Anatomical study of the cardiac conduction system in swine hearts.

The cardiac conduction system (CCS) is crucial for regulating heartbeats; therefore, clinicians and comedicals involved in cardiovascular medicine treatment must have a thorough understanding of the CCS structure and function. However, anatomical education of the CCS based on actual dissection and observation is uncommon, although such educational methodology promotes three-dimensional structural understanding of the observed object. Based on previous studies, we examined the CCS structure in the heart of a swine (pig, Sus scrofa domestica) which has been used in the biological, medical and anatomical curricula as science teaching materials, by using macroscopic dissection procedures. Most CCS structures in a young pig heart were successfully identified and illustrated on a macroscopic scale. The atrioventricular bundle (His bundle) was located on the lower edge of the membranous interventricular septum and was clearly distinguished from the general myocardial fibres by its colour and fibre arrangement direction. Following the atrioventricular bundle towards the atrium or ventricle with properly removing the endocardium and myocardium, the atrioventricular node or the right and left bundles appeared respectively. In contrast, the sinoatrial node was not identified. The anatomy of the CCS in young pig hearts was essentially similar to that previously reported in humans and several domestic animals. Our findings of the CCS in young pig hearts are expected to be useful for medical and anatomical education for medical and comedical students, young clinicians and comedical workers.

Relationship of paced left bundle branch pacing morphology with anatomic location and physiological outcomes.

BACKGROUND: Left bundle branch pacing (LBBP) is an emerging physiological pacing modality. However, little is known about pacing at different locations on the left bundle branch (LBB). OBJECTIVE: The purpose of this study was to explore pacing and physiological characteristics associated with different LBBP locations. METHODS: The study included 68 consecutive patients with normal unpaced QRS duration and successful LBBP implantation. Patients were divided into 3 groups according to the paced QRS complex as left bundle branch trunk pacing (LBTP), left posterior fascicular pacing (LPFP), or left anterior fascicular pacing (LAFP). Electrocardiographic (ECG) characteristics, pacing parameters, and fluoroscopic localization were collected and analyzed. RESULTS: There were 17 (25.0%), 35 (51.5%), and 16 (23.5%) patients in the LBTP, LPFP, and LAFP groups, respectively. All subgroups had relatively narrow paced QRS complex (128.6 ± 9.1 ms vs 133.7 ± 11.2 ms vs 134.8 ± 9.6 ms; P = .170), fast left ventricular activation (70.4 ± 9.0 ms vs 70.6 ± 10.2 ms vs 71.0 ± 9.0 ms; P = .986), as well as low and stable pacing thresholds. Delayed right ventricular activation and interventricular dyssynchrony were similar between groups. Fluoroscopic imaging indicated that the lead tip was located most commonly in the basal-middle region of the septum (67.7%), and this was independent of paced QRS morphology group (88.2% vs 57.1% vs 68.8%; P = .106). CONCLUSION: Pacing at different sites of the LBB resulted in similar intraventricular and interventricular electrical synchrony in patients with an intact conduction system. Fluoroscopic imaging alone could not predict specific LBBP paced ECG morphology.

His bundle pacing: Tips and tricks.

His bundle (HB) pacing is an established modality for achieving physiological pacing with a low risk of long-term lead-related complications. The development of specially designed lead and delivery tools has improved the feasibility and safety of HB pacing (HBP). Knowledge of the anatomy of HB region and the variations is essential for successful implantation. Newer delivery systems have further improved procedural outcomes. Challenging implant cases can be successfully performed by reshaping the current sheaths, using "sheath in sheath" technique or "two-lead implantation technique." Special attention to the lead parameters at implant, programming, and follow-up is necessary for successful long-term outcomes with HBP. Widespread use of HBP by electrophysiologists and further advances in dedicated delivery systems and leads are essential to further improve the effectiveness of the implantation.

An Electro-Anatomic Atlas of His Bundle Pacing: Combining Fluoroscopic Imaging and Recorded Electrograms.

Permanent His bundle pacing (PHBP) has gained significant popularity given improved implant success rates given better tools and increasing data on the clinical benefits of PHBP. In this article, the authors hope to review the relevant anatomy of the bundle of His (HB) and help correlate PHBP implant characteristics with patient anatomy using fluoroscopic and electro-anatomic correlations.

His Bundle Pacing.

