Damián Sánchez-Quintana

ANATOMY OF THE LEFT ATRIUM : IMPLICATIONS FOR RADIOFREQUENCY ABLATION OF ATRIAL FIBRILLATION

Anatomy of the Left Atrium. 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.

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.

Atrial structure and fibres: morphologic bases of atrial conduction

The relationship between anatomy and function has long been recognised. Understanding the gross structure, and the myoarchitecture, of the atriums is fundamental to investigations into the substrates and therapy of atrial fibrillation. Based primarily on our experience with normal human hearts, this review provides, firstly, a basis of comparison of gross structures as seen in the clinical situation, and in animals commonly used in experimental studies. Secondly, we discuss the general arrangement of myocardial fibres with respect to gross topography in the normal human heart. The right atrium is dominated by an extensive array of pectinate muscles within the extensive appendage, whereas the left atrium is relatively smooth-walled, with a much smaller tubular appendage. Myoarchitecture displays parallel alignment of fibres along distinct muscle bundles, such as the terminal crest and Bachmanns bundle. Within the smooth wall of the left atrium, there is a marked transmural change in the orientation of the muscular fibres. Abrupt changes in orientation, and mixed arrangements, are common between bundles. Other than Bachmanns bundle, the muscular bridges which provide interatrial connections, and connections between the left atrium and the coronary sinus and inferior caval vein, are highly variable. Inhomogeneities both in gross structure and myoarchitecture are common in the normal heart. These should be taken into account when investigating hearts from patients known to have had a history of arrhythmias, in devising computer models, or when refining diagnostic and therapeutic strategies.

Anatomic Relations Between the Esophagus and Left Atrium and Relevance for Ablation of Atrial Fibrillation

Background—Esophageal injury is a potential complication after intraoperative or percutaneous transcatheter ablation of the posterior aspect of the left atrium. Understanding the spatial relations between the esophagus and the left atrium is essential to reduce risks. Methods and Results—We examined by gross dissection the course of the esophagus in 15 cadavers. We measured the minimal distance of the esophageal wall to the endocardium of the left atrium with histological studies in 12 specimens. To measure the transmural thickness of the atrial wall, we sectioned another 30 human heart specimens in the sagittal plane at 3 different regions of the left atrium. The esophagus follows a variable course along the posterior aspect of the left atrium; its wall was <5 mm from the endocardium in 40% of specimens. The posterior left atrial wall has a variable thickness, being thickest adjacent to the coronary sinus and thinnest more superiorly. Behind is a layer of fibrous pericardium and fibrofatty tissue of irregular thickness that contains esophageal arteries of 0.4±0.2-mm external diameters. Conclusions—The nonuniform thickness of the posterior left atrial wall and the variable fibrofatty layer between the wall and the esophagus are risk factors that must be considered during ablation procedure. Esophageal arteries and vagus nerve plexus on the anterior surface of the esophagus may be affected by ablative procedures.

How close are the phrenic nerves to cardiac structures? Implications for cardiac interventionalists.

Background: Phrenic nerve injury is a recognized complication following cardiac intervention or surgery. With increasing use of transcatheter procedures to treat drug‐refractory arrhythmias, clarification of the spatial relationships between the phrenic nerves and important cardiac structures is essential to reduce risks.

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 Bachmanns 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. Clin. Anat. 22:52–63, 2009.

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.

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.

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.

Left Atrial Anatomy Revisited

Recent decades have seen rapid developments in arrhythmia treatment, especially the use of catheter ablation. Although the substrates of atrial fibrillation, its initiation and maintenance, remain to be fully elucidated, catheter ablation in the left atrium has become a therapeutic option for patients with this arrhythmia. With ablation techniques, various isolation lines and focal targets are deployed; the majority of these are anatomic approaches. It has been over a decade since we published our first article on the anatomy of the left atrium relevant to interventional electrophysiologists.1 Our aim then, as now, was to increase awareness of anatomic structures inside the left atrium. In this review of anatomy, we revisit the left atrium, inside as well as outside, for a better understanding of the atrial component parts and the spatial relationships of specific structures. ### Location and Atrial Walls Viewed from the frontal aspect of the chest, the left atrium is the most posteriorly situated of the cardiac chambers. Owing to the obliquity of the plane of the atrial septum and the different levels of the orifices of the mitral and tricuspid valves, the left atrial chamber is more posteriorly and superiorly situated relative to the right atrial chamber. The pulmonary veins enter the posterior part of the left atrium with the left veins located more superior than the right veins. The transverse pericardial sinus lies anterior to the left atrium, and in front of the sinus is the root of the aorta. The tracheal bifurcation, the esophagus, and descending thoracic aorta are immediately behind the pericardium overlying the posterior wall of the left atrium. Further behind is the vertebral column. Following the direction of blood flow, the atrial chamber begins at the pulmonary veno-atrial junctions and terminates at the fibro-fatty tissