Prevalence and risk factors for prolonged QTc in a multiethnic cohort in rural Hawaii

Factors associated with prolonged QTc interval in Iranian population: MASHAD cohort study

AIM

QTc interval prolongation is a growing global issue which can cause torsades de pointes, a potentially fatal arrhythmia. We aimed to identify risk factors for prolonged QT interval in men and women.

METHODS

The Mashhad stroke and heart atherosclerotic disorder (MASHAD) cohort study collected electrocardiogram interval data. QT was corrected for heart rate using the Bazett's formula. Ordinal logistic regression with crude (univariable) and adjusted (multivariate) association analyses in the form of odds ratio and corresponding 95% confidence interval (CI) were used to identify the factors associated with QTc prolongation.

RESULTS

A total of 8878 individuals including 5318 females and 3560 males, aged 35 to 65 years, were included in this cross-sectional study. Participants with QTc prolongation were more likely to be older and have hypercholesterolemia, hypertension (HTN), and Type 2 diabetes mellitus (T2DM), but to have lower levels of physical activity (P < 0.05). Age (OR = 1.68, 95%CI = 1.18-2.39), hypercholesterolemia (OR = 1.77, 95%CI = 1.24-2.51), HTN (OR = 1.36, 95%CI = 1.06-1.73), T2DM (OR = 1.59, 95%CI = 1.19-2.13), severe anxiety (OR = 1.80, 95%CI = 1.05-3.11) and mild depression (OR = 1.38, 95%CI = 1.01-1.88) were independent risk factors for prolonged QTc interval in men. For women, only HTN (OR = 1.29, 95%CI = 1.02-1.63) and T2DM (OR = 1.50, 95%CI = 1.14-1.97) were independent risk factors.

CONCLUSIONS

Older age, Hypercholesterolemia, HTN, T2DM, severe anxiety and mild depression in men, and HTN and T2DM in women were associated with high risk of prolonged QTc interval. Healthcare practitioners should be aware of the risk factors of QTc interval prolongation and should exercise caution in the management of certain patients.

The Impact of Chronic Disease on the Corrected QT (QTc) Value in Women in a British Columbia First Nations Population

BACKGROUND

Indigenous women have higher rates of chronic disease than Indigenous men and non-Indigenous women. Long QT syndrome (LQTS) can be inherited or acquired; the latter may occur with chronic disease. A prolonged corrected QT value (QTc) is an independent risk factor for ventricular arrhythmias and sudden death, but few studies have quantified the impact of chronic disease on the QTc. We assessed the association between chronic disease and QTc prolongation in a population of First Nations women previously ascertained to study a high rate of inherited LQTS due to a unique genetic (founder) variant in their community.

METHODS

This substudy focusing on women expands on the original research where patients with clinical features of LQTS and their relatives were assessed for genetic variants discovered to affect the QTc. Medical records were retrospectively reviewed and chronic diseases documented. Using multivariate linear regression, adjusting for the effect of genetic variants, age, and QTc-prolonging medications, we evaluated the association between chronic disease and the QTc.

RESULTS

In total, 275 women were included. After adjustments, a prolonged QTc was associated with coronary artery disease (26.5 ms, 95% confidence interval [CI] 9.0-44.1 ms; P = 0.003), conduction system disease (26.8 ms, 95% CI 2.2-51.4 ms; P = 0.033), rheumatoid arthritis (28.9 ms, 95% CI 12.7-45.1 ms; P = 0.001), and type 2 diabetes mellitus (17.9 ms, 95% CI 3.6-32.3 ms; P = 0.015).

CONCLUSIONS

This quantification of the association between chronic disease and QTc prolongation in an Indigenous cohort provides insight into the nongenetic determinants of QTc prolongation. Corroboration in other populations will provide evidence for generalisability of these results.

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.

