Atrioventricular Node Research Articles

Catheter ablation of atrioventricular nodal reentrant tachycardia, when AVNRT presented as a fetus or infant.

Atrioventricular nodal reentrant tachycardia (AVNRT) does not commonly present during infancy. Although relative safety of catheter ablation of AVNRT has been demonstrated in pediatrics, this procedure is rarely indicated in children <15kg. Retrospective review of seven cases of AVNRT that presented in children younger than 1 year of age and required catheter ablation for definitive management. Electrophysiology (EP) study was planned with two or three catheters. Area of ablation determined by voltage mapping, propagation sinus wave collision and slow pathway potential location. Ablation performed with cryothermal energy. No fluoroscopy was used. Presentation ranged from 36weeks of gestation to 11 months of age. Two presented in fetal life and two in the neonatal period. The median age of ablation was 20months (range 17-31 months). The median weight at ablation was 11.4kg (range 8.9-14.9kg). Median follow-up time was 16 months. All had typical AVNRT. The median tachycardia cycle length was 216ms. 100% successful rate using cryoablation. No complications. No recurrence of tachycardia during the follow-up period. Slow AV nodal pathway cryoablation may be safely performed, with good short and medium-term outcomes in patients under 15kg.

Landiolol, an intravenous β1-selective blocker, is useful for dissociating a fusion of atrial activation via accessory pathway and atrioventricular node.

During ventricular pacing, a fusion of atrial activation may occur owing to the simultaneous retrograde conduction of the atrioventricular (AV) node and accessory pathway (AP), potentially leading to an inaccurate mapping of the atrial AP insertion site. We tested the hypothesis that landiolol, an ultra-short-acting intravenous β1-blocker, could dissociate a fusion of atrial activation. We conducted a prospective before-and-after study to investigate the effect of landiolol on retrograde conduction via the AV node and AP. We enrolled 21 consecutive patients with orthodromic AV reciprocating tachycardia who underwent electrophysiological studies at our hospital between January 1, 2018, and August 31, 2020. Six patients exhibited a fusion of atrial activation. After landiolol administration (10 μg/kg/min), the effective refractory period was unchanged in AP (280 [240-290] ms vs. 280 [245-295] ms, p = .91), whereas that of the AV node was prolonged (275 [215-380] ms vs. 332 [278-445] ms, p = .03). The Wenckebach pacing rate via retrograde AV node decreased after landiolol administration (180 [140-200] beats per minute [bpm] vs. 140 [120-180] bpm, p = .02). Thus, landiolol decreased the minimum ventricular pacing rate required to dissociate a fusion of atrial activation (180 [160-200] bpm vs. 140 [128-155] bpm, p = .007). Radiofrequency catheter ablation under landiolol administration successfully eliminated AP in all patients during ventricular pacing without complications or recurrence. Landiolol inhibited the AV node without affecting the AP and helped dissociate a fusion of atrial activation at a lower ventricular pacing rate.

Supraventricular tachycardia in pregnancy: a rare case series and dilemmatic antiarrhythmic drug choices in the rural area

Background: The prevalence of cardiovascular disease in pregnancy is reported to be increasing and becoming a major cause of maternal morbidity and mortality. The incidence of arrhythmia during pregnancy has been linked to increased fetal mortality and complications. Arrhythmias can develop de novo during pregnancy or be exacerbated by pregnancy. Case Description: A 35-year-old (third trimester) and a 25-year-old (second trimester) woman complained of shortness of breath and palpitations. The first patient was in her sixth pregnancy, with three live births and two miscarriages. Meanwhile, the second patient was in her first pregnancy and had never miscarried. The first and second patients' pulse rates were 180 and 160 beats per minute, respectively. In both cases, 12-lead electrocardiography revealed an atrioventricular nodal re-entrant tachycardia rhythm. Initially, both patients were given carotid artery massages. The first patient's rhythm returned to normal sinus, but carotid artery massage failed in the second patient. Then, the second patient received a slow bolus of 0.5 mg digoxin IV. The heart rate returned to normal sinus rhythm following the observation. Both patients were admitted to the intensive care unit. Conclusion: Atrioventricular nodal re-entrant tachycardia is a type of paroxysmal supraventricular tachycardia. Effective management highly depends on both clinical presentation and the trimester of pregnancy. This arrhythmia can be treated with vagal maneuvers in mild cases. When vagal maneuvers fail, medical management is preferred. The main concern with using antiarrhythmic drugs during pregnancy is the risk of fetal harm and the decision should be tailored based.

