history. The findings of this study indicate that especially in deeper sleep, OSA patients with a previous stroke have an elevated risk for QTc prolongation further increasing the risk for ventricular arrhythmogenicity and sudden cardiac death.

A large genome-wide association study of QT interval length utilizing electronic health records

QT interval length is an important risk factor for adverse cardiovascular outcomes; however, the genetic architecture of QT interval remains incompletely understood. We conducted a genome-wide association study of 76,995 ancestrally diverse Kaiser Permanente Northern California members enrolled in the Genetic Epidemiology Research on Adult Health and Aging cohort using 448,517 longitudinal QT interval measurements, uncovering 9 novel variants, most replicating in 40,537 individuals in the UK Biobank and Population Architecture using Genomics and Epidemiology studies. A meta-analysis of all 3 cohorts (n = 117,532) uncovered an additional 19 novel variants. Conditional analysis identified 15 additional variants, 3 of which were novel. Little, if any, difference was seen when adjusting for putative QT interval lengthening medications genome-wide. Using multiple measurements in Genetic Epidemiology Research on Adult Health and Aging increased variance explained by 163%, and we show that the ≈6 measurements in Genetic Epidemiology Research on Adult Health and Aging was equivalent to a 2.4× increase in sample size of a design with a single measurement. The array heritability was estimated at ≈17%, approximately half of our estimate of 36% from family correlations. Heritability enrichment was estimated highest and most significant in cardiovascular tissue (enrichment 7.2, 95% CI = 5.7-8.7, P = 2.1e-10), and many of the novel variants included expression quantitative trait loci in heart and other relevant tissues. Comparing our results to other cardiac function traits, it appears that QT interval has a multifactorial genetic etiology.

Nonalcoholic Fatty Liver Disease Is Related to Abnormal Corrected QT Interval and Left Ventricular Hypertrophy in Chinese Male Steelworkers

OBJECTIVES

Nonalcoholic fatty liver disease (NAFLD) has been associated with an increased risks of corrected QT (QTc) prolongation and left ventricular hypertrophy (LVH), both of which are associated with the development of cardiovascular disease. Rotating night shift work and a higher risk of incident NAFLD have been reported in male steelworkers. This study aimed to investigate the association of the severity of NAFLD with a prolonged QTc interval and LVH in a large cohort of Chinese male steelworkers.

METHODS

We examined baseline data of 2998 male steel workers aged 26 to 71 years at two plants. All workers at both plants received regular health assessments, including 12-lead ECG and echocardiography. Abdominal ultrasonography was performed to evaluate the severity of NAFLD. QTc prolongation was defined as follows: normal ≤ 430 ms, borderline 431-450 ms, and abnormal ≥ 451 ms. LVH was defined as a left ventricular mass index (LVMI) >131 g/m². Associations of NAFLD with an abnormal QTc interval and LVH were examined using univariate and multivariate analyses.

RESULTS

The QTc interval and the LVMI were significantly correlated with the NAFLD fibrosis score, and the severity of NAFLD was correlated with an abnormal QTc interval and LVH (p for trend < 0.05). Multivariate analysis showed that in comparison to the workers without NAFLD, the odds ratios of having an abnormal QTc interval and LVH were 2.54 (95% CI: 1.22-5.39, p = 0.013) times and 2.23 (95% CI: 1.02-5.01, p = 0.044) times higher in the workers with moderate/severe NAFLD.

CONCLUSIONS

NAFLD may be closely associated with the risks of an abnormal QTc interval and LVH, suggesting that regular electrocardiogram and echocardiogram monitoring could be used to evaluate the risk of arrhythmia and LVH in male steelworkers with NAFLD.

E-cigarettes and their lone constituents induce cardiac arrhythmia and conduction defects in mice

E-cigarette use has surged, but the long-term health effects remain unknown. E-cigarette aerosols containing nicotine and acrolein, a combustion and e-cigarette byproduct, may impair cardiac electrophysiology through autonomic imbalance. Here we show in mouse electrocardiograms that acute inhalation of e-cigarette aerosols disturbs cardiac conduction, in part through parasympathetic modulation. We demonstrate that, similar to acrolein or combustible cigarette smoke, aerosols from e-cigarette solvents (vegetable glycerin and propylene glycol) induce bradycardia, bradyarrhythmias, and elevations in heart rate variability during inhalation exposure, with inverse post-exposure effects. These effects are slighter with tobacco- or menthol-flavored aerosols containing nicotine, and in female mice. Yet, menthol-flavored and PG aerosols also increase ventricular arrhythmias and augment early ventricular repolarization (J amplitude), while menthol uniquely alters atrial and atrioventricular conduction. Exposure to e-cigarette aerosols from vegetable glycerin and its byproduct, acrolein, diminish heart rate and early repolarization. The pro-arrhythmic effects of solvent aerosols on ventricular repolarization and heart rate variability depend partly on parasympathetic modulation, whereas ventricular arrhythmias positively associate with early repolarization dependent on the presence of nicotine. Our study indicates that chemical constituents of e-cigarettes could contribute to cardiac risk by provoking pro-arrhythmic changes and stimulating autonomic reflexes.

