Sinus node dysfunction in patients with Fontan circulation: could heart rate variability be a predictor for pacemaker implantation?

Brady-arrhythmias requiring permanent pacemaker implantation during and after staged Fontan palliation

BACKGROUND

Brady-arrhythmia requiring pacemaker implantation remains one of the Fontan-specific complications before and after total cavopulmonary connection.

METHODS

A retrospective analysis of 620 patients who underwent total cavopulmonary connection between 1994 and 2021 was performed to evaluate the incidence of brady-arrhythmia and the outcomes after pacemaker implantation. Factors associated with the onset of brady-arrhythmia were identified.

RESULTS

A total of 52 patients presented with brady-arrhythmia and required pacemaker implantation. Diagnosis included 16 sinus node dysfunctions, 29 atrioventricular blocks, and 7 junctional escape rhythms. Pacemaker implantation was performed before total cavopulmonary connection (n = 16), concomitant with total cavopulmonary connection (n = 8), or after total cavopulmonary connection (n = 28, median 1.8 years post-operatively). Freedom from pacemaker implantation following total cavopulmonary connection at 10 years was 92%. Twelve patients needed revision of electrodes due to lead dysfunction (n = 9), infections (n = 2), or dislocation (n = 1). Lead energy thresholds were stable, and freedom from pacemaker lead revision at 10 years after total cavopulmonary connection was 78%. Congenitally corrected transposition of the great arteries (odds ratio: 6.6, confidence interval: 2.0-21.5, p = 0.002) was identified as a factor associated with pacemaker implantation before total cavopulmonary connection. Pacemaker rhythms for Fontan circulation were not a risk factor for survival (p = 0.226), protein-losing enteropathy/plastic bronchitis (p = 0.973), or thromboembolic complications (p = 0.424).

CONCLUSIONS

In our cohort of patients following total cavopulmonary connection, freedom from pacemaker implantation at 10 years was 92% and stable atrial and ventricular lead energy thresholds were observed. Congenitally corrected transposition of the great arteries was at increased risk for pacemaker implantation before total cavopulmonary connection. Having a pacemaker in the Fontan circulation had no adverse effect on survival, protein-losing enteropathy/plastic bronchitis, or thromboembolic complications.

Roles and mechanisms of natural drugs on sinus node dysfunction

Sinus node dysfunction is a common arrhythmia disorder with a high incidence and significant social and economic burden. Currently, there are no effective drugs for treating chronic sinus node dysfunction. The disease is associated with ion channel disturbances caused by aging, fibrosis, inflammation, oxidative stress, and autonomic dysfunction. Natural active substances and Chinese herbal medicines have been widely used and extensively studied in the medical community for the treatment of arrhythmias. Multiple studies have demonstrated that various active ingredients and Chinese herbal medicines, such as astragaloside IV, quercetin, and ginsenosides, exhibit antioxidant effects, reduce fibrosis, and maintain ion channel stability, providing promising drugs for treating sinus node dysfunction. This article summarizes the research progress on natural active ingredients and Chinese herbal formulas that regulate sick sinoatrial node function, providing valuable references for the treatment of sinus node dysfunction.

Heart rate variability in congenital central hypoventilation syndrome: relationships with hypertension and sinus pauses

BACKGROUND

Autonomic nervous system (ANS) dysregulation has been described in congenital central hypoventilation syndrome (CCHS). The objectives were to describe heart rate variability (HRV) analyses in children suffering from CCHS both while awake and asleep and their relationships with both ambulatory blood pressure (BP) and ECG monitoring results.

METHODS

This retrospective study enrolled children with CCHS (n = 33, median age 8.4 years, 18 girls) who had BP and ECG monitored during the same 24 h. From the latter, HRV analyses were obtained during daytime and nighttime.

