Dynamic QT Interval Changes from Supine to Standing in Healthy Children

The Effects of Cycle Ergometer Versus Treadmill Exercise Stress Testing on QTc Interval Prolongation in Patients With Long QT Syndrome: A Systematic Review and Meta-analysis

OBJECTIVE

The safest and most effective exercise stress tests (EST) modalities for long QT syndrome (LQTS) are currently unknown. The main objective was to explore the effects of EST on the corrected QT interval (QTc) in patients with LQTS, and to compare the effects of different EST modalities (cycle ergometer vs treadmill).

DATA SOURCES

Systematic searches were performed in September 2022 in accordance with the PRISMA statement through PubMed, Medline, EBM Reviews, Embase, and Web of Science.

MAIN RESULTS

A total of 1728 patients with LQTS, whether congenital or acquired, without any age restrictions (pediatric age ≤18 years and adult age >19 years), and 2437 control subjects were included in the 49 studies. The QT interval data were available for 15 studies. Our analyses showed that the QT interval prolonged in a similar manner using either a cycle ergometer or a treadmill (standardized mean difference [SMD] = 1.89 [95% CI, 1.07-2.71] vs SMD = 1.46 [95% CI, 0.78-2.14], respectively). Therefore, it seems that either modality may be used to evaluate patients with LQTS.

CONCLUSIONS

The methodology for the measurement of the QT interval was very heterogeneous between studies, which inevitably influenced the quality of the analyses. Hence, researchers should proceed with caution when exploring and interpreting data in the field of exercise and LQTS.

Adolescents on psychotropic treatment displayed longer corrected QT intervals than unmedicated controls when they rose rapidly from the supine position

AIM

Psychotropic medication can contribute to arrhythmia and identifying individuals at risk is crucial. This Swedish study compared the corrected QT (QTc) intervals of adolescents on psychotropic medication with unmedicated controls, when supine and after rising rapidly.

METHODS

The study was carried out at Östersund County Hospital in March 2022 and February to March 2023. It comprised 16 cases, aged 10-17 years and 28 controls. QTc intervals were measured with electrocardiography and calculated using Bazett's and Fridericia's formulas. Univariate and multiple linear regressions were used to assess differences in QTc intervals between the cases and controls and across sex, age and body mass index.

RESULTS

The mean QTc interval when supine, calculated with Bazett's formula, was longer for the adolescents on psychotropic medication than the controls (p = 0.046). The same was true for the mean QTc interval after rising rapidly from the supine position, calculated with both Bazett's formula (p = 0.009) and Fridericia's formula (p = 0.007). Mean QTc intervals varied by sex and age groups. Psychotropic medication prolonged QTc intervals, particularly in girls.

CONCLUSION

Longer QTc intervals were found in adolescents on psychotropic medication, particularly after rising rapidly from the supine position.

Provocation testing in congenital long QT syndrome: A practical guide

Congenital long QT syndrome (LQTS) is a hereditary cardiac channelopathy with an estimated prevalence of 1 in 2500. A prolonged resting QT interval corrected for heart rate (QTc interval) remains a key diagnostic component; however, the QTc value may be normal in up to 40% of patients with genotype-positive LQTS and borderline in a further 30%. Provocation of QTc prolongation and T-wave changes may be pivotal to unmasking the diagnosis and useful in predicting genotype. LQTS provocation testing involves assessment of repolarization during and after exercise, in response to changes in heart rate or autonomic tone, with patients with LQTS exhibiting a maladaptive repolarization response. We review the utility and strengths and limitations of 4 forms of provocation testing-stand-up test, exercise stress test, epinephrine challenge, and mental stress test-in diagnosing LQTS and provide some practical guidance for performing provocation testing. Ultimately, exercise testing, when feasible, is the most useful form of provocation testing when considering diagnostic sensitivity and specificity.