ECG Markers of Acute Melatonin Treatment in a Porcine Model of Acute Myocardial Ischemia

In myocardial ischemia, melatonin confers antiarrhythmic action, but its electrocardiographic expression is unclear. We aimed to evaluate the effects of melatonin treatment on electrocardiogram (ECG) parameters reflecting major arrhythmogenic factors and to test the association of these parameters with ventricular fibrillation (VF) incidence. Myocardial ischemia was induced by 40 min coronary artery occlusion in 25 anesthetized pigs. After induction of ischemia, 12 and 13 animals were given melatonin or placebo, respectively. Twelve-lead ECGs were recorded and durations of QRS, QT, Tpeak-Tend intervals and extrasystolic burden were measured at baseline and during occlusion. During ischemia, VF episodes clustered into early and delayed phases (<10 and >20 min, respectively), and QRS duration was associated with VF incidence. QT interval and extrasystolic burden did not differ between the groups. The Tpeak-Tend interval was progressively prolonged, and the prolongation was less pronounced in the treated animals. QRS duration increased, demonstrating two maxima (5−10 and 25 min, respectively). In the melatonin group, the earlier maximum was blunted, and VF development in this period was prevented. Thus, acute melatonin treatment prevented excessive prolongation of the QRS and Tpeak-Tend intervals in the porcine myocardial infarction model, and QRS duration can be used for the assessment of antiarrhythmic action of melatonin.

Biological noise is a key determinant of the reproducibility and adaptability of cardiac pacemaking and EC coupling

Each heartbeat begins with the generation of an action potential in pacemaking cells in the sinoatrial node. This signal triggers contraction of cardiac muscle through a process termed excitation-contraction (EC) coupling. EC coupling is initiated in dyadic structures of cardiac myocytes, where ryanodine receptors in the junctional sarcoplasmic reticulum come into close apposition with clusters of CaV1.2 channels in invaginations of the sarcolemma. Cooperative activation of CaV1.2 channels within these clusters causes a local increase in intracellular Ca2+ that activates the juxtaposed ryanodine receptors. A salient feature of healthy cardiac function is the reliable and precise beat-to-beat pacemaking and amplitude of Ca2+ transients during EC coupling. In this review, we discuss recent discoveries suggesting that the exquisite reproducibility of this system emerges, paradoxically, from high variability at subcellular, cellular, and network levels. This variability is attributable to stochastic fluctuations in ion channel trafficking, clustering, and gating, as well as dyadic structure, which increase intracellular Ca2+ variance during EC coupling. Although the effects of these large, local fluctuations in function and organization are sometimes negligible at the macroscopic level owing to spatial-temporal summation within and across cells in the tissue, recent work suggests that the "noisiness" of these intracellular Ca2+ events may either enhance or counterintuitively reduce variability in a context-dependent manner. Indeed, these noisy events may represent distinct regulatory features in the tuning of cardiac contractility. Collectively, these observations support the importance of incorporating experimentally determined values of Ca2+ variance in all EC coupling models. The high reproducibility of cardiac contraction is a paradoxical outcome of high Ca2+ signaling variability at subcellular, cellular, and network levels caused by stochastic fluctuations in multiple processes in time and space. This underlying stochasticity, which counterintuitively manifests as reliable, consistent Ca2+ transients during EC coupling, also allows for rapid changes in cardiac rhythmicity and contractility in health and disease.

Genetic analyses of the electrocardiographic QT interval and its components identify additional loci and pathways

The QT interval is an electrocardiographic measure representing the sum of ventricular depolarization and repolarization, estimated by QRS duration and JT interval, respectively. QT interval abnormalities are associated with potentially fatal ventricular arrhythmia. Using genome-wide multi-ancestry analyses (>250,000 individuals) we identify 177, 156 and 121 independent loci for QT, JT and QRS, respectively, including a male-specific X-chromosome locus. Using gene-based rare-variant methods, we identify associations with Mendelian disease genes. Enrichments are observed in established pathways for QT and JT, and previously unreported genes indicated in insulin-receptor signalling and cardiac energy metabolism. In contrast for QRS, connective tissue components and processes for cell growth and extracellular matrix interactions are significantly enriched. We demonstrate polygenic risk score associations with atrial fibrillation, conduction disease and sudden cardiac death. Prioritization of druggable genes highlight potential therapeutic targets for arrhythmia. Together, these results substantially advance our understanding of the genetic architecture of ventricular depolarization and repolarization.

Effect and benefit of percutaneous coronary intervention in chronic total occlusion on ventricular repolarization: QT correction and dispersion

ST segment, T wave changes, QT interval changes, and QTc dispersion are among the parameters used to diagnose ischemic heart disease. The increase in the QT dispersion can be caused by myocardial ischemia, among other heart diseases, whereas cardiac diseases such as coronary artery disease (CAD) can be diagnosed by observing an abnormally high QTc dispersion. This study aimed to evaluate the variations in the QTc dispersion (depolarization and repolarization) of surface electrocardiography as a result of percutaneous coronary intervention (PCI) in patients with chronic total occlusion. This study took place in the Iraqi Center for Heart Disease from October 2020 to February 2021. 110 patients who suffered from chronic occlusion of the coronary artery and underwent PCI revascularization were examined. Twelve-lead electrocardiograms were recorded at the time of admission (12 hours before intervention) and more than one hour after the intervention. The measured ECG parameters included corrected QT interval durations and corrected QT dispersion in both pre and post-PCI electrocardiograms, and their values were compared. The average corrected QT interval and QTC dispersion changed significantly before and after the percutaneous coronary intervention. Performing percutaneous coronary intervention on patients who suffer from coronary artery total occlusion shows a major reduction in the corrected QT dispersion.

