Lack of evidence for longitudinal dissociation of the atrioventricular conduction axis.

Longitudinal dissociation of the aggregated specialized cardiomyocytes within the non-branching portion of atrioventricular conduction axis has proved a controversial topic for both morphologists and electrophysiologists. We have now used morphological methods, including three-dimensional assessment, to revisit, in human, canine, and bovine hearts, the presence or absence of interconnections between the aggregated cardiomyocytes making up the non-branching bundle. We analyzed three datasets from human and canine hearts, and two from bovine hearts, using longitudinal and orthogonal serial histological sections. In addition, we assessed three hearts using translucent India ink injected specimens, permitting assessment of the three-dimensional arrangement of the cardiomyocytes. Using the longitudinal sections, we found numerous oblique interconnections between the groups of specialized cardiomyocytes. When assessing orthogonal sections, we noted marked variation in the grouping of the cardiomyocytes. We interpreted this finding as evidence of bifurcation and convergence of the groups seen in the longitudinal sections. The three-dimensional assessment of the bovine material confirmed the presence of the numerous interconnections. The presence of multiple connections between the cardiomyocytes in the non-branching bundle rules out the potential for longitudinal dissociation.

Hallazgo de una hiperplasia lipomatosa del septum interauricular en un caso de muerte súbita / Finding of a lipomatous hyperplasia in the interatrial septum in a case of sudden death

La hiperplasia lipomatosa del septum interauricular (HLSI) es una entidad benigna de naturaleza desconocida que se caracteriza por la acumulación de grasa no encapsulada en el interior del surco interauricular sin participación de la fosa oval. A pesar de su carácter benigno, clínicamente se ha asociado con arritmias cardiacas, generalmente de origen supraventricular, insuficiencia cardiaca y muerte súbita. Presentamos el caso de una mujer de edad media (47 años), con obesidad mórbida e insuficiencia cardiaca congestiva, que falleció súbitamente y la autopsia puso de manifiesto una HLSI. El estudio macroscópico de la pieza de resección mostró un tamaño de 5 x 2,5 cm y la histología típica de esta entidad, es decir, adipocitos maduros y pocos lipoblastos entremezclados con miocitos auriculares. Hemos analizado microscópicamente los nodos sinoauricular y auriculoventricular, lo que puso de manifiesto que la infiltración grasa los rodeada pero no los aislaba del miocardio auricular de trabajo circundante. El miocardio del ventrículo izquierdo y del tabique interventricular presentaba áreas con una intensa fibrosis intersticial por isquémica crónica y que esta fibrosis pudo ser la causa de una arritmia ventricular y muerte súbita. Aunque esta entidad es cada vez más frecuentemente reconocida gracias al desarrollo creciente de las técnicas de imagen no invasivas, rara vez necesita ser corregida quirúrgicamente (AU)

The lipomatous hyperplasia of the interatrial septum (LHIS) is a benign entity of unknown nature, characterized by the accumulation of fat tissue not encapsulated into the interatrial groove without participation of the fossa ovalis. Despite its benign nature, it has been clinically associated with cardiac arrhythmias, usually of supraventricular origin, heart failure and sudden death. We present the case of a woman of middle age (47 years), with morbid obesity and heart failure congestive who died suddenly and the autopsy revealed a LHIS. The macroscopic study of resection piece showed a size of 5 x 2.5 cm and the typical histology of this entity, i.e. mature adipocytes and few lipoblastos interspersed with atrial myocytes. We have analysed microscopically both sinoatrial and atrioventricular nodes, which they revealed fat tissue infiltration that surrounded them but not isolated from atrial working myocardium. The interventricular septum and left ventricle myocardium presented areas with severe interstitial fibrosis by chronic ischemic and this fibrosis may be the cause of ventricular arrhythmia and sudden death. Although this entity is most frequently recognized due to the development of noninvasive imaging techniques, rarely needs to be corrected surgically (AU)

Topology and conduction in the inferior right atrial isthmus measured in rabbit hearts.