Histopathological changes in the electrical conduction of cardiac nodes after acute myocardial infarction in dogs and horses, compared with findings in humans: A histological, morphometrical, and immunohistochemical study.

The heart conduction system is responsible for the occurrence of various types of cardiac arrhythmia. This study aimed to histologically and morphometrically describe damaged cardiac nodes during acute myocardial infarction and to compare them with normal tissues in dogs and horses. This study describes the morphometry of cardiac nodes in five dogs and five elderly horses that succumbed to sudden cardiac death (SCD). A computerized morphometric study was conducted to determine the number of cells composing the nodes, different shape and size parameters of nodes, and their relationship with degenerative changes due to cardiac conditions. In both species, the sinoatrial node (SAN) was ovoid in shape whereas the atrioventricular node (AVN) was pyramidal in shape. The percentage of collagen fibers inside the SAN of dogs (47%) and horses (50%) was found to be higher than that of cells. In contrast, the percentage of cells in the AVN of dogs (24%) and horses (16%) was higher than that of connective tissues. In the SAN, the area (p = 0.09), maximum diameter (<0.001), and mean diameter (0.003) of P cells were larger in dogs than in horses. Overall, the SAN cells and surrounding cardiomyocytes in dogs and horses as well as the AVN cells in dogs that succumbed to SCD decreased in size compared with those in normal hearts.

An effective mathematical model of cardiac electrical activities for Bundle Branch Blocks

In this paper a mathematical model of cardiac induction system is developed. Sinoatrial node (SA), atrioventricular node (AV) and His Purkinje system (HP) are represented by modified Van der Pol-type oscillators (VDP) connected with time-delay coupling. Atrial and ventricular muscles are modeled using modified Aliev-Panfilov equations (AP), with stimulation current from the related pacemakers, to represent the P, QRS, Ta, and T waves. The main aim of this paper is to model bundle branch blocks (BBBs) for right (RBBB) and left (LBBB) branches. In fact, the right and left ventricles are directly affected by these blocks since the HP bundle is composed of right and left bundle branches that provide electrical signals, respectively, to the right and left ventricles. Four VDP oscillators are utilized, one for each of SA, AV, right HP, and left HP. The depolarization of the right and left ventricular muscles are represented by two systems of AP equations to produce right QRS and left QRS waves. The results of the simulation are compared with real normal and pathological electrocardiograms (ECGs) to show the effectiveness and the accuracy of the proposed model. The simulation proves that the model can reproduce the blocks in the HP bundle branches.

Outcomes After Supraventricular Tachycardia Ablation in Patients With Group 1 Pulmonary Hypertension.

Pulmonary hypertension (PH) is associated with right ventricular pressure overload and atrial remodeling, which may result in supraventricular tachycardias (SVTs). The outcomes of catheter SVT ablation in patients with World Health Organization (WHO) group 1 PH are incompletely characterized. We conducted a retrospective cohort study of all patients with WHO group 1 PH undergoing catheter SVT ablation during a 10-year period at a major academic tertiary care hospital. Baseline patient characteristics and procedural outcomes at 3 months and 1 year were extracted from the electronic medical record. Ablation of 60 SVTs was attempted in 38 patients with group 1 PH. The initial procedural success rates were 80% for atrial fibrillation (AF, n = 5), 89.7% for typical atrial flutter (AFL, n = 29), 57.1% for atypical AFL (n = 7), 60% for atrial tachycardia (AT, n = 15), and 75% for atrioventricular nodal reentrant tachycardia (AVNRT, n = 4). The 1-year post-procedural recurrence rates were 100% for AF (n = 4), 25% for typical AFL (n = 20), 50% for atypical AFL (n = 2), and 28.6% for AT (n = 7). No patients had recurrent AVNRT (n = 2). There were seven (18.4%) peri-procedural decompensations requiring pressor initiation and transfer to intensive care and one (2.6%) peri-procedural death. The study demonstrates that SVT ablation in group 1 PH can be performed relatively safely and effectively, albeit with lower initial success rates and higher risk of clinical decompensation than in the general population. Recurrence rates at 1 year were higher in AF and atypical AFL ablations and similar for typical AFL and AT ablations when compared to the general population.