Traditional right ventricular (RV) pacing for the management of bradyarrhythmias has been pursued successfully for decades, although there remains debate regarding optimal pacing site with respect to both hemodynamic and clinical outcomes. The deleterious effects of long-term RV apical pacing have been well recognized. This has generated interest in approaches providing more physiological stimulation, namely, His bundle pacing (HBP). This paper reviews the anatomy of the His bundle, early clinical observations, and current approaches to permanent HBP. By stimulating the His-Purkinje network, HBP engages electrical activation of both ventricles and may avoid marked dyssynchrony. Recent studies have also demonstrated the potential of HBP in patients with underlying left bundle branch block and cardiomyopathy. HBP holds promise as an attractive mode to achieve physiological pacing. Widespread adaptation of this technique is dependent on enhancements in technology, as well as further validation of efficacy in large randomized clinical trials.

Associação entre bloqueio de ramo esquerdo e bloqueio divisional ântero-superior: revisitando as evidências / Association between left bundle branch block and anterosuperior hemiblock: revisiting evidences

diagnóstico concomitante de bloqueio de ramo esquerdo e bloqueio divisional ântero-superior esquerdo é motivo de controvérsias entre cardiologistas, principalmente quando há desvio do eixo vetorcardiográfico do coração para a esquerda. Em uma breve revisão da literatura, descrevemos a anatomia do feixe de His e sua natureza trifascicular, apresentamos a teoria tetrafascicular de Medrano e relembramos os critérios diagnósticos dessas duas entidades eletrocardiográficas. Concluímos que o bloqueio concomitante pode ser encontrado em casos de bloqueios pós-divisionais bifasciculares com maior acometimento do bloqueio divisional ântero-superior. Por outro lado, o cardiologista precisa ter em mente que existem outras causas de desvio do eixo para a esquerda em vigência de bloqueio de ramo esquerdo, entre elas: bloqueio de ramo esquerdo com infarto inferior, bloqueio de ramo esquerdo com infarto agudo do miocárdio ântero-septal e lateral, e vias acessórias atípicas

The concomitant diagnosis of left bundle branch block and anterosuperior hemi-block is controversial among cardiologists, especially when there is left vectorcardiographic axis deviation. In a brief literature review, we describe His bundle's anatomy and its trifascicular nature, we present Medrano's quadrifascicular theory and revise the diagnostic criteria of these two electrocardiographic entities. We conclude that concomitant block might be found in cases of post-divisional bifascicular blocks with greater involvement of the anterosuperior hemiblock. On the other hand, the cardiologist must keep in mind that there are other causes of left axis deviation in the presence of left bundle branch block, such as: inferior infarction, anterior-septal and lateral infarction, and atypical bypass tracts

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

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

The normal variants in the left bundle branch system.

This article reviewed the main anatomic and physiopathological aspects of the left bundle branch from its origin in the His bundle and its intraventricular distribution on the left endocardial surface. The results are based on the relevant literature and on personal observations executed on 206 hearts distributed as follows: 67 dogs, 60 humans, 45 sheep, 22 pigs, 10 cows, 2 monkeys, 1 guanaco, and 1 sea lion. The main anatomical features of the His-Purkinje conducting system may be summarized as follows: The bundle of His is composed by two segments: the penetrating and branching portions. LBB originates in the branching portion located underneath the membranous septum. There is no true bifurcation of the bundle of His in a human heart. Short after its origin the LBB gives rise to its two main fascicles, anterior and posterior, both heading the anterior and posterior papillary muscles, respectively. The anterior division is thinner and longer than the posterior one. The RBB and the most anterior fibers of the LBB arise at the end of the branching portion. In some cases a well-defined left septal fascicle can be identified, usually arising from the posterior division. Each division gives off small fibers and false tendons crossing the left ventricular cavity connecting the papillary between them or the papillary muscles with the septal surface. From each division of the LBB, their corresponding Purkinje networks emerge covering the subendocardium of the septum and the free wall of the left ventricles. There are critical relationships of the proximal segments of the His-Purkinje system with the surrounding cardiac structures whose pathologic processes may damage the conducting tissue.

The Cardiac Conduction System: Generation and Conduction of the Cardiac Impulse.

In this article, the authors outline the key components behind the automated generation of the cardiac impulses and the effect these impulses have on cardiac myocytes. Also, a description of the key components of the normal cardiac conduction system is provided, including the sinoatrial node, the atrioventricular node, the His bundle, the bundle branches, and the Purkinje network. Finally, an outline of how each stage of the cardiac conduction system is represented on the electrocardiogram is described, allowing the reader of the electrocardiogram to translate background information about the normal cardiac conduction system to everyday clinical practice.

Wilhelm His Junior and his bundle.

We have reviewed the evidence relative to the initial description of the penetrating atrioventricular bundle, seeking to determine whether Wilhelm His Junior is deserving of his eponym.

Location and functional characterization of the right atrioventricular pacemaker ring in the adult avian heart.