The inferior right atrial isthmus consisting of the terminal crest, the network of pectinate muscles, and the vestibule shows very complex anatomical structure. It is seen as potential substrate for atrial flutter. In this work we present results from an electro-anatomical characterization of this region based on Cardiac Near Field recordings taken from five preparations of rabbit atrium. Pectinate muscles in the region of interest were divided into three segments: central as well as proximal and distal with respect to the terminal crest. Electrograms measured in these segments showed differences in the degree of fractionation, i.e. the numbers of distinct local activation events, indicating heterogeneities in microstructure. From 249 recording sites 63.9% showed no fractionation, 26.9% showed two activation events, and 9.2% were highly fractionated. The proximal starting sequence of activation in a series of adjacent pectinate muscles is not sorted but rather seems to be arbitrary. The same applies to the arrival sequence of activation close to the vestibule. In the network of pectinate muscles on average one proximal segment branches into two central strands and two central strands merge into one distal stem.

The importance of atrial structure and fibers.

Atrial structures are important in the current era of cardiac interventions using percutaneous transcatheter procedures. Understanding their locations and component parts helps to reduce risks of procedural-related damage. The general arrangement of the myofibers that make up the atrial walls is reviewed to provide a morphologic basis for atrial conduction and potential substrates of arrhythmias. The right atrium, dominated by its appendage, is characterized by having an extensive array of pectinate muscles. These extend almost perpendicularly from the terminal crest. The left atrium has relatively smooth walls and a small tubular-shaped appendage. The myofibers show changes in orientations when traced through the thickness of the walls. Extensions of atrial myocardium onto the pulmonary veins and the superior caval vein are common. Apart from Bachmann's bundle, there are other muscular bridges of variable numbers and sizes that provide interatrial connections, connections between the left atrium and the coronary sinus, and connections between the muscular sleeves of the right pulmonary veins and the right atrium. The purpose of this review is to summarize the three-dimensional arrangement of gross atrial structures, the myoarchitecture and variations in muscular interatrial connections. These are important features in intra- and interatrial conduction.

A new floating sensor array to detect electric near fields of beating heart preparations.

A new flexible sensor for in vitro experiments was developed to measure the surface potential, Phi, and its gradient, E (electric near field), at given sites of the heart. During depolarisation, E describes a vector loop from which direction and magnitude of local conduction velocity theta can be computed. Four recording silver electrodes (14 microm x 14 microm) separated by 50 microm, conducting leads, and solderable pads were patterned on a 50 microm thick polyimide film. The conductive structures, except the electrodes, were isolated with polyimide, and electrodes were chlorided. Spacer pillars mounted on the tip fulfil two functions: they keep the electrodes 70 microm from the tissue allowing non-contact recording of Phi and prevent lateral slipping. The low mass (9.1 mg) and flexibility (6.33 N/m) of the sensor let it easily follow the movement of the beating heart without notable displacement. We examined the electrodes on criteria like rms-noise of Phi, signal-to-noise ratio of Phi and E, maximum peak-slope recording dPhi/dt, and deviation of local activation time (LAT) from a common signal and obtained values of 24-28 microV, 46 and 41 dB, 497-561 V/s and no differences, respectively. With appropriate data acquisition (sampling rate 100 kHz, 24-bit), we were able to record Phi and to monitor E and theta on-line from beat-to-beat even at heart rates of 600 beats/min. Moreover, this technique can discriminate between uncoupled cardiac activations (as occur in fibrotic tissue) separated by less than 1 mm and 1 ms.

Sinus node revisited in the era of electroanatomical mapping and catheter ablation.