Concomitant ablation of atrial fibrillation: New pacemakers and early rhythm recovery

ObjectiveNew permanent pacemaker (PPM) implantation after concomitant atrial fibrillation (AF) ablation has been associated with surgical ablation (SA). We sought to determine factors for PPM use as well as early rhythm recovery. MethodsFrom 2004 through 2019, 6135 patients underwent valve surgery and were grouped: No AF (n = 4584), AF no SA (n = 346), and AF with SA (n = 1205) to evaluate predischarge PPM and 3-month rhythm recovery (intrinsic heart rate >40 beats per minute). ResultsOverall, 282 (4.6%) patients required a predischarge PPM: atrioventricular node dysfunction in 75.3%, sick sinus syndrome in 19.1%, both (5%), and indeterminate (0.7%). Patients with AF had more PPMs: AF with SA (7.9%) versus AF no SA (6.9%) versus No AF (3.6%) (P < .001). For patients with AF, PPM rates were not significantly higher for ablation patients (7.6% SA vs 6.9% AF no SA; P = .56). There were differences in PPM by SA lesion set (biatrial 12.8%; left atrial only 6.1%; pulmonary vein isolation 3.0%; P < .001). Among patients with AF treated with 3-month PPM follow-up, rhythm recovery was common (35 out of 62 [56.5%]) and did not differ by lesion set. Rhythm recovery was seen in 63 out of 141 (44.7%) in the atrioventricular node dysfunction group versus 24 out of 35 (68.6%) in the sick sinus syndrome group (P = .011). In propensity score-matched groups, late survival was similar (P = .63) for new PPM patients. ConclusionsAvoiding conduction system trauma and delaying implantation reduces the need for postoperative PPM. Rhythm recovery within 3 months is frequent, especially for patients with sick sinus syndrome. A conservative approach to the implantation of a new PPMs is warranted.

Sinoatrial Node Irradiation in Patients Undergoing Definitive Stereotactic Body Radiation Therapy (SBRT) for Central Lung Cancers

The clinical consequences of sinoatrial node (SAN) and atrioventricular node (AVN) irradiation in patients undergoing thoracic stereotactic body radiation therapy (SBRT) remains unclear. We examined the relationship between SAN and AVN dose with survival outcomes in patients with central non-small cell lung cancer (NSCLC) tumors. A single-institutional retrospective review of patients with primary NSCLC undergoing definitive SBRT for centrally located tumors from February 2007 to December 2021 was performed. Central tumors were defined as within 2 cm of the proximal airway, mediastinum, great vessels, or spinal cord whereas ultracentral tumors were directly abutting any of the above structures. All patients underwent five-fraction SBRT to a total dose of 50 to 60 Gy. The SAN and AVN were contoured in accordance with a published contouring atlas and the maximum dose (Dmax) and mean dose (Dmean) for each structure were calculated. Sequential log rank testing between the 50th and 90th percentiles was used to identify potential cutoff values for the corresponding dosimetric parameters and non-cancer associated survival. Among 93 eligible patients, the median age was 72.5 years (Inter-Quartile Range [IQR], 66.6-78.3), median follow up was 32.4 months (IQR, 13.0-49.6), and 48 patients were female (52%). There were 49 ultracentral tumors (53%) and the median planning target volume (PTV) was 31.0 cc (IQR, 18.0-53.3). The median SAN Dmax and Dmean were 95 cGy (IQR, 37-1,072) and 58 cGy (IQR, 26-641), respectively. The median AVN Dmax and Dmean were 45 cGy (IQR, 19-506) and 34 cGy (IQR, 15-160), respectively. Candidate cutoff values for SAN Dmax and Dmean were 1,309 cGy and 814 cGy, respectively. No significant cutoff values were identified for either AVN parameter. Kaplan-Meier analysis for the proposed SAN Dmean constraint was significantly associated with overall (p = 0.016) and non-cancer associated survival (p = 0.028). The SAN Dmax constraint was significantly associated with only overall survival (p = 0.029). In a multivariate model, the SAN Dmean cutoff significantly correlated with both overall (Hazard Ratio [HR] 2.1 [1.13-3.78], p = 0.019) and non-cancer associated survival (HR 2.39 [1.12-5.10], p = 0.025) whereas the SAN Dmax cutoff was only significantly associated with overall survival (HR 1.95 [1.03-3.68], p = 0.041). SAN Dmax and Dmean were associated with significantly worse overall survival using cut-off values of 1,309 cGy and 814 cGy, respectively. SAN dose should be considered in radiation planning and further study on the consequence of SAN irradiation during SBRT is warranted.

