Sympathetic stimulation produces a greater increase in both transmural and spatial dispersion of repolarization in LQT1 than LQT2 forms of congenital long QT syndrome

Congenital Long QT Syndrome Unmasked by Albuterol in an Adolescent with Asthma

BACKGROUND

Patients with congenital long QT syndrome (LQTS) are prone to ventricular dysrhythmia but may be initially asymptomatic with a normal QTc interval on resting electrocardiogram (ECG). Albuterol is listed as a medication that poses a "special risk" to patients with congenital LQTS, but its effects have been rarely described. We present a case of previously unknown, asymptomatic congenital LQTS unmasked by albuterol in an adolescent with asthma.

CASE REPORT

A 12-year-old girl with a history of asthma presented to the emergency department (ED) with shortness of breath, wheezing, and tachycardia for 24 h, consistent with acute asthma exacerbation. She received two doses of her home albuterol inhaler 2 h prior to presentation. Initial ECG demonstrated a QTc of 619 ms. Her remaining history, clinical examination, and laboratory workup, including electrolytes, were unremarkable. She was observed with cardiac monitoring before being discharged from the ED in stable condition for next-day outpatient pediatric cardiology follow-up. Resting office ECGs revealed QTcs from 440-470 ms. Exercise stress test revealed QTc prolongation of 520 ms and 500 ms at minute-2 and minute-4 of recovery, respectively. Genetic testing revealed heterozygous pathogenic variants in KCNQ1, consistent with type 1 LQTS. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Albuterol may be a cause of marked QTc prolongation in ED patients with underlying congenital LQTS, which can be a diagnostic clue in previously unidentified patients. Extreme QTc prolongation also serves as an indication in the ED for Cardiology consultation, laboratory evaluation for electrolyte imbalances, and observation with cardiac monitoring.

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.

Autonomic control of ventricular function in health and disease: current state of the art

PURPOSE

Cardiac autonomic dysfunction is one of the main pillars of cardiovascular pathophysiology. The purpose of this review is to provide an overview of the current state of the art on the pathological remodeling that occurs within the autonomic nervous system with cardiac injury and available neuromodulatory therapies for autonomic dysfunction in heart failure.

METHODS

Data from peer-reviewed publications on autonomic function in health and after cardiac injury are reviewed. The role of and evidence behind various neuromodulatory therapies both in preclinical investigation and in-use in clinical practice are summarized.

RESULTS

A harmonic interplay between the heart and the autonomic nervous system exists at multiple levels of the neuraxis. This interplay becomes disrupted in the setting of cardiovascular disease, resulting in pathological changes at multiple levels, from subcellular cardiac signaling of neurotransmitters to extra-cardiac, extra-thoracic remodeling. The subsequent detrimental cycle of sympathovagal imbalance, characterized by sympathoexcitation and parasympathetic withdrawal, predisposes to ventricular arrhythmias, progression of heart failure, and cardiac mortality. Knowledge on the etiology and pathophysiology of this condition has increased exponentially over the past few decades, resulting in a number of different neuromodulatory approaches. However, significant knowledge gaps in both sympathetic and parasympathetic interactions and causal factors that mediate progressive sympathoexcitation and parasympathetic dysfunction remain.

CONCLUSIONS

Although our understanding of autonomic imbalance in cardiovascular diseases has significantly increased, specific, pivotal mediators of this imbalance and the recognition and implementation of available autonomic parameters and neuromodulatory therapies are still lagging.

Prolonged T-peak to T-end Interval Predicts Implantable Cardioverter Defibrillator Therapy in Patients With Cardiac Sarcoidosis

BACKGROUND

The association between the T-peak to T-end interval (Tp-e) and ventricular arrhythmia (VA) events in cardiac sarcoidosis (CS) is unknown. The purpose of this study was to investigate whether Tp-e was associated with VA events in CS patients with implantable cardioverter defibrillators (ICDs) or cardiac resynchronization therapy defibrillators (CRT-Ds).

METHODS AND RESULTS

We retrospectively studied 50 patients (16 men; mean [±SD] age 56.3±10.5 years) with CS and ICD/CRT-D. The maximum Tp-e in the precordial leads recorded by a 12-lead electrocardiogram after ICD/CRT-D implantation was evaluated. The clinical endpoint was defined as appropriate ICD therapy. During a median follow-up period of 85.0 months, 22 patients underwent appropriate therapy and 10 patients died. Kaplan-Meier analysis revealed that the probability of the clinical endpoint was 28.3% at 2 years and 35.3% at 4 years. The optimal cut-off value of the Tp-e for the prediction of the clinical endpoint was 91 ms, with a sensitivity of 72.7% and a specificity of 87.0% (area under the curve=0.81). Multivariate Cox regression analysis showed that Tp-e ≥91 ms (hazard ratio [HR] 5.10; 95% confidence interval [CI] 1.99-13.1; P<0.001) and a histological diagnosis of CS (HR 3.84; 95% CI 1.28-11.5; P=0.016) were significantly associated with the clinical endpoint.

CONCLUSIONS

Tp-e ≥91 ms was a significant predictor of VA events in patients with CS and ICD/CRT-D.

A predictive model of response to metoprolol in children and adolescents with postural tachycardia syndrome

BACKGROUND

The present work was designed to explore whether electrocardiogram (ECG) index-based models could predict the effectiveness of metoprolol therapy in pediatric patients with postural tachycardia syndrome (POTS).

METHODS

This study consisted of a training set and an external validation set. Children and adolescents with POTS who were given metoprolol treatment were enrolled, and after follow-up, they were grouped into non-responders and responders depending on the efficacy of metoprolol. The difference in pre-treatment baseline ECG indicators was analyzed between the two groups in the training set. Binary logistic regression analysis was further conducted on the association between significantly different baseline variables and therapeutic efficacy. Nomogram models were established to predict therapeutic response to metoprolol. The receiver-operating characteristic curve (ROC), calibration, and internal validation were used to evaluate the prediction model. The predictive ability of the model was validated in the external validation set.

RESULTS

Of the 95 enrolled patients, 65 responded to metoprolol treatment, and 30 failed to respond. In the responders, the maximum value of the P wave after correction (Pcmax), P wave dispersion (Pd), Pd after correction (Pcd), QT interval dispersion (QTd), QTd after correction (QTcd), maximum T-peak-to-T-end interval (Tpemax), and T-peak-to-T-end interval dispersion (Tped) were prolonged (all P < 0.01), and the P wave amplitude was increased (P < 0.05) compared with those of the non-responders. In contrast, the minimum value of the P wave duration after correction (Pcmin), the minimum value of the QT interval after correction (QTcmin), and the minimum T-peak-to-T-end interval (Tpemin) in the responders were shorter (P < 0.01, < 0.01 and < 0.01, respectively) than those in the non-responders. The above indicators were screened based on the clinical significance and multicollinearity analysis to construct a binary logistic regression. As a result, pre-treatment Pcmax, QTcmin, and Tped were identified as significantly associated factors that could be combined to provide an accurate prediction of the therapeutic response to metoprolol among the study subjects, yielding good discrimination [area under curve (AUC) = 0.970, 95% confidence interval (CI) 0.942-0.998] with a predictive sensitivity of 93.8%, specificity of 90.0%, good calibration, and corrected C-index of 0.961. In addition, the calibration curve and standard curve had a good fit. The accuracy of internal validation with bootstrap repeated sampling was 0.902. In contrast, the kappa value was 0.769, indicating satisfactory agreement between the predictive model and the results from the actual observations. In the external validation set, the AUC for the prediction model was 0.895, and the sensitivity and specificity were 90.9% and 95.0%, respectively.

CONCLUSIONS

A high-precision predictive model was successfully developed and externally validated. It had an excellent predictive value of the therapeutic effect of metoprolol on POTS among children and adolescents.