OBJECTIVE: To study the architecture of the human sinus node to facilitate understanding of mapping and ablative procedures in its vicinity. METHODS: The sinoatrial region was examined in 47 randomly selected adult human hearts by histological analysis and scanning electron microscopy. RESULTS: The sinus node, crescent-like in shape, and 13.5 (2.5) mm long, was not insulated by a sheath of fibrous tissue. Its margins were irregular, with multiple radiations interdigitating with ordinary atrial myocardium. The distances from the node to endocardium and epicardium were variable. In 72% of the hearts, the whole nodal body was subepicardial and in 13 specimens (28%) the inner aspect of the nodal body was subendocardial. The nodal body cranial to the sinus nodal artery was more subendocardial than the remaining nodal portion, which was separated from the endocardium by the terminal crest. In 50% of hearts, the most caudal boundaries of the body of the node were at least 3.5 mm from the endocardium. When the terminal crest was > 7 mm thick (13 hearts, 28%), the tail was subepicardial or intramyocardial and at least 3 mm from the endocardium. CONCLUSIONS: The length of the node, the absence of an insulating sheath, the presence of nodal radiations, and caudal fragments offer a potential for multiple breakthroughs of the nodal wavefront. The very extensive location of the nodal tissue, the cooling effect of the nodal artery, and the interposing thick terminal crest caudal to this artery have implications for nodal ablation or modification with endocardial catheter techniques.

[Anatomy of the atria for rhythmologists]. / Anatomie des oreillettes à l'usage des rythmologues.

The anatomy of the atria is always in the mind of interventional rhythmologists. There is a mental superposition of the anatomical structures and the references obtained by different incidences of fluoroscopy and the endocavitary electrocardiogram. But understanding the anatomy also requires a certain knowledge of dissection to determine, for example, the orientation of bundles of muscle fibres and anatomical sections. The sino-atrial node is situated at a distance from the endocardium. It is long and protected by its own artery which makes it difficult to reach. The atrio-ventricular node has multiple posterior expansions which correspond to the sites where radiofrequency ablation is effective. The cavo-tricuspid isthmus is the target zone for the treatment of atrial flutter but radiofrequency ablation which must be long may be applied at three different levels: inferolateral, median (the most common site) or inferoseptal. Finally, atrial fibrillation has incited many studies of the muscular extensions of the left atrium to the pulmonary veins, the morphological variations of these veins and the organisation of the muscle fibres of the left atrial wall. They have inspired new concepts of atrial fibrillation.

The terminal crest: morphological features relevant to electrophysiology.

OBJECTIVE: To investigate the detailed anatomy of the terminal crest (crista terminalis) and its junctional regions with the pectinate muscles and intercaval area to provide the yardstick for structural normality. DESIGN: 97 human necropsy hearts were studied from patients who were not known to have medical histories of atrial arrhythmias. The dimensions of the terminal crest were measured in width and thickness from epicardium to endocardium, at the four points known to be chosen as sites of ablation. RESULTS: The pectinate muscles originating from the crest and extending along the wall of the appendage towards the vestibule of the tricuspid valve had a non-uniform trabecular pattern in 80% of hearts. Fine structure of the terminal crest studied using light and scanning electron microscopy consisted of much thicker and more numerous fibrous sheaths of endomysium with increasing age of the patient. 36 specimens of 45 (80%) specimens studied by electron microscopy had a predominantly uniform longitudinal arrangement of myocardial fibres within the terminal crest. In contrast, in all specimens, the junctional areas of the terminal crest with the pectinate muscles and with the intercaval area had crossing and non-uniform architecture of myofibres. CONCLUSIONS: The normal anatomy of the muscle fibres and connective tissue in the junctional area of the terminal crest/pectinate muscles and terminal crest/intercaval bundle favours non-uniform anisotropic properties.

Architecture of the pulmonary veins: relevance to radiofrequency ablation.

BACKGROUND: Radiofrequency ablation of tissues in pulmonary veins can eliminate paroxysmal atrial fibrillation. OBJECTIVE: To explore the characteristics of normal pulmonary veins so as to provide more information relevant to radiofrequency ablation. METHODS: 20 structurally normal heart specimens were examined grossly. Histological sections were made from 65 pulmonary veins. RESULTS: The longest myocardial sleeves were found in the superior veins. The sleeves were thickest at the venoatrial junction in the left superior pulmonary veins. For the superior veins, the sleeves were thickest along the inferior walls and thinnest superiorly. The sleeves were composed mainly of circularly or spirally oriented bundles of myocytes with additional bundles that were longitudinally or obliquely oriented, sometimes forming mesh-like arrangements. Fibrotic changes estimated at between 5% and 70% across three transverse sections were seen in 17 veins that were from individuals aged 30 to 72 years. CONCLUSIONS: The myocardial architecture in normal pulmonary veins is highly variable. The complex arrangement, stretch, and increase in fibrosis may produce greater non-uniform anisotropic properties.