Congenital Long QT Syndrome

Congenital long QT syndrome (LQTS) encompasses a group of heritable conditions that are associated with cardiac repolarization dysfunction. Since its initial description in 1957, our understanding of LQTS has increased dramatically. The prevalence of LQTS is estimated to be ∼1:2,000, with a slight female predominance. The diagnosis of LQTS is based on clinical, electrocardiogram, and genetic factors. Risk stratification of patients with LQTS aims to identify those who are at increased risk of cardiac arrest or sudden cardiac death. Factors including age, sex, QTc interval, and genetic background all contribute to current risk stratification paradigms. The management of LQTS involves conservative measures such as the avoidance of QT-prolonging drugs, pharmacologic measures with nonselective β-blockers, and interventional approaches such as device therapy or left cardiac sympathetic denervation. In general, most forms of exercise are considered safe in adequately treated patients, and implantable cardioverter-defibrillator therapy is reserved for those at the highest risk. This review summarizes our current understanding of LQTS and provides clinicians with a practical approach to diagnosis and management.

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.

Diagnostic accuracy of the response to the brief tachycardia provoked by standing in children suspected for long QT syndrome

Background

Adult long QT syndrome (LQTS) patients have inadequate corrected QT interval (QTc) shortening and an abnormal T-wave response to the sudden heart rate acceleration provoked by standing. In adults, this knowledge can be used to aid an LQTS diagnosis and, possibly, for risk stratification. However, data on the diagnostic value of the standing test in children are currently limited.

Objective

To determine the potential value of the standing test to aid LQTS diagnostics in children.

Methods

In a prospective cohort including children (≤18 years) who had a standing test, comprehensive analyses were performed including manual and automated QT interval assessments and determination of T-wave morphology changes.

Results

We included 47 LQTS children and 86 control children. At baseline, the QTc that identified LQTS children with a 90% sensitivity was 435 ms, which yielded a 65% specificity. A QTc ≥ 490 ms after standing only slightly increased sensitivity (91%, 95% confidence interval [CI]: 80%–98%) and slightly decreased specificity (58%, 95% CI: 47%–70%). Sensitivity increased slightly more when T-wave abnormalities were present (94%, 95% CI: 82%–99%; specificity 53%, 95% CI: 42%–65%). When a baseline QTc ≥ 440 ms was accompanied by a QTc ≥ 490 ms and T-wave abnormalities after standing, sensitivity further increased (96%, 95% CI: 85%–99%) at the expense of a further specificity decrease (41%, 95% CI: 30%–52%). Beat-to-beat analysis showed that 30 seconds after standing, LQTS children had a greater increase in heart rate compared to controls, which was more evidently present in LQTS boys and LQTS type 1 children.

Conclusion

In children, the standing test has limited additive diagnostic value for LQTS over a baseline electrocardiogram, while T-wave abnormalities after standing also have limited additional value. The standing test for LQTS should only be used with caution in children.

2020 APHRS/HRS expert consensus statement on the investigation of decedents with sudden unexplained death and patients with sudden cardiac arrest, and of their families

This international multidisciplinary document intends to provide clinicians with evidence-based practical patient-centered recommendations for evaluating patients and decedents with (aborted) sudden cardiac arrest and their families. The document includes a framework for the investigation of the family allowing steps to be taken, should an inherited condition be found, to minimize further events in affected relatives. Integral to the process is counseling of the patients and families, not only because of the emotionally charged subject, but because finding (or not finding) the cause of the arrest may influence management of family members. The formation of multidisciplinary teams is essential to provide a complete service to the patients and their families, and the varied expertise of the writing committee was formulated to reflect this need. The document sections were divided up and drafted by the writing committee members according to their expertise. The recommendations represent the consensus opinion of the entire writing committee, graded by Class of Recommendation and Level of Evidence. The recommendations were opened for public comment and reviewed by the relevant scientific and clinical document committees of the Asia Pacific Heart Rhythm Society (APHRS) and the Heart Rhythm Society (HRS); the document underwent external review and endorsement by the partner and collaborating societies. While the recommendations are for optimal care, it is recognized that not all resources will be available to all clinicians. Nevertheless, this document articulates the evaluation that the clinician should aspire to provide for patients with sudden cardiac arrest, decedents with sudden unexplained death, and their families.

