Who Is at Risk for Cardiac Events in Young Patients With Long QT Syndrome?

Paediatric/young versus adult patients with long QT syndrome

Introduction

Long QT syndrome (LQTS) is a less prevalent cardiac ion channelopathy than Brugada syndrome in Asia. The present study compared the outcomes between paediatric/young and adult LQTS patients.

Methods

This was a population-based retrospective cohort study of consecutive patients diagnosed with LQTS attending public hospitals in Hong Kong. The primary outcome was spontaneous ventricular tachycardia/ventricular fibrillation (VT/VF).

Results

A total of 142 LQTS (mean onset age=27±23 years old) were included. Arrhythmias other than VT/VF (HR 4.67, 95% CI (1.53 to 14.3), p=0.007), initial VT/VF (HR=3.25 (95% CI 1.29 to 8.16), p=0.012) and Schwartz score (HR=1.90 (95% CI 1.11 to 3.26), p=0.020) were predictive of the primary outcome for the overall cohort, while arrhythmias other than VT/VF (HR=5.41 (95% CI 1.36 to 21.4), p=0.016) and Schwartz score (HR=4.67 (95% CI 1.48 to 14.7), p=0.009) were predictive for the adult subgroup (>25 years old; n=58). A random survival forest model identified initial VT/VF, Schwartz score, initial QTc interval, family history of LQTS, initially asymptomatic and arrhythmias other than VT/VF as the most important variables for risk prediction.

Conclusion

Clinical and ECG presentation varies between the paediatric/young and adult LQTS population. Machine learning models achieved more accurate VT/VF prediction.

Quality of Life of Pediatric Patients With Long QT Syndrome

Children with long QT syndrome (LQTS) live with the risk of sudden death, activity restrictions, and the need for daily medications. We sought to evaluate the quality of life (QOL), self-perception, and behavior of patients with LQTS as perceived by both patients and their parents and identify predictors of lower QOL. QOL (Pediatric QOL Inventory [PedsQL] and Pediatric Cardiac Quality of Life Inventory [PCQLI]), self-perception, and behavioral inventories were completed by patients with LQTS and their parents. Comparison of PedsQL scores was made to published data for healthy children using t tests, and PCQLI scores were compared with those of patients with differing complexity of congenital heart disease. Mixed modeling was used for multivariable analysis. Sixty-one patients with LQTS were evaluated (age 13.6 ± 3.0 years; male 49%). Compared with healthy children, the PedsQL Total, Psychosocial, and Physical Health Summary scores were significantly lower for patients with LQTS and parent proxy reports (p ≤0.001). In general, PCQLI scores of patients with LQTS and parents were similar to those of patients with tetralogy of Fallot (p ≥0.2), lower than those of patients with bicuspid aortic valve (p ≤0.02), and higher than those of patients with single ventricle (p ≤0.03). Lower patient and parent PCQLI scores were associated with internalizing problems. For parents, the presence of a cardiac device and medication side effects were additionally associated with lower PCQLI scores. In conclusion, patients with LQTS and their parents report lower QOL than normal children secondary to physical and psychosocial factors. Increasing focus on the psychological well-being of these patients is needed in an effort to improve their QOL.

Genetic Characteristics of Children and Adolescents With Long-QT Syndrome Diagnosed by School-Based Electrocardiographic Screening Programs

Background—

A school-based electrocardiographic screening program has been developed in Japan. However, few data are available on the genetic characteristics of pediatric patients with long-QT syndrome who were diagnosed by this program.

Methods and Results—

A total of 117 unrelated probands aged ≤18 years were the subjects who were referred to our centers for genetic testing. Of these, 69 subjects diagnosed by the program formed the screened group. A total of 48 subjects were included in the clinical group and were diagnosed with long-QT syndrome–related symptoms, familial study, or by chance. Mutations were classified as radical, of high probability of pathogenicity, or of uncertain significance. Two subjects in the clinical group died. Genotypes were identified in 50 (72%) and 23 (48%) of subjects in the screened and clinical groups, respectively. Of the KCNQ1 or KCNH2 mutations, 31 of 33 (94%) in the screened group and 14 of 15 (93%) in the clinical group were radical and of high probability of pathogenicity. Prevalence of symptoms before (9/69 versus 31/48; P <0.0001) and after (12/69 versus 17/48; P =0.03) diagnosis was significantly lower in the screened group when compared with that in the clinical group although the QTc values, family history of long-QT syndrome, sudden death, and follow-up periods were not different between the groups.

Conclusions—

These data suggest that the screening program may be effective for early diagnosis of long-QT syndrome that may allow intervention before symptoms. In addition, screened patients should have follow-up equivalent to clinically identified patients.

Risk factors for symptoms in long QT syndrome patients in a single pediatric center

BACKGROUND

Long QT syndrome (LQTS) is a leading cause of sudden cardiac death due to arrhythmia in the pediatric population. This study aimed to determine risk factors for the presence of LQTS-related symptoms in a single pediatric center.

METHODS

Subjects were 146 consecutive LQTS patients (M:F = 72:74) who visited our hospital between April 2005 and August 2012 and during the preceding 24 months. A total of 103 subjects were discovered by the school-based screening, 15 subjects visited because of their symptoms, and the others were 28 subjects. One subject died.