QT prolongation is over-estimated by Bazett compared to Friderica in Japanese child and adolescent inpatients

Recent researches suggested that the risk of drug-induced QTc prolongation is low in child and adolescent psychiatry setting. However, these cohorts enrolled mainly of Caucasian background. We aimed to assess the prevalence of QTc prolongation and its association with antipsychotic use in Japanese youth. The medical records of inpatients were reviewed. Two different definitions of QT prolongation, Bazett's corrected QT interval (QTcB) >450 msec and Fridericia's corrected QT interval (QTcF) >450 msec, were adopted. In 220 participants [age: 13.4 ± 2.3 years, antipsychotics according to the chlorpromazine equivalence: 50 (25th-75th percentiles; 0-150) mg/day], the prevalence of QTcB and QTcF prolongation was 13.6 and 2.3%, respectively. Patients with QTcB >450 msec had a significantly higher heart rate than those with QTcB ≤450 msec (91.2 ± 20.6 bpm vs. 76.1 ± 15.2 bpm; P < 0.001). The other variables, except potassium level (4.1 ± 0.4 mEq/L vs. 4.2 ± 0.3 mEq/L; P = 0.030), showed no significant difference. Clinically meaningful QTc prolongation was rare even in this Japanese cohort. This study also suggested that if QTcB is used, clinicians should be aware of possible overdiagnosis of QTc prolongation due to accelerated heart rate.

Different body parts' fat mass and corrected QT interval on the electrocardiogram: The Fasa PERSIAN Cohort Study

Background

Previous studies suggested that obesity and fat mass are associated with QT interval prolongation, but the role of different body parts' fat mass is unclear. The associations between total and regional fat mass (FM) and corrected QT interval (QTc) were investigated for the first time in this study.

Methods

In this sub-analysis of Fasa PERSIAN cohort Study data, 3217 subjects aged 35–70 entered our study. Body fat mass was assessed by bioelectrical impedance analysis and QTc interval calculated by the QT interval measured by Cardiax^® software from ECGs and Bazett’s formula. Uni- and multi-variable linear and logistic regression was performed in IBM SPSS Statistics v23.

Results

In males, the fat mass to fat-free mass (FM/FFM) ratio in the trunk, arms, total body, and legs were significantly higher in the prolonged QTc group (QTc > 450 ms). Trunk (B = 0.148), total (B = 0.137), arms (B = 0.124), legs (B = 0.107) fat mass index (FMI) showed significant positive relationship with continuous QTc (P-value < 0.001). Also, just the fat-free mass index of legs had significant positive associations with QTc interval (P-value < 0.05). Surprisingly, in females, the mean of FM/FFM ratio in trunk and legs in the normal QTc group had higher values than the prolonged QTc group (QTc > 470 ms). Also, none of the body composition variables had a significant correlation with continuous QTc.

Conclusion

Our study suggested that FMI ratios in the trunk, total body, arms, and legs were positively associated with QTc interval in males, respectively, from a higher to a lower beta-coefficient. Such associations were not seen in females. Our study implies that body fat mass may be an independent risk factor for higher QTc interval and, consequently, more cardiovascular events that should be investigated.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-021-02095-2.

Relationship of QTc Interval Prolongation with Acute Ischemic Stroke

Introduction:

Many electrocardiographic (ECG) changes have been observed after strokes. We analyzed the QTc interval prolongation following stroke.

Aim:

The study aimed to assess if the prolongation in QTc interval is related to the occurrence of acute ischemic stroke.

Methods:

This cross-sectional study was conducted from July to December 2018. We included 100 consecutive patients with first-ever ischemic stroke who were admitted to our emergency department, who were age-matched and gender-matched with a control group of 100 non-stroke patients that visited our outpatients department for diseases other than cerebrovascular or cardiovascular ones. A single 12-lead resting ECG examination was done in all patients at the time of their emergency department admission.

Results:

No significant difference between the two groups regarding the age distribution and mean age was found. 56.5% of the sample were males but the difference was not significant between both gender groups. The main presenting symptoms of stroke cases were right-sided weakness (47%), left-sided weakness (36%), and right-sided weakness and aphasia (10%). 34% of the cases had prolonged QTc interval while none of the controls had a prolonged interval (p-value<0.001). No significant difference was observed among stroke patients concerning gender (p-value=0.584).

Conclusion:

Our findings support many previous studies on the brain-heart interaction during acute ischemic strokes and reinforce previous conclusions that assessment of the QTc interval might aid to stratify morbidity and mortality risks in patients with acute ischemic stroke. To accomplish the acute stroke effects on QTc interval prolongation, we need further larger size analytic studies.

Clinical Risk Factors for Therapeutic Lithium-Associated Electrocardiographic Changes in Patients With Bipolar Disorder

PURPOSE/BACKGROUND

Lithium, a common medication used in bipolar disorder treatment, can exert an inhibitory effect on sodium and potassium channels and potentially cause cardiac electrical conduction disturbance and corrected QT (QTc) prolongation. This study aimed to examine whether lithium at therapeutic levels can change electrocardiographic parameters in different groups of patients with bipolar disorder and to identify the potential clinical risk factors.

