Sinus node dysfunction and atrial fibrillation-Relationships, clinical phenotypes, new mechanisms, and treatment approaches

Although the anatomical basis of the pathogenesis of sinus node dysfunction (SND) and atrial fibrillation (AF) is located primarily in the left and right atria, increasing evidence suggests a strong correlation between SND and AF, in terms of both clinical presentation and formation mechanisms. However, the exact mechanisms underlying this association are unclear. The relationship between SND and AF may not be causal, but is likely to involve common factors and mechanisms, including ion channel remodeling, gap junction abnormalities, structural remodeling, genetic mutations, neuromodulation abnormalities, the effects of adenosine on cardiomyocytes, oxidative stress, and viral infections. Ion channel remodeling manifests primarily as alterations in the "funny" current (I_f) and Ca²⁺ clock associated with cardiomyocyte autoregulation, and gap junction abnormalities are manifested primarily as decreased expression of connexins (Cxs) mediating electrical impulse propagation in cardiomyocytes. Structural remodeling refers primarily to fibrosis and cardiac amyloidosis (CA). Some genetic mutations can also cause arrhythmias, such as SCN5A, HCN4, EMD, and PITX2. The intrinsic cardiac autonomic nervous system (ICANS), a regulator of the heart's physiological functions, triggers arrhythmias.In addition, we discuss arrhythmias caused by viral infections, notably Coronavirus Disease 2019 (COVID-19). Similarly to upstream treatments for atrial cardiomyopathy such as alleviating CA, ganglionated plexus (GP) ablation acts on the common mechanisms between SND and AF, thus achieving a dual therapeutic effect.

Effects of pulsed field ablation on autonomic nervous system in paroxysmal atrial fibrillation: A pilot study

BACKGROUND

Vagal responses and phrenic activation are commonly observed during pulsed field ablation (PFA). However, whether the vagal responses and phrenic activations are nerve damage or a neurological stress response due to electrical stimulation is unclear.

OBJECTIVE

The purpose of this study was to evaluate the effect of a PFA system for performing pulmonary vein isolation on the autonomic nervous system.

METHODS

Patients with paroxysmal atrial fibrillation (AF) who underwent PFA between August 2021 and November 2021 were included. Nerve injury biomarkers and heart rate variability were obtained preablation and postablation. Patients were scheduled to undergo magnetic resonance imaging and diffusion-weighted imaging to evaluate cerebral microembolus formation postablation.

RESULTS

Acute electrical isolation was achieved in 100% of pulmonary veins (n = 72) in the 18 patients. Mean total procedural time was 64.1 ± 18.2 minutes, and mean fluoroscopy time was 12.3 ± 3.5 minutes. Serum nerve injury biomarkers did not show any changes preablation and immediately postablation and 24 hours after ablation (all P >.05). Preablation and 30-day postablation heart rate variability did not differ (all P >.05). Postablation diffusion-weighted imaging revealed no acute cerebral microembolus events. Moreover, there were no other procedure-related complications. The 8-month Kaplan-Meier estimate of freedom from arrhythmia was 83% ± 9%.

CONCLUSION

PFA does not induce nerve injury during pulmonary vein isolation for paroxysmal AF.

Transcriptomic profile analysis of the left atrium in spontaneously hypertensive rats in the early stage

Left atrial remodeling, characterized by enlargement and hypertrophy of the left atrium and increased fibrosis, was accompanied by an increased incidence of atrial fibrillation. While before morphological changes at the early stage of hypertension, how overloaded hypertension influences the transcriptomic profile of the left atrium remains unclear. Therefore, RNA-sequencing was performed to define the RNA expressing profiles of left atrium in spontaneously hypertensive rats (SHRs) and normotensive Wistar-Kyoto (WKY) rats as a control group. We also compared the changes in the RNA expression profiles in SHRs treated with an angiotensin receptor blocker (ARB) and angiotensin receptor-neprilysin inhibitor (ARNI) to assess the distinct effects on the left atrium. In total, 1,558 differentially expressed genes were found in the left atrium between WKY rats and SHRs. Bioinformatics analysis showed that these mRNAs could regulate upstream pathways in atrial remodeling through atrial fibrosis, inflammation, electrical remodeling, and cardiac metabolism. The regulated transcripts detected in the left atrial tissue in both the ARB-treated and ARNI-treated groups were related to metabolism. In contrast to the ARB-treated rates, the transcripts in ARNI-treated rats were mapped to the cyclic guanosine monophosphate-protein kinase G signaling pathway.