Compact Atrioventricular Node Research Articles

Irrigated contact force sensing catheter for redo ablation of slow-fast atrioventricular nodal reentrant tachycardia in pediatric and adolescent patients: A case series.

Conventional nonirrigated catheters cannot be able to create adequate lesions for effective slow pathway modulation in certain cases of pediatric atrioventricular nodal reentrant tachycardia ablation. Irrigated contact force sensing catheters may be considered in pediatric and adolescent patients to obtain a more extensive slow pathway modulation for redo ablation, avoiding dangerous radiofrequency applications close to the compact atrioventricular node or complex left-sided procedures.

P101 HIGH–DENSITY MAPPING OF KOCH‘S TRIANGLE DURING SINUS RHYTHM AND TYPICAL AV NODAL REENTRANT TACHYCARDIA INTEGRATED WITH THE DIRECT RECORDING OF ATRIOVENTRICULAR NODE STRUCTURES POTENTIAL: A MULTICENTER NON–RANDOMIZED STUDY

Abstract Background Atrioventricular nodal re–entrant tachycardia (AVNRT) is humans‘ most frequent regular tachycardia. Nevertheless, understanding the exact mechanism and pathways involved in the circuit that sustains the arrhythmia is still incomplete. Also, the recording of nodal potential was performed previously in animals with relative success, but not in humans. The aim of our study is to identify the potential of the compact atrioventricular node (AVN) and inferior extensions by using an electroanatomic mapping of the right atrium and the Koch‘s triangle in sinus rhythm and during AVNRT. Methods From March 2021 to July 2022, 79 patients with AVNRT underwent high–resolution mapping and complete ablation in 12 Italian Hospitals. No patients with atrial fibrillation or sustained ventricular tachycardia were included. The diagnosis of AVNRT was established according to standard criteria and diagnostic pacing manoeuvres. The presence and location of SP potentials, i.e., Jackman potential (JP) and Haïssaguerre potential (HP) were evaluated in each patient. The electroanatomic mapping obtained were merged with cardiac computerized tomography (CT) scan. Results Forty–five cases of successful AVNRT ablation were included in the analysis. The AVN potential has been demonstrated to be a very low frequency signal distinct from atrial, His bundle or ventricular activations, that can be recorded from electrodes overlying the region of the compact AVN by using a non–conventional bipolar electrogram filtering both during sinus rhythm and slow fast AVNRT. AVN potential was identified in all cases in the mid–septal region (#5) in both sinus rhythm and tachycardia. The mid–septal region and the postero–septal regions (#7) bounded anteriorly by the tricuspid annulus and posteriorly by the lateral wall toward the crista terminalis showed a higher prevalence of HP than other regions (46.7% in region #5 and 51.1% in region #7, p<0.0001 vs other regions, respectively). JPs seemed to have a converse distribution across the KT and they were mainly observed in the mid–postero–septal region (73.3%). After 359±121 days of follow–up, no patients had a recurrence of AVNRT. Conclusion The exact anatomical site and pathways involved in AVNRT are still unclear as well as the analysis and characterisation of the AVN potential. Our results represent the first evidence of the recording of AVN potential. Further studies and technological improvements are needed to confirm our results.

New insights into the mechanisms of fast and slow conduction in the atrioventricular node

