Normal Cardiac Anatomy

We report a case of sudden death in a 20 years old male who colapsed just minues after the beggining of a football training session. The autopsy evidenced the presence of a unique combination of coronary abnormalities: myocardial bridging at the level of both branches of the LCA; abnormal origin of the right coronary artery: 1 mm above the left semilunar valve of aorta; the initial segment of the RCA coursing within the aortic wall (0,7 cm); myocardial bridging at the level of LCX; sinoatrial node artery originated from the LCX. Histological examination revealed the presence of Hypertrophic Cardiomyopathy markers within the left ventricle and interventricular septum and the cumulative effects of the coronary cardiac anomalies on the myocardial blood flow: extensive interstitial and perivascular sclerolipomatosis, dissecting fibrosis at the level of the sinoatrial node, subendocardial hyaline fibrosis. 20 years old male, colapsed just several minues after the begining of a football training session. The ressuscitation attempts were unsuccesfull. He was recently transffered to a first league football team, and was considered a promissing goal keeper. The medical check-up, performed immediately after his transfer had not revealed any health problems. The autopsy evidenced several cardiac abnormal findings. The ostium of the right coronary artery (RCA) was identified above the left aortic sinus and the initial segment of the RCA coursed for 0.7 cm intramurally (fig. 3, 4), within the aortic wall, behind the pulmonary trunk (PT), before leaving the ascending aorta (AA) at the level of the right aortic sinus and finally resuming its normal position within the atrioventricular groove. RCA didn't give any branches until the posterior interventricular groove where, terminally, was divided in two branches: a short and threadlike one in the interventricular groove, and one which crossed over the left ventricle, after which it ended up in two short and threadlike branches on the diafragmatic face of the left ventricle. The main trunk of the left coronary artery (LCA) was 1 cm. long and coursed in the left part of the coronary groove, between the PT and the left atrial appendage (LAA); it was then divided into the anterior interventricular artery or left anterior descendent artery (LAD) and the circumflex artery (LCX). The initial segment of the LAD had a subepicardial trajectory within the anterior interventricular groove where the first diagonal branch of the left ventricle (LV) originated; in its course it went under two consecutive myocardial bridges, of 1.68 and, 2.22 cm respectively (fig. 1).

Concomitant with the development of catheter ablation techniques for the treatment of atrial arrhythmias, there is renewed interest in the morphologic arrangement of the cardiac conduction system. In this article, we revisit the anatomy of the specialized tissues, making special reference to the descriptions given at the time of their discovery. According to criteria for histologic distinction of morphologically specialized tracts set nearly 100 years ago, the penetrating bundle (of His) and the ventricular bundle branches are tracts of specialized cells encased by insulating sheaths of fibrous tissue. In contrast, the sinus and AV nodes are recognized histologically but are not insulated from the working atrial myocardium. At its distal extent, the AV node is distinguished from the penetrating bundle not so much by cellular characteristics, but by the presence of a fibrous collar that surrounds the specialized cells. At the atrial part, a zone of histologically transitional cells interposes between the compact node and the working atrial myocardium. Transitional cells enter the triangle of Koch to join the compact node from superiorly, inferiorly, posteriorly, and from the left. Transitional cells of the sinus node, in contrast, are limited to short tongues that interdigitate with musculature of the terminal crest. Apart from a variable extension of its tail, there are no prominent histologically discrete extensions from the sinus node into the working atrial musculature. The internodal myocardium does not contain discrete conducting tracts comparable with the ventricular bundle branches. Preferential conduction more likely reflects the arrangement of the working internodal cells and their related cellular properties.