METHODS/PROCEDURES

Standard 12-lead electrocardiogram data before and after lithium treatment in bipolar disorder patients after at least 2-week dropout of psychotropic medications were analyzed.

FINDINGS/RESULTS

A total of 39 patients with bipolar disorder receiving lithium treatment were enrolled. Nineteen patients (48.7%) exhibited increased from P wave beginning to QRS complex beginning intervals after lithium treatment (mean serum level, 0.653 ± 0.247 mmol/L). Twenty-four patients (61.5%) exhibited increased a combination of Q, R, and S waves complex durations and increased QTc intervals. Twenty-three patients (59.0%) exhibited increased corrected JT (JTc) intervals. The patient group with increased QTc or JTc intervals exhibited a higher mean systolic blood pressure than did the patient group without increased QTc (134.7 ± 19.2 mm Hg vs 115.7 ± 11.8 mm Hg, P = 0.020) or JTc intervals (134.4 ± 19.6 mm Hg vs 117.6 ± 13.3 mm Hg, P = 0.054), respectively. Biochemical and hemodynamic parameters were comparable between patients with and without increased a combination of Q, R, and S waves complex durations or from P wave beginning to QRS complex beginning intervals.

IMPLICATIONS/CONCLUSIONS

Elevated systolic blood pressure may be the risk factor for the ventricular conduction delay in bipolar disorder patients receiving lithium at therapeutic levels.

Association of QTc Interval with Risk of Cardiovascular Diseases and Related Vascular Traits: A Prospective and Longitudinal Analysis

Background:

Prolonged heart rate corrected QT (QTc) interval was reported to be associated with cardiovascular diseases (CVDs).

Objective:

There exists little data on the association between QTc interval and cardiovascular risk in Asian populations. We prospectively investigated the association of QTc interval with CVDs and vascular traits in a large cohort of Chinese adults.

Methods:

A total of 7,605 participants aged 40 years or older from a well-defined community without CVDs at baseline were included and followed up for an average of 4.5 years. Association of baseline QTc interval with incident CVDs was evaluated using Cox regression analysis. Associations of QTc interval with brachial-ankle pulse wave velocity (baPWV), carotid intima-media thickness (CIMT), and risk of microalbuminuria and peripheral arterial diseases (PAD) were secondarily examined.

Results:

Prolonged QTc interval (≥460 ms in women and ≥450 ms in men) was associated with 51% higher risk of total major CVDs (hazard ratio [HR] = 1.51, 95% confidence interval [CI] [1.20, 1.90]), particularly, 48% increased risk of stroke (95% CI [1.16, 1.88]). Prolonged QTc interval was positively associated with baPWV (β = 38.10 cm/s, standard error [SE] = 8.04, P < 0.0001) and CIMT (β = 0.01 mm, SE = 0.01, P = 0.04). Prolonged QTc interval was associated with increased risk of incident microalbuminuria (odds ratio [OR] = 1.65, 95% CI [1.21, 2.24]) and PAD (2.49, 95% CI [1.35, 4.59]).

Conclusions:

Prolonged QTc interval is positively and significantly associated with increased risk of CVDs and related vascular traits in Chinese population.

Prevalence and risk factors of prolonged corrected QT interval in general Chinese population

BACKGROUND

Corrected QT (QTc) interval has been correlated with total and CVD mortality. Although much is known about the relation between prolonged QTc interval and clinical outcome, there is no information on the prevalence and specific risk factors of QTc prolongation in general Chinese population. We evaluated the prevalence of prolonged QTc interval and its risk factors in general Chinese population, aiming to fill in the gaps in the literature and provide evidence for potential CVD risk prediction and disease burden estimate in community.

METHODS

A population-based survey was conducted on 11,209 participants over the age of 35 in rural areas of Liaoning Province from 2012 to 2013. Twelve-lead ECGs and automatic analysis were performed on all participants. Logistic regression adjustments were made by using the Bazett's formula to correlate specific risk factors with prolonged QTc intervals (> 440 ms) for potential confounders.