Topographic anatomy of the inferior pyramidal space: relevance to radiofrequency catheter ablation.

INTRODUCTION: Radiofrequency catheter ablation carried out in the vicinity of the triangle of Koch risks damaging not only the AV conduction tissues but also their arterial supply. The aim of this study was to examine the relationship of the AV nodal artery to the inferior pyramidal space, the triangle of Koch, and the right atrial endocardial surface. METHODS AND RESULTS: We studied 41 heart specimens, 24 by gross dissections and 17 by histologic sections. The proximity of the AV nodal artery to the surface landmarks of the triangle of Koch was variable, but it was notable that in 75% of specimens the artery passed close to the endocardial surface of the right atrium and within 0.5 to 5 mm of the mouth of the coronary sinus. In all specimens, the mean distance of the artery to the endocardial surface was 3.5 +/- 1.5 mm at the base of Koch's triangle. The location of the compact AV node and its inferior extensions varied within the landmarks of the triangle. At the mid-level of Koch's triangle, the compact node was medially situated in 82% of specimens, but it was closer to the hinge of the tricuspid valve in the remaining 18% of specimens. In 12% of specimens, the inferior parts of the node extended to the level of the mouth of the coronary sinus. CONCLUSION: The nodal artery runs close to the orifice of the coronary sinus, the endocardial surface of the right atrium, the middle cardiac vein, and the specialized conduction tissues in most hearts. The nodal artery and/or the AV conduction tissues can be at risk of damage when ablative procedures are carried out at the base of the triangle of Koch.

Late ventricular structure after partial left ventriculectomy.

Nine months after partial ventriculectomy, a 53-year-old man died of progressive heart failure. His heart was examined to determine the alignment of the muscle fibers around the ventricular scar, which was 11 cm long, 1.3 cm thick and 4 cm wide. The scar reached 2 to 12 mm beyond the surgical suture line. The fibers in the middle and subendocardial layers were malaligned, resulting in convergence, compression and regional necrosis.

Anatomy of the left atrium: implications for radiofrequency ablation of atrial fibrillation.

INTRODUCTION: The feasibility of treating atrial fibrillation with radiofrequency ablation has revived interest in the structure of the left atrium, a chamber that has been neglected in many textbooks of anatomy. METHODS AND RESULTS: We reviewed the gross structure of the left atrium by examining the septum, the appendage, and insertions of the pulmonary veins in normal hearts. The limited extent of the true septal component is relevant to procedures using the transseptal approach. On gross examination, the musculature of the atrial wall is composed of overlapping bundles of aligned fibers that, in the majority of hearts, are arranged in characteristic patterns with only minor individual variations. Muscular sleeves extend into the walls of the pulmonary veins to varying distances. The longest sleeves are in the left upper veins. Bachmann's bundle anteriorly, and other smaller bundles superiorly and posteriorly, bridge the septal raphe to blend with musculature of the right atrium. Tongues of left atrial musculature from the posterior wall also extend into the wall of the coronary sinus. CONCLUSION: The left atrium is more complex than usually conceived. Understanding its structure, and the arrangement of its musculature, will help in improving strategies for linear lesions when attempting to compartmentalize the chamber, or when placing focal lesions for ablating ectopic sources.

Angiographic anatomy of the inferior right atrial isthmus in patients with and without history of common atrial flutter.