Previous histological studies showed that in addition to a sinus node, an atrioventricular (AV) node, an AV bundle, left and right bundle branches, birds also possess a right AV-Purkinje ring that is located in the atrial sheet of the right muscular AV-valve along all its base length. The functionality of the AV-Purkinje ring is unknown. In this work, we studied the topology of pacemaker myocytes in the atrial side of the isolated chicken spontaneously contracting right muscular AV-valve using the method of microelectrode mapping of action potentials. We show that AV-cells having the ability to show pacemaking reside in the right muscular AV-valve. Pacemaker action potentials were exclusively recorded close to the base of the valve along its whole length from dorsal to the ventral attachment to the interventricular septum. These action potentials have much slower rate of depolarization, lower amplitude, and higher diastolic depolarization than action potentials of Purkinje (conducting) cells. We conclude the right AV-valve has a ring bundle of pacemaker cells (but not Purkinje cells) in the adult chicken heart.

Functional, anatomical, and molecular investigation of the cardiac conduction system and arrhythmogenic atrioventricular ring tissue in the rat heart.

BACKGROUND: The cardiac conduction system consists of the sinus node, nodal extensions, atrioventricular (AV) node, penetrating bundle, bundle branches, and Purkinje fibers. Node-like AV ring tissue also exists at the AV junctions, and the right and left rings unite at the retroaortic node. The study aims were to (1) construct a 3-dimensional anatomical model of the AV rings and retroaortic node, (2) map electrical activation in the right ring and study its action potential characteristics, and (3) examine gene expression in the right ring and retroaortic node. METHODS AND RESULTS: Three-dimensional reconstruction (based on magnetic resonance imaging, histology, and immunohistochemistry) showed the extent and organization of the specialized tissues (eg, how the AV rings form the right and left nodal extensions into the AV node). Multiextracellular electrode array and microelectrode mapping of isolated right ring preparations revealed robust spontaneous activity with characteristic diastolic depolarization. Using laser microdissection gene expression measured at the mRNA level (using quantitative PCR) and protein level (using immunohistochemistry and Western blotting) showed that the right ring and retroaortic node, like the sinus node and AV node but, unlike ventricular muscle, had statistically significant higher expression of key transcription factors (including Tbx3, Msx2, and Id2) and ion channels (including HCN4, Cav3.1, Cav3.2, Kv1.5, SK1, Kir3.1, and Kir3.4) and lower expression of other key ion channels (Nav1.5 and Kir2.1). CONCLUSIONS: The AV rings and retroaortic node possess gene expression profiles similar to that of the AV node. Ion channel expression and electrophysiological recordings show the AV rings could act as ectopic pacemakers and a source of atrial tachycardia.

Approach to the difficult septal atrioventricular accessory pathway: the importance of regional anatomy.

Ablation of accessory tracts in the posteroseptal region can be challenging, as illustrated by these 2 cases. Familiarity of the anatomy of this region and recognition of the ECG patterns can help identify the AP origin and potentially improve success rates of ablation. The isoelectric initial preexcited QRS complex with rSR' pattern in lead V1 of the surface ECG but not the relatively earlier local ventricular activation at PSMA region may indicate a left-sided ablation approach for these APs.

The arrangement of fascicles in whole muscle.

The architecture of the muscle fascicles, here meaning their lengths and their arrangement relative to one another, has important implications for the force a muscle can produce. Therefore, quantifying this architectural arrangement and understanding the implications of the architecture are important for understanding muscle function in vivo. There were two purposes of this study: (1) to assess, via blunt dissection, the number and the length of all the fascicles comprising the First Dorsal Interosseous (FDI) muscle and (2) to visually identify, via magnetic resonance imaging (MRI), the arrangement of the fascicles comprising the FDI. Simple blunt dissection of all the fascicles comprising four FDI muscles and their subsequent measurement demonstrated that the fascicles comprising the whole muscle were not as long as the muscle belly from which they were extracted. Muscle fascicles are surrounded by connective tissue hence the paths of the fascicles in two whole FDI muscles were identified via MRI by tracking the connective tissue surrounding the fascicles. The fascicles had a spiral pattern along the length of each muscle, within both muscles many of the fascicles were arranged in series with other fascicles. These architectural features of the fascicles of the FDI have important implications for the force-length and force-velocity properties of the whole muscle.

Contrast enhanced micro-computed tomography resolves the 3-dimensional morphology of the cardiac conduction system in mammalian hearts.