Utility of Provocative Testing in the Diagnosis and Genotyping of Congenital Long QT Syndrome: A Systematic Review and Meta-Analysis

Background Diagnosis is particularly challenging in concealed or asymptomatic long QT syndrome (LQTS). Provocative testing, unmasking the characterization of LQTS, is a promising alternative method for the diagnosis of LQTS, but without uniform standards. Methods and Results A comprehensive search was conducted in PubMed, Embase, and the Cochrane Library through October 14, 2021. The fixed effects model was used to assess the effect of the provocative testing on QTc interval. A total of 22 studies with 1137 patients with LQTS were included. At baseline, QTc interval was 40 ms longer in patients with LQTS than in controls (mean difference [MD], 40.54 [95% CI, 37.43-43.65]; P<0.001). Compared with the control group, patients with LQTS had 28 ms longer ΔQTc upon standing (MD, 28.82 [95% CI, 23.05-34.58]; P<0.001), nearly 30 ms longer both at peak exercise (MD, 27.31 [95% CI, 21.51-33.11]; P<0.001) and recovery 4 to 5 minutes (MD, 29.85 [95% CI, 24.36-35.35]; P<0.001). With epinephrine infusion, QTc interval was prolonged both in controls and patients with QTS, most obviously in LQT1 (MD, 68.26 [95% CI, 58.91-77.60]; P<0.001) and LQT2 (MD, 60.17 [95% CI, 50.18-70.16]; P<0.001). Subgroup analysis showed QTc interval response to abrupt stand testing and exercise testing varied between LQT1, LQT2, and LQT3, named Type Ⅰ, Type Ⅱ, and Type Ⅲ. Conclusions QTc trend Type Ⅰ and Type Ⅲ during abrupt stand testing and exercise testing can be used to propose a prospective evaluation of LQT1 and LQT3, respectively. Type Ⅱ QTc trend combined epinephrine infusion testing could distinguish LQT2 from control. A preliminary diagnostic workflow was proposed but deserves further evaluation.

Genotype-Specific ECG-Based Risk Stratification Approaches in Patients With Long-QT Syndrome

Background

Congenital long-QT syndrome (LQTS) is a major cause of sudden cardiac death (SCD) in young individuals, calling for sophisticated risk assessment. Risk stratification, however, is challenging as the individual arrhythmic risk varies pronouncedly, even in individuals carrying the same variant.

Materials and Methods

In this study, we aimed to assess the association of different electrical parameters with the genotype and the symptoms in patients with LQTS. In addition to the heart-rate corrected QT interval (QTc), markers for regional electrical heterogeneity, such as QT dispersion (QT_max-QT_min in all ECG leads) and delta T_peak/end (T_peak/end V5 – T_peak/end V2), were assessed in the 12-lead ECG at rest and during exercise testing.

Results

QTc at rest was significantly longer in symptomatic than asymptomatic patients with LQT2 (493.4 ms ± 46.5 ms vs. 419.5 ms ± 28.6 ms, p = 0.004), but surprisingly not associated with symptoms in LQT1. In contrast, post-exercise QTc (minute 4 of recovery) was significantly longer in symptomatic than asymptomatic patients with LQT1 (486.5 ms ± 7.0 ms vs. 463.3 ms ± 16.3 ms, p = 0.04), while no such difference was observed in patients with LQT2. Enhanced delta T_peak/end and QT dispersion were only associated with symptoms in LQT1 (delta T_peak/end 19.0 ms ± 18.1 ms vs. −4.0 ms ± 4.4 ms, p = 0.02; QT-dispersion: 54.3 ms ± 10.2 ms vs. 31.4 ms ± 10.4 ms, p = 0.01), but not in LQT2. Delta T_peak/end was particularly discriminative after exercise, where all symptomatic patients with LQT1 had positive and all asymptomatic LQT1 patients had negative values (11.8 ± 7.9 ms vs. −7.5 ± 1.7 ms, p = 0.003).

Conclusion

Different electrical parameters can distinguish between symptomatic and asymptomatic patients in different genetic forms of LQTS. While the classical “QTc at rest” was only associated with symptoms in LQT2, post-exercise QTc helped distinguish between symptomatic and asymptomatic patients with LQT1. Enhanced regional electrical heterogeneity was only associated with symptoms in LQT1, but not in LQT2. Our findings indicate that genotype-specific risk stratification approaches based on electrical parameters could help to optimize risk assessment in LQTS.

Effects of beta-blockers on ventricular repolarization documented by 24-h electrocardiography in long-QT syndrome type 2

BACKGROUND

Long QT syndrome (LQTS) is an inherited arrhythmia disorder characterized by ventricular repolarization abnormalities and a risk of sudden cardiac death. The electrophysiological components generating the high risk of arrhythmias in LQTS are prolonged repolarization, increased dispersion of repolarization, and early afterdepolarizations, which are clinically estimated as QT interval, T-wave peak to end (TPE) interval, and T2/T1-wave amplitude ratio, respectively. In experimental LQTS type 2 (LQT2) models, beta-blockers decrease dispersion of repolarization and prevent early afterdepolarizations. In clinical studies among LQT2 patients beta-blockers are more effective against exercise-induced than arousal-induced cardiac events.

OBJECTIVES AND METHODS

The aim of the study was to investigate the effects of beta-blocker therapy on QT and TPE intervals, and maximal T2/T1-wave amplitude ratios recorded by 24-h electrocardiograms (ECG) among 25 LQT2 patients.

RESULTS

Beta-blocker therapy decreased the maximal T2/T1-wave amplitude ratio from 2.9±1.1 to 1.8±0.7 (p<0.001), but did not change pause-induced T2/T1-wave amplitude ratio. Under medication abrupt maximal TPE intervals were shorter at heart rates of 75 beats/min or over, and maximal QT intervals were shorter at a heart rate of 100 beats/min.

CONCLUSIONS

Beta-blockers stabilize ventricular repolarization in LQT2 by reducing electrocardiographic early afterdepolarizations, and by reducing abrupt prolongation of electrocardiographic dispersion of repolarization and ventricular repolarization duration at elevated heart rates. The effect of beta-blockers on pause-induced electrocardiographic early afterdepolarizations is weak. The findings provide electrocardiographic explanation for the protective effects of beta-blockers against exercise-induced cardiac events in LQT2.

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.

Unmasking Long QT Syndrome in the Emergency Department: A Case Report

Introduction

Long QT syndrome (LQTS) is an uncommon disorder that can lead to potentially life-threatening dysrhythmias. LQTS can be genetic, acquired, or both.

Case Report

A 44-year-old female with well-controlled hypertension and asthma presented with chest tightness. An initial electrocardiogram yielded a normal corrected QT interval of 423 milliseconds (ms) (normal <480 ms in females). Albuterol was administered and induced agitation, tremulousness, and tachycardia. Follow-up electrocardiograms demonstrated extreme prolongation of the corrected QT interval to 633 ms and morphology change of the T wave. Lab values were later notable for hypokalemia and hypomagnesemia, attributable to a recently started thiazide diuretic. The patient was ultimately diagnosed with congenital LQTS after initial unmasking by albuterol in the emergency department.

Conclusion

LQTS can be unmasked or exacerbated by electrolyte abnormalities and QT prolonging medications.