Atrioventricular nodal reentry tachycardia treatment using CARTO 3 V7 activation mapping: a new era of slow pathway radiofrequency ablation is under coming.

Slow pathway (SP) ablation is the cornerstone for atrioventricular nodal reentry tachycardia (AVNRT) treatment, and a low-voltage bridge offers a good target during mapping using low x-ray exposure. We aimed to assess a new tool to identify SP by activation mapping using the last CARTO3® version, i.e., CARTO PRIME® V7 (Biosense Webster, Diamond Bar, CA, USA). Right atrial septum and triangle of Koch 3D-activation map were obtained from intracardiac contact mapping during low x-ray CARTO 3® procedure. In 60 patients (mean age 60.3 ± 14.7, 61% females) undergoing ablation for AVNRT, an automatic activation map using a DECANAV® mapping catheter and CARTO® Confidense™, Coherent, and FAM DX software modules were obtained. The SP was identified in all patients as the latest atrioventricular node activation area; RF catheter ablation (RFCA) in that region elicited junctional beats. The mean procedural time was 150.3 ± 48.3 min, the mean fluoroscopy time exposure was 2.9 ± 2 min, the mean dose-area product (DAP) was 16.5 ± 2.7 cGy/cm2. The mean number of RF applications was 3.9 ± 2, the mean ablation index was 428.6 ± 96.6, and the mean contact force was 8 ± 2.8 g. There were no adverse event during the procedure, and no AVNRT recurrences occurred during a mean follow-up of 14.3 ± 8.3 months. Ablation of the SP by automatic mapping using Confidense™, Coherent, and FAM DX software modules is an innovative, safe, and effective approach to AVNRT ablation. The CARTO3® V7 system shows on a 3D map the latest AV node activation area during sinus rhythm allowing low fluoroscopy time and highly effective RFCA.

New drug discovery of cardiac anti-arrhythmic drugs: insights in animal models

Cardiac rhythm regulated by micro-macroscopic structures of heart. Pacemaker abnormalities or disruptions in electrical conduction, lead to arrhythmic disorders may be benign, typical, threatening, ultimately fatal, occurs in clinical practice, patients on digitalis, anaesthesia or acute myocardial infarction. Both traditional and genetic animal models are: In-vitro: Isolated ventricular Myocytes, Guinea pig papillary muscles, Patch-Clamp Experiments, Porcine Atrial Myocytes, Guinea pig ventricular myocytes, Guinea pig papillary muscle: action potential and refractory period, Langendorff technique, Arrhythmia by acetylcholine or potassium. Acquired arrhythmia disorders: Transverse Aortic Constriction, Myocardial Ischemia, Complete Heart Block and AV Node Ablation, Chronic Tachypacing, Inflammation, Metabolic and Drug-Induced Arrhythmia. In-Vivo: Chemically induced arrhythmia: Aconitine antagonism, Digoxin-induced arrhythmia, Strophanthin/ouabain-induced arrhythmia, Adrenaline-induced arrhythmia, and Calcium-induced arrhythmia. Electrically induced arrhythmia: Ventricular fibrillation electrical threshold, Arrhythmia through programmed electrical stimulation, sudden coronary death in dogs, Exercise ventricular fibrillation. Genetic Arrhythmia: Channelopathies, Calcium Release Deficiency Syndrome, Long QT Syndrome, Short QT Syndrome, Brugada Syndrome. Genetic with Structural Heart Disease: Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia, Dilated Cardiomyopathy, Hypertrophic Cardiomyopathy, Atrial Fibrillation, Sick Sinus Syndrome, Atrioventricular Block, Preexcitation Syndrome. Arrhythmia in Pluripotent Stem Cell Cardiomyocytes. Conclusion: Both traditional and genetic, experimental models of cardiac arrhythmias’ characteristics and significance help in development of new antiarrhythmic drugs.