The general anatomy of the cardiac conduction system (CCS) has been known for 100 years, but its complex and irregular three-dimensional (3D) geometry is not so well understood. This is largely because the conducting tissue is not distinct from the surrounding tissue by dissection. The best descriptions of its anatomy come from studies based on serial sectioning of samples taken from the appropriate areas of the heart. Low X-ray attenuation has formerly ruled out micro-computed tomography (micro-CT) as a modality to resolve internal structures of soft tissue, but incorporation of iodine, which has a high molecular weight, into those tissues enhances the differential attenuation of X-rays and allows visualisation of fine detail in embryos and skeletal muscle. Here, with the use of a iodine based contrast agent (I(2)KI), we present contrast enhanced micro-CT images of cardiac tissue from rat and rabbit in which the three major subdivisions of the CCS can be differentiated from the surrounding contractile myocardium and visualised in 3D. Structures identified include the sinoatrial node (SAN) and the atrioventricular conduction axis: the penetrating bundle, His bundle, the bundle branches and the Purkinje network. Although the current findings are consistent with existing anatomical representations, the representations shown here offer superior resolution and are the first 3D representations of the CCS within a single intact mammalian heart.

The structure of the atrioventricular node in the heart of the female laying ostrich (Struthio camelus).

The electrical impulse for cardiac contraction is generated in the Sinoatrial node (SA node), subsequently spreads to the Atrioventricular node (AV node) and continues in the Atrioventricular bundle (AV bundle). The AV node may not always be present in different avian species and seems to differ in location and contents between species. In this study, the anatomy and histology of the AV node were studied five female adult ostriches (Struthio camelus). Routine paraffin sectioning and transmission electron microscopic method were performed. The study showed that in the ostrich, the AV node is located in the endocardium of the atrial surface of the right atrioventricular valve adjacent to the fibrous ring. The parenchyma of the AV node is formed by small specialized muscle fibres that are spread within a loose connective tissue network. The AV node is not covered by a connective tissue sheath and some arterioles are present. Nerve fibres are seen related to the node. Ultrastructurally, they stain lighter and contain fewer organized myofibrils than usual myocardial cells. The myofibril bundles run parallel to one another and have interspersed mitochondria, which display distinct cristae. The cells have a large euchromatic nucleus with a clear perinuclear area, and they connected by desmosomes. The ostrich is, thus, one of the birds that have the AV node, whose position varies from the other birds.

Anatomical and molecular mapping of the left and right ventricular His-Purkinje conduction networks.

Functioning of the cardiac conduction system depends critically on its structure and its complement of ion channels. Therefore, the aim of this study was to document both the structure and ion channel expression of the left and right ventricular His-Purkinje networks, as we have previously done for the sinoatrial and atrioventricular nodes. A three-dimensional (3D) anatomical computer model of the His-Purkinje network of the rabbit heart was constructed after staining the network by immunoenzyme labelling of a marker protein, middle neurofilament. The bundle of His is a ribbon-like structure and the architecture of the His-Purkinje network differs between the left and right ventricles. The 3D model is able to explain the breakthrough points of the action potential on the ventricular epicardium during sinus rhythm. Using quantitative PCR, the expression levels of the major ion channels were measured in the free running left and right Purkinje fibres of the rabbit heart. Expression of ion channels differs from that of the working myocardium and can explain the specialised electrical activity of the Purkinje fibres as suggested by computer simulations; the expression profile of the left Purkinje fibres is more specialised than that of the right Purkinje fibres. The structure and ion channel expression of the Purkinje fibres are highly specialised and tailored to the functioning of the system. The His-Purkinje network in the left ventricle is more developed than that in the right ventricle and this may explain its greater clinical importance.

Anatomy of the septomarginal trabecula in goat hearts.

Our aim in this study was to examine the right septomarginal trabecula of goats regarding the frequency, origin course of the septal and free component, attachment to the papillaris magnus muscle and size . The material used consisted in 32 hearts from non-pedigree goats of both sexes, preserved in 10% formalin. The right septomarginal trabecula was present in all hearts. It could also present a prominence in the form of a cord in the septum before detaching and going towards the wall or the papillary muscle. We called this a septal component and found it in 69% of all hearts studied. In the remaining specimens, the exit of the septomarginal trabecula was abrupt, without presenting a septal component. It could be attached solely to the papillaris magnus muscle or to the papillary muscle and the ventricle wall, originated in the cranial third of the septum, and was attached to the middle third of the papillary muscle or its caudal third. Its free part, from the septum to the papillaris magnus muscle, ranged in length from 1.3 cm to 2.6 cm. The mean value was 1.7 cm, and the most frequent values were 1.9 and 1.5 cm. In conclusion, in goats, the septomarginal trabecula is a constant and invariable structure.

A simple dissection method for the conduction system of the human heart.

A simple dissection guide for the conduction system of the human heart is shown. The atrioventricular (AV) node, AV bundle, and right bundle branch were identified in a formaldehyde-fixed human heart. The sinu-atrial (SA) node could not be found, but the region in which SA node was contained was identified using the SA nodal artery. Gross anatomical observation of the conduction system is useful for understanding the structure and function of the heart.