Targeting the β-adrenergic receptor in the clinical management of congenital long QT syndrome

The long QT syndrome (LQTS) is largely treated pharmacologically with β-blockers, despite the role of sympathetic activity in LQTS being poorly understood. Using the trigger-substrate model of cardiac arrhythmias in this review, we amalgamate current experimental and clinical data from both animal and human studies to explain the mechanism of adrenergic stimulation and blockade on LQT arrhythmic risk and hence assess the efficacy of β-adrenoceptor blockade in the management of LQTS. In LQTS1 and LQTS2, sympathetic stimulation increases arrhythmic risk by enhancing early afterdepolarizations and transmural dispersion of repolarization. β-Blockers successfully reduce cardiac events by reducing these triggers and substrates; however, these effects are less marked in LQTS2 compared with LQTS1. In LQTS3, clinical and experimental investigations of the effects of sympathetic stimulation and β-blocker use have produced contradictory findings, resulting in significant clinical uncertainty. We offer explanations for these contradicting results relating to study sample size, the dose of the β-blocker administered associated with its off-target Na⁺ channel effects, as well as the type of β-blocker used. We conclude that the antiarrhythmic efficacy of β-blockers is a genotype-specific phenomenon, and hence the use of β-blockers in clinical practice should be genotype dependent.

Influence of disease severity and cardiac autonomic tone on ventricular repolarization and dispersion in electrocardiographic assessment of patients with systemic lupus erythematosus

Background

There are no data on the influence of disease severity and cardiac autonomic tone on ventricular repolarization and dispersion in 24-hour Holter monitoring in systemic lupus erythematosus (SLE).

Methods

Consecutive 92 SLE and 51 healthy subjects were studied. The standard 12-lead electrocardiography (ECG), Holter monitoring with heart rate turbulence (HRT) and QT, Tp-e and Tp-e/QT ratio assessment (including corrected values) were performed. Subjects with conditions causing repolarization abnormalities or insufficient number of beats suitable for QT evaluation were excluded (17 SLE and 8 controls).

Results

Finally, 75 SLE and 43 sex- and age-matched controls were included to the study. In SLE patients, the median disease severity score (Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index (SLICC/ACR-DI)) was 3.0. The mean values of QTc, cTp-e and cTp-e/QTc were significantly higher in SLE patients than in controls. QTc ≥ 460 ms was observed in 18.7% of patients using standard ECG and in 58.7% using Holter monitoring. With Holter monitoring, patients with SLICC/ACR-DI >3.0 presented longer QTc than those with SLICC/ACR-DI ≤3.0 (418±15 vs. 409 ± 16, p = 0.04), while cTp-e and cTp-e/QTc values were similar. Patients with abnormal HRT presented longer cTp-e and higher cTp-e/QTc than those with normal HRT (92 ± 52 vs. 71 ± 16 ms, p = 0.04; 0.244 ± 0.126 vs. 0.187 ± 0.035, p = 0.03), while QTc values were similar. No differences in QT and Tp-e parameters were observed according to disease duration.

Conclusion

In SLE patients, Holter monitoring revealed QTc prolongation more frequently than standard ECG. Longer QTc values were observed in patients with more advanced disease, while increased cTp-e and cTp-e/QTc were related to cardiac autonomic dysfunction expressed by abnormal HRT.

Switching from ramipril to sacubitril/valsartan favorably alters electrocardiographic indices of ventricular repolarization in heart failure with reduced ejection fraction

Background: Angiotensin receptor neprilysin inhibitor (ARNI, sacubitril/valsartan) reduces sudden death in heart failure with reduced ejection fraction (HFrEF). Corrected QT (QTc), T-wave peak to T-wave end interval (Tp-e) and Tp-e/QTc are electrocardiographic indices of ventricular repolarization heterogeneity. We aimed to assess the effects of switching from ramipril to ARNI on electrocardiographic indices of ventricular repolarization.Methods: A total of 48 patients with HFrEF (mean age: 63.3 ± 11.7 years; 36 males, 77.1% ischaemic etiology) were enrolled. All patients had New York Heart Association functional class II-III, left ventricular ejection fraction ≤35% and previously switched from ramipril to ARNI treatment. The standard 12-lead electrocardiograms on ramipril treatment and 1 month after ARNI treatment were analysed; heart rate, QTc, Tp-e and Tp-e/QTc were calculated. Minnesota Living with Heart Failure Questionnaire (MLWHFQ) scores and N-terminal pro-BNP (NT-proBNP) values were recorded.Results: QTc (415.2 ± 19.7 ms vs. 408.5 ± 20.8 ms, p = 0.022), Tp-e (100.7 ± 13.8 ms vs. 92.9 ± 12.1 ms, p < 0.001), Tp-e/QTc (0.242 ± 0.028 vs. 0.227 ± 0.029, p = 0.003) and heart rate (73.2 ± 4.7 bpm vs. 71.1 ± 4.9 bpm, p = 0.027) were reduced after ARNI. ARNI switch associated with improvement in MLWHFQ scores (32.4 ± 7.1 ms vs. 22.6 ± 7.0 ms, p < 0.001) and reduction of NT-proBNP (2457 ± 1879 pg/ml to 1377 ± 874 pg/ml, p < 0.001). Pearson's correlation analysis revealed moderate correlations of MLWHFQ score with Tp-e (r = 0.543, p = 0.001) and Tp-e/QTc (r = 0.556, p = 0.001).Conclusions: Switching from ramipril to ARNI favourably alters QTc, Tp-e and Tp-e/QTc in HFREF. ARNI reduces symptoms of HFREF assessed by MLWHFQ and lowers NT-proBNP levels. Reduction in Tp-e and Tp-e/QTc correlate with clinical improvement in patients with HFrEF.

Periodic repolarization dynamics as a risk predictor after myocardial infarction: Prospective validation study

BACKGROUND

Periodic repolarization dynamics (PRD) is a novel electrocardiographic phenomenon that refers to sympathetic activity-associated low-frequency modulations of cardiac repolarization. Retrospective post-myocardial infarction (MI) studies revealed that increased PRD indicates an increased risk of subsequent death.

OBJECTIVE

This is the first prospective study to validate PRD in patients after MI receiving up-to-date treatment.

METHODS

Four hundred fifty-five survivors of MI (age ≤80 years) in sinus rhythm were enrolled. PRD was assessed from 20-minute electrocardiographic recordings (2048 Hz) and prospectively dichotomized at 5.75 deg². Primary and secondary end points were total mortality and cardiovascular mortality, respectively. Multivariable analyses additionally included Global Registry of Acute Coronary Events score (dichotomized at >140), left ventricular ejection fraction (dichotomized at ≤35%), diabetes mellitus, and deceleration capacity of heart rate (dichotomized at ≤2.5 ms). The prognostic power of PRD was evaluated using receiver operating characteristic curve analysis, Cox regression analysis, and the integrated discrimination improvement index.

RESULTS

During a median follow-up period of 27 months, 47 patients died. Twenty-three of these deaths were classified as cardiovascular. Increased PRD was significantly associated with both end points, yielding areas under receiver operating characteristic curves of 69.3% (60.2%-77.8%) and 79.1% (69.7%-86.7%) for total mortality and cardiovascular mortality, respectively (P < .001 for both). In multivariable analysis, increased PRD indicated a 2.2- and 9.5-fold risk of total mortality and cardiovascular mortality (P = .024 and P = .003, respectively). Addition of PRD to the models significantly improved the integrated discrimination improvement index for total (P = .047) and cardiovascular mortality (P = .007).

CONCLUSION

PRD is a strong and independent predictor of total mortality and cardiovascular mortality in patients after MI treated with contemporary therapy.

Substrates and potential therapeutics of ventricular arrhythmias in heart failure

Heart failure (HF) is a clinical syndrome characterized by ventricular contractile dysfunction. About 50% of death in patients with HF are due to fetal ventricular arrhythmias including ventricular tachycardia and ventricular fibrillation. Understanding ventricular arrhythmic substrates and discovering effective antiarrhythmic interventions are extremely important for improving the prognosis of patients with HF and reducing its mortality. In this review, we discussed ventricular arrhythmic substrates and current clinical therapeutics for ventricular arrhythmias in HF. Base on the fact that classic antiarrhythmic drugs have the limited efficacy, side effects, and proarrhythmic potentials, we also updated some therapeutic strategies for the development of potential new antiarrhythmic interventions for patients with HF.