RESULTS

Risk factors for the presence of symptoms after diagnosis were longer QTc values (P = 0.01), the presence of history of LQTS-related symptoms (P = 0.04), and longer follow-up periods (P = 0.03). Non-compliance with medicine was the sole risk factor for frequent symptoms after diagnosis (P = 0.02). In subjects discovered by the school-based screening, nine subjects (9%) had LQTS-related symptoms after diagnosis. Longer follow-up periods were the sole risk for the presence of symptoms (P = 0.04). The mean period until the presence of symptoms after diagnosis was 3.1 ± 2.7 years (0.1-7.1 years).

CONCLUSION

Good compliance with medicine is essential to prevent recurrent episodes. A new strategy is required to prevent subjects, including school-based screened subjects, from dropping out of hospital visits.

Swimming and the heart

Exercise training is accepted to be beneficial in lowering morbidity and mortality in patients with cardiac disease. Swimming is a popular recreational activity, gaining recognition as an effective option in maintaining and improving cardiovascular fitness. Swimming is a unique form of exercise, differing from land-based exercises such as running in many aspects including medium, position, breathing pattern, and the muscle groups used. Water immersion places compressive forces on the body with resulting physiologic effects. We reviewed the physiologic effects and cardiovascular responses to swimming, the cardiac adaptations to swim training, swimming as a cardiac disease risk factor modifier, and the effects of swimming in those with cardiac disease conditions such as coronary artery disease, congestive heart failure and the long-QT syndrome.

Arrhythmogenesis in the short-QT syndrome associated with combined HERG channel gating defects: a simulation study

BACKGROUND

This study aimed to show the mechanism how the HERG channel gating defects causes life-threatening arrhythmia in the short-QT syndrome, using a simulation model of ventricular action potentials (APs).

METHODS AND RESULTS

To evaluate the electrophysiological consequences of the short-QT syndrome at the level of the cardiac AP, the Markov model of wild-type (WT) KCNH2 channel was modified to obtain a model of the KCNH2 channel with the N588K mutation associated with the short-QT syndrome. Two parameters (betai and betabeta) were changed to reconstruct the N588K mutant Markov model, which successfully reproduced the experimental results of voltage-clamp recordings. The WT and mutant models were then integrated into the Luo-Rudy theoretical model of the cardiac ventricular AP. Unexpectedly, 1 parameter change alone, which caused gain of function, could shorten the AP duration (APD) but failed to induce early after-depolarizations (EADs). Only the condition with the combined gating defects could lead to EAD.

CONCLUSIONS

Although the gain of function for KCNH2 shortened APD in the short-QT syndrome, this simulation study suggested that arrhythmogenesis was associated not only with gain of function, but also with accelerated deactivation of KCNH2.

Cold-Water Face Immersion Per Se Elicits Cardiac Parasympathetic Activity

BACKGROUND

Cold-water face immersion (FI) is known to produce physiological changes, including bradycardia, by stimulating the parasympathetic system. However, other factors such as sympathetic activity, intrapleural pressures, and changes in chemical mediators may also contribute to these changes.

METHODS AND RESULTS

Eight healthy volunteers underwent a series of experiments designed to observe the effects of FI on heart rate and its variability, as detected using wavelet transformation. Each subject was instructed to bend over and put the entire face into an empty basin with and without breathing (protocols 1 and 2, respectively), and then perform FI in warm-water (protocols 3 and 4, respectively) and cold-water (protocols 5 and 6, respectively) while breathing and breath holding. Change in the R-R interval with FI was only significantly greater for protocol 6 than for the control procedure (protocol 1). Also, changes in the natural logarithm of high-frequency power with FI were significantly greater for protocols 5 and 6 than the protocol 1.

CONCLUSIONS

Bradycardia associated with cold-water FI is mainly attributed to cardiac vagal activity, which is independent of both the change in body position caused by bending over a basin and breath holding.

The treatment of cardiac causes of sudden death, syncope, and seizure

The treatment for pediatric causes for sudden cardiac death can either be general and supportive or, in 2005, can be much more etiology specific. While antiarrhythmic therapy and activity restriction have been for years the mainstay of therapy, newer technologies such as radiofrequency ablation and automatic implantable cardioverter defibrillators (AICDs) are now more commonly applied for certain disease entities. The evolving role for clinical genetic testing to determine the specific etiology of pediatric sudden cardiac death continues to evolve. Further improvements in risk stratification will allow us to determine which patients are at greatest risk, so that aggressive treatment can be delivered to these subgroups. In the future, there may be gene-specific therapies and/or genetic modification.

Interval Representative of Transmural Dispersion of Repolarization in Children and Young Adolescents With Congenital Long QT Syndrome

BACKGROUND

It has been shown experimentally that the interval from the nadir of the initial negative T wave to the end of the T wave is representative of transmural dispersion of repolarization (TDR) when complex T waves are present. In the clinical setting, however, the interval representative of TDR in patients with long QT syndrome (LQTS) is a controversial subject.

METHODS AND RESULTS

Five symptomatic patients (3 boys, 2 girls; 3 LQT1, 2 LQT2) were evaluated by a face immersion test before and after treatment to compare the configuration of the T wave. When the notch disappeared after treatment, the single peak of the T wave after treatment coincided with the nadir of the notch before treatment. When the notch remained the same after treatment as before treatment and when the QTc decreased, the corrected interval from the nadir of the notch to the end of the T wave was for the most part shortened.

CONCLUSIONS

The present study showed that the interval representative of the TDR in the clinical surface electrocardiogram can be obtained from the nadir of the notch to the end of the T wave in children and adolescents with LQTS, as was shown in the experimental study.