[Corrected QT interval and GRACE score relationship in patients with non-ST segment elevation myocardial infarction]

Background

The Global Registry of Acute Coronary Events (GRACE) prediction model stratifies patients with non-ST-segment elevation myocardial infarction (NSTEMI). Corrected QT interval (QTc) is not considered in this model.

Objective

To evaluate the relationship between the QTc interval and the GRACE score in patients with NSTEMI.

Materials and methods

An observational, retrospective study was carried between 2016 and 2019. We included patients with diagnosis of NSTEMI, QTc intervals were calculated with Bazett's formula, and they were classified into 2 groups: a normal QTc interval (<440 ms) and prolonged (≥440 ms). According to the GRACE score they were classified in three ranges: low risk (≤109 points), intermedium (110 - 139 points) and high (≥140 points), we determined if there were a correlation between QTc interval and the GRACE score.

Results

A total of 940 patients with a diagnosis of NSTEMI were admitted in our institution, 634 met the inclusion criteria, there were 390 patients with normal QTc interval and 244 with a prolonged QTc interval. Patients with prolonged QTc were older (65.5 vs 61, p=0.001) with a lower proportion of males (71.7% vs 82.8%, p=0.001). An association was found between the GRACE score and the QTC interval, subjects with a normal QTc had a greater proportion of low and intermediate risk than those with a prolonged QTc (p=0.001). Conclusions. In NSTEMI patients, a normal QTc interval (<440 ms) is associated with a GRACE risk score of low or intermediate risk.

The genetics of drug-induced QT prolongation: evaluating the evidence for pharmacodynamic variants

Drug-induced long QT syndrome (diLQTS) is an adverse effect of many commonly prescribed drugs, and it can increase the risk for lethal ventricular arrhythmias. Genetic variants in pharmacodynamic genes have been associated with diLQTS, but the strength of the evidence for each of those variants has not yet been evaluated. Therefore, the purpose of this review was to evaluate the strength of the evidence for pharmacodynamic genetic variants associated with diLQTS using a novel, semiquantitative scoring system modified from the approach used for congenital LQTS. KCNE1-D85N and KCNE2-T8A had definitive and strong evidence for diLQTS, respectively. The high level of evidence for these variants supports current consideration as risk factors for patients that will be prescribed a QT-prolonging drug.

Assessment of the QT interval in right bundle branch block

BACKGROUND

Identifying prolonged QT interval in RBBB has been problematic.

METHODS

Four approaches were compared to adjust for the QT prolongation in intermittent RBBB. The implications were assessed in a separate group of 200 persons with established RBBB.

RESULTS

In 12 individuals, mean age 74.5 years with intermittent RBBB, the presence of RBBB significantly (p < 0.05) increased the QT interval in each of six different heart rate correction formulae by an amount ranging from 35.4 ms in the Hodges formula to 50.2 ms in the Bazett formula. Four different equations were tested to adjust the QT interval and one approach QTc_RBBB = 0.945*QTc_RBBB - 26 was the best method to adjust for the increased QT in RBBB as it produced a QT value that was not significantly different from the QT interval in the absence of RBBB in intermittent RBBB.Failure to adjust the QT interval in RBBB produces an overestimate of the QT interval which in some heart rate adjustment formulae was marked. For the Bazett heart rate adjustment approach QTc 450 ms was found in 73.9% of men and QTc over 460 ms was found in 60.6% of women.

CONCLUSION

These data suggest the implementation of a new approach to recalculate the QT intervals in RBBB. QTc_RBBB = 0.945*QTc_RBBB - 26 with an appropriate heart rate adjustment formula (other than the Bazett formula) accurately predicts the QT interval in the absence of RBBB.

Comparison of Heart Rate Variability, QTc, and JT Interval Between Diabetic Patients and Healthy Controls: Role of Gender and Phases of Menstrual Cycle

Background and objectives

Type 2 Diabetes mellitus (T2DM) is a heterogeneous group of metabolic disorders with variable degrees of insulin resistance and altered glucose metabolism. Increased attention in studying the role of gonadal hormones in diabetes is not only due to their relation to insulin sensitivity, and glucose tolerance but also to the gender-specific nature of the prevalence of various diabetic complications. The cyclical change in the hormone level in females will make it necessary to consider the menstrual cycle while analyzing the risk factors for diabetes. Hence, the role of gender and menstrual cycle in T2DM are analyzed here using the simple non-invasive cardiovascular risk indices like heart rate variability (HRV), QT interval corrected for heart rate (QTc), and JT interval.

Materials and methods

In this analytical study, T2DM patients in the age group of 18-45 years with less than five years duration from diagnosis and taking not more than two anti-hyperglycemic drugs were included. Time and frequency domains of HRV analysis, QTc, and JT intervals were compared with age and BMI matched control group. The comparison of these parameters was also made between two genders in the diabetic group and they were analyzed across different phases of the menstrual cycle in female diabetic patients when physiological variation in the gonadal hormones occurred as a natural phenomenon.