Cardiac pathologists and electrophysiologists have studied the atrioventricular (AV) node since 1906, when Tawara 1 Tawara S. Das Reitzleitungssystem des Saugetierherzens: Eine anatomisch-histologische Studie uber das Atrioventrikularbundel und die Purkinjeschen Faden. Gustav Fischer, Jena, Germany1906: 135-136 Google Scholar described its inferior extensions in the human heart. One century later, this important cardiac structure still carries the reputation of a profound enigma, invoked as the riddle of Sphinx, by means of its electrophysiological properties during both normal conduction and reentrant tachycardia. 2 Katritsis D.G. The human atrioventricular node: oedipus and the riddle of the Sphinx. Arrhythm Electrophysiol Rev. 2020; 9: 52-53 Crossref PubMed Scopus (0) Google Scholar In recent years, considerable evidence has accrued pertaining to its anatomic structure, 3 Inoue S. Becker A.E. Posterior extensions of the human compact atrioventricular node: a neglected anatomic feature of potential clinical significance. Circulation. 1998; 97: 188-193 Crossref PubMed Scopus (271) Google Scholar , 4 Hikspoors J. Macias Y. Tretter J.T. et al. Miniseries 1–part I: the development of the atrioventricular conduction axis. Europace. 2022; 24: 432-442 Crossref PubMed Scopus (1) Google Scholar , 5 Macias Y. de Almeida M.C. Tretter J.T. et al. Miniseries 1–part II: the compara-tive anatomy of the atrioventricular conduction axis. Europace. 2022; 24: 443-454 Crossref PubMed Scopus (3) Google Scholar , 6 Anderson R.H. Sanchez-Quintana D. Mori S. Cabrera J.A. Back Sternick E. Re-evaluation of the structure of the atrioventricular node and its connections with the atrium. Europace. 2020; 22: 821-830 Crossref PubMed Scopus (32) Google Scholar along with the electrophysiological properties, which have allowed identification of the so-called fast and slow pathways involved in atrioventricular nodal reentrant tachycardia (AVNRT). 7 Katritsis D.G. Josephson M.E. Classification, electrophysiological features and therapy of atrioventricular nodal reentrant tachycardia. Arrhythm Electrophysiol Rev. 2016; 5: 130-135 Crossref PubMed Scopus (29) Google Scholar , 8 Katritsis D.G. A unified theory for the circuit of atrioventricular nodal re-entrant tachycardia. Europace. 2020; 22: 1763-1767 Crossref PubMed Scopus (7) Google Scholar , 9 Katritsis D.G. Calkins H. Anderson R.H. The specialized atrioventricular ring tissues participate in the circuit of atrioventricular nodal reentrant tachycardia. J Am Heart Assoc. 2021; 10e022811 Crossref Scopus (0) Google Scholar But still the nature of these patterns of conduction in the context of sinus rhythm, as opposed to those observed during tachycardia, remains obscure. In the great Sophoclean tragedy, in light of its insurmountable difficulty, the denouement of the riddle of Sphinx by mortal Oedipus was initially perceived by the Athenians as a form of hubris against the gods by a human. 10 Sophocles. Oedipus Tyrannus. 429 BC. Google Scholar We believe that the accumulation of recent anatomic and electrophysiological evidence now enables us to provide the rationale for solving the nodal riddle without committing scientific hubris.

High-resolution parahisian mapping and ablation using microelectrode embedded ablation catheters.

Accurate mapping of the compact atrioventricular (AV) node is critical during ablation of a range of arrhythmias. The purpose of this multicenter prospective study was to test the hypothesis that microelectrode (ME)-embedded catheters more accurately define the near-field compact AV node compared to conventional catheters. For the mapping phase, detailed AV junction maps were created in 47 patients using an ME-embedded catheter. His electrograms (EGMs) detected by conventional electrodes (Hisc) and by ME (Hisμ) were annotated. For the ablation phase, AV nodal ablation (Qmode 50 W) was performed in 10 patients after pacemaker implantation, with initial Hisc-only ablation in group 1 (n = 6) and initial Hisμ ablation in group 2 (n = 4). For the clinical phase, a prospective registry of parahisian tachycardia using QDOT was obtained. In the mapping phase, 7.0 ± 5.4 Hisc and 8.0 ± 5.6 Hisμ points were acquired per map (n = 47). Hisμ cloud was smaller and more proximally located than Hisc cloud: (99.4 ± 74.7 mm2 vs 197.6 ± 110.6 mm2; P = .0008). Hisμ EGMs had larger amplitudes than Hisc EGMs (0.40 ± 0.38 mV vs 0.16 ± 0.1 mV; P = .0002). In the ablation phase, for group 1: Hisc-only ablation never resulted in AV block, whereas Hisμ ablation resulted in AV block after limited ablation in all patients (after 13.3 ± 9.2 s); and for group 2: Hisμ ablation always resulted in AV block after 1 application (after 14.3 ± 10.3 s). In the clinical phase, a Hisμ-avoidance strategy could avoid AV block in a prospective registry of 11 patients. ME more accurately defines the region of the compact node, and ablation in this region is associated with a high risk for AV block. ME-based mapping has the potential to significantly enhance ablation safety and efficacy.

Miniseries 1-Part III: 'Behind the scenes' in the triangle of Koch.