Junctional Ectopic Tachycardia Caused by Junctophilin-2 Expression Silencing Is Selectively Sensitive to Ryanodine Receptor Blockade

Junctional ectopic tachycardia (JET) is a potentially fatal cardiac arrhythmia. Hcn4:shJph2 mice serve as a model of nodal arrhythmias driven by ryanodine type 2 receptor (RyR2)-mediated Ca2+ leak. EL20 is a small molecule that blocks RyR2 Ca2+ leak. In a novel invivo model of JET, Hcn4:shJph2 mice demonstrated rapid conversion of JET to sinus rhythm with infusion of EL20. Primary atrioventricular nodal cells demonstrated increased Ca2+ transient oscillation frequency and increased RyR2-mediated stored Ca2+ leak which was normalized by EL20. EL20 was found to be rapidly degraded in mouse and human plasma, making it a potential novel therapy for JET.

Etripamil Nasal Spray for Conversion of Repeated Spontaneous Episodes of Paroxysmal Supraventricular Tachycardia During Long-Term Follow-Up: Results From the NODE-302 Study.

Background Self-administration of investigational intranasal L-type calcium channel blocker etripamil during paroxysmal supraventricular tachycardia (PSVT) appeared safe and well-tolerated in the phase 3 NODE-301 (Multi-Centre, Randomized, Double-Blind, Placebo-Controlled, Efficacy, and Safety Study of Etripamil Nasal Spray for the Termination of Spontaneous Episodes of Paroxysmal Supraventricular Tachycardia) trial of adults with sustained atrioventricular nodal-dependent PSVT. The NODE-302 open-label extension further characterized etripamil safety and efficacy. Methods and Results Eligible patients were monitored via self-applied cardiac monitoring system for 5 hours after etripamil self-administration. The primary end point was time-to-conversion of positively adjudicated PSVT to sinus rhythm after etripamil treatment. Probability of conversion to sinus rhythm was reported via Kaplan-Meier plot. Adverse events were based on self-reported symptoms and clinical evaluations. Among 169 patients enrolled, 105 self-administered etripamil ≥1 time for perceived PSVT (median [range], 232 [8-584] days' follow-up). Probability of conversion within 30 minutes of etripamil was 60.2% (median time to conversion, 15.5 minutes) among 188 PSVT episodes (92 patients) positively adjudicated as atrioventricular nodal dependent by independent ECG analysis. Among 40 patients who self-treated 2 episodes, 75% had a significantly consistent response by 30 minutes; 9 did not convert on either episode, and 21 converted on both episodes (χ2=8.09; P=0.0045). Forty-five of 105 patients (42.9%) had ≥1 treatment-emergent adverse event, generally transient and mild-to-moderate, including nasal congestion (14.3%), nasal discomfort (14.3%), or rhinorrhea (12.4%). No serious cardiac safety events were observed within 24 hours of etripamil. Conclusions In this extension study, investigational etripamil nasal spray was well tolerated for self-treating recurrent episodes of PSVT without medical supervision. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT03635996.

Termination of slow-fast atrioventricular reentrant tachycardia by a single cryoablation of the slow pathway guided by a fractionation map.

This is a slow-fast atrioventricular nodal reentrant tachycardia (AVNRT) case wherein the fractionation map-guided cryoablation of the slow pathway (SP) successfully terminated the tachycardia. In this case, the Advisor™ HD Grid catheter and fractionation map in the EnSite™ X EP system with relatively high-sensitive settings were useful for detecting the target SP area. Direct AVNRT termination by cryomapping at the fractionated potential area might be a quick and safe ablation strategy, which may provide a new workflow for SP ablation.

Design of intelligent hybrid NAR-GRNN paradigm for fractional order VDP chaotic system in cardiac pacemaker with relaxation oscillator

Managing cardiac disease and abnormal heart rate variability is a challenging problem with its psychological impact on lifesaving intervention. The research presents a novel machine learning approach to paradigm dynamic pacemaker design based on fractional order modified Van der Pol oscillator system implemented to generate rich non-sinusoidal signals for cardiac intervention and treatment. The physical framework of the novel contribution comprises Sino-Atrial (SA) and Atrio-Ventricular (AV) nodes, designed to utilize fractional order excitation signals derived from the VDP dynamic system. Hybrid paradigm is designed by integrating the dynamical nonlinear autoregressive (NAR) neural networks and generalized regression neural networks (GRNNs) to analyze the parametric fractal impulse model for cardiac muscle. The chaotic pattern of the proposed nonlinear system is explored in terms of phase portraits and Lyapunov exponents. The exceptional performance of the cutting-edge fractional order multimodal computing paradigm is validated by achieving an RMSE of 0.1E-14. The dynamic chaotic and fractal trajectory of relaxation oscillator based on its computed control parameters can provide valuable insight to design robust and efficient electronic implantable cardioverter defibrillators (ICDs) as pacemakers to stabilize cardiac impulse variability and alleviate healthcare burden as compared to traditional cardiac rehabilitation procedures.