Results

HRV parameters were reduced and the QTc and JT intervals were prolonged in diabetic patients of both genders. Reduction in low-frequency (LF) band power and high-frequency (HF) band power of HRV analysis in diabetic females were statistically significant in the luteal phase of the menstrual cycle in comparison with age and BMI-matched healthy controls. There was no significant difference in the HRV parameters, QTc, and JT interval between the male and female diabetic groups. HF band power is significantly reduced in the menstrual phase and relatively higher in the follicular phase when compared to the luteal phase among female diabetic patients.

Conclusion

The reduced sympathetic and parasympathetic activity were observed in diabetic patients of both genders and they were significant in the luteal phase of diabetic females compared to the healthy control group. Vagal activity is relatively higher in the follicular phase of the menstrual cycle in female diabetic patients.

Deep neural networks reveal novel sex-specific electrocardiographic features relevant for mortality risk

Aims

Incorporation of sex in study design can lead to discoveries in medical research. Deep neural networks (DNNs) accurately predict sex based on the electrocardiogram (ECG) and we hypothesized that misclassification of sex is an important predictor for mortality. Therefore, we first developed and validated a DNN that classified sex based on the ECG and investigated the outcome. Second, we studied ECG drivers of DNN-classified sex and mortality.

Methods and results

A DNN was trained to classify sex based on 131 673 normal ECGs. The algorithm was validated on internal (68 500 ECGs) and external data sets (3303 and 4457 ECGs). The survival of sex (mis)classified groups was investigated using time-to-event analysis and sex-stratified mediation analysis of ECG features. The DNN successfully distinguished female from male ECGs {internal validation: area under the curve (AUC) 0.96 [95% confidence interval (CI): 0.96, 0.97]; external validations: AUC 0.89 (95% CI: 0.88, 0.90), 0.94 (95% CI: 0.93, 0.94)}. Sex-misclassified individuals (11%) had a 1.4 times higher mortality risk compared with correctly classified peers. The ventricular rate was the strongest mediating ECG variable (41%, 95% CI: 31%, 56%) in males, while the maximum amplitude of the ST segment was strongest in females (18%, 95% CI: 11%, 39%). Short QRS duration was associated with higher mortality risk.

Conclusion

Deep neural networks accurately classify sex based on ECGs. While the proportion of ECG-based sex misclassifications is low, it is an interesting biomarker. Investigation of the causal pathway between misclassification and mortality uncovered new ECG features that might be associated with mortality. Increased emphasis on sex as a biological variable in artificial intelligence is warranted.

The best QT correction formula in a non-hospitalized population: the Fasa PERSIAN cohort study

Background

QT interval as an indicator of ventricular repolarization is a clinically important parameter on an electrocardiogram (ECG). QT prolongation predisposes individuals to different ventricular arrhythmias and sudden cardiac death. The current study aimed to identify the best heart rate corrected QT interval for a non-hospitalized Iranian population based on cardiovascular mortality.

Methods

Using Fasa PERSIAN cohort study data, this study enrolled 7071 subjects aged 35–70 years. Corrected QT intervals (QTc) were calculated by the QT interval measured by Cardiax® software from ECGs and 6 different correction formulas (Bazett, Fridericia, Dmitrienko, Framingham, Hodges, and Rautaharju). Mortality status was checked using an annual telephone-based follow-up and a minimum 3-year follow-up for each participant. Bland–Altman, QTc/RR regression, sensitivity analysis, and Cox regression were performed in IBM SPSS Statistics v23 to find the best QT. Also, for calculating the upper and lower limits of normal of different QT correction formulas, 3952 healthy subjects were selected.

Results

In this study, 56.4% of participants were female, and the mean age was 48.60 ± 9.35 years. Age, heart rate in females, and QT interval in males were significantly higher. The smallest slopes of QTc/RR analysis were related to Fridericia in males and Rautaharju followed by Fridericia in females. Thus, Fridericia’s formula was identified as the best mathematical formula and Bazett’s as the worst in males. In the sensitivity analysis, however, Bazett’s formula had the highest sensitivity (23.07%) among all others in cardiac mortality. Also, in the Cox regression analysis, Bazett’s formula was better than Fridericia’s and was identified as the best significant cardiac mortality predictor (Hazard ratio: 4.31, 95% CI 1.73–10.74, p value = 0.002).

Conclusion

Fridericia was the best correction formula based on mathematical methods. Bazett’s formula despite its poorest performance in mathematical methods, was the best one for cardiac mortality prediction. Practically, it is suggested that physicians use QTcB for a better evaluation of cardiac mortality risk. However, in population-based studies, QTcFri might be the one to be used by researchers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-022-02502-2.

Prediction of sudden cardiac arrest in the general population: Review of traditional and emerging risk factors

Sudden cardiac death (SCD) is the most common and devastating outcome of sudden cardiac arrest (SCA), defined as an abrupt and unexpected cessation of cardiovascular function leading to circulatory collapse. The incidence of SCD is relatively infrequent for individuals in the general population, in the range of 0.03-0.10% per year. Yet, the absolute number of cases around the world is high due to the sheer size of the population at risk, making SCA/SCD a major global health issue. Based on conservative estimates, there are at least 2 million cases of SCA occurring worldwide on a yearly basis. As such, identification of risk factors associated with SCA in the general population is an important objective from a clinical and public health standpoint. This review will provide an in-depth discussion of established and emerging factors predictive of SCA/SCD in the general population beyond coronary artery disease and impaired left ventricular ejection fraction. Contemporary studies evaluating the association between age, sex, race, socioeconomic status and the emerging contribution of diabetes and obesity to SCD risk beyond their role as atherosclerotic risk factors will be reviewed. In addition, the role of biomarkers, particularly electrocardiographic ones, on SCA/SCD risk prediction in the general population will be discussed. Finally, the use of machine learning as a tool to facilitate SCA/SCD risk prediction will be examined.

