Effects of continuous enhanced vagal tone on dual atrioventricular node and accessory pathways

Impact of dexmedetomidine on electrophysiological properties and arrhythmia inducibility in adult patients referred for reentrant supraventricular tachycardia ablation

BACKGROUND

Drugs used for sedation/analgesia may affect the basic cardiac electrophysiologic properties or even supraventricular tachycardia (SVT) inducibility. Dexmedetomidine (DEX) is a selective alpha-2 adrenergic agonist with sedative and analgesic properties. A comprehensive evaluation on use of DEX for reentrant SVT ablation in adults is lacking. The present study aims to systematically assess the impact of DEX on cardiac electrophysiology and SVT inducibility.

METHODS

Hemodynamic, electrocardiographic, and electrophysiological parameters and SVT inducibility were assessed before and after DEX infusion in patients scheduled for ablation of reentrant SVT.

RESULTS

The population of this prospective observational study included 55 patients (mean age of 58.7 ± 14 years, 29 males [52.7%]). A decrease in systolic and diastolic blood pressure and in heart rate was observed after DEX infusion (p = 0.001 for all). DEX increased corrected sinus node refractory time, atrial effective refractory period, AH interval, AV Wenckebach cycle length, and AV node effective refractory period without affecting the His-Purkinje conduction or ventricular myocardium refractoriness. No AV blocks or sinus arrests occurred during DEX infusion. Globally, there was no difference in SVT inducibility in basal condition or after DEX infusion (46/55 [83.6%] vs. 43/55 [78.1%] patients; p = 0.55), without a difference in isoprenaline use (p = 1.0). In 4 (7.3%) cases, the SVT was inducible only after DEX infusion. In 34.5% of cases, DEX infusion unmasked the presence of an obstructive sleeping respiratory pattern, represented mainly by snoring.

CONCLUSIONS

DEX depresses sinus node function and prolongs atrioventricular refractoriness without significantly affecting the rate of SVT inducibility in patients scheduled for reentrant SVT ablation.

Atrioventricular Conduction: Physiology and Autonomic Influences

Atrioventricular (AV) nodal conduction is decremental and very prone to alterations in autonomic tone. Conduction through the His-Purkinje system (HPS) is via fast channel tissue and typically not that dependent on autonomic perturbations. Applying these principles, when the sinus rate is stable and then heart block suddenly occurs preceded by even a subtle slowing of heart rate, it typically is caused by increased vagal tone, and block occurs in the AV node. Heart block with activity strongly suggests block in the HPS. Enhanced sympathetic tone and reduced vagal tone can facilitate induction of both AV and atrioventricular node reentry.

Successful radiofrequency ablation of swallowing-induced atrial tachycardia arising from left superior ganglionated plexus

A man in his early 40s developed palpitations brought on by swallowing and was found to have short runs of atrial tachycardia induced by swallowing solid food. Atrial tachycardia during swallowing was documented on electrocardiography and 24-hour Holter monitoring. No structural heart disease or esophageal disorders were found by echocardiography. The patient then underwent an electrophysiological study and catheter ablation. We mapped the left atrium with a multipolar mapping catheter while the patient swallowed bread and found that the earliest endocardial breakthrough was on the left anterior superior atrium, where the left superior ganglionated plexus was located. We successfully eliminated the paroxysmal atrial tachycardia at this site. Interestingly, in the process of ablation, atrioventricular node reentrant tachycardia was triggered. After the slow-pathway ablation procedure, no further tachycardia was induced.

Atrioventricular Conduction: Physiology and Autonomic Influences

Atrioventricular (AV) nodal conduction is decremental and very prone to alterations in autonomic tone. Conduction through the His-Purkinje system (HPS) is via fast channel tissue and typically not that dependent on autonomic perturbations. Applying these principles, when the sinus rate is stable and then heart block suddenly occurs preceded by even a subtle slowing of heart rate, it typically is caused by increased vagal tone, and block occurs in the AV node. Heart block with activity strongly suggests block in the HPS. Enhanced sympathetic tone and reduced vagal tone can facilitate induction of both AV and atrioventricular node reentry.

Identification of potential candidate genes and pathways in atrioventricular nodal reentry tachycardia by whole-exome sequencing

Background

Atrioventricular nodal reentry tachycardia (AVNRT) is the most common manifestation of paroxysmal supraventricular tachycardia (PSVT). Increasing data have indicated familial clustering and participation of genetic factors in AVNRT, and no pathogenic genes related to AVNRT have been reported.