BACKGROUND: Although most ablative procedures undertaken for common atrial flutter target the inferior right atrial isthmus, comparative studies of the morphology of this area are lacking. Our study examines its angiographic anatomy, making correlations with postmortem specimens, to provide a better understanding of the anatomic substrate of this arrhythmia. METHODS AND RESULTS: The gross morphological features and dimensions of the area between the orifice of the inferior caval vein and the attachment of the septal leaflet of the tricuspid valve were determined from angiograms made in 23 patients with documented atrial flutter and 30 control subjects. For comparison, we studied 20 normal heart specimens. When viewed in right anterior oblique projection, 2 morphologically distinct areas were identified. In the specimens, the inferior isthmus measured a mean length of 30+/-4 mm, not significantly different from the dimensions obtained from angiograms of control subjects. The mean length of the isthmus, however, was greater in patients with common atrial flutter than those without (37+/-8 versus 28+/-6 mm). Patients with atrial flutter and structural heart disease had an even longer isthmus than those with flutter alone (39. 6+/-8 versus 33+/-7 mm). Compared with those without flutter, the atrial diameter was also larger in patients with flutter (57.6+/-9 versus 48.5+/-6 mm). Reevaluation carried out at follow-up 10+/-2 months after ablation did not show any reduction in atrial size, although contractility improved. CONCLUSIONS: The inferior isthmus and right atrium in patients with common atrial flutter were significantly larger than those in a control population.

Myoarchitecture and connective tissue in hearts with tricuspid atresia.

OBJECTIVE: To compare the atrial and ventricular myoarchitecture in the normal heart and the heart with tricuspid atresia, and to investigate changes in the three dimensional arrangement of collagen fibrils. METHODS: Blunt dissection and cell maceration with scanning electron microscopy were used to study the architecture of the atrial and ventricular musculature and the arrangement of collagen fibrils in three specimens with tricuspid atresia and six normal human hearts. RESULTS: There were significant modifications in the myoarchitecture of the right atrium and the left ventricle, both being noticeably hypertrophied. The middle layer of the ventricle in the abnormal hearts was thicker than in the normal hearts. The orientation of the superficial layer in the left ventricle in hearts with tricuspid atresia was irregular compared with the normal hearts. Scanning electron microscopy showed coarser endomysial sheaths and denser perimysial septa in hearts with tricuspid atresia than in normal hearts. CONCLUSIONS: The overall architecture of the muscle fibres and its connective tissue matrix in hearts with tricuspid atresia differed from normal, probably reflecting modelling of the myocardium that is inherent to the malformation. This is in concordance with clinical observations showing deterioration in pump function of the dominant left ventricle from very early in life.

The architecture of the atrial musculature between the orifice of the inferior caval vein and the tricuspid valve: the anatomy of the isthmus.

INTRODUCTION: Electrophysiologists recognize a so-called "isthmus" in the right atrium through which passes the reentrant circuit of common atrial flutter. Ablative lesions placed in this narrow channel have proved effective in breaking the circuit. To the best of our knowledge, however, no study has been performed to establish the arrangement and orientation of the atrial myocardial fibers in this crucial area. METHODS AND RESULTS: We examined 28 normal heart specimens, identifying a quadrilateral area composed of three morphologic sectors between the inferior caval vein and the tricuspid valve confluent superiorly with the triangle of Koch. Within this quadrilateral, there are constant recesses, or sinuses, inferior and lateral to the orifice of the coronary sinus. The inferior isthmus measured an average of 31+/-4 mm (range 19 to 40). Gross examination identified marked differences in the atrial wall forming the quadrilateral. A smooth anterior component forming the vestibule of the tricuspid valve was found in all the hearts, but variations in the remaining sectors were seen in ten specimens. The usually membranous posterior sector was noticeably muscular in three specimens, while the middle, trabecular sector was more membranous in five specimens. We demonstrated the orientation of the subendocardial atrial fibers by dissection in 14 specimens, revealing a relatively constant overall pattern in eight specimens and variations in fiber orientation in the remaining specimens. CONCLUSION: There are considerable anatomic variations in the atrial wall that comprises the so-called isthmus. The presence of recesses and membranous areas in some hearts and the variations in arrangement of the subendocardial fibers are relevant in improving understanding of conduction in this area.