RESULTS

The overall prevalence of prolonged QTc interval was 31.6%. The prevalence increased significantly with age (24.1% among those aged 35-44 years; 28.3%, 45-54 years; 35.2%, 55-64 years; 43.4%, ≥65 years, P < 0.001). Participants with a history of CVD had a higher prevalence of QTc prolongation (40.7% vs. 30.0%). In the fully adjusted logistic regress model, older age, abdominal obesity, hypertension, diabetes, hypokalemia and any medicine used in the past two weeks were associated independently with increased risk for prolonged QTc interval (All P < 0.05). We found no significant differences between general obesity, hypocalcemia and hypomagnesemia with prolongation of QTc interval. Female sex showed opposite results after applying clinical diagnostic criteria, and high physical activity could reduce the risk of prolonged QTc interval.

CONCLUSIONS

The prevalence of prolonged QTc interval was relatively high in general Chinese population and listed relevant factors, which would help identify patients at risk in pre-clinical prevention and provide evidence for estimating potential CVD burden and making management strategies in community.

Prevalence of ECG abnormalities and risk factors for QTc interval prolongation in hospitalized psychiatric patients

BACKGROUND

Psychiatric patients are at risk of cardiovascular diseases, and many psychotropic drugs can prolong QTc interval. Requirements for electrocardiogram (ECG) monitoring have been set up in our psychiatric university hospital. The objective of this study was to determine the proportion of adult patients who had an ECG during their hospitalization, the prevalence of ECG abnormalities, the evolution of the QTc after admission, and the risk factors for QTc prolongation.

METHODS

Retrospective analysis of ECGs and clinical data of all patients with a complete hospitalization in 2015. Assessment of the influence of covariates on QTc using linear mixed-effects models.

RESULTS

At least one ECG (n = 600) was performed during 37.6% of the stays (n = 1198) and in 45.5% of the patients (n = 871). Among the patients with an ECG, 17.9% had significant ECG abnormalities, including 7.6% with a prolonged QTc. QTc measured at admission and during hospitalization did not change significantly (n = 46, 419.4 ± 29.7 ms, 417.2 ± 27.6 ms, p = 0.71). In the multivariate model (292 patients, 357 ECGs), the covariates significantly associated with the QTc were gender (+15.9 ms if female, p < 0.0001), age (+0.4 ms/year, p = 0.0001), triglyceride levels (+5.7 ms/mmol/l, p = 0.005), and drugs with known risk of torsades de pointes (+6.2 ms if ⩾1 drug, p = 0.028).

CONCLUSIONS

The prevalence of hospitalized psychiatric patients with an abnormal ECG indicates that ECGs should be performed systematically in this population. Prescription of psychotropic drugs should be done cautiously, particularly in patients with QTc prolongation risk factors.

Risk factors for QTc-prolongation: systematic review of the evidence

Background QTc-interval prolongation has been associated with serious adverse events, such as Torsade de Pointes and sudden cardiac death. In the prevention of QTc-prolongation, special attention should go to high-risk patients. Aim of the review The aim of this review is to summarize and assess the evidence for different risk factors for QTc-prolongation (demographic factors, comorbidities, electrolytes, QTc-prolonging medication). Methods Potential studies were retrieved based on a systematic search of articles published until June 2015 in the databases Medline and Embase. Both terms about QTc-prolongation/Torsade de Pointes and risk factors were added in the search strategy. The following inclusion criteria were applied: randomized controlled trials and observational studies; inclusion of ≥500 patients from a general population (not limited to specific disease states); assessment of association between QTc-interval and risk factors. For the articles that met the inclusion criteria, the following data were extracted: study design, setting and study population, number of patients and cases of QTc-prolongation, method of electrocardiogram-monitoring, QTc-correction formula, definition of QTc-prolongation, statistical methods and results. Quality assessment was performed using the GRADE approach (for randomized controlled trials) and the STROBE-recommendations (for observational studies). Based on the number of significant results and the level of significance, a quotation of the evidence was allocated. Results Ten observational studies could be included, with a total of 89,532 patients [prospective cohort design: N = 6; multiple regression analyses: N = 5; median STROBE score = 17/22 (range 15-18)]. Very strong evidence was found for hypokalemia, use of diuretics, antiarrhythmic drugs and QTc-prolonging drugs of list 1 of CredibleMeds. Little or no evidence was found for hyperlipidemia, the use of digoxin or statins, neurological disorders, diabetes, renal failure, depression, alcohol abuse, heart rate, pulmonary disorders, hormone replacement therapy, hypomagnesemia, history of a prolonged QTc-interval/Torsade de Pointes, familial history of cardiovascular disease, and the use of only QTc-prolonging drugs of list 2 or 3 of CredibleMeds. Conclusion This systematic review gives a clear overview of the available evidence for a broad range of risk factors for QTc-prolongation.