Prediction of sudden and non-sudden cardiac death in post-infarction patients with reduced left ventricular ejection fraction by periodic repolarization dynamics: MADIT-II substudy

Aims

To test the value of Periodic Repolarization Dynamics (PRD), a recently validated electrocardiographic marker of sympathetic activity, as a novel approach to predict sudden cardiac death (SCD) and non-sudden cardiac death (N-SCD) and to improve identification of patients that profit from ICD-implantation.

Methods and results

We included 856 post-infarction patients with left-ventricular ejection fraction (LVEF) ≤30% of the MADIT-II trial in sinus rhythm. Of these, 507 and 348 patients were randomized to ICD or conventional treatment. PRD was assessed from multipolar 10-min baseline ECGs. Primary and secondary endpoints were total mortality, SCD and N-SCD. Multivariable analyses included treatment group, QRS-duration, New York Heart Association classification, blood-urea nitrogen, diabetes mellitus, beta-blocker therapy and LVEF. During follow-up of 20.4 months, 119 patients died (53 SCD and 36 N-SCD). On multivariable analyses, increased PRD was a significant predictor of mortality (standardized coefficient 1.37[1.19–1.59]; P < 0.001) and SCD (1.40 [1.13–1.75]; P = 0.003) but also predicted N-SCD (1.41[1.10–1.81]; P = 0.006). While increased PRD predicted SCD in conventionally treated patients (1.61[1.23–2.11]; P < 0.001), it was predictive of N-SCD (1.63[1.28–2.09]; P < 0.001) and adequate ICD-therapies (1.20[1.03–1.39]; P = 0.017) in ICD-treated patients. ICD-treatment substantially reduced mortality in the lowest three PRD-quartiles by 53% (P = 0.001). However, there was no effect in the highest PRD-quartile (mortality increase by 29%; P = 0.412; P < 0.001 for difference) as the reduction of SCD was compensated by an increase of N-SCD.

Conclusion

In post-infarction patients with impaired LVEF, PRD is a significant predictor of SCD and N-SCD. Assessment of PRD is a promising tool to identify post-MI patients with reduced LVEF who might benefit from intensified treatment.

Orgasm induced torsades de pointes in a patient with a novel mutation with long-QT syndrome type 2: a case report

Introduction

Congenital long-QT (LQT) syndrome can lead to torsades de pointes (TdP), which can deteriorate into ventricular fibrillation resulting in sudden death. Thus far, more than 16 genes have been linked to the LQT syndrome. We report an orgasm-induced TdP in a patient with LQT syndrome type 2 with a novel mutation in the KCNH2 gene.

Case presentation

A 24-year-old Caucasian woman with a medical history of depression, no medication use and no family history of sudden death, presented with recurrent syncope during sexual activity. Immediately after achieving orgasm during sexual intercourse she lost consciousness. Baseline 12-lead electrocardiogram revealed a wide based T-wave with a prolonged QTc-interval of 507 ms. During hospital admission runs of TdP were recorded. The patient was treated with magnesium, an oral beta-blocker, and an implantable cardioverter-defibrillator. Genetic testing (Sanger sequencing) revealed a novel mutation (c.361del) in the KCNH2 gene (chromosome 7q36).

Discussion

To date, orgasm-induced TdP as a first symptom in a patient with LQT2 has not been published previously. In studies with continuous blood sampling in healthy volunteers, large peaks in plasma epinephrine levels during orgasm were observed with fast post-orgasmic decline. However, in a large cohort study (402 patients of which 129 with LQT2), no patients experienced cardiac events during sexual activity, suggesting that these are indeed very rare. Nevertheless, the high levels of sympathetic adrenal hormones during orgasm may explain the timing of the TdP in our patient. The patient has remained free of syncope at 6 months of follow-up.

The control of cardiac ventricular excitability by autonomic pathways

Central to the genesis of ventricular cardiac arrhythmia are variations in determinants of excitability. These involve individual ionic channels and transporters in cardiac myocytes but also tissue factors such as variable conduction of the excitation wave, fibrosis and source-sink mismatch. It is also known that in certain diseases and particularly the channelopathies critical events occur with specific stressors. For example, in hereditary long QT syndrome due to mutations in KCNQ1 arrhythmic episodes are provoked by exercise and in particular swimming. Thus not only is the static substrate important but also how this is modified by dynamic signalling events associated with common physiological responses. In this review, we examine the regulation of ventricular excitability by signalling pathways from a cellular and tissue perspective in an effort to identify key processes, effectors and potential therapeutic approaches. We specifically focus on the autonomic nervous system and related signalling pathways.

Identification of Concealed and Manifest Long QT Syndrome Using a Novel T Wave Analysis Program

Background—

Congenital long QT syndrome (LQTS) is characterized by QT prolongation. However, the QT interval itself is insufficient for diagnosis, unless the corrected QT interval is repeatedly ≥500 ms without an acquired explanation. Further, the majority of LQTS patients have a corrected QT interval below this threshold, and a significant minority has normal resting corrected QT interval values. Here, we aimed to develop and validate a novel, quantitative T wave morphological analysis program to differentiate LQTS patients from healthy controls.

Methods and Results—

We analyzed a genotyped cohort of 420 patients (22±16 years, 43% male) with either LQT1 (61%) or LQT2 (39%). ECG analysis was conducted using a novel, proprietary T wave analysis program that quantitates subtle changes in T wave morphology. The top 3 discriminating features in each ECG lead were determined and the lead with the best discrimination selected. Classification was performed using a linear discriminant classifier and validated on an untouched cohort. The top 3 features were Tpeak–Tend interval, T wave left slope, and T wave center of gravity x axis (last 25% of the T wave). Lead V6 had the best discrimination. It could distinguish 86.8% of LQTS patients from healthy controls. Moreover, it distinguished 83.33% of patients with concealed LQTS from controls, despite having essentially identical resting corrected QT interval values.

Conclusions—

T wave quantitative analysis on the 12-lead surface ECG provides an effective, novel tool to distinguish patients with either LQT1/LQT2 from healthy matched controls. It can provide guidance while mutation-specific genetic testing is in motion for family members.

QT Adaptation and Intrinsic QT Variability in Congenital Long QT Syndrome

BACKGROUND

Increased variability of QT interval (QTV) has been linked to arrhythmias in animal experiments and multiple clinical situations. Congenital long QT syndrome (LQTS), a pure repolarization disease, may provide important information on the relationship between delayed repolarization and QTV.

METHODS AND RESULTS

Twenty-four-hour Holter monitor tracings from 78 genotyped congenital LQTS patients (52 females; 51 LQT1, 23 LQT2, 2 LQT5, 2 JLN, 27 symptomatic; age, 35.2±12.3 years) were evaluated with computer-assisted annotation of RR and QT intervals. Several models of RR-QT relationship were tested in all patients. A model assuming exponential decrease of past RR interval contributions to QT duration with 60-second time constant provided the best data fit. This model was used to calculate QTc and residual "intrinsic" QTV, which cannot be explained by heart rate change. The intrinsic QTV was higher in patients with long QTc (r=0.68; P<10(-4)), and in LQT2 than in LQT1/5 patients (5.65±1.28 vs 4.46±0.82; P<0.0002). Both QTc and intrinsic QTV were similar in symptomatic and asymptomatic patients (467±52 vs 459±53 ms and 5.10±1.19 vs 4.74±1.09, respectively).