To take full advantage of the knowledge of cardiac anatomy, structures should be considered in their correct attitudinal orientation. Our aim was to discuss the triangle of Koch in an attitudinally appropriate fashion. We reviewed our material prepared by histological sectioning, along with computed tomographic datasets of human hearts. The triangle of Koch is the right atrial surface of the inferior pyramidal space, being bordered by the tendon of Todaro and the hinge of the septal leaflet of the tricuspid valve, with its base at the inferior cavotricuspid isthmus. The fibro-adipose tissues of the inferior pyramidal space separate the atrial wall from the crest of the muscular interventricular septum, thus producing an atrioventricular muscular sandwich. The overall area is better approached as a pyramid rather than a triangle. The apex of the inferior pyramidal space overlaps the infero-septal recess of the subaortic outflow tract, permitting the atrioventricular conduction axis to transition directly to the crest of the muscular ventricular septum. The compact atrioventricular node is formed at the apex of the pyramid by union of its inferior extensions, which represent the slow pathway, with the septal components formed in the buttress of the atrial septum, thus providing the fast pathway. To understand its various implications in current cardiological catheter interventions, the triangle of Koch must be considered in conjunction with the inferior pyramidal space and the infero-septal recess. It is better to consider the overall region in terms of a pyramidal area of interest.

Miniseries 2-Septal and paraseptal accessory pathways-Part III: Mid-paraseptal accessory pathways-revisiting bypass tracts crossing the pyramidal space.

The mid-paraseptal region corresponds to the portion of the pyramidal space whose right atrial aspect is known as the triangle of Koch. The superior area of this mid-paraseptal region is also para-Hisian, and is close to the compact atrioventricular node and the His bundle. The inferior sector of the mid-paraseptal area is unrelated to the normal atrioventricular conduction pathways. It is, therefore, a safe zone in which, if necessary, to perform catheter ablation. The middle part of the mid-paraseptal zone may, however, in some patients, house components of the compact atrioventricular node. This suggests the need for adopting a prudent attitude when considering catheter ablation in this area. The inferior extensions of the atrioventricular node, which may represent the substrate for the slow atrioventricular nodal pathway, take their course through the middle, and even the inferior, sectors of the mid-paraseptal region. In this review, we contend that the middle and inferior areas of the mid-paraseptal region correspond to what, in the past, was labelled by most groups as the 'midseptal' zone. We describe the electrocardiographic patterns observed during pre-excitation and orthodromic reciprocating tachycardia in patients with pathways ablated in the middle or inferior sectors of the region. We discuss the modification of the ventriculo-atrial conduction times during tachycardia after the development of bundle branch block aberrancy. We conclude that the so-called 'intermediate septal' pathways, as described in the era of surgical ablation, were insufficiently characterized. They should not be considered the surrogate of the 'midseptal' pathways defined using endocardial catheter electrode mapping.

Inferior Extensions of the Atrioventricular Node

The pathways for excitation of the atrioventricular node enter either superiorly, as the so-called ‘fast’ pathway, or inferiorly as the ‘slow’ pathway. However, knowledge of the specific anatomical details of these pathways is limited. Most of the experimental studies that established the existence of these pathways were conducted in mammalian hearts, which have subtle differences to human hearts. In this review, the authors summarise their recent experiences investigating human cardiac development, correlating these results with the arrangement of the connections between the atrial myocardium and the compact atrioventricular node as revealed by serial sectioning of adult human hearts. They discuss the contributions made from the atrioventricular canal myocardium, as opposed to the primary ring. Both these rings are incorporated into the atrial vestibules, albeit with the primary ring contributing only to the tricuspid vestibule. The atrial septal cardiomyocytes are relatively late contributors to the nodal inputs. Finally, they relate our findings of human cardiac development to the postnatal arrangement.

Spatial characterization of the tachycardia circuit of atrioventricular nodal re-entrant tachycardia.