Methods

Whole‐exome sequencing (WES) was performed in 82 patients with AVNRT and 100 controls. Reference genes, genome‐wide association analysis, gene‐based collapsing, and pathway enrichment analysis were performed. A protein‐protein interaction (PPI) network was then established; WES database in the UK Biobank and one only genetic study of AVNRT in Denmark were used for external data validation.

Results

Among 95 reference genes, 126 rare variants in 48 genes were identified in the cases (minor allele frequency < 0.001). Gene‐based collapsing analysis and pathway enrichment analysis revealed six functional pathways related to AVNRT as with neuronal system/neurotransmitter release cycles and ion channel/cardiac conduction among the top 30 enriched pathways, and then 36 candidate pathogenic genes were selected. By combining with PPI analysis, 10 candidate genes were identified, including RYR2, NOS1, SCN1A, CFTR, EPHB4, ROBO1, PRKAG2, MMP2, ASPH, and ABCC8. From the UK Biobank database, 18 genes from candidate genes including SCN1A, PRKAG2, NOS1, and CFTR had rare variants in arrhythmias, and the rare variants in PIK3CB, GAD2, and HIP1R were in patients with PSVT. Moreover, one rare variant of RYR2 (c.4652A > G, p.Asn1551Ser) in our study was also detected in the Danish study. Considering the gene functional roles and external data validation, the most likely candidate genes were SCN1A, PRKAG2, RYR2, CFTR, NOS1, PIK3CB, GAD2, and HIP1R.

Conclusion

The preliminary results first revealed potential candidate genes such as SCN1A, PRKAG2, RYR2, CFTR, NOS1, PIK3CB, GAD2, and HIP1R, and the pathways mediated by these genes, including neuronal system/neurotransmitter release cycles or ion channels/cardiac conduction, might be involved in AVNRT.

Atrioventricular Nodal Reentrant Tachycardia Triggered by Marijuana Use: A Case Report and Review of the Literature

Marijuana is the most commonly abused recreational substance. With the increasing legalization of marijuana, its use is expected to rise. Delta-9-tetrahydrocannabinol (THC) is the psychotropic component of marijuana, acting via CB1 and CB2 G-protein coupled cannabinoid receptors. Marijuana has serious cardiovascular effects including tachycardia, orthostatic hypotension, angina and myocardial infarction to name a few. Previous reports by our group and others documented various arrhythmias other than atrioventricular nodal reentrant tachycardia (AVNRT) that are associated with marijuana use. In this report, we present a case of AVNRT associated with marijuana use. Marijuana in high doses stimulates parasympathetic nerves. While parasympathetic stimulation can increase the refractory period of the fast conduction pathway, it has no effect on the slow and retrograde pathways, therefore its use creates an ideal milieu for AVNRT initiation and maintenance. Our case report highlights the importance of including marijuana use in the differential diagnosis, as a possible trigger, for patients presenting with AVNRT that is otherwise unexplainable.

At the Atrioventricular Crossroads: Dual Pathway Electrophysiology in the Atrioventricular Node and its Underlying Heterogeneities

The atrioventricular node (AVN) is a complex structure that performs a variety of functions in the heart. The AVN is primarily an electrical gatekeeper between the atria and ventricles and introduces a delay between atrial and ventricular excitation, allowing for efficient ventricular filling. The AVN is composed of several compartments that safely transmit electrical excitation from the atria to the ventricles via the fast or slow pathways. There are many electrophysiological differences between these pathways, including conduction time and electrical refractoriness, that increase the predisposition of the atrioventricular junction to arrhythmias such as atrioventricular nodal re-entrant tachycardia. These varied electrophysiological characteristics of the fast and slow pathways stem from their unique structural and molecular composition (tissue and cellular geometry, ion channels and gap junctions). This review summarises the structural and molecular heterogeneities of the human AVN and how they result in electrophysiological variations and arrhythmias.

Atrioventricular Node Slow-Pathway Ablation Reduces Atrial Fibrillation Inducibility: A Neuronal Mechanism

BACKGROUND

Radiofrequency ablation (RFA) for atrioventricular nodal reentrant tachycardia appears to reduce atrial tachycardia, which might relate to parasympathetic denervation at cardiac ganglionated plexuses.