Anisotropic conduction in the triangle of Koch of mammalian hearts: electrophysiologic and anatomic correlations.

OBJECTIVES: The purpose of this study was to characterize anisotropy in the triangle of Koch by relating electrophysiology with anatomy. BACKGROUND: Atrioventricular (AV) node fast and slow pathway characteristics have been suggested to be due to nonuniform anisotropy in the triangle of Koch. METHODS: During atrial pacing, we determined the electrical activity within the triangle of Koch by multichannel mapping in 11 isolated hearts from pigs and dogs. Orientation of fibers was determined in nine hearts. RESULTS: Fibers were parallel to the tricuspid valve annulus (TVA) in the posterior part of the triangle of Koch. In the midjunctional area, the direction of the fibers changed to an orientation perpendicular to the TVA. During stimulation from posterior and anterior sites, activation proceeded parallel to the TVA at a high conduction velocity (0.5 to 0.6 m/s). During stimulation from sites near the coronary sinus, a narrow zone of slow conduction occurred in the posterior part of the triangle of Koch where activation proceeded perpendicular to the fiber orientation. Above and below this zone, conduction was fast and parallel to the annulus. After premature stimulation, conduction delay in the triangle of Koch increased by 4 to 21 ms; in contrast, the AH interval increased by 80 to 210 ms. CONCLUSIONS: Data support the concept of anisotropic conduction in the triangle of Koch. Activation maps correlated well with the arrangement of superficial atrial fibers. Comparison of conduction delay in the triangle of Koch and AH delay after premature stimulation disproves that anisotropy in the superficial layers plays an important role in slow AV conduction.

Architecture of the atrial musculature in and around the triangle of Koch: its potential relevance to atrioventricular nodal reentry.

INTRODUCTION: Recent studies suggest that atrial fibers in the approaches to the AV node form part of the dual pathways recognized electrophysiologically in patients with AV nodal reentrant tachycardia (AVNRT). Our aim was to determine, by gross dissection, the arrangement of the superficial musculature in the area of the triangle of Koch in normal hearts and in hearts with documented AVNRT, hoping to ascertain anatomic features that might contribute to the debate. METHODS AND RESULTS: We used blunt dissection to study the architecture of the superficial atrial musculature in 16 autopsied hearts from adults who died of noncardiac disease. A well-defined pattern of architecture of muscle fibers was found in the region of the triangle of Koch, showing marked variations in 7 of the 16 specimens. The relationship of these fibers to the histologically specialized AV node was confirmed by histology in three cases. Two hearts from patients with known AVNRT, treated by ablation in one, were examined further histologically. These sections showed that the site of ablation was well distant from the histologically discrete AV node. CONCLUSION: The variability in the arrangement of the superficial atrial muscle fibers in the area of the triangle of Koch may be one of the factors influencing the route for impulses entering the AV node. Lesions that ablate nodal reentry are within these atrial fibers rather than the histologically specialized AV node.

Ventricular myoarchitecture in tetralogy of Fallot.

BACKGROUND: Little attention has been paid to the architecture of the muscle fibres of the ventricular walls in congenitally malformed hearts. In this study the gross pattern of myocardial fibres in normal hearts was compared with that in cases of tetralogy of Fallot. METHODS AND RESULTS: After morphological examination nine specimens with tetralogy were dissected to study the ventricular myoarchitecture. Changes were found in the shape of the malformed ventricles. The ventricular walls were arranged in layers in all hearts. Superficial and deep layers were present in both ventricles, with the superficial layer showing a more oblique orientation in the specimens with tetralogy than in normal hearts. Modifications of muscle fibre that were related to the type of malformation were seen in the deep layer. A middle layer was present in the left ventricles of normal hearts and specimens with tetralogy: this showed a horizontal orientation in both groups. In contrast, a middle layer was found in the right ventricle only in specimens showing tetralogy. CONCLUSIONS: The malformed hearts showed modifications in ventricular shape, in the arrangement of muscle in the right ventricle, and in the overall myoarchitecture. These changes could well be the consequence of the same agent (or agents) that caused the structural defect.