RESULTS

The prevalences of hypertension and sinus pauses were 33% (95% confidence interval [CI]: 18-52) and 18% (95% CI: 7-35), respectively. The decrease in systolic BP at night negatively correlated with an increase in very low frequency (VLF) and LF powers at night, and the longest RR interval positively correlated with daytime VLF and LF powers. Among the three groups of children (polyalanine repeat expansion mutation [PARM], moderate [20/25 and 20/26], severe [20/27 and 20/33], and non-PARMs), the prevalence of elevated BP or hypertension was different: in PARM subjects: 6/18 moderate, 7/9 severe versus 0/6 in non-PARM (p = 0.002).

CONCLUSION

Modifications of cardiac ANS are associated with systemic hypertension and the occurrence of sinus pauses in CCHS.

IMPACT

Children with congenital central hypoventilation syndrome (CCHS) exhibit an increased prevalence of hypertension and sinus pauses that are linked to cardiac autonomic nervous system dysfunction. Sinus pauses are the main manifestation of sinus nodal dysfunction in children with CCHS. The increased prevalence of hypertension, especially at nighttime, is a new finding in CCHS. Sinus nodal dysfunction can be due to the sole impairment of the cardiac autonomic nervous system. Ambulatory blood pressure and ECG monitoring are mandatory in patients with CCHS.

ß-tubulin contributes to Tongyang Huoxue decoction-induced protection against hypoxia/reoxygenation-induced injury of sinoatrial node cells through SIRT1-mediated regulation of mitochondrial quality surveillance

BACKGROUND

TYHX-Tongyang Huoxue decoction has been used clinically for nearly 40 years. The ingredients of TYHX are Radix Astragali (Huangqi), Red Ginseng (Hongshen), Rehmannia Glutinosa (Dihuang), Common Yam Rhizome (Shanyao) and Cassia-bark-tree Bark (Rougui). Our previous experiments confirmed that TYHX can protect sinoatrial node cells. However, its mechanism of action is not completely understood yet.

PURPOSE

The present study aimed to determine the protective effects of TYHX against Sinus node cell injury under hypoxic stress and elucidate the underlying mechanisms of protection.

METHODS

Through RNA sequencing analysis and network pharmacology analysis, we found significant differences in mitochondrial-related genes before and after hypoxia-mimicking SNC, resolved the main regulatory mechanism of TYHX. Through the intervention of TYHX on SNC, a series of detection methods such as laser confocal, fluorescence co-localization, mitochondrial membrane potential and RT-PCR. The regulatory effect of TYHX on β-tubulin in sinoatrial node cells was verified by in vitro experiments. The mechanism of action of TYHX and its active ingredient quercetin to maintain mitochondrial homeostasis and protect sinoatrial node cells through mitophagy, mitochondrial fusion/fission and mitochondrial biosynthesis was confirmed.

RESULTS

Through RNA sequencing analysis, we found that there were significant differences in mitochondrial related genes before and after SNC was modeled by hypoxia. Through pharmacological experiments, we showed that TYHX could inhibit the migration of Drp1 to mitochondria, inhibit excessive mitochondrial fission, activate mitophagy and increase the mitochondrial membrane potential. These protective effects were mainly mediated by β-tubulin. Furthermore, the active component quercetin in TYHX could inhibit excessive mitochondrial fission through SIRT1, maintain mitochondrial energy metabolism and protect SNCs. Our results showed that protection of mitochondrial function through the maintenance of β-tubulin and activation of SIRT1 is the main mechanism by which TYHX alleviates hypoxic stress injury in SNCs. The regulatory effects of TYHX and quercetin on mitochondrial quality surveillance are also necessary. Our findings provide empirical evidence supporting the use of TYHX as a targeted treatment for sick sinus syndrome.

CONCLUSION

Our data indicate that TYHX exerts protective effects against sinus node cell injury under hypoxic stress, which may be associated with the regulation of mitochondrial quality surveillance (MQS) and inhibition of mitochondrial homeostasis-mediated apoptosis.