Sex-specific association between serum uric acid and prolonged corrected QT interval: Result from a general rural Chinese population

Recently, it has been found that high level of serum uric acid (SUA) is causally related to sudden cardiac death (SCD). We examined the sex-specific associations of SUA with prolonged heart rate-corrected QT (QTc) interval in a general Chinese population.A large sample of 11,206 Chinese research participants aged 35 years and older was recruited from rural areas of Liaoning Province during 2012 to 2013. SUA were divided into quartiles separated for males and females. Prolonged QTc interval, assessed by the Bazett formula, was defined as cut points of 460 ms or longer in females and 450 ms or longer in males. Mean (+/- standard deviation) QTc intervals were 422.1 ± 24.2 ms among 5104 males and 436.1 ± 23.5 ms among 6102 females, respectively. In both sexes, SUA showed significant correlations with QTc interval (both P < 0.001). Among male participants, the highest quartile of SUA (>379 μmol/L) was related to an increased risk for prolonged QTc interval (odds ratios: 1.402, 95% confidence interval: 1.073-1.831) compared to the lowest quartile (≤276 μmol/L) after fully adjustment. However, there were no significant relationships between SUA and prolonged QTc interval among females in all the models.Males with high SUA are prone to a higher risk for prolonged QTc interval. This study provides novel explanation for population-based findings on SUA and SCD, as well as important implications for management strategies for hyperuricemic patients in clinical practice.

Prolonged QTc Interval Predicts Poststroke Paroxysmal Atrial Fibrillation

Background and Purpose—

Paroxysmal atrial fibrillation (PAF) is often difficult to detect in patients with acute ischemic stroke. We aimed to assess the predictive value of a prolonged QT interval corrected for heart rate (QTc) in PAF detection after acute ischemic stroke.

Methods—

We enrolled 972 patients with acute ischemic stroke consecutively extracted from our observational stroke registry system. Exclusion criteria were as follows: (1) AF on the initial 12-lead ECG (n=171); (2) previously diagnosed PAF (n=47); and (3) the use of a cardiac pacemaker (n=10). Of the 972 patients, 744 (mean age, 67.6 years; men, 62.6%) were eligible for analysis. The clinical characteristics and 12-lead ECG findings of the patients with and without PAF were compared, and multiple logistic regression analysis was performed to identify predictors of poststroke PAF.

Results—

The poststroke cardiac work-up yielded 69 (9.3%) de novo PAF cases among the 744 patients. The QTc interval was significantly longer in patients with PAF than in those without PAF (436 versus 417 ms; P <0.001). Each 10-ms increase in the QTc interval was associated with an increased risk of PAF after multivariate adjustments (odds ratio, 1.41; 95% confidence interval, 1.24–1.61; P <0.001). The optimal threshold value of QTc interval calculated by a receiver-operating characteristic curve was 438 ms, and the area under the curve was 0.73 in this data set.

Conclusions—

The QTc interval prolongation is potentially a strong and useful predictor for poststroke PAF.

Hyperglycemia is associated with corrected QT prolongation and mortality in acutely ill patients

BACKGROUND

The QT interval on an electrocardiogram represents ventricular repolarization time. Increased length of this interval, known as corrected QT (QTc) prolongation, can be a precursor to torsade de pointes, a potentially life-threatening ventricular dysrhythmia. An association exists between blood glucose and QTc interval in ambulatory populations. Because both hyperglycemia and QTc prolongation are common in critically ill patients, we sought to examine the relationship between blood glucose, QTc interval prolongation, and all-cause mortality in critically ill patients.

METHODS

We studied adult patients admitted to cardiac monitoring units. Blood glucose and other clinical variables were abstracted from the medical record. Corrected QT measurements were automatically derived from continuous bedside cardiac monitoring systems.

RESULTS

Twenty-five percent (233/940) of the patients had QTc prolongation, and 53% had elevated blood glucose (>140 mg/dL) during hospitalization. Adjusted odds for QTc prolongation were 2.1 (95% confidence interval, 1.5-3.1) for moderately elevated blood glucose (140-180 mg/dL) and 3.7 (95% confidence interval, 2.5-5.4) for severely elevated blood glucose (>180 mg/dL). Mortality rate was highest (16%) in patients experiencing both severely elevated blood glucose (>180 mg/dL) and QTc interval prolongation.