CONCLUSIONS

In LQTS patients, QT interval adaptation to heart rate changes occurs with time constant ≈60 seconds, similar to results reported in control subjects. Intrinsic QTV correlates with the degree of repolarization delay and might reflect action potential instability observed in animal models of LQTS.

Sympathetic nerve stimulation, not circulating norepinephrine, modulates T-peak to T-end interval by increasing global dispersion of repolarization

BACKGROUND

T-peak to T-end interval (Tp-e) is an independent marker of sudden cardiac death. Modulation of Tp-e by sympathetic nerve activation and circulating norepinephrine is not well understood. The purpose of this study was to characterize endocardial and epicardial dispersion of repolarization (DOR) and its effects on Tp-e with sympathetic activation.

METHODS AND RESULTS

In Yorkshire pigs (n=13), a sternotomy was performed and the heart and bilateral stellate ganglia were exposed. A 56-electrode sock and 64-electrode basket catheter were placed around the epicardium and in the left ventricle (LV), respectively. Activation recovery interval, DOR, defined as variance in repolarization time, and Tp-e were assessed before and after left, right, and bilateral stellate ganglia stimulation and norepinephrine infusion. LV endocardial and epicardial activation recovery intervals significantly decreased, and LV endocardial and epicardial DOR increased during sympathetic nerve stimulation. There were no LV epicardial versus endocardial differences in activation recovery interval during sympathetic stimulation, and regional endocardial activation recovery interval patterns were similar to the epicardium. Tp-e prolonged during left (from 40.4±2.2 ms to 92.4±12.4 ms; P<0.01), right (from 47.7±2.6 ms to 80.7±11.5 ms; P<0.01), and bilateral (from 47.5±2.8 ms to 78.1±9.8 ms; P<0.01) stellate stimulation and strongly correlated with whole heart DOR during stimulation (P<0.001, R=0.86). Of note, norepinephrine infusion did not increase DOR or Tp-e.

CONCLUSIONS

Regional patterns of LV endocardial sympathetic innervation are similar to that of LV epicardium. Tp-e correlated with whole heart DOR during sympathetic nerve activation. Circulating norepinephrine did not affect DOR or Tp-e.

The safety of modern anesthesia for children with long QT syndrome

BACKGROUND

Patients with long QT syndrome (LQTS) may experience a clinical spectrum of symptoms, ranging from asymptomatic, through presyncope, syncope, and aborted cardiac arrest, to sudden cardiac death. Arrhythmias in LQTS are often precipitated by autonomic changes. This patient population is believed to be at high risk for perioperative arrhythmia, specifically torsades de pointes (TdP), although this perception is largely based on limited literature that predates current anesthetic drugs and standards of perioperative monitoring. We present the largest multicenter review to date of anesthetic management in children with LQTS.

METHODS

We conducted a multicentered retrospective chart review of perioperative management of children with clinically diagnosed LQTS, aged 18 years or younger, who received general anesthesia (GA) between January 2005 and January 2010. Data from 8 institutions were collated in an anonymized database.

RESULTS

One hundred three patients with LQTS underwent a total of 158 episodes of GA. The median (interquartile range) age and weight of the patients at the time of GA was 9 (3-15) years and 30.3 (15.4-54) kg, respectively. Surgery was LQTS-related in 81 (51%) GA episodes (including pacemaker, implantable cardioverter-defibrillator, and loop recorder insertions and revisions and lead extractions) and incidental in 77 (49%). β-blocker therapy was administered to 76% of patients on the day of surgery and 47% received sedative premedication. Nineteen percent of patients received total IV anesthesia, 30% received total inhaled anesthesia, and the remaining 51% received a combination. No patient received droperidol. There were 5 perioperative episodes of TdP, all in neonates or infants, all in surgery that was LQTS-related, and none of which was overtly attributable to anesthetic regimen. Thus the incidence (95% confidence interval) of perioperative TdP in incidental versus LQTS-related surgery was 0/77 (0%; 0%-5%) vs 5/81 (6.2%; 2%-14%).

CONCLUSIONS

With optimized perioperative management, modern anesthesia for incidental surgery in patients with LQTS is safer than anecdotal case report literature might suggest. Our series suggests that the risk of perioperative TdP is concentrated in neonates and infants requiring urgent interventions after failed first-line management of LQTS.

A new method of building permanent A-V block model: ablating his-bundle potential through femoral artery with pre-implanted biventricular pacemaker

Background

To explore the feasibility of a new method of achieving a permanent A-V block animal model.

Methods

16 beagles were randomly divided into two groups based on the method of their pre-implanted biventricular pacemakers. (1) In the first group (8 beagles), the A-V block model was achieved by ablating his-bundle potential at the site of the left ventricular superior-septum, under the aortic sinus, through femoral artery. (2) In the second group (8 beagles), the A-V block model was achieved by ablating his-bundle potential at the triangle of Koch, through femoral vein. A complete A-V block model was achieved as a standard in this study. The success rates, intraoperative arrhythmias, operative and X-ray exposure time, intraoperative bleeding amount were assessed in this two groups, both animal models were followed up for four weeks and then fasted to monitor myocardial pathological changes.

Results

The success rate of the first group, which with fewer intraoperative arrhythmias, and less operative and X-ray exposure time, was significantly higher than the second group.

Conclusions

Compared with traditional animal method, our new method of ablating his-bundle potential at the left ventricle from the femoral artery has a higher success rate, fewer occurrence of malignant arrhythmias, and less operation and X-ray time. Thus, our new method should be preferred in the building of Permanent A-V Block Model.

Sympathetic activity-associated periodic repolarization dynamics predict mortality following myocardial infarction

BACKGROUND

Enhanced sympathetic activity at the ventricular myocardium can destabilize repolarization, increasing the risk of death. Sympathetic activity is known to cluster in low-frequency bursts; therefore, we hypothesized that sympathetic activity induces periodic low-frequency changes of repolarization. We developed a technique to assess the sympathetic effect on repolarization and identified periodic components in the low-frequency spectral range (≤0.1 Hz), which we termed periodic repolarization dynamics (PRD).

METHODS

We investigated the physiological properties of PRD in multiple experimental studies, including a swine model of steady-state ventilation (n=7) and human studies involving fixed atrial pacing (n=10), passive head-up tilt testing (n=11), low-intensity exercise testing (n=11), and beta blockade (n=10). We tested the prognostic power of PRD in 908 survivors of acute myocardial infarction (MI). Finally, we tested the predictive values of PRD and T-wave alternans (TWA) in 2,965 patients undergoing clinically indicated exercise testing.

RESULTS

PRD was not related to underlying respiratory activity (P<0.001) or heart-rate variability (P=0.002). Furthermore, PRD was enhanced by activation of the sympathetic nervous system, and pharmacological blockade of sympathetic nervous system activity suppressed PRD (P≤0.005 for both). Increased PRD was the strongest single risk predictor of 5-year total mortality (hazard ratio 4.75, 95% CI 2.94-7.66; P<0.001) after acute MI. In patients undergoing exercise testing, the predictive value of PRD was strong and complementary to that of TWA.

CONCLUSION

We have described and identified low-frequency rhythmic modulations of repolarization that are associated with sympathetic activity. Increased PRD can be used as a predictor of mortality in survivors of acute MI and patients undergoing exercise testing.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00196274.

FUNDING

This study was funded by Angewandte Klinische Forschung, University of Tübingen (252-1-0).

The terminal part of the QT interval (T peak to T end): a predictor of mortality after acute myocardial infarction

BACKGROUND

The terminal part of the QT interval (T peak to T end; Tp-e)-an index for dispersion of cardiac repolarization-is often prolonged in patients experiencing malignant ventricular arrhythmias after acute myocardial infarction (AMI). We wanted to explore whether high Tp-e might predict mortality or fatal arrhythmia post-AMI.