Cardiac Implantable Electronic Devices in the Fontan Patient

As a result of remarkable progress in operative techniques and cardiology care during childhood, Fontan patients continue to age and require team-based multidisciplinary expertise to manage complications encountered in adulthood. They face particular challenges in terms of altered hemodynamic stressors, cardiac and hepatic failure, and arrhythmias. Arrhythmias in Fontan patients are highly prevalent and associated with underlying anatomy, surgical technique, and postoperative sequelae. Diagnostic tools, treatments, and device strategies for arrhythmias in Fontan patients should be adapted to the specific anatomy, type of surgical repair, and clinical status. Great strides in our understanding of arrhythmia mechanisms, options and techniques to obtain access to relevant cardiac structures, and application of both old and new technologies have contributed to improving cardiac implantable electronic device (CIED) therapies for this unique population. In this state-of-the-art review, we discuss the various arrhythmias encountered in Fontan patients, their diagnosis, and options for treatment and prevention, with a focus on CIEDs. Throughout, access challenges particular to the Fontan circulation are considered. Recently developed technologies, such as the sub-cutaneous implantable cardioverter defibrillator carry the potential to be transformative but require awareness of Fontan-specific issues. Moreover, new leadless pacing technology represents a promising strategy that may soon become applicable to Fontan patients with sinus node dysfunction. CIEDs are essential tools in managing Fontan patients but the complex clinical scenarios that arise in this patient population are among the most challenging for the congenital electrophysiologist.

Heart Rate Variability and Its Associations with Organ Complications in Adults after Fontan Operation

Reduction of heart rate variability (HRV) parameters may be a risk factor and precede the occurrence of arrhythmias or the development of heart failure and complications in people with postinfarct left ventricular dysfunction and after coronary artery bypass grafting. Data on this issue in adults after a Fontan operation (FO) are scarce. This study assessed the association between HRV, exercise capacity, and multiorgan complications in adults after FO. Data were obtained from 30 FO patients (mean age 24 ± 5.4 years) and 30 healthy controls matched for age and sex. HRV was investigated in all patients by clinical examination, laboratory tests, echocardiography, a cardiopulmonary exercise test, and 24-h electrocardiogram. The HRV parameters were reduced in the FO group. Reduced HRV parameters were associated with patients’ age at the time of FO, time since surgery, impaired exercise capacity, chronotropic incompetence parameters, and multiorgan complications. Univariate analysis showed that saturated O₂ at rest, percentage difference between adjacent NN intervals of >50 ms duration, and peak heart rate were associated with chronotropic index. Multivariable analysis revealed that all three variables were independent predictors of the chronotropic index. The results of this study suggest novel pathophysiological mechanisms that link HRV, physical performance, and organ damage in patients after FO.

Cardiac Autonomic Function in the First Hours of Postnatal Life: An Observational Cross-Sectional Study in Term Neonates

The aim of this study was to evaluate heart rate variability (HRV) within the first hours of extrauterine life in term neonates. HRV at 2-h and 14-h postpartum were compared by means of time domains (iRR, SDNN, and rMSSD); frequency domains (TP, LF, HF, and LF/HF ratio); and Poincare's Plot (SD1 and SD2) indices of HRV in 27 healthy, male, term newborns (NBs) born of elective cesarean delivery. Within 14 h after birth, the mean of the iRRs increased (Δ% = 4.4, p < 0.001) as well as parasympathetic indices (rMSSD: Δ% = 32.6; p < 0.03; HF: Δ% = 43.6; p < 0.00; SD1: Δ% = 32.6, p < 0.03). Respiratory rate (RR) decreased (RR: 2 h = 48 (43-55) cycle/min vs. 14 h = 45 (40-48) cycle/min p < 0.01). We concluded that within the first 14 h of birth, cardiac autonomic adjustments are characterized by an increase in parasympathetic activity. Concurrently, there were no significant changes observed in all other HRV indices in healthy, male, term neonates, and born of elective cesarean delivery.