CONCLUSIONS

Hyperglycemia is linked with QTc prolongation, and both are associated with increased odds of mortality in critically ill patients. Further studies are needed to extrapolate the relationship between glucose and ventricular repolarization, as well as appropriate glucose control parameters and QTc interval monitoring in critical care units.

Boosted protease inhibitors and the electrocardiographic measures of QT and PR durations

BACKGROUND

There are contradictory reports regarding the effects of protease inhibitors on the ECG measures of QT and PR interval durations. The effect of interrupting use of protease inhibitors on QT and PR progression is also unknown.

METHODS

This analysis included 3719 participants from the Strategies for Management of Antiretroviral Therapy (SMART) study, of whom 1879 were randomized to receive intermittent antiretroviral therapy (ART) (drug conservation group), whereas the rest received these drugs continuously (viral suppression group). Linear regression analysis was used to compare four ritonavir-boosted protease inhibitor (protease inhibitor/r) regimens [saquinavir (SQV/r), lopinavir (LPV/r), atazanavir (ATV/r), and other protease inhibitor/r], and nonboosted protease inhibitor regimens with nonnucleoside reverse transcriptase inhibitor (NNRTI) regimens for Bazett's (QTcB) and Fredericia's (QTcF) heart rate corrected QT and PR. Changes in QTcB, QTcF, and PR after 12 and 24 months of randomization were compared in the drug conservation group and viral suppression group.

RESULTS

Average levels of QTcB, QTcF, and PR duration at entry were 415, 406, and 158 ms. At study entry, 49% of participants were taking an NNRTI (no protease inhibitor)-based regimen and 31% were prescribed a boosted protease inhibitor, the most common being LPV/r. After adjustment for baseline factors, QTcB and QTcF levels did not vary by boosted protease inhibitor group (P = 0.26 and P = 0.34, respectively). For those given any of the boosted protease inhibitors, QTcB was 1.5 ms lower than the NNRTI group (P = 0.04). Both boosted and nonboosted protease inhibitor-containing regimens were significantly associated (P < 0.01 for each) with longer PR intervals compared to the NNRTI group. After adjustment, the difference between boosted protease inhibitors and the NNRTI group was 5.11 ms (P < 0.01); for nonboosted protease inhibitors, this difference was 3.00 ms (P < 0.01). Following ART interruption, PR duration declined for both the boosted and nonboosted protease inhibitor groups and compared to the viral suppression group, significant changes in PR interval were observed 24 months after ART interruption of boosted protease inhibitors (P < 0.01).

CONCLUSION

Different protease inhibitor-based regimens have a similar, minimal effect on QT compared to NNRTI-based regimens. All protease inhibitor-based regimens (boosted and nonboosted) were associated with prolongation of PR, and interruption of protease inhibitor regimens reduced the prolonged PR duration. Further research is needed to confirm the findings of this study and assess the clinical relevance of the differences.

Patients with metabolic syndrome have prolonged corrected QT interval (QTc)

BACKGROUND

Prolongation of corrected QT interval (QTc) increases morbidity and mortality and QTc has been found to be longer in patients with diabetes mellitus than in healthy controls. It is still inconclusive whether the metabolic syndrome results in QTc prolongation.

HYPOTHESIS

We hypothesized that metabolic syndrome might contribute to risk of QTc prolongation. The hypothesis was tested in a large population.

METHODS

A total of 5,815 individuals (men: 1,950, women: 3,865 aged 20-80 years) were enrolled. Metabolic syndrome was defined according to the revised third National Cholesterol Education Program Adult Treatment Panel (NCEP-ATP III). QTc was calculated by using Bazett and Fridericia equations and the corrected JT interval (JTc) was derived by subtracting the QRS duration from the QTcB. All individuals had physical examinations, electrocardiograms, echocardiography, and blood tests.

RESULTS

Individuals with metabolic syndrome had longer QTcs and JTc than those without metabolic syndrome (439.84 ms versus 430.90 ms in men, 456.37 ms versus 445.12 ms in women, respectively, p < 0.001 using Bazett formula). The more the number of abnormal metabolic parameters they had, the longer the QTcs and JTc they had. Trend analysis indicated that QTcB, QTcF, and JTc were significantly correlated to the number of abnormal metabolic parameters both in men and in women. After being adjusted for conventional risk factors, QTcB, QTcF, and JTc remained negatively associated with serum potassium concentration and positively associated with interventricular septal thickness.