METHODS AND RESULTS

Compared to 7 control canines without RFA, in 14 canines, RFA at the bottom of Koch's triangle attenuated vagal stimulation-induced effective refractory periods prolongation in atrioventricular nodal and discontinuous atrioventricular conduction curves but had no effect on the sinoatrial node. RFA attenuated vagal stimulation-induced atrial effective refractory periods shortening and vulnerability window of atrial fibrillation widening in the inferior right atrium and proximal coronary sinus but not in the high right atrium and distal coronary sinus. Moreover, RFA anatomically impaired the epicardial ganglionated plexuses at the inferior vena cava‒inferior left atrial junction. This method was also investigated in 42 patients who had undergone ablation of atrioventricular nodal reentrant tachycardia, or 12 with an accessory pathway (AP) at the posterior septum (AP-PS), and 34 patients who had an AP at the free wall as control. In patients with atrioventricular nodal reentrant tachycardia and AP-PS, RFA at the bottom of Koch's triangle prolonged atrial effective refractory periods and reduced vulnerability windows of atrial fibrillation widening at the inferior right atrium, distal coronary sinus and proximal coronary sinus but not the high right atrium. In patients with AP-free wall, RFA had no significant atrial effects.

CONCLUSIONS

RFA at the bottom of Koch's triangle attenuated local autonomic innervation in the atrioventricular node and atria, decreased vagal stimulation-induced discontinuous atrioventricular nodal conduction, and reduced atrial fibrillation inducibility due to impaired ganglionated plexuses. In patients with atrioventricular nodal reentrant tachycardia or AP-PS, RFA prolonged atrial effective refractory periods, and narrowed vulnerability windows of atrial fibrillation.

Dual atrioventricular nodal pathways physiology: a review of relevant anatomy, electrophysiology, and electrocardiographic manifestations

More than half a century has passed since the concept of dual atrioventricular (AV) nodal pathways physiology was conceived. Dual AV nodal pathways have been shown to be responsible for many clinical arrhythmia syndromes, most notably AV nodal reentrant tachycardia. Although there has been a considerable amount of research on this topic, the subject of dual AV nodal pathways physiology remains heavily debated and discussed. Despite advances in understanding arrhythmia mechanisms and the widespread use of invasive electrophysiologic studies, there is still disagreement on the anatomy and physiology of the AV node that is the basis of discontinuous antegrade AV conduction. The purpose of this paper is to review the concept of dual AV nodal pathways physiology and its varied electrocardiographic manifestations.

Ectopic atrial rhythm is a preablation predictor of atrioventricular nodal reentrant tachycardia in children

BACKGROUND

Supraventricular tachycardia (SVT) is a common tachyarrhythmia among pediatric patients. Usually, non-preexcited SVT is attributable to either atrioventricular nodal reentry tachycardia (AVNRT) or unidirectional retrograde accessory pathway (URAP), but these cannot be differentiated on a baseline electrocardiogram (ECG). The ability to identify the SVT mechanism in children may guide decision-making about treatment and counseling regarding electrophysiology study (EPS). Clinical experience suggested that ectopic atrial rhythm (EAR) is more frequently observed on preablation ECGs of pediatric patients with AVNRT. This study aimed to determine whether EAR is predictive of AVNRT.

METHODS

A 10-year single-center retrospective review was conducted with patients who underwent ablation for SVT from 1997 through 2006. All pediatric patients with documented AVNRT or URAP during EPS were included. The exclusion criteria specified prior ablation, Wolff-Parkinson-White syndrome, or complex congenital heart disease. A patient was considered to have EAR if a preablation ECG had a p-wave axis less than 0 degrees or greater than 90 degrees or a wandering atrial pacemaker with at least three different p-wave morphologies.

RESULTS

The review found 457 eligible patients ages 0.5 to 21 years: 285 with AVNRT and 172 with URAP. Patients with congenital heart defects represented 5.6% of the AVNRT group and 2.9% of the URAP group. Ectopic atrial rhythm was seen in 45 (16%) of 285 patients with AVNRT compared with 10 (6%) of 172 URAP patients (p = 0.001). The sensitivity and specificity of EAR for AVNRT was 16% and 94%, respectively, and the positive predictive value was 82%. There was no difference in heart rate or QRS duration between the two groups.

CONCLUSION

On preablation ECG for pediatric SVT patients, EAR is a reasonably specific marker for AVNRT.