Role of pacemaking current in cardiac nodes: Insights from a comparative study of sinoatrial node and atrioventricular node

BackgroundThe symptomatic bradyarrhythmia is Class I indication for pacing therapy which is not a radical cure. The present study aimed to assess the feasibility and to present the initial results of the restricted ablation of the parasympathetic innervation surrounding sinus and atrioventricular (AV) nodes for treating patients with bradyarrhythmia.MethodsA total of 13 patients with cardiogenic syncope were included from May 2008 to June 2015. Under the guidance of fluoroscopy and /or three-dimensional geometry by 64-slice spiral computed tomography, atrial activation sequence in sinus rhythm was mapped. Chamber geometry was reconstructed manually or automatically using the Niobe II magnetic navigation system integrated with the CARTO-remote magnetic technology (RMT) system. Cardioneuroablation was targeted at the high-amplitude fractionated electrograms surrounding the regions of His bundle and the site with the earliest activation in sinus rhythm. Areas surrounding the sinus node, AV node, and the phrenic nerve were avoided.ResultsThirteen patients completed the studies. Ablation was successfully performed in 12 patients and failed in one. The high-frequency potential was recorded in atrial electrograms surrounding the sinus or AV nodes in all the patients and disappeared in 15 s after radiofrequency applications. The vagal reaction was observed before the improvement of the sinus and AV node function. No complications occurred during the procedures. Patients were followed up for a mean of 13.0 ± 5.9 months. During the follow up ten patients remained free of symptoms, and two patients had a permanent cardiac pacemaker implanted due to spontaneous recurrence of syncope. The heart rate of post-ablation was higher than pre-ablation (69.0 ± 11.0 vs. 49.0 ± 10.0 beats/min, t = 4.56, P = 0.008). The sinus node recovery time, Wenckebach block point, and atrium-His bundle interval were significantly shorter after ablation (1386.0 ± 165.0 vs. 921.0 ± 64.0 ms, t = 7.45, P = 0.002; 590.0 ± 96.0 vs. 464.0 ± 39.0 ms, t = 2.38, P = 0.023; 106.0 ± 5.0 vs. 90.0 ± 12.0 ms, t = 9.80, P = 0.013 before and after ablation procedure, respectively).ConclusionsAblation of sinoatrial and AV nodal peripheral fibrillar myocardium electrical activity might provide a new treatment to ameliorate paroxysmal sinus node dysfunction, high degree AV block, and vagal-mediated syncope.

Bachmann’s bundle (BB), also known as the interatrial bundle, is well recognized as a muscular bundle comprising of parallel aligned myocardial strands connecting the right and left atrial walls and is considered to be the main pathway of interatrial conduction.1 Disruption of the bundle’s structure causes interatrial conduction block (IAB),2 which is associated with development of various atrial tachyarrhythmias3,4 and with electromechanical dysfunction of the left atrium.5 Technological progress providing sophisticated mapping and imaging techniques in the past decade has increased our knowledge of specific anatomic structures and their role in development of both atrial brady- and tachyarrhythmias. This review outlines the current knowledge of the relation between anatomic and electrophysiological properties of BB and its possible role in initiation and perpetuation of atrial fibrillation (AF). In 1963, Thomas N. James described 3 pathways connecting the sinus node to the atrioventricular node (AVN), namely the anterior, medial, and posterior internodal pathways.6 Whether these conduction pathways were because of the presence of specialized conduction tissue or because of the anisotropic orientation of the muscle fibers remains controversial. Nevertheless, James described the anterior pathway as leaving the sinus node in anterior direction and giving off a secondary branch at the level of the superior vena cava to form BB.1 BB stretches subepicardially across the interatrial groove (septal raphe). It is at the interatrial groove that the BB can be identified as a discrete bundle (Figures 1 and 2) separated by fatty tissues from the infolded right atrial wall that is the limbus of the oval fossa. Notably, the bundle is not surrounded by a fibrous tissue sheath. Instead, the bundle is comprised of strands of atrial myocardium that are similarly aligned in parallel fashion. Its rightward and leftward extensions bifurcate to pass to either …

