Heart rate variability alterations in Dravet Syndrome: The role of status epilepticus and a possible association with mortality risk

Cardiac-Specific Deletion of Scn8a Mitigates Dravet Syndrome-Associated Sudden Death in Adults

BACKGROUND

Sudden unexpected death in epilepsy (SUDEP) is a fatal complication experienced by otherwise healthy epilepsy patients. Dravet syndrome (DS) is an inherited epileptic disorder resulting from loss of function of the voltage-gated sodium channel, NaV 1.1, and is associated with particularly high SUDEP risk. Evidence is mounting that NaVs abundant in the brain also occur in the heart, suggesting that the very molecular mechanisms underlying epilepsy could also precipitate cardiac arrhythmias and sudden death. Despite marked reduction of NaV 1.1 functional expression in DS, pathogenic late sodium current (INa,L) is paradoxically increased in DS hearts. However, the mechanisms by which DS directly impacts the heart to promote sudden death remain unclear.

OBJECTIVES

In this study, the authors sought to provide evidence implicating remodeling of Na+ - and Ca2+ -handling machinery, including NaV 1.6 and Na+/Ca2+exchanger (NCX) within transverse (T)-tubules in DS-associated arrhythmias.

METHODS

The authors undertook scanning ion conductance microscopy (SICM)-guided patch clamp, super-resolution microscopy, confocal Ca2+ imaging, and in vivo electrocardiography studies in Scn1a haploinsufficient murine model of DS.

RESULTS

DS promotes INa,L in T-tubular nanodomains, but not in other subcellular regions. Consistent with increased NaV activity in these regions, super-resolution microscopy revealed increased NaV 1.6 density near Ca2+release channels, the ryanodine receptors (RyR2) and NCX in DS relative to WT hearts. The resulting INa,L in these regions promoted aberrant Ca2+ release, leading to ventricular arrhythmias in vivo. Cardiac-specific deletion of NaV 1.6 protects adult DS mice from increased T-tubular late NaV activity and the resulting arrhythmias, as well as sudden death.

CONCLUSIONS

These data demonstrate that NaV 1.6 undergoes remodeling within T-tubules of adult DS hearts serving as a substrate for Ca2+ -mediated cardiac arrhythmias and may be a druggable target for the prevention of SUDEP in adult DS subjects.

Clinical and Genetic Features of Dravet Syndrome: A Prime Example of the Role of Precision Medicine in Genetic Epilepsy

Dravet syndrome (DS), also known as severe myoclonic epilepsy of infancy, is a rare and drug-resistant form of developmental and epileptic encephalopathies, which is both debilitating and challenging to manage, typically arising during the first year of life, with seizures often triggered by fever, infections, or vaccinations. It is characterized by frequent and prolonged seizures, developmental delays, and various other neurological and behavioral impairments. Most cases result from pathogenic mutations in the sodium voltage-gated channel alpha subunit 1 (SCN1A) gene, which encodes a critical voltage-gated sodium channel subunit involved in neuronal excitability. Precision medicine offers significant potential for improving DS diagnosis and treatment. Early genetic testing enables timely and accurate diagnosis. Advances in our understanding of DS's underlying genetic mechanisms and neurobiology have enabled the development of targeted therapies, such as gene therapy, offering more effective and less invasive treatment options for patients with DS. Targeted and gene therapies provide hope for more effective and personalized treatments. However, research into novel approaches remains in its early stages, and their clinical application remains to be seen. This review addresses the current understanding of clinical DS features, genetic involvement in DS development, and outcomes of novel DS therapies.

Short- vs long-term assessment of heart rate variability: Clinical significance in Dravet Syndrome

PURPOSE

Heart rate variability (HRV) is a promising prognostic biomarker in Dravet Syndrome (DS), but different studies are not always comparable, limiting its clinical application. In fact, multiple HRV parameters, analyzed over different timescales and in different states are reported. The aim of this study was to assess which HRV parameter is more reproducible and clinically significant, analyzing differences between wake and sleep.

METHOD

Patients with DS, with available 24 h-ECG Holter-derived HRV, were screened to evaluate if they had EEG-derived ECG traces available within one month before/after the Holter. A 5-minute period in the awake and sleep state were analyzed and correlated with the 24 h-HRV. Several relevant clinical features such as age, a recent history of status epilepticus (SE), and frequent generalized tonic-clonic seizures (GTCS) were correlated to HRV parameters with multiple linear regression models.

RESULTS

Thirty-oneawake recordings and 22 sleep recordings were included. HF was the parameter with the highest correlation in awake (Rho 0.745, p < 0.001) and in sleep (Rho 0.727, p < 0.001). Age was a significant factor in simple models for most of the parameters except RMSSD. A recent history of SE was associated with a significant reduction of HRV, both in simple and multiple regressions for all parameters except for awake LF and for sleep RMSSD and PNN50. Frequent GTCS were associated with a significant decrease in sleep RMSSD, HF, and LF, also when correcting for the effect of age and history of SE. When compared pairwise, a significant increase in sleep was seen for HF (median + 24.45 ms2, IQR -7.51/+172.18 ms2, p = 0.036; increase in 15/22 patients).

CONCLUSION

A moderate degree of correlation between long- and short-term HRV was seen both in sleep and in awake, and a strong correlation for awake HF. HF, both in awake and sleep, was significantly associated with high seizure burden, including SE and frequent GTCS.

Sudden unexpected death in epilepsy

PURPOSE OF REVIEW

Sudden unexpected death in epilepsy (SUDEP) is a leading cause of death in patients with epilepsy. This review highlights the recent literature regarding epidemiology on a global scale, putative mechanisms and thoughts towards intervention and prevention.

RECENT FINDINGS

Recently, numerous population-based studies have examined the incidence of SUDEP in many countries. Remarkably, incidence is quite consistent across these studies, and is commensurate with the recent estimates of about 1.2 per 1000 patient years. These studies further continue to support that incidence is similar across the ages and that comparable factors portend heightened risk for SUDEP. Fervent research in patients and animal studies continues to hone the understanding of potential mechanisms for SUDEP, especially those regarding seizure-induced respiratory dysregulation. Many of these studies and others have begun to lay out a path towards identification of improved treatment and prevention means. However, continued efforts are needed to educate medical professionals about SUDEP risk and the need to disclose this to patients.

SUMMARY

SUDEP is a devastating potential outcome of epilepsy. More is continually learned about risk and mechanisms from clinical and preclinical studies. This knowledge can hopefully be leveraged into preventive measures in the near future.