Reversible Pulsed Electrical Fields as an In Vivo Tool to Study Cardiac Electrophysiology: The Advent of Pulsed Field Mapping.

During electrophysiological mapping of tachycardias, putative target sites are often only truly confirmed to be vital after observing the effect of ablation. This lack of mapping specificity potentiates inadvertent ablation of innocent cardiac tissue not relevant to the arrhythmia. But if myocardial excitability could be transiently suppressed at critical regions, their suitability as targets could be conclusively determined before delivering tissue-destructive ablation lesions. We studied whether reversible pulsed electric fields (PFREV) could transiently suppress electrical conduction, thereby providing a means to dissect tachycardia circuits in vivo. PFREV energy was delivered from a 9-mm lattice-tip catheter to the atria of 12 swine and 9 patients, followed by serial electrogram assessments. The effects on electrical conduction were explored in 5 additional animals by applying PFREV to the atrioventricular node: 17 low-dose (PFREV-LOW) and 10 high-dose (PFREV-HIGH) applications. Finally, in 3 patients manifesting spontaneous tachycardias, PFREV was applied at putative critical sites. In animals, the immediate post-PFREV electrogram amplitudes diminished by 74%, followed by 78% recovery by 5 minutes. Similarly, in patients, a 69.9% amplitude reduction was followed by 84% recovery by 3 minutes. Histology revealed only minimal to no focal, superficial fibrosis. PFREV-LOW at the atrioventricular node resulted in transient PR prolongation and transient AV block in 59% and 6%, while PFREV-HIGH caused transient PR prolongation and transient AV block in 30% and 50%, respectively. The 3 tachycardia patients had atypical atrial flutters (n=2) and atrioventricular nodal reentrant tachycardia. PFREV at putative critical sites reproducibly terminated the tachycardias; ablation rendered the tachycardias noninducible and without recurrence during 1-year follow-up. Reversible electroporation pulses can be applied to myocardial tissue to transiently block electrical conduction. This technique of pulsed field mapping may represent a novel electrophysiological tool to help identify the critical isthmus of tachycardia circuits.

Brash Syndrome: A Rare Presentation of Hyperkalemia

Brash syndrome stands for Bradycardia, Renal Failure, AV Node Blocker, Shock and Hyperkalaemia, and is a rare complication of patients suffering from chronic kidney disease, who are usually on dialytic support. These patients are usually on AV node blockers (either calcium channel blockers or beta blockers) and renal failure causes the accumulation of these medicines plus hyperkalaemia.1 Here we present a case of a patient who was diagnosed with Brash syndrome, was treated medically and was discharged. The purpose of this article is to highlight BRASH syndrome, recognise it and improve its’s medical management.

Novel method to avoid serious injurious effects on the atrioventricular nodal (AVN) conduction during catheter ablation of the AVN slow pathway utilizing cryofreezing energy

BackgroundSlow pathway elimination of the atrioventricular node (AVN) is essential to treat AVN reentrant tachycardia (AVNRT). However, injury to the AVN conduction (IAVN) is one of the serious complications. Cryofreezing energy is expected to reduce the incidence of IAVN. This study aimed to investigate the usefulness of a novel method to avoid IAVN during cryoablation of AVNRT. MethodsA total of 157 patients (average age, 65.8 years; male, 71) suffering from AVNRT were included. Once the AVNRT terminated during cryo-ablation, then rapid atrial constant pacing (RACP) was performed during freezing at a rate lower 10 bpm than that inducing Wenchebach AV block in 74 (47.1 %) patients (Group A). The RACP rate was decreasingly reduced by 10 bpm in case of the occurrence of IAVN. When the RACP reached 100 bpm, the cryoablation was prematurely terminated. Group B patients (83 = 52.9 %) underwent cryoablation during sinus rhythm. All patients were allocated in a randomized fashion. We compared the severity of the IAVN between Groups A and B. ResultsThere were no significant differences at 12 months regarding the freedom from the AVNRT between Groups A and B. However, the duration of the IAVN was significantly longer in Group B than A (p = 0.02). There were no significant differences regarding the distance between the His recording sites and successful ablation sites between Groups A and B. No permanent IAVN requiring pacemaker implantation was provoked in either group. ConclusionRACP was useful to avoid sustained and serious IAVN during cryoablation of AVNRT.