Following radiofrequency catheter ablation of AV nodal reentrant tachycardia (AVNRT), inappropriate sinus tachycardia may occur, possibly due to damage to autonomic cardiac nerve fibers. Furthermore, inducibility of AVNRT is often critically dependent on the autonomic balance. We investigated whether successful ablation of AVNRT is associated with an alteration of autonomic input to the sinus and AV nodes. To estimate changes in the autonomic modulation of the sinus and AV nodes, power spectra of beat-to-beat PP and PR intervals were analyzed from high-quality nighttime ECG recordings of 11 patients before and after radiofrequency application. Normalized HF power (nHF) of PP and PR intervals was used as an index of efferent vagal modulation and the LF/HF ratio as an index of sympathovagal balance of the sinus node (PP) and AV node (PR). Before ablation, LF/HF(PP) was 3.2 and nHF(PP) was 0.3 in the sinus node. For the AV node, LF/HF(PR) was 1.2 and nHF(PR) was 0.5. Following ablation, LF/HF(PP) (3.5) and nHF(PP) (0.3) of the PP intervals did not change. Similarly to the sinus node, there were no changes in the autonomic modulation of the AV node, as both LF/HF(PR) (1.2) and nHF(PR) (0.5) remained unchanged. Our results indicate that autonomic control of the sinus and AV nodes is preserved following successful radiofrequency ablation of AVNRT. The effects of posteroseptal radiofrequency current application are not necessarily mediated by changes in the autonomic input to the AV node.

BackgroundEpicardial adipose tissue (EAT) is a fat depot with secretive and neuromodulative properties, involved in the pathogenesis of cardiovascular diseases. Transfusion-dependent β-thalassemia (TDβT) is an inherited disorder characterized by chronic anemia and at risk for the development of several comorbidities. Patients with TDβT have a higher incidence of cardiovascular diseases compared to the general population.MethodsThe aim of this study was to evaluate EAT thickness in a cohort of patients with TDβT (study group), compared to age- and sex-balanced patients with no TDβT (control group). Secondary endpoint included evaluation of differences in the regional distribution of EAT between patients with or without cardiovascular disease (NCT05508932).ResultsOverall, 272 patients were enrolled, of whom 136 in study group and 136 in control group. EAT thickness was significantly higher in the study group at left atrium, left atrioventricular groove and right atrioventricular groove compared to control group (4.2 vs. 3.0, 12.2 vs. 10.0 and 13.0 vs. 11.0 mm, respectively, p < 0.05 for all). Multivariable analysis confirmed an independent association between EAT and TDβT. The regional distribution of EAT showed significant differences between patients with or without atrial fibrillation, diabetes mellitus, stroke or heart failure.ConclusionsPatients with TDβT have higher values of EAT compared to controls with no TDβT.Graphical abstractCentral illustration

Little is known about the electrophysiological characteristics of telocytes found in the working myocardium and sinoatrial node (SAN). Telocyte expres -sion of HCN4 suggests the ability to generate pacemaker potentials. To prove the impulse conduction, the presence of voltage-gated sodium channels is required. It is assumed that telocytes are also located in the atrioventricular node (AVN). Aim . Morphological and electrophysiological study of AVN and SAN telocytes. Material and methods. Fragments of the right atrium, AVN of 7 hearts of recipients and 3 hearts of pigs were taken, respectively, during heart transplantation and after the experiment. Isolation of telocyte cultures, histological, immunohis tochemical tests with anti-CD117, anti-NaV1.5 (SCN5A), anti-CD34 antibodies, intravital confocal laser microscopy were carried out. The patch-clamp technique was used. Results . In AVN cultures, CD117 + cells with long processes were found. There was a potassium current with a density of 700 pA/pF during membrane depolarization up to +90 mW in humans and pigs using the patch-clamp technique. Calcium oscillations with a period of about 200 seconds in a pig with an increase in calcium concentration. In elongated cells located between cardiomyocytes and among the fibrous tissue of SAN perifocal zone, the co-expression of anti-NaV1.5 and anti-CD34 antibodies was revealed. Conclusion . In AVN, telocytes were found, in whose cultures potassium current and calcium oscillations were determined. SCN5A sodium channels were found in telocytes of the perifocal area of human SAN. This fact indicates the ability of cells to conduct an electrical impulse.