The exact circuit of atrioventricular nodal re-entrant tachycardia (AVNRT) remains elusive. To assess the location and dimensions of the AVNRT circuit. Both typical and atypical AVNRT were induced at electrophysiology study of 14 patients. We calculated the activation time of the fast and slow pathways, and consequently, the length of the slow pathway, by assuming an average conduction velocity of 0.04 mm/ms in the nodal area. The distance between the compact atrioventricular node and the slow pathway ablating electrode was measured on three-dimensionally reconstructed fluoroscopic images obtained in diastole and systole. We also measured the length of the histologically discrete right inferior nodal extension in 31 human hearts. The length of the slow pathway was calculated to be 10.8 ± 1.3 mm (range 8.2-12.8 mm). The distance from the node to the ablating electrode was measured in five patients 17.0 ± 1.6 mm (range 14.9-19.2 mm) and was consistently longer than the estimated length of the slow pathway (P < 0.001). The length of the right nodal inferior extension in histologic specimens was 8.1 ± 2.3 mm (range 5.3-13.7 mm). There were no statistically significant differences between these values and the calculated slow pathway lengths. Successful ablation affects the tachycardia circuit without necessarily abolishing slow conduction, probably by interrupting the circuit at the septal isthmus.

Transcatheter ablation of the atrioventricular junction in refractory atrial fibrillation: A clinicopathological study

BackgroundCatheter ablation of the specialized atrioventricular junction (AVJ) with a right-side approach is an effective therapy for refractory atrial fibrillation with fast ventricular rate. Our aim is to assess the efficacy of the procedure in a single center experience and investigate the histologic findings of AVJ after catheter ablation. MethodsA) Analysis of AVJ ablation efficacy in a consecutive series of patients with refractory atrial fibrillation; B) Histopathologic study of the conduction system by serial section technique and clinical-electrophysiologic correlation in four patients who underwent AVJ ablation. ResultsA) Right-sided AVJ ablation was successful in all 87 consecutive patients (mean procedural time 19.2±17.9 min). Energy applications ranged from 1 to 27 (mean 5.8±5.1) with eight patients (9%) requiring > 15 applications. B) Fibrotic disruption of atrioventricular (AV) node and/or His bundle interruption was found in three cases with previous AVJ ablation. In the case requiring a left side approach, the compact AV node and common His bundle appeared undamaged whereas extensive fibrosis of the summit of the ventricular septum, branching His bundle and proximal bundle branches was found. Noteworthy, a continuity between the septal and anterior tricuspid valve leaflets was present. ConclusionOur data confirm that the ideal site for ablation of the specialized AVJ is the AV node. In selected cases with unsuccessful AV node ablation, a shift towards the His bundle is needed. A continuity between the septal and anterior leaflets of the tricuspid valve may protect the His bundle as to require multiple shocks and prolong the procedure.

Aortic Valve Calcification as a Predictor of Post-Transcatheter Aortic Valve Replacement Pacemaker Dependence.

BackgroundAtrioventricular block requiring permanent pacemaker (PPM) implantation is a common complication of transcatheter aortic valve replacement (TAVR). The mechanism of atrioventricular (AV) block during TAVR is not fully understood, but it may be due to the mechanical stress of TAVR deployment, resulting in possible injury to the nearby compact AV node. Aortic valve calcification (AVC) may worsen this condition and has been associated with an increased risk for post-TAVR PPM implantation. We performed a retrospective analysis to determine if AVC is predictive for long-term right ventricular (RV) pacing in post-TAVR pacemaker patients at 30 days.MethodsA total of 262 consecutive patients who underwent TAVR with a balloon-expandable valve were analyzed. AVC data were derived from contrast-enhanced computed tomography and characterized by leaflet sector and region.ResultsA total of 25 patients (11.1%) required post-TAVR PPM implantation. Seventeen patients did not require RV pacing at 30 days. Nine of these 17 patients had no RV pacing requirement within 10 days. The presence of intra-procedural heart block (P = 0.004) was the only significant difference between patients who did not require PPM and those who required PPM but they were not RV pacing-dependent at 30 days. Non-coronary cusp (NCC) calcium volume was significantly higher in patients who were pacemaker-dependent at 30 days (P = 0.01) and a calcium volume of > 239.2 mm3 in the NCC was strongly predictive of pacemaker dependence at 30 days (area under the curve (AUC) = 0.813). Pre-existing right bundle branch block (RBBB) (odds ratio (OR) 105.4, P = 0.004), bifascicular block (OR 12.5, P = 0.02), QRS duration (OR 70.43, P = 0.007) and intra-procedural complete heart block (OR 12.83, P = 0.03) were also predictive of pacemaker dependence at 30 days.ConclusionsIn patients who required PPM after TAVR, quantification of AVC by non-coronary leaflet calcium volume was found to be a novel predictor for RV pacing dependence at 30 days. The association of NCC calcification and PPM dependence may be related to the proximity of the conduction bundle to the non-coronary leaflet. Further studies are necessary to improve risk prediction for long-term RV pacing requirements following TAVR.