METHODS

Tp-e was measured prospectively in 1359/1384 (98.2%) consecutive patients with ST elevation (n = 525) or non-ST elevation (n = 859) myocardial infarction (STEMI or NSTEMI) admitted for coronary angiography.

RESULTS

Tp-e was significantly correlated with age, heart rate (HR), heart failure, LVEF, creatinine, three-vessel disease, previous AMI and QRS and QT duration. During a mean follow-up of 1.3 years (range 0.4-2.3),109 patients (7.9%) died; 25, 45, and 39 from cardiac arrhythmia, nonarrhythmic cardiac causes and other causes, respectively. Long Tp-e was strongly associated with increased risk of death, and Tp-e remained a significant predictor of death in multivariable Cox analyses (RR 1.5, 95% CI[1.3-1.7]). HR-corrected Tp-e (cTp-e) was the strongest predictor of death (RR 1.6 [1.4-1.9]). Tp-e and cTp-e were particularly strong predictors of fatal cardiac arrhythmia (RR 1.6 [1.2-2.1] and RR 1.8 [1.4-2.4]). Findings were similar in STEMI and NSTEMI. When comparing two methods for measuring Tp-e, one including the tail of the T wave and one not, the former had markedly higher predictive power (P < 0.001).

CONCLUSION

Tp-e, and in particular cTp-e, were strong predictors of mortality during the first year post-AMI, and should be further evaluated as prognostic factors additional to established post-AMI risk factors.

Long-QT syndrome

Acquired and hereditary long-QT syndromes are important causes of sudden cardiac death. Both categories are characterized by abnormally prolonged cardiac repolarization arising from a complex interaction between genetic and environmental factors. This produces a potentially dangerous substrate for polymorphic ventricular tachycardia and sudden cardiac death. In this review, the pathophysiologic, diagnostic, and prognostic features of long-QT syndromes, as well as recommendations regarding therapy, are reviewed.

Derivation and Validation of a Simple Exercise-Based Algorithm for Prediction of Genetic Testing in Relatives of LQTS Probands

Background—

Genetic testing can diagnose long-QT syndrome (LQTS) in asymptomatic relatives of patients with an identified mutation; however, it is costly and subject to availability. The accuracy of a simple algorithm that incorporates resting and exercise ECG parameters for screening LQTS in asymptomatic relatives was evaluated, with genetic testing as the gold standard.

Methods and Results—

Asymptomatic first-degree relatives of genetically characterized probands were recruited from 5 centers. QT intervals were measured at rest, during exercise, and during recovery. Receiver operating characteristics were used to establish optimal cutoffs. An algorithm for identifying LQTS carriers was developed in a derivation cohort and validated in an independent cohort. The derivation cohort consisted of 69 relatives (28 with LQT1, 20 with LQT2, and 21 noncarriers). Mean age was 35±18 years, and resting corrected QT interval (QTc) was 466±39 ms. Abnormal resting QTc (females ≥480 ms; males ≥470 ms) was 100% specific for gene carrier status, but was observed in only 48% of patients; however, mutations were observed in 68% and 42% of patients with a borderline or normal resting QTc, respectively. Among these patients, 4-minute recovery QTc ≥445 ms correctly restratified 22 of 25 patients as having LQTS and 19 of 21 patients as being noncarriers. The combination of resting and 4-minute recovery QTc in a screening algorithm yielded a sensitivity of 0.94 and specificity of 0.90 for detecting LQTS carriers. When applied to the validation cohort (n=152; 58 with LQT1, 61 with LQT2, and 33 noncarriers; QTc=443±47 ms), sensitivity was 0.92 and specificity was 0.82.

Conclusions—

A simple algorithm that incorporates resting and exercise-recovery QTc is useful in identifying LQTS in asymptomatic relatives.

Epinephrine bolus test in detecting long QT syndrome mutation carriers with indeterminable electrocardiographic phenotype

BACKGROUND

In long QT syndrome (LQTS), prolonged and heterogeneous ventricular repolarization predisposes to serious arrhythmias. We examined how QT intervals are modified by epinephrine bolus in mutation carriers of three major LQTS subtypes with indefinite QT interval.

METHODS

Genotyped, asymptomatic subjects with LQTS type 1 (LQT1; n = 10; four different KCNQ1 mutations), type 2 (LQT2; n = 10; three different HERG mutations), and type 3 (LQT3; n = 10; four different SCN5A mutations), and healthy volunteers (n = 15) were examined. Electrocardiogram was recorded with body surface potential mapping system. After an epinephrine 0.04 μg/kg bolus QT end, QT apex, and T-wave peak-to-end (Tpe) intervals were determined automatically as average of 12 precordial leads. Standard deviation (SD) of the 12 channels was calculated.

RESULTS

Heart rate increased 26 ± 10 bpm with epinephrine bolus, and similarly in all groups. QT end interval lengthened, and QT apex interval shortened in LQTS and normals, leading to lengthening of Tpe interval. However, the lengthening in Tpe was larger in LQTS than in normals (mean 32 vs 18 ms; P < 0.05) and SD of QT apex increased more in LQTS than in normals (mean 23 vs 7 ms; P < 0.01). The increase in Tpe was most pronounced in LQT2, and in SD of QT apex in LQT1 and LQT2.

CONCLUSIONS

Abrupt adrenergic stimulation with a moderate dose of exogenous epinephrine affects ventricular repolarization in genotype-specific fashion facilitating distinction from normals. This delicate modification may help in diagnosing electrocardiographically silent mutation carriers when screening LQTS family members.

β-blockers protect against dispersion of repolarization during exercise in congenital long-QT syndrome type 1

INTRODUCTION

β-Blocker therapy reduces syncope and sudden death in long-QT syndrome type 1 (LQT1), but the mechanism of protection is incompletely understood. This study tested the hypothesis that β-blockade reduces QT prolongation and dispersion of repolarization, measured as the T peak-to-end interval (T(pe) ), during exercise and recovery in LQT1 patients.

METHODS AND RESULTS

QT and T(pe) were measured in 10 LQT1 patients (33 ± 13 years) and 35 normal subjects (32 ± 12 years) during exercise tests on and off β-blockade. In LQT1 patients, β-blockade reduced QT (391 ± 25 milliseconds vs 375 ± 26 milliseconds, P = 0.04 during exercise; 419 ± 41 milliseconds vs 391 ± 39 milliseconds, P = 0.02 during recovery) and markedly reduced T(pe) (91 ± 26 milliseconds vs 67 ± 19 milliseconds, P = 0.03 during exercise; 103 ± 26 milliseconds vs 78 ± 11 milliseconds, P = 0.02 during recovery). In contrast, in normal subjects, β-blockade had no effect on QT (320 ± 17 milliseconds vs 317 ± 16 milliseconds, P = 0.29 during exercise; 317 ± 13 milliseconds vs 315 ± 14 milliseconds, P = 0.15 during recovery) and mildly reduced T(pe) (69 ± 13 milliseconds vs 61 ± 11 milliseconds, P = 0.01 during exercise; 77 ± 19 milliseconds vs. 68 ± 14 milliseconds, P < 0.001 during recovery).

CONCLUSION

In LQT1 patients, β-blockers reduced QT and T(pe) during exercise and recovery, supporting the theory that β-blocker therapy protects LQT1 patients by reducing dispersion of repolarization during exercise and recovery.

Comparison of QT peak and QT end interval responses to autonomic adaptation in asymptomatic LQT1 mutation carriers

Background

LQT1 subtype of long QT syndrome is characterized by defective I_Ks, which is intrinsically stronger in the epicardium than in the midmyocardial region. Electrocardiographic QT peak and QT end intervals may reflect complete repolarization of epicardium and midmyocardial region of the ventricular wall, respectively. Repolarization abnormalities in LQT1 carriers may therefore be more easily detected in the QT peak intervals.