Potential overdiagnosis of long QT syndrome using exercise stress and QT stand testing in children and adolescents with a low probability of disease

BACKGROUND

Long QT syndrome (LQTS) is a dangerous arrhythmia disorder that often presents in childhood and adolescence. The exercise stress test (EST) and QT-stand test may unmask QT interval prolongation at key heart rate transition points in LQTS, but their utility in children is debated.

OBJECTIVE

To determine if the QT-stand test or EST can differentiate children with a low probability of LQTS from those with confirmed LQTS.

METHODS

This retrospective study compares the corrected QT intervals (QTc) of children (<19 years) during the QT-stand test and EST. Patients were divided into three groups for comparison: confirmed LQTS (n = 14), low probability of LQTS (n = 14), and a control population (n = 9).

RESULTS

Using the Bazett formula, confirmed LQTS patients had longer QTc intervals than controls when supine, standing, and at 3-4 min of recovery (p ≤ .01). Patients with a low probability of LQTS had longer QTc duration upon standing (p = .018) and at 1 min of recovery (p = .016) versus controls. There were no significant QTc differences at any transition point between low probability and confirmed LQTS. Using the Fridericia formula, differences in QTc between low probability and confirmed LQTS were also absent at the transition points examined, except at 1 min into exercise, where low probability patients had shorter QTc intervals (437 vs. 460 ms, p = .029).

CONCLUSION

The diagnostic utility of the QT stand test and EST remains unclear in pediatric LQTS. The formula used for heart rate correction may influence accuracy, and dynamic T-U wave morphology changes may confound interpretation in low probability situations.

2020 APHRS/HRS expert consensus statement on the investigation of decedents with sudden unexplained death and patients with sudden cardiac arrest, and of their families

This international multidisciplinary document intends to provide clinicians with evidence-based practical patient-centered recommendations for evaluating patients and decedents with (aborted) sudden cardiac arrest and their families. The document includes a framework for the investigation of the family allowing steps to be taken, should an inherited condition be found, to minimize further events in affected relatives. Integral to the process is counseling of the patients and families, not only because of the emotionally charged subject, but because finding (or not finding) the cause of the arrest may influence management of family members. The formation of multidisciplinary teams is essential to provide a complete service to the patients and their families, and the varied expertise of the writing committee was formulated to reflect this need. The document sections were divided up and drafted by the writing committee members according to their expertise. The recommendations represent the consensus opinion of the entire writing committee, graded by Class of Recommendation and Level of Evidence. The recommendations were opened for public comment and reviewed by the relevant scientific and clinical document committees of the Asia Pacific Heart Rhythm Society (APHRS) and the Heart Rhythm Society (HRS); the document underwent external review and endorsement by the partner and collaborating societies. While the recommendations are for optimal care, it is recognized that not all resources will be available to all clinicians. Nevertheless, this document articulates the evaluation that the clinician should aspire to provide for patients with sudden cardiac arrest, decedents with sudden unexplained death, and their families.

QTc interval-dependent body posture in pediatrics

BACKGROUND

Syncope is a common and often benign disorder presenting at the pediatric emergency department. Long-QT syndrome may be presented with syncope, ventricular arrhythmias or sudden death and is vital to exclude as an underlying cause in children presented with syncope. Few studies have assessed QTc in relation to body posture in children. In this study, we assessed the QTc interval while laying down and during active standing in children with known long-QT syndrome compared to healthy controls.

METHODS

Children aged 1-18 years with long-QT syndrome (N = 17) matched to two healthy controls (N = 34) were included in this case-control study. The ECG standing was performed immediately after the ECG in the supine position. The QTc interval and QTc-difference by changing the body position were calculated.

RESULTS

All children with long-QT syndrome were treated with propranolol. QTc was prolonged among long-QT syndrome children while lying down and when standing up, compared to controls. A prolongation of QTc appeared when standing up for both cases and controls. There was no significant difference in QTc increase between the groups. A QTc over 440 ms was observed among four cases lying down and in eight cases while standing, but not in any of the controls. The standing test with a cut-off of 440 ms showed a sensitivity of 47% and a specificity of 100% for case-status in our study.

CONCLUSION

QTc measured on ECG when rapidly rising up is prolonged in both healthy and LQTS children. More importantly, it prolongs more in children with LQTS and increases in pathological levels.