Prevalence and risk factors of QTc prolongation in prostate cancer patients undergoing brachytherapy

QTc prolongation is linked to Torsade de Pointes, sudden cardiac death, and overall cardiovascular mortality. 754 prostate cancer patients undergoing brachytherapy were analyzed, prolonged QTc was defined as ≥450ms. A prolonged QTc was more frequent (10.1% vs 5.1%, p = 0.040) in patients with high-risk cancer than in low to intermediate risk patients. The absolute QTc-time was correlated with age (r = 0.125), neutrophil count (r = 0.130) and negatively correlated with the testosterone level (r=-0.205). Treating physicians should be aware of this and monitor the QTc during ADT to possibly decrease cardiac morbidity/mortality in these patients who are more likely to require ADT.

Effects of adjunctive pimavanserin and current antipsychotic treatment on QT interval prolongation in patients with schizophrenia

BACKGROUND

Pimavanserin prolongs the QT interval, with mean increases in corrected QT (QTc) of 5-8 ms, and is currently being investigated for the treatment of negative symptoms of schizophrenia.

OBJECTIVES

To assess QT interval prolongation in 3 studies investigating once-daily pimavanserin as an adjunct to current antipsychotic treatment in patients with schizophrenia.

METHODS

Electrocardiograms were unblinded from trials in which pimavanserin or placebo was added to main antipsychotics over 6 weeks (ENHANCE), 26 weeks (ADVANCE), and up to 78 weeks (ongoing 52-week, open-label extension study [study 035]) of treatment. Antipsychotic treatment was permitted throughout these studies. The 3 most frequently used antipsychotic treatments were examined-aripiprazole (including long-acting injectable), risperidone (including long-acting injectable), and olanzapine. QT intervals were corrected (QTc) using Fridericia's method, with elevated risk defined as either postbaseline value maximum of >500 ms or change from baseline to postbaseline maximum of >60 ms.

RESULTS

Of patients treated with adjunctive pimavanserin in ENHANCE, there were no postbaseline QTc values >481 ms; one patient in each of the risperidone and aripiprazole groups had change from baseline to postbaseline maximum >60 ms. More patients had change from baseline to postbaseline maximum ranging from 31 to 60 ms in the risperidone plus adjunctive placebo group (n = 5; 6.6%) than those in the risperidone plus adjunctive pimavanserin group (n = 3, 4.1%). In the pimavanserin plus antipsychotic group of ADVANCE, one patient had postbaseline QTc value >481 ms, and one patient treated with aripiprazole had change from baseline to postbaseline maximum of >60 ms. In study 035, a change from double-blind baseline to overall postbaseline maximum >60 ms occurred in one patient treated with aripiprazole and pimavanserin and in one patient treated with risperidone and pimavanserin. Similar proportions of patients had changes from double-blind baseline to post double-blind baseline maximum between 31 and 60 ms across treatments. No adverse events associated with an increase in the QTc interval were reported.

CONCLUSIONS

Adjunctive pimavanserin with background antipsychotic treatment showed no evidence of QTc prolongation >500 ms postbaseline, consistent with previously reports on QT prolongation with pimavanserin.

Prognostic Significance of Prolonged Corrected QT Interval in Acute Ischemic Stroke

Background and Purpose: The aim of this study was to determine the relationship between the heart rate-corrected QT (QTc) interval and the risk of incident long-term mortality in patients with acute ischemic stroke (AIS), considering the impact of sex differences on clinical characteristics, outcomes, and QTc intervals.

Methods: We analyzed prospectively registered data included patients with AIS who visited the emergency room within 24 h of stroke onset and underwent routine cardiac testing, such as measurements of cardiac enzymes and 12-lead ECG. QTc interval was corrected for heart rate using Fridericia's formula and was stratified by sex-specific quartiles. Cox proportional hazards models were used to examine the association between baseline QTc interval and incident all-cause death.

Results: A total of 1,668 patients with 1,018 (61.0%) men and mean age 66.0 ± 12.4 years were deemed eligible. Based on the categorized quartiles of the QTc interval, cardiovascular risk profile, and stroke severity increased with prolonged QTc interval, and the risk of long-term mortality increased over a median follow-up of 33 months. Cox proportional hazard model analysis showed that the highest quartile of QTc interval (≥479 msec in men and ≥498 msec in women; hazard ratio [HR]: 1.49, 95% confidence interval [CI]: 1.07–2.08) was associated with all-cause death. Furthermore, dichotomized QTc interval prolongation, defined by the highest septile of the QTc interval (≥501 ms in men and ≥517 m in women: HR: 1.33, 95% CI: 1.00–1.80) was significantly associated with all-cause mortality after adjusting for all clinically relevant variables, such as stroke severity.

Conclusions: Prolonged QTc interval was associated with increased risk of long-term mortality, in parallel with the increasing trend of prevalence of cardiovascular risk profiles and stroke severity, across sex differences in AIS patients.