High-resolution mapping of the circuit of typical atrioventricular nodal reentrant tachycardia.

Recent anatomic and electrophysiologic evidence has provided new insight into the anatomic substrate. Previous reports on electroanatomic mapping (EAM) of the circuit of atrioventricular nodal reentrant tachycardia (AVNRT) have been limited by mapping only the triangle of Koch on the right side of the septum and by the use of conventional mapping tools. The objectives are to obtain comprehensive high-resolution mapping of typical AVNRT and to investigate the role of the atrioventricular ring tissues in the circuit. We employed EAM with the use of novel modules and algorithms for studying typical AVNRT from the right and the left sides of the septum. We performed extensive mapping of both the atrial septum and the septal vestibule of the tricuspid valve during typical AVNRT in 9 (6 females) patients, aged 49.6 ± 12.1years. In two of these, left septal mapping was also obtained through the aorta. The earliest initial activation was variable, emanating from the superior or medial septum. The impulse consistently appeared below the orifice of the coronary sinus, at the site where its inferoanterior margin merged with the septal vestibule of the tricuspid valve at its entrance to the right atrium. It then returned to the initial activation site, presumably through the septal vestibular myocardium. The left septal activation area corresponded to that recorded on the right side. Typical AVNRT uses a circuit confined within the pyramid of Koch from the AV node to the septal isthmus, involving the myocardial walls of the pyramidal space.

The role of the Cx43/Cx45 gap junction voltage gating on wave propagation and arrhythmogenic activity in cardiac tissue

Gap junctions (GJs) formed of connexin (Cx) protein are the main conduits of electrical signals in the heart. Studies indicate that the transitional zone of the atrioventricular (AV) node contains heterotypic Cx43/Cx45 GJ channels which are highly sensitive to transjunctional voltage (Vj). To investigate the putative role of Vj gating of Cx43/Cx45 channels, we performed electrophysiological recordings in cell cultures and developed a novel mathematical/computational model which, for the first time, combines GJ channel Vj gating with a model of membrane excitability to simulate a spread of electrical pulses in 2D. Our simulation and electrophysiological data show that Vj transients during the spread of cardiac excitation can significantly affect the junctional conductance (gj) of Cx43/Cx45 GJs in a direction- and frequency-dependent manner. Subsequent simulation data indicate that such pulse-rate-dependent regulation of gj may have a physiological role in delaying impulse propagation through the AV node. We have also considered the putative role of the Cx43/Cx45 channel gating during pathological impulse propagation. Our simulation data show that Vj gating-induced changes in gj can cause the drift and subsequent termination of spiral waves of excitation. As a result, the development of fibrillation-like processes was significantly reduced in 2D clusters, which contained Vj-sensitive Cx43/Cx45 channels.

Internodal conduction pathways: Revisiting a century-long debate on their existence, morphology, and location in the context of 2023 best science.

Internodal conduction pathways are the communication apparatus of the cardiac conduction system conveying sinus node action potentials to the atrioventricular node and atrial working myocytes. In 1910, at the Deutschen Pathologischen Gesellschaft held in Erlangen, Charles Thörel related his discovery of an internodal bundle structured with Purkinje-like cells which was rejected by the participants who endorsed the leading doctrine that atrial contractile cardiomyocytes operated as internodal routes. Starting in 1963 and for five subsequent decades, two groups have continued to revisit this issue. The first, led by Thomas James, defended the histological existence of uninsulated, high-speed cord-like internodal conduction tracts. Although not supported by robust experimental data, this hypothesis achieved the status of a physiological creed in the scientific community. The second, led by Robert Anderson, systematically refuted this stance and adopted anisotropy as an innovative internodal conduction mechanism operating via spindle-shaped atrial contractile myocytes arranged in anisotropic bundles relaying SAN APs to their atrial destinations at physiologically required (fit-for-purpose) velocities to enable synchronized atrial systoles. Modern imaging and electrophysiological techniques can now clearly visualize muscular internodal and interatrial tracts and SAN depolarization electrical waves, confirming the existence of atrial conduction paths muscular in nature. Mastery of the current best science, anatomy, and physiology of the human atria is necessary for electrophysiologists to safely perform atrial radiofrequency ablation interventions to restore sinus rhythm in patients distressed by supraventricular arrhythmias.