Methods

Asymptomatic KCNQ1 mutation carriers (LQT1, n = 9) and unaffected healthy controls (n = 8) were studied during Valsalva manoeuvre, mental stress, handgrip and supine exercise. Global QT peak and QT end intervals derived from 25 simultaneous electrocardiographic leads were measured beat to beat with an automated method.

Results

In unaffected subjects, the percentage shortening of QT peak was greater than that of QT end during mental stress and during the recovery phases of Valsalva and supine exercise. In LQT1 carriers, the percentage shortening of the intervals was similar. At the beginning of Valsalva strain under abrupt endogenous sympathetic activation, QT peak shortened in LQT1 but not in control patients yielding increased electrocardiographic transmural dispersion of repolarization in LQT1.

Conclusions

In asymptomatic KCNQ1 mutation carriers, repolarization abnormalities are more evident in the QT peak than in the QT end interval during adrenergic adaptation, possibly related to transmural differences in the degree of I_Ks block.

The effects of droperidol and ondansetron on dispersion of myocardial repolarization in children

OBJECTIVES

To compare the effects of droperidol and ondansetron on electrocardiographic indices of myocardial repolarization in children.

AIM

To refine understanding of the torsadogenic risk to children exposed to anti-emetic prophylaxis in the perioperative period.

BACKGROUND

QT interval prolongation is associated with torsades des pointes (TdP), but is a poor predictor of drug torsadogenicity. Susceptibility to TdP arises from increased transmural dispersion of repolarization (TDR) across the myocardial wall, rather than QT interval prolongation per se. TDR can be measured on the electrocardiogram as the time interval between the peak and end of the T wave (Tp-e). Tp-e may therefore provide a readily available, noninvasive assay of drug torsadogenicity. The perioperative period is one of high risk for TdP in children with or at risk of long QT syndromes. Droperidol and ondansetron are two drugs commonly administered perioperatively, for prophylaxis of nausea and vomiting, which can prolong the QT interval. This study investigated their effects on myocardial repolarization.

METHODS

One hundred and eight ASA1-2 children undergoing elective day-case surgery were randomized to receive droperidol, ondansetron, both or neither. Pre- and post-administration 12-lead electrocardiogram (ECGs) were recorded. QT and Tp-e intervals were measured and compared within and between groups, for the primary endpoint of a 25 ms change in Tp-e.

RESULTS

Eighty children completed the study. There were no demographic or baseline ECG differences between groups. QT intervals lengthened by 10-17 ms after allocated treatments, with no between-group differences. Values remained within normal limits for all groups. Tp-e intervals increased by 0-7 ms, with no between-group differences. There were no instances of dysrhythmia.

CONCLUSIONS

Droperidol and ondansetron, in therapeutic anti-emetic doses, produce equivalent, clinically insignificant QT prolongation and negligible Tp-e prolongation, suggesting that neither is torsadogenic in healthy children at these doses.

The risk of cardiac events and genotype-based management of LQTS patients

This review discusses the risk of cardiac events and genotype-based management of LQTS. We describe here the genetic background of long QT syndrome and the eleven different genes for ion-channels and a structural anchoring protein associated with that disorder. Clinical Background section discusses the risk of cardiac events associated with different LQTS types. Management and Prevention section describes in turn gene-specific therapy, which was based on the identification of the gene defect and the dysfunction of the associated transmembrane ion channel. In patients affected by LQTS, genetic analysis is useful for risk stratification and for making therapeutic decisions. A recent study reported a quite novel pathogenic mechanism for LQTS and suggested that treatments aimed at scaffolding proteins rather than specific ion channels may be an alternative to antiarrhythmic strategy in the future.

Clinical and electrophysiological features of Japanese pediatric long QT syndrome patients with KCNQ1 mutations

BACKGROUND

The purpose of the present paper was to determine the clinical and electrophysiological features of Japanese pediatric long QT syndrome (LQTS) patients with KCNQ1 mutations (LQT1).

METHODS

KCNQ1 mutations were analyzed in 13 Japanese pediatric patients with prolonged QT interval on electrocardiogram (ECG). These LQT1 patients were reviewed, retrospectively, for the presence of past and family histories of LQTS-related cardiac events, other complications, and their ECG findings evaluated at rest and during exercise).

RESULTS

KCNQ1 mutations were identified in eight patients (61.5%) from six unrelated families. Four missense mutations were identified in seven patients and an insertion/deletion in one. The mutations were located in the transmembrane domain in four patients and the C-terminal domain in four. Syncope did not occur in patients with the C-terminal domain mutations up to the age of 6-9 years, but family members of patients with the C-terminal domain mutations had a history of syncope in their elementary school days. Compared with a non-LQTS control group, peak heart rate (HR) on exercise and the HR increase during exercise were significantly lower in the LQT1 group (LQT1 vs control, 155 +/- 16 beats/min vs 182 +/- 13 beats/min, P < 0.01, 66 +/- 16 beats/min vs 99 +/- 24 beats/min, P < 0.01, respectively).

CONCLUSIONS

The risk of LQTS-related cardiac events may not be different in pediatric LQT1 patients with C-terminal domain mutations than in patients with transmembrane domain mutations. Possible sinus node dysfunction or a poor HR response to sympathetic stimulation has been suggested in pediatric LQT1 patients.

Pharmacological approach to the treatment of long and short QT syndromes

Inherited channelopathies have received increasing attention in recent years. The past decade has witnessed impressive progress in our understanding of the molecular and cellular basis of arrhythmogenesis associated with inherited channelopathies. An imbalance in ionic forces induced by these channelopathies affects the duration of ventricular repolarization and amplifies the intrinsic electrical heterogeneity of the myocardium, creating an arrhythmogenic milieu. Today, many of the channelopathies have been linked to mutations in specific genes encoding either components of ion channels or membrane or regulatory proteins. Many of the channelopathies are genetically heterogeneous with a variable degree of expression of the disease. Defining the molecular basis of channelopathies can have a profound impact on patient management, particularly in cases in which genotype-specific pharmacotherapy is available. The long QT syndrome (LQTS) is one of the first identified and most studied channelopathies where abnormal prolongation of ventricular repolarization predisposes an individual to life threatening ventricular arrhythmia called Torsade de Pointes. On the other hand of the spectrum, molecular defects favoring premature repolarization lead to Short QT syndrome (SQTS), a recently described inherited channelopathy. Both of these channelopathies are associated with a high risk of sudden cardiac death due to malignant ventricular arrhythmia. Whereas pharmacological therapy is first line treatment for LQTS, defibrillators are considered as primary treatment for SQTS. This review provides a comprehensive review of the molecular genetics, clinical features, genotype-phenotype correlations and genotype-specific approach to pharmacotherapy of these two mirror-image channelopathies, SQTS and LQTS.

Electrocardiographic interventricular dispersion of repolarization during autonomic adaptation in LQT1 subtype of long QT syndrome

OBJECTIVES

In LQT1 subtype of inherited long QT syndrome, repolarization abnormalities originating from defective I(Ks) render patients vulnerable to ventricular arrhythmia during sudden sympathetic activation. Experimental studies show lower I(Ks) density and longer action potential duration in left (LV) than in right (RV) ventricle. We studied interventricular dispersion of repolarization in patients with I(Ks) defect during autonomic tests.

DESIGN

We measured interventricular (difference of QT intervals between LV and RV type leads) and transmural electrocardiographic dispersion of repolarization from 25-lead electrocardiograms in nine asymptomatic KCNQ1 mutation carriers (LQT1) and eight controls during rest, Valsalva maneuver, mental stress, sustained handgrip and supine exercise.