CONCLUSIONS

Metabolic syndrome is a risk factor for prolonged QTc, which may further increase cardiovascular morbidity and mortality in the subjects with metabolic syndrome.

Association of increased QTc interval with the cardiometabolic syndrome

Recent studies indicate a high prevalence of increased QTc interval length in patients affected by the metabolic syndrome, but there is no data available to demonstrate the correlation of the QTc interval with severity of the cardiometabolic syndrome (CMS). The objective of this study was to estimate the association between increasing number of cardiometabolic abnormalities and increasing QTc interval length. Electrocardiograms were collected from 1420 participants in a cross-sectional study. The QTc interval lengths were corrected for heart rate using Bazett's formula. CMS was determined according to the National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATP III) guidelines. Multiple linear regression models were used examining associations between increasing number of individual components of syndrome with QTc interval length. Participants with CMS had significantly longer QTc interval length, controlling for age, body mass index (BMI), sex, and ethnic group. Increasing number of CMS components was significantly associated with increased QTc interval length, even after adjusting for age, BMI, total cholesterol, fasting C peptide, and history of heart disease. These findings suggest that QTc interval length is increased in the presence of CMS and is linearly related to an increase in number of metabolic abnormalities.

Analysis of genetic and non-genetic factors that affect the QTc interval in a Mongolian population: the GENDISCAN study

The QTc interval is a complex quantitative trait and a strong prognostic indicator of cardiovascular mortality in general, healthy people. The aim of this study was to identify non-genetic factors and quantitative trait loci that govern the QTc interval in an isolated Mongolian population. We used multiple regression analysis to determine the relationship between the QTc interval and non-genetic factors including height, blood pressure, and the plasma lipid level. Whole genome linkage analyses were performed to reveal quantitative trait loci for the QTc interval with 349 microsatellite markers from 1,080 Mongolian subjects. Among many factors previously known for association with the QTc interval, age, sex, heart rate, QRS duration of electrocardiogram and systolic blood pressure were also found to have influence on the QTc interval. A genetic effect for the QTc interval was identified based on familial correlation with a heritability value of 0.31. In a whole genome linkage analysis, we identified the four potential linkage regions 7q31-34, 5q21, 4q28, and 2q36.

Relationship between HIV protease inhibitors and QTc interval duration in HIV-infected patients: a cross-sectional study

AIMS

QTc interval prolongation and torsades de pointes have been reported in HIV-infected patients. Protease inhibitors (PIs) are suspected to contribute to this adverse reaction. However, many factors can prolong QTc interval. We examined factors influencing QTc duration in HIV-infected patients.

METHODS

Unselected HIV-infected patients (n = 978) were enrolled in this prospective, single-centre cross-sectional study. Variables related to infection and treatments were collected. A digital electrocardiographic record was recorded in each patient and QT interval duration was measured and corrected using both Bazett's (QTcB) and Fridericia's (QTcF) formula. Results were analysed with a multivariable linear model.

RESULTS

After excluding arrhythmias and complete bundle branch blocks, QT interval was measured in 956 patients. The mean (SD) QTcB was 418 ms (23) and QTcF was 405 ms (20). QTc was found prolonged (>450 ms in women and >440 ms in men) in 129 [13.5%; 95% confidence interval (CI) 11.5, 15.8] and 38 (4%; 95% CI 2.9, 5.4) patients using Bazett and Fridericia corrections, respectively. On multivariable analysis, incomplete bundle branch block, ventricular hypertrophy, signs of ischaemic cardiopathy, female gender, White ethnic origin and age were significantly associated with QTc prolongation. The only HIV variable independently associated with QTc prolongation was the duration of infection (P = 0.023). After adjustment, anti-HIV treatment, in particular PI (P = 0.99), was not associated with QTc prolongation.

CONCLUSIONS

Although PIs block in vitro hERG current, they are not independently associated with QTc interval prolongation. Prolonged QTc interval in HIV-infected patients is primarily associated with factors commonly known to prolong QT and with the duration of HIV infection.

Association between angiotensin-converting enzyme gene polymorphisms and QT duration in a multiethnic population in Hawaii

OBJECTIVES

Recent studies have suggested that heart-rate corrected QT interval (QTc) in normal populations may be influenced by genetic factors. We report findings of a study of the relationship between QTc, increased QTc (> 440 ms) and angiotensin-converting enzyme (ACE) genotype in a multiethnic, population-based study completed in rural Hawaii.