Imaging of Atrioventricular Nodal Conduction Tissue in Porcine Hearts Using Optical Coherence Tomography.

Optical coherence tomography (OCT) employs near-infrared light to image the microstructure of different tissues. Clinically, it has been used to image the walls of coronary arteries. In research settings, one of the applications for OCT is visualizing endocardial and subendocardial structures. The present experiment sought to determine whether OCT can identify native conduction tissues in adult porcine hearts. During the study, the right atrial endocardial surfaces of excised adult porcine hearts were exposed. The triangle of Koch was imaged with the OCT system and the conduction tissue was identified. The area was then prepared for histologic examination with Masson’s trichrome stain. The results of histologic preparations and OCT images were then compared. Ultimately, nine porcine hearts were examined using this methodology. OCT imaging successfully identified subendocardial structures presumed to be the compact atrioventricular node. Histologic images of the preparations delineated the different tissue types and conduction tissue was easily identified. The location of distinctive hyporeflective areas in the OCT images correlated with the location of conduction tissue in the histology images. In light of the findings of this study, it is suggested that atrioventricular nodal tissue can be identified by OCT in freshly dissected unfixed porcine hearts. OCT images distinguished the differentiated conduction tissue in close proximity with the endocardium, myofibers, and fibrous tissue, and the success of this was verified with histology. This technology may be useful for the direct visualization of the native conduction system during procedures in the operating room and electrophysiology laboratory. Further studies with perfused tissue samples and live animal experiments are needed to better assess the efficacy of this novel application.

Disruption of RHOA-ROCK Signaling Results in Atrioventricular Block and Disturbed Development of the Putative Atrioventricular Node.

The RHOA-ROCK signaling pathway is involved in numerous developmental processes, including cell proliferation, differentiation and migration. RHOA is expressed in the atrioventricular node (AVN) and altered expression of RHOA results in atrioventricular (AV) conduction disorders in mice. The current study aims to detect functional AVN disorders after disturbing RHOA-ROCK signaling in chicken embryos. RHOA-ROCK signaling was inhibited chemically by using the Rho-kinase inhibitor compound Y-27632 in avian embryos (20 experimental and 29 control embryos). Morphological examination of control embryos show a myocardial sinus venosus to atrioventricular canal continuity, contributing to the transitional zone of the AVN. ROCK inhibited embryos revealed lateralization and diminished myocardial sinus venosus to atrioventricular canal continuity and at the severe end of the phenotype hypoplasia of the AVN region. Ex ovo micro-electrode recordings showed an AV conduction delay in all treated embryos as well as cases with first, second (Wenkebach and Mobitz type) and third-degree AV block which could be explained by the spectrum of severity of the morphological phenotype. Laser capture microdissection and subsequent qPCR of tissue collected from this region revealed disturbed expression of HCN1, ISL1, and SHOX2. We conclude that RHOA-ROCK signaling is essential for normal morphological development of the myocardial continuity between the sinus venosus and AVN, contributing to the transitional zone, and possibly the compact AVN region. Disturbing the RHOA-ROCK signaling pathway results in AV conduction disturbances including AV block. The RHOA-ROCK inhibition model can be used to further study the pathophysiology and therapeutic strategies for AV block. Anat Rec, 302:83-92, 2019. © 2018 Wiley Periodicals, Inc.

Morphological Substrates for Atrial Arrhythmogenesis in a Heart With Atrioventricular Septal Defect.