Previous studies have suggested that maintained vagal stimulation or acetylcholine infusion results in a fade of responses in the sinoatrial node but not in the atrioventricular node, implying different muscarinic receptor subtypes in the two regions. We investigated this hypothesis in 23 isolated rabbit atrial preparations made quiescent by continuous superfusion with verapamil (1 microgram/ml). Transmembrane potentials were recorded simultaneously from cells in the sinoatrial pacemaker region and from the "N" region of the atrioventricular node. Postganglionic vagal stimulation was achieved by the application of trains of pulses (50-150 microseconds; 10-20 V; 200 Hz). Simultaneous application of long-lasting (1-10 sec) vagal trains produced hyperpolarizations which were nearly identical for both nodal regions. Maximal hyperpolarizations (approximately or equal to 24 mV for sinoatrial node; 26 mV for atrioventricular node) were reached about 500 msec after initiation of the vagal train. Thereafter, hyperpolarizations faded, following a biphasic time course, and thus displaying two different time constants, one fast (tau fast = 580 msec for sinoatrial node; 550 msec for atrioventricular node), and one slow (tau slow = 9.2 sec for both sinoatrial and atrioventricular nodes). Hyperpolarizations during brief (200-msec) but repetitive vagal trains also faded biphasically, but approached a steady state much more rapidly than responses to long-lasting trains. Recovery from hyperpolarization decay occurred rather slowly and was linear. Our results demonstrate that the membrane potential responses to vagal stimulation in the atrioventricular node are indistinguishable from those in the sinoatrial node, and suggest that similar muscarinic receptors are operative in both regions. These phenomena may play an important role in the response of the cardiac conducting system to direct or reflexly mediated vagal input.

The immunocytochemical demonstration of a relative lack of nerve fibres in the atrioventricular node and bundle of His in the sudden infant death syndrome (SIDS)

The proximity to vascular structures is a limiting factor during radiofrequency ablation. However, little or no attention has been given to the atrial arterial circulation during the development of atrial fibrillation (AF) catheter ablation techniques. We examined the atrial arterial circulation in areas involved in AF ablation in 24 heart specimens by colored resin injection and careful dissection. The sinus node artery (SNA) arose from the circumflex artery in 42% of case; proximal to the LA appendage in 29%, crossing the left atrium (LA) anterior wall; and after the LA appendage in the remaining 13%, crossing the mitral isthmus and passing close to the left pulmonary veins (PVs), the LA roof, and the right superior PV. In 58%, the SNA arose from the right coronary artery. Major arteries (≥ 1 mm in external diameter) were found in the mitral isthmus in 54%, at the LA roof in 54%, and at the LA anterior wall in 29%. Around the left PV ostia, there were areas with major arteries in up to 37% (at the roof and inferior segments) and around the right PV ostia in up to 29% (at the roof segment). Major atrial coronary arteries, including the SNA, were commonly found in the areas involved in AF ablation and could cause difficulties in obtaining transmural lesions and electric isolation or even lead to ischemic sinus node or atrial dysfunction.

AIUM Practice Parameter for the Performance of Fetal Echocardiography.

Two-dimensional echocardiographic identification of high anatomically inserted venous atrioventricular valve in the diagnosis of corrected transposition of the great arteries

Dimensions of the left ventricle, atrium, and aortic root in pregnancy-induced hypertension

The present study sought to characterize vagally induced desensitization at the sinoatrial (SA) node of the intact dog and to determine whether these findings could be extended to atrioventricular (AV) Nodal conduction. Autonomically decentralized anesthetized dogs were instrumented to record electrocardiograms, arterial pressure, and electrograms from the SA node, right atrium, right ventricle, and His bundle. During right- or left-vagal stimulation for 60 s, cycle length (CL) increased initially, followed by a gradual recovery toward control during stimulation; atrio-His (AH) interval remained prolonged throughout the stimulation. Atrial drive increased AH interval during stimulation, but AH prolongation was maintained throughout the stimulation period. To rule out acetylcholine (ACh) depletion, ACh was administered before and during vagal stimulation. Although control CL and AH interval were lengthened by ACh, no significant CL increases occurred when ACh was given during stimulation, but the AH interval became longer. Propranolol increased control CL and AH interval but did not alter the relationship between vagal stimulation and CL or AH interval. Thus the negative chronotropic effect of ACh at the SA node is diminished upon prolonged vagal stimulation, whereas the negative dromotropic effect upon AV nodal conduction remains unaltered. These results suggest differences in muscarinic receptor behavior at the SA and AV nodes.