METHODS

Blood samples were obtained while fasting and after an oral glucose challenge from 1452 individuals between 1997 and 2000. The clinical examination included an electrocardiogram. Medical histories, behavioral and socio-demographic information were obtained during the interview. Ethnicity was estimated by self-report. The insertion/deletion (I/D) polymorphism in intron 16 of the ACE gene was determined by polymerase chain reaction (PCR) from a random sample of 588 participants. Multiple linear and logistic regression was used to test for associations between QTc and ACE gene polymorphisms.

RESULTS

The overall crude prevalence of increased QTc was 21.2%. The prevalence of increased QTc was lowest among those with ACE DD genotype, and highest among those with ACE insertion/insertion (II) genotype. The adjusted odds ratio for increased QTc was 2.29 (95% CI 1.02-5.12) and 3.61 (95% CI 1.60-8.13) for ID and II genotypes, respectively, compared to the DD genotype. The test for trend was highly significant (p < 0.001).

CONCLUSIONS

The ACE insertion allele was associated with increased prevalence of prolonged QTc independent of ethnicity, age, gender, and BMI. These findings may implicate the ACE gene as an important genetic risk factor for cardiovascular disease morbidity and mortality.

Possible interethnic differences in quinidine-induced QT prolongation between healthy Caucasian and Korean subjects

AIMS

The aim of this study was to evaluate the pharmacokinetics and pharmacodynamics of quinidine-induced QT prolongation in healthy Caucasian and Korean subjects to investigate interethnic differences in susceptibility to drug-induced arrhythmia.

METHODS

A randomized, double-blind crossover study was conducted in 24 (12 male and 12 female) Korean and 13 (seven male and six female) Caucasian subjects. After a 20 min infusion of quinidine (4 mg kg(-1)) or saline, the serum concentration of quinidine and the QT interval corrected by Bazett's formula (QTc) were monitored. The dynamic data were analyzed by means of a population modelling approach using NONMEM.

RESULTS

There were no statistical differences in the pharmacokinetic profiles of quinidine between ethnic groups. The QTc values in Caucasians were higher than those in Koreans at the same quinidine concentrations, especially at higher quinidine concentrations and in female subjects. According to an E(max) model [equation: see text], the population modelling approach revealed that E0 (ms) was related to gender (408 + [34*(1 - Sex)]; 1 for male and 0 for female), DeltaE(max) (ms) was related to ethnicity ((136*f(ETHN)) + C(female): f(ETHN) = 1 for Koreans and 1.26 for Caucasians; C(female) was 106 only for Caucasian females), and EC50 was estimated to be 3.13 microm.

CONCLUSIONS

These results suggest that Korean subjects were less sensitive to quinidine-induced QT prolongation than Caucasian subjects, and that this trend was particularly true for females. Further population-based studies are merited to characterize more completely the ethnic differences in drug-induced QT prolongation between Asians and other ethnic groups.

Normal standards for QT and QT subintervals derived from a large ethnically diverse population of women aged 50 to 79 years (the Women's Health Initiative [WHI])

Available normal standards for rate-adjusted QT intervals in women are based on samples that include only whites, and no normal standards are available for QT subintervals. This study derived normal limits from percentile distributions for QT as well as QT and T-wave subintervals in 22,311 participants in the Women's Health Initiative (WHI), including 19,059 white, 1,771 African-American, 819 Hispanic, 82 American Indian, and 580 Asian women. Excluded were women with cardiovascular disease or who were using cardioactive drugs at baseline and cardiovascular morbidity or death during the subsequent mean 6.3-year follow-up. Normal limits for QT adjusted by Bazett's formula were strongly rate dependent, invalidating their use in practical applications. QT adjusted as a linear function of RR (QTrr) or by power functions of RR with exponent 0.5 (QTsqr) or 0.42 (QT0.42) using an appropriate regression function produced rate-invariant upper and lower normal limits for rate-adjusted QT. Adjusted QT is preferable to adjusted JT because the latter requires the incorporation of QRS duration as a covariate with RR. Normal limits were also derived for T-wave subintervals. Normal limits of QTrr in Asian women were 10 ms longer than in other ethnic groups. In conclusion, QT adjusted for rate as a linear function of RR is preferable to JT and other QT subintervals in the evaluation of QT prolongation. The adaptation of considerable revisions of the currently used limits for prolonged QT in women is suggested, with an additional race-specific adjustment in Asian women. Bazett's formula is inappropriate for testing new drugs or other applications.