Due to advances in corrective surgery, congenital heart disease has an ever growing patient population. Atrial arrhythmias are frequently observed pre- and post-surgical correction. Pharmaceutical antiarrhythmic therapy is not always effective, therefore many symptomatic patients undergo catheter ablation therapy. In patients with atrioventricular septal defects (AVSD), ablation therapy itself has mixed success; arrhythmogenic recurrences are common, and because of the anatomical displacement of the atrioventricular node, 3-degree heart block post-ablation is a real concern. In order to develop optimal and safe ablation strategies, the field of congenital cardiac electrophysiology must combine knowledge from clinical electrophysiology with a thorough understanding of the anatomical substrates for arrhythmias. Using image-based analysis and multi-cellular mathematical modeling of electrical activation, we show how the anatomical alterations characteristic of an AVSD serve as arrhythmogenic substrates. Using ex-vivo contrast enhanced micro-computed tomography we imaged post-mortem the heart of a 5 month old male with AVSD at an isometric spatial resolution of 38 μm. Morphological analysis revealed the 3D disposition of the cardiac conduction system for the first time in an intact heart with this human congenital malformation. We observed displacement of the compact atrioventricular node inferiorly to the ostium of the coronary sinus. Myocyte orientation analysis revealed that the normal arrangement of the major atrial muscle bundles was preserved but was modified in the septal region. Models of electrical activation suggest the disposition of the myocytes within the atrial muscle bundles associated with the “fast pathway,” together with the displaced atrioventricular node, serve as potential substrates for re-entry and possibly atrial fibrillation. This study used archived human hearts, showing them to be a valuable resource for the mathematical modeling community, and opening new possibilities for the investigations of arrhythmogenesis and ablation strategies in the congenitally malformed heart.

Clarifying the anatomy of the atrioventricular node artery

BackgroundReports of conduction abnormalities necessitating permanent pacemaker implantation due to atrioventricular node artery injury and increasing evidence of stenosis of the atrioventricular node artery in cases of sudden death are of unsolved clinical importance. Unfortunately, technical issues associated with physical and virtual dissections of the atrioventricular conduction axis make it difficult to accurately assess its arterial supply. MethodsWe used a specialized dissection technique to gather anatomical information on the atrioventricular node artery and described them using attitudinally appropriate terminology. ResultsThe mean number of atrioventricular node artery branches was 1.6 in 103 submacroscopic examinations and 2.3 in 17 histological reconstructions. The artery had 5 origins in the modified AHA anatomy guidelines: distal RCA (#3), 10.4%; right posterior interventricular artery (#4PI), 7.3%; proximal RCA posterolateral branch (proximal #4PL), 76.8%; distal RCA posterolateral branch detouring the coronary sinus (distal #4PL), 1.8%; distal LCX (#13), 3.7%. Histological examination revealed that most atrioventricular node arteries immediately left the distal compact node (71.8%), suggesting that they supply mainly the proximal part of the AV conduction axis. The artery to the atrioventricular node tended to originate from the medial and atrial aspect of RCA posterolateral branch, and supplied adjacent structures within the inferior pyramidal space before entering the compact atrioventricular node. ConclusionsBased on the visualisation of the atrioventricular conduction axis and its arterial supply, we herein provide the ‘gold standard’ for understanding the origin, course and distribution of the artery to the atrioventricular node.

Histological topography of the atrioventricular node and its extensions in relation to the cardiothoracic surgical landmarks in normal human hearts.

Atrioventricular (AV) nodal injury which results in cardiac conduction disorders is one of the potential complications of heart valve surgeries and radiofrequency catheter ablations. Understanding the topography of the AV conduction system in relation to the tricuspid and mitral valves will help in reducing these complications. A tissue block of 3cmx4cm, which contain the AV node, bundle of His and the AV nodal extensions, was excised at the AV septal junction in 20 apparently normal human hearts. The block was divided into three equal segments through vertical incisions perpendicular to the insertion of the septal leaflet of the tricuspid valve. Each segment was processed and stained with H&E and Gomori to study the different parts of the AV conduction system. The lower pole of the AV node was located vertically above the tricuspid septal leaflet (TSL) in 100% (20/20) of cases and at the level of the muscular interventricular septum in 65% (13/20) of cases. The upper pole of the compact AV node was located at the level of the mitral valve leaflet (MVL) in 50% (10/20) of cases. The penetrating bundle of His was seen at the level of the TSL, while the branching bundle of His was situated 1.9±1.5 mm inferior to the TSL. The right and left posterior extensions of the AV node spanned from the MVL to 2.9±1.3 mm above the TSL. A rectangular area (2.5 mm × 12 mm) in the Koch's triangle was devoid of AV nodal tissue and could be labeled as a safe area with no risk of conduction defects during valve surgeries. Information on the separation of AV nodal extensions from the TSL, MVL and muscular interventricular septum may play a crucial role in guiding and improving the safety of radiofrequency ablations.