Association Between Dynamic Change of QT Interval and Long-Term Cardiovascular Outcomes: A Prospective Cohort Study

Background: The prolongation or shortening of heart rate-corrected QT (QTc) predisposes patients to fatal ventricular arrhythmias and sudden cardiac death (SCD), but the association of dynamic change of QTc interval with mortality in the general population remains unclear.

Methods: A total of 11,798 middle-aged subjects from the prospective, population-based cohort were included in this analysis. The QTc interval corrected for heart rate was measured on two occasions around 3 years apart in the Atherosclerosis Risk in Communities (ARIC) study. The ΔQTc interval was calculated by evaluating a change in QTc interval from visit 1 to visit 2.

Results: After a median follow-up of 19.5 years, the association between the dynamic change of QTc interval and endpoints of death was U-shaped. The multivariate-adjusted hazard ratios (HRs) comparing subjects above the 95th percentile of Framingham–corrected ΔQTc (ΔQTcF) (≥32 ms) with subjects in the middle quintile (0–8 ms) were 2.69 (95% CI, 1.68–4.30) for SCD, 2.51 (1.68–3.74) for coronary heart disease death, 2.10 (1.50–2.94) for cardiovascular death, and 1.30 (1.11–1.55) for death from any cause. The corresponding HRs comparing subjects with a ΔQTcF below the fifth percentile (<-23 ms) with those in the middle quintile were 1.82 (1.09–3.05) for SCD, 1.83 (1.19–2.81) for coronary heart disease death, 2.14 (1.51–2.96) for cardiovascular death, and 1.31 (1.11–1.56) for death from any cause. Less extreme deviations of ΔQTcF were also associated with an increased risk of death. Similar, albeit weaker associations also were observed with ΔQTc corrected with Bazett's formula.

Conclusions: A dynamic change of QTc interval is associated with increased mortality risk in the general population, indicating that repeated measurements of the QTc interval may be available to provide additional prognostic information.

QT prolongation in patients with index evaluation for seizure or epilepsy is predictive of all-cause mortality

BACKGROUND

Refractory epilepsy confers a considerable lifetime risk of sudden unexplained death in epilepsy (SUDEP). Mechanisms may overlap with sudden cardiac death (SCD), particularly regarding QTc prolongation. Guidelines in the United States do not mandate the use of electrocardiography (ECG) in diagnostic evaluation of seizures or epilepsy.

OBJECTIVE

The purpose of this study was to determine the frequency of ECG use and of QT prolongation, and whether QT prolongation predicts mortality in patients with seizures.

METHODS

We performed a retrospective cohort study including all patients seen at Mayo Clinic in Rochester, Minnesota, from January 1, 2000, to July 31, 2015, with index evaluation for seizure or epilepsy. Patients with an ECG were categorized by the presence of a prolonged QT interval with a primary endpoint of all-cause mortality after the 15-year observation period.

RESULTS

Optimal cutoff QT intervals most predictive of mortality were identified. Median age was 40.0 years. An ECG was obtained in 18,222 patients (57.4%). After patients with confounding ECG findings were excluded, primary prolonged QT intervals were seen in 223 cases (1.4%), similar to the general population. Kaplan-Meier analysis demonstrated a significant increase in mortality (Cox hazard ratio [HR] 1.90; 95% confidence interval [CI] 1.76-2.05) for prolonged optimal cutoff QT, maintained after adjustments for age, Charlson comorbidity index, and sex (HR 1.48; 95% CI 1.37-1.59).

CONCLUSION

Use of ECG in diagnostic workup of patients with seizures is poor. A prolonged optimal cutoff QTc interval predicts all-cause mortality in patients evaluated for seizure and those diagnosed with epilepsy. We advocate the routine use of a 12-lead ECG at index evaluation in patients with seizure or epilepsy.

Assessment of proarrhythmic ventricular electrophysiological remodeling in patients with rheumatoid arthritis

INTRODUCTION

Rheumatoid arthritis (RA) is related to cardiovascular disease and results in increased mortality rates. Ischemia, autonomic nervous system dysfunction, impaired cardiac ionic currents, and genetic predisposition may be the underlying mechanisms. Proarrhythmic ventricular electrophysiological remodeling detected on the basis of Tp‑e interval, Tp-e/QT, and Tp-e/QTc ratios plays a key role in the prognosis. Our aim was to assess proarrhythmic ventricular electrophysiological remodeling in patients with RA, a well-known chronic inflammatory disorder.

MATERIALS AND METHODS

A total of 163 patients with RA and 47 patients as a control group were included in this retrospective study. Proarrhythmic ventricular electrophysiological remodeling markers were evaluated in both groups along with baseline demographic and clinical variables. Patients using medication or with chronic disorders that can affect ventricular repolarization markers were excluded.

RESULTS

The patients with RA had prolonged Tp‑e interval (66 ms [44-80]; 80 ms [78-96], p < 0.001) and increased Tp-e/QT ratio (0.18 [0.12-0.22]; 0.22 [0.20-0.24], p < 0.001) and Tp-e/QTc ratio (0.16 [0.11-0.19]; 0.20 [0.17-0.22], p < 0.001) compared to the control group.

CONCLUSION

The Tp‑e interval and Tp-e/QT ratio, which may help to clarify the pathophysiological mechanisms of ventricular arrhythmias, were increased in patients with RA.