Routine ganglionic plexi ablation during Maze procedure improves hospital and early follow-up results of mitral surgery

OBJECTIVE

Ganglionic plexi are claimed to be potentially responsible for atrial fibrillation. We evaluated whether ganglionic plexi isolation improves the results of the Maze procedure during mitral valve surgery.

METHODS

A total of 75 patients with atrial fibrillation underwent radiofrequency ablation during mitral valve surgery without (group A) or with (group B) ganglionic plexi ablation with bipolar radiofrequency plus fat pad resection along the Waterston groove, left pulmonary veins, and Marshall's ligament. Ganglionic plexi were intraoperatively mapped, and fat pad specimens were sectioned and analyzed. Hospital and follow-up results were recorded. Amiodarone was discontinued at the sixth month.

RESULTS

Active ganglionic plexi were mainly located in the upper parts of fat pads. Active specimens demonstrated more ganglionic plexi than inactive specimens (P <or= .015 at different levels) but did not correlate with atrial fibrillation recurrence (P = not significant). Atrial fibrillation was higher in group A at aortic declamping (P = .03) and discharge (P = .03). Early events were comparable (P = .565). At 16.7 +/- 0.95 (standard error) months, the cumulative freedom from atrial fibrillation, atrial flutter, and atrial tachycardia with antiarrhythmic therapy was 63.2% +/- 7.3% and proved higher in group B (83.9% +/- 7.9% vs group A 52.8% +/- 8.7%; P = .035). However, after the sixth month, at 12.8 +/- 0.80 months, freedom from atrial fibrillation, atrial flutter, and atrial tachycardia without antiarrhythmic therapy was 72.5% +/- 7.7% and proved higher in group B (92.9% +/- 6.9% vs 62.5% +/- 9.4%; P = .023). A higher proportion of patients in group B showed normalized E/A ratio (61.3% vs group A 36.4%; P = .029). No differences were detected in follow-up freedom from congestive heart failure (group A: 83.4% +/- 7.0% vs group B: 93.5% +/- 4.4%; P = .978) and hospital readmission (group A: 84.2% +/- 5.9% vs group B: 92.6% +/- 5.1%; P = .376).

CONCLUSION

Ganglionic plexi isolation can improve hospital and follow-up results during mitral valve surgery and possibly ameliorate echocardiographic recovery of atrial function during follow-up.

Simultaneous Dual Fast and Slow Pathway Conduction upon Induction of Typical Atrioventricular Nodal Reentrant Tachycardia: Electrophysiologic Characteristics in a Series of Patients

INTRODUCTION

Simultaneous dual atrioventricular nodal conduction (SDNC) through slow (SP) and fast pathway (FP) is a rare phenomenon observed upon the induction of atrioventricular nodal reciprocating tachycardia (AVNRT). The aim of this study is to report the electrophysiological features of patients showing typical AVNRT induced through SDNC.

METHODS AND RESULTS

Among 461 consecutive patients with typical AVNRT submitted to radiofrequency catheter ablation (RFCA), seven patients (1.5%) with SDNC at tachycardia onset (group I: 6 female; age 60-72 years, mean 65.2 +/- 3.8 years) and 118 age-matched controls (group II: 60 female; age 60-88 years, mean 68.4 +/- 6.8 years) were considered. Controls were further subdivided into two subgroups according to age: subgroup A (94 patients, age 60-75 years) and subgroup B (24 patients, age >75 years). The value of the following parameters was significantly higher in group I than in group II and in subgroup A: A-H interval [113 +/- 26 vs. 89 +/- 27 (P < 0.01) vs. 84 +/- 19 (P < 0.001)], ventriculoatrial conduction effective refractory period [355 +/- 85 vs. 293 +/- 87 (P < 0.05) vs. 281 +/- 82 (P < 0.05)], SP conduction time upon AVNRT induction [444 +/- 104 vs. 350 +/- 72 (P < 0.01); vs. 345 +/- 67 (P < 0.001)], AVNRT cycle length [484 +/- 103 vs. 396 +/- 71 ms (P < 0.05); vs. 384 +/- 69 (P < 0.05)], and rate of AVNRT induction from ventricle [71% vs. 10% (P = 0.001); vs. 6% (P = 0.001)]. Differences were mostly not significant between group I and subgroup B. SP location and RFCA success rate were similar in all groups.

CONCLUSION

In a population of AVNRT patients, SDNC at AVNRT induction is infrequent and it prevails beyond the fifth decade of life and in females. SDNC is associated with peculiar AVN conduction features, which resemble the age-related modifications of AVN conduction.