RESULTS

LQT1 carriers showed increased interventricular dispersion of repolarization (13+/-9 ms vs. 4+/-4 ms, p=0.03) during all tests. Valsalva strain increased the difference between the study groups. In LQT1 carriers, interventricular dispersion of repolarization correlated weakly with electrocardiographic transmural dispersion of repolarization.

CONCLUSIONS

Asymptomatic KCNQ1 mutation carriers exhibit increased and by abrupt sympathetic activation augmented interventricular difference in electrocardiographic repolarization times. Interventricular and transmural repolarization dispersion behave similarly in patients with I(Ks) defect.

Rate-independent QT shortening during exercise in healthy subjects: terminal repolarization does not shorten with exercise

INTRODUCTION

QT interval for a given heart rate differs between exercise and recovery (QT hysteresis) due to slow QT adaptation to changes in heart rate. We hypothesized that QT hysteresis is evident within stages of exercise and investigated which component of the QT contributes to hysteresis.

METHODS AND RESULTS

Nineteen healthy volunteers performed a staged exercise test (four stages, 3 min each). Continuous telemetry was analyzed with software to compare QT intervals in a rate-independent fashion. QRST complexes during each minute were sorted by RR interval, and complexes in bins of 20 ms width were signal-averaged. QT and QTp (onset of QRS to peak T wave) were measured, and terminal QT calculated (peak to end of T wave, Tpe = QT - QTp). QT, QTp, and Tpe at the same heart rate were compared between the first and last minute of each stage. QT shortened from the first to last minute of exercise in each stage (Stage I: 358 +/- 30 to 346 +/- 25 ms, P < 0.001; Stage II: 342 +/- 27 to 331 +/- 24 ms, P = 0.003; Stage III: 329 +/- 21 to 322 +/- 18 ms, P = 0.03; Stage IV: 313 +/- 22 to 303 +/- 23 ms, P = 0.005). QTp also shortened in each stage, while Tpe was unchanged.

CONCLUSION

QT hysteresis occurs during exercise in normals, and the major determinant is shortening of the first component of the T wave. Terminal repolarization (peak to end of T wave), a surrogate for transmural dispersion of repolarization, does not shorten significantly with exercise.

Effect of chronic arsenic exposure from drinking waters on the QT interval and transmural dispersion of repolarization

This study investigated the effects of chronic arsenic exposure on QT- and QTc-interval prolongation, QTc dispersion (QTcd) and transmural dispersion of repolarization (TDR). We compared cardiac parameters from 40 male subjects chronically exposed to arsenic (group A) with those of 40 male subjects not exposed to arsenic (group B). Although subjects in both groups had non-corrected QT intervals within normal limits, subjects in group A had significantly longer QTc and QTcd intervals compared with group B. A total of 70% of group A compared with 10% of group B had QTcd values > 50 ms. The mean TDR value was also significantly higher in group A compared with group B. Although non-corrected QT intervals were within normal limits, those subjects chronically exposed to arsenic had a slight QT prolongation and a higher prevalence of subtle repolarization abnormalities, which might be clinically relevant.

Coronary calcium score from multislice computed tomography correlates with QT dispersion and left ventricular wall thickness

Coronary calcium score is a marker of coronary atherosclerosis and is an important factor of cardiac events. Ventricular hypertrophy and QT dispersion increase the risk of cardiac events. The purpose of the study was to investigate whether coronary calcium score may be related to the changes of QT, QT dispersion, heart chamber size, and wall thickness. The coronary calcium score was studied in 97 patients through multislice computed tomography (MSCT). There were 32 patients with high calcium score (> or =200), 29 patients with low calcium score (1-199), and 36 patients with zero calcium score. The gender, age, incidence of hypertension, diabetics, smoking, and dyslipidemia were similar among the three groups. The QT dispersion, QTc dispersion, and R-wave amplitude in the high calcium score group were larger than those in the other two groups. There were similar P-wave duration. QRS duration, and PR interval among the three groups. The left ventricular anterior-posterior diameter and left ventricular wall thickness in the high coronary calcium score group were larger than those in the other two groups. Coronary calcium score had strong correlations with QT dispersion and left ventricular wall thickness. These findings may contribute further evidence regarding the increased risk of cardiac events in those patients with high coronary calcium score.

Ionic, molecular, and cellular bases of QT-interval prolongation and torsade de pointes

Torsade de pointes (TdP) is a life-threatening arrhythmia that develops as a consequence of a reduction in the repolarization reserve of cardiac cells leading to amplification of electrical heterogeneities in the ventricular myocardium as well as to the development of early after depolarization-induced triggered activity. Electrical heterogeneities within the ventricles are due to differences in the time course of repolarization of the three predominant cell types that make up the ventricular myocardium, giving rise to transmural voltage gradients and a dispersion of repolarization that contributes to the inscription of the electrocardiographic T wave. A number of non-antiarrhythmic drugs and antiarrhythmic agents with class III actions and/or the various mutations and cardiomyopathies associated with the long QT syndrome reduce net repolarizing current and amplify spatial dispersion of repolarization, thus creating the substrate for re-entry. This results in a prolongation of the QT interval, abnormal T waves, and development of TdP. Agents that prolong the QT interval but do not cause an increase in transmural dispersion of repolarization (TDR) do not induce TdP, suggesting that QT prolongation is not the sole or optimal determinant for arrhythmogenesis. This article reviews recent advances in our understanding of these mechanisms, particularly the role of TDR in the genesis of drug-induced TdP, and examines how these may guide us towards development of safer drugs.

Heterogeneity and cardiac arrhythmias: an overview

This lecture examines the hypothesis that amplification of spatial dispersion of repolarization in the form of transmural dispersion of repolarization (TDR) underlies the development of life-threatening ventricular arrhythmias associated with inherited ion channelopathies, including the long QT, short QT, and Brugada syndromes as well as catecholaminergic polymorphic ventricular tachycardia. In the long QT syndrome, amplification of TDR often is secondary to preferential prolongation of the action potential duration of M cells, whereas in Brugada syndrome, it is thought to be due to selective abbreviation of the action potential duration of right ventricular epicardium. In the short QT syndrome, preferential abbreviation of action potential duration of either endocardium or epicardium appears to be responsible for amplification of TDR. In catecholaminergic polymorphic ventricular tachycardia, reversal of the direction of activation of the ventricular wall is responsible for the increase in TDR. Thus, the long QT, short QT, Brugada, and catecholaminergic ventricular tachycardia syndromes are pathologies with very different phenotypes and etiologies. However, these syndromes share a common final pathway in their predisposition to sudden cardiac death.

Role of spatial dispersion of repolarization in inherited and acquired sudden cardiac death syndromes

This review examines the role of spatial electrical heterogeneity within the ventricular myocardium on the function of the heart in health and disease. The cellular basis for transmural dispersion of repolarization (TDR) is reviewed, and the hypothesis that amplification of spatial dispersion of repolarization underlies the development of life-threatening ventricular arrhythmias associated with inherited ion channelopathies is evaluated. The role of TDR in long QT, short QT, and Brugada syndromes, as well as catecholaminergic polymorphic ventricular tachycardia (VT), is critically examined. In long QT syndrome, amplification of TDR is often secondary to preferential prolongation of the action potential duration (APD) of M cells; in Brugada syndrome, however, it is thought to be due to selective abbreviation of the APD of the right ventricular epicardium. Preferential abbreviation of APD of the endocardium or epicardium appears to be responsible for the amplification of TDR in short QT syndrome. In catecholaminergic polymorphic VT, reversal of the direction of activation of the ventricular wall is responsible for the increase in TDR. In conclusion, long QT, short QT, Brugada, and catecholaminergic polymorphic VT syndromes are pathologies with very different phenotypes and etiologies, but they share a common final pathway in causing sudden cardiac death.