Diagnostic Perturbations.

Diagnostic Perturbations.

Microscopic Topography of Atrioventricular Conduction System–A Feature of Potential Clinical Significance

ObjectivesProximity of atrioventricular (AV) conduction system to tricuspid, mitral and aortic valves renders it susceptible to injury leading to disturbances in patients undergoing valve operations and radiofrequency catheter ablations. Hence, the knowledge of topography of AV conduction system and its relations with surrounding cardiac structures is indispensible.MethodsIn 20 cases, a tissue block of 3×4 cm at AV septal junction was excised which included the borders of Koch's triangle. The block was divided into three equal segments by parallel vertical incisions made perpendicular to insertion of septal leaflet of tricuspid valve. Each segment was processed for Hematoxylin &amp; Eosin and Gomori stain.ResultsThe upper pole of compact AV node was at the level of mitral valve leaflet in 50% cases. Lower pole of AV node was vertically above tricuspid septal leaflet and at the level of muscular IV septum in 100% and 66.7% cases respectively. The subendocardial depth of upper and lower pole of AV node was 1.45±0.6 mm and 0.92±0.3 mm respectively. Minimum subendocardial depth (0.68±0.2mm) was seen at the center of compact AV node. Penetrating bundle of His was seen at the level of tricuspid septal leaflet just deep to it, while Branching bundle of His was 1.98±1.5 mm below the tricuspid septal leaflet. AV nodal extensions began at the level of mitral valve leaflet while its inferior extension ended 2.92±1.3 mm above tricuspid septal leaflet.ConclusionPrior knowledge of distances of AV conduction system from the surrounding landmarks might help in surgical incision planning, safe suture placement and successful device insertion.Support or Funding InformationFrom Director PGIMER, Chandigarh, India.

Location.

Location.

GATA-Binding Factor 6 Contributes to Atrioventricular Node Development and Function.

Several transcription factors regulate cardiac conduction system (CCS) development and function but the role of each in specifying distinct CCS components remains unclear. GATA-binding factor 6 (GATA6) is a zinc-finger transcription factor that is critical for patterning the cardiovascular system. However, the role of GATA6 in the embryonic heart and CCS has never been shown. We report that Gata6 is expressed abundantly in the proximal CCS during midgestation in mice. Myocardial-specific deletion of the carboxyl zinc-finger of Gata6 induces loss of hyperpolarizing cyclic nucleotide-gated channel, subtype 4 staining in the compact atrioventricular node with some retention of hyperpolarizing cyclic nucleotide-gated channel, subtype 4 staining in the atrioventricular bundle, but has no significant effect on the connexin-40-positive bundle branches. Furthermore, myocardial-specific deletion of the carboxyl zinc-finger of Gata6 alters atrioventricular conduction in postnatal life as assessed by surface and invasive electrophysiological evaluation, as well as decreasing the number of ventricular myocytes and inducing compensatory myocyte hypertrophy. Myocardial-specific deletion of the carboxyl zinc-finger of Gata6 is also associated with downregulation of the transcriptional repressor ID2 and the cardiac sodium-calcium exchanger NCX1 in the proximal CCS, where GATA6 transactivates both of these factors. Finally, carboxyl zinc-finger deletion of Gata6 reduces cell-cycle exit of TBX3+ myocytes in the developing atrioventricular bundle during the period of atrioventricular node specification, which results in fewer TBX3+ cells in the proximal CCS of mature mutant mice. GATA6 contributes to the development and postnatal function of the murine atrioventricular node by promoting cell-cycle exit of specified cardiomyocytes toward a conduction system lineage.

A case of typical atrioventricular nodal (AVN) reentrant tachycardia confined to the compact AV node, showing a variety of rare electrophysiological findings, including eccentric AVN echoes

Herein, we report the case of a 49-year-old woman with typical atrioventricular nodal (AVN) reentrant tachycardia, confined to the compact atrioventricular node, showing numerous rare electrophysiological findings such as unique AVN reentrant echoes, double ventricular responses, latent retrograde dual AVN pathways, antegrade triple AVN pathways, and longitudinal dissociation within the lower final common pathway.