Electrocardiographic Predictors of Cognitive Decline and Dementia: A Systematic Review

BACKGROUND

Markers of altered cardiac function might predict cognitive decline and dementia.

OBJECTIVE

This systematic review aims to review the literature that examines the associations of various electrocardiogram (ECG) markers with cognitive decline and dementia in middle-aged and elderly populations.

METHODS

We searched PubMed, Embase, and Web of Science through 1 July 2020 for literature and conducted a systematic literature review. We included studies examining the associations of ECG markers (e.g., left ventricular hypertrophy [LVH], spatial QRS-T angle, and QT prolongation) with cognitive function and dementia in adult populations regardless of study setting and design, but excluded studies examining atrial fibrillation and heart rate variability.

RESULTS

Fourteen community-based cross-sectional and longitudinal studies were identified. ECG markers were investigated in association with dementia in four prospective studies, and with cognitive decline in ten prospective studies. ECG-assessed LVH was associated with dementia in one study while five heterogeneous prospective studies yielded inconsistent associations with cognitive decline. Regarding ventricular repolarization markers, spatial QRS-T angle was associated with cognitive decline in one study while another study found no association between QT prolongation and cognitive decline. High resting heart rate was associated with both dementia and cognitive decline in one study but not associated with dementia in another study. P-wave abnormality was significantly associated with incident dementia and cognitive decline in one prospective study.

CONCLUSION

Some ECG markers were associated with incident dementia and cognitive decline. However, limited number of heterogeneous studies did not allow us to make firm conclusions. Further studies are needed.

Electrocardiographic QRS duration is influenced by body mass index and sex

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In a large group of subjects without overt conduction system disease, there was a positive association between increasing BMI and electrocardiographic QRS duration that was independent of other covariates such as sex and age.

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Females had narrower QRS complex than the males at similar age and in the similar BMI category.

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Findings of this research should prompt further studies to explore the underlying mechanisms for these observations and potential reversibility of the conduction abnormality with weight loss

Background

Electrocardiogram (ECG) measured QRS duration has been shown to influence cardiovascular outcomes. However, there is paucity of data on whether ECG QRS duration is influenced by obesity and sex in large populations.

Methods

All ECGs performed by a pathology provider over a 2-year period were included. ECGs with confounding factors and those not in sinus rhythm were excluded from the primary analysis.

Results

Of the 76,220 who met the inclusion criteria, 41,685 (55%) were females. The median age of the study cohort was 61 years (interquartile [IQR] range 48–71 years). The median QRS duration was 86 ms (IQR 80–94 ms). The median BMI was 27.6 kg/m² (IQR 24.2–31.8 kg/m²). When stratified according to the World Health Organization classification of BMI < 18.50 kg/m², 18.50–24.99 kg/m², 25.00–29.99 kg/m², and ≥ 30.00 kg/m², the median QRS durations were 82 ms (IQR 76–88 ms), 86 ms (IQR 80–92 ms), 88 ms (IQR 80–94 ms) and 88 ms (IQR 82–94 ms), respectively (p < 0.001 for linear trend). Median QRS duration for females was 84 ms (IQR 78–88 ms); for males, it was 92 ms (IQR 86–98 ms), p < 0.001. Compared to males, females had narrower QRS complexes at similar age and similar BMI. In multiple linear regression analysis, BMI correlated positively with QRS duration (standardized beta 0.095, p < 0.001) independent of age, sex, and heart rate.

Conclusions

In this large cohort there was a positive association between increasing BMI and QRS duration. Females had narrower QRS duration than males at similar age and similar BMI.

QT Interval Dynamics and Cardiovascular Outcomes: A Cohort Study in an Integrated Health Care Delivery System

Background

Long QT has been associated with ventricular dysrhythmias, cardiovascular disease (CVD) mortality, and sudden cardiac death. However, no studies to date have investigated the dynamics of within‐person QT change over time in relation to risk of incident CVD and all‐cause mortality in a real‐world setting.

Methods and Results

A cohort study among members of an integrated health care delivery system in Northern California including 61 455 people (mean age, 62 years; 60% women, 42% non‐White) with 3 or more ECGs (baseline in 2005–2009; mean±SD follow‐up time, 7.6±2.6 years). In fully adjusted models, tertile 3 versus tertile 1 of average QT corrected (using the Fridericia correction) was associated with cardiac arrest (hazard ratio [HR], 1.66), heart failure (HR, 1.62), ventricular dysrhythmias (HR, 1.56), all CVD (HR, 1.31), ischemic heart disease (HR, 1.28), total stroke (HR, 1.18), and all‐cause mortality (HR, 1.24). Tertile 3 versus tertile 2 of the QT corrected linear slope was associated with cardiac arrest (HR, 1.22), ventricular dysrhythmias (HR, 1.12), and all‐cause mortality (HR, 1.09). Tertile 3 versus tertile 1 of the QT corrected root mean squared error was associated with ventricular dysrhythmias (HR, 1.34), heart failure (HR, 1.28), all‐cause mortality (HR, 1.20), all CVD (HR, 1.14), total stroke (HR, 1.08), and ischemic heart disease (HR, 1.07).

Conclusions

Our results demonstrate improved predictive ability for CVD outcomes using longitudinal information from serial ECGs. Long‐term average QT corrected was more strongly associated with CVD outcomes than the linear slope or the root mean squared error. This new evidence is clinically relevant because ECGs are frequently used, noninvasive, and inexpensive.

Rare Coding Variants Associated With Electrocardiographic Intervals Identify Monogenic Arrhythmia Susceptibility Genes: A Multi-Ancestry Analysis

BACKGROUND

Alterations in electrocardiographic (ECG) intervals are well-known markers for arrhythmia and sudden cardiac death (SCD) risk. While the genetics of arrhythmia syndromes have been studied, relations between electrocardiographic intervals and rare genetic variation at a population level are poorly understood.

METHODS

Using a discovery sample of 29 000 individuals with whole-genome sequencing from Trans-Omics in Precision Medicine and replication in nearly 100 000 with whole-exome sequencing from the UK Biobank and MyCode, we examined associations between low-frequency and rare coding variants with 5 routinely measured electrocardiographic traits (RR, P-wave, PR, and QRS intervals and corrected QT interval).

RESULTS

We found that rare variants associated with population-based electrocardiographic intervals identify established monogenic SCD genes (KCNQ1, KCNH2, and SCN5A), a controversial monogenic SCD gene (KCNE1), and novel genes (PAM and MFGE8) involved in cardiac conduction. Loss-of-function and pathogenic SCN5A variants, carried by 0.1% of individuals, were associated with a nearly 6-fold increased odds of the first-degree atrioventricular block (P=8.4×10^-5). Similar variants in KCNQ1 and KCNH2 (0.2% of individuals) were associated with a 23-fold increased odds of marked corrected QT interval prolongation (P=4×10^-25), a marker of SCD risk. Incomplete penetrance of such deleterious variation was common as over 70% of carriers had normal electrocardiographic intervals.

CONCLUSIONS

Our findings indicate that large-scale high-depth sequence data and electrocardiographic analysis identifies monogenic arrhythmia susceptibility genes and rare variants with large effects. Known pathogenic variation in conventional arrhythmia and SCD genes exhibited incomplete penetrance and accounted for only a small fraction of marked electrocardiographic interval prolongation.

Matrix Metalloproteinase-3 (MMP-3) Polymorphisms Are Associated with Prolonged ECG-Derived QTc Interval: A Cross-Sectional Study of the Australian Rural Population

Matrix metalloproteinases (MMPs) are enzymes that are integral in extracellular matrix (ECM) remodeling. In age or disease, ECM may become dysregulated and contribute to fibrosis, which impairs cardiac electrical conduction. Two alleles regulate matrix metalloproteinase-3 (MMP-3) activity: one with five adenosine bases (5A; associated with higher MMP-3 activity and decreased fibrosis) and another with six adenosine bases (6A; associated with lower MMP-3 activity and increased fibrosis). Here, we determined whether ECG-derived QTc and related parameters are associated with the MMP-3 5A/6A genotype in a cross-section of the Australian rural population. A retrospective cross-sectional population was obtained from the Charles Sturt University Diabetes Screening Research Initiative. Genotype and resting 12-lead ECG parameters of 295 participants were analyzed. Amongst these participants, 85 individuals carried the 5A/5A genotype, 141 individuals carried the 5A/6A genotype, and 65 individuals carried the 6A/6A genotype. Compared to 5A/5A genotype carriers, 5A/6A genotype carriers had a significantly longer QTc duration by 9.50 ms (95% CI: 3.48-15.52, p = 0.002), whilst 6A/6A genotype carriers had an even longer QTc duration by 12.19 ms (95% CI: 5.04-19.34, p = 0.001). We found an association between MMP-3 5A/6A polymorphisms and QTc, independent of adjustments for age, gender, alcohol consumption, smoking status, body mass index and blood pressure.

Corrected QT Interval Is Associated With Stroke but Not Coronary Heart Disease: Insights From a General Chinese Population

Background: Prolonged heart rate-corrected QT (QTc) interval has been associated with incident cardiovascular diseases (CVD) in general Western populations. However, this association is unclear in Asian population. We aim to estimate the association between QTc interval and incident CVD in a general Chinese population.

Methods: We analyzed 8,867 participants age ≥35 years and free of CVD at baseline in the Northeast China Rural Cardiovascular Health Study. A resting 12-lead electrocardiogram was performed on all participants, and QTc interval computed using the Framingham formula. Cox proportional hazards models were used to calculate hazard ratios (HRs) with 95% confidence intervals (CIs) for associations between QTc interval and incident stroke, coronary heart disease, and combined CVD events.

Results: Over a median follow-up of 4.66 years, a total of 439 CVD events occurred (298 stroke cases and 152 CHD cases). After full adjustment, prolonged QTc defined by a sex-specific cutoff was associated with increased risk of developing stroke (HR: 1.82, 95% CI 1.20–2.75, P = 0.004) and combined CVD (HR: 1.52, 95% CI 1.05–2.19, P = 0.026). Spline analyses demonstrated no clear thresholds; when modeled as a linear relationship, each 10 ms increase of QTc interval was associated with an HR of 1.12 (95% CI 1.06–1.19, P < 0.001) for stroke and an HR of 1.10 (95% CI 1.05–1.15, P < 0.001) for combined CVD. Baseline QTc interval was not associated with incident CHD with either modeling strategy.

Conclusions: Baseline QTc interval is associated with incident stroke and CVD in adults without prior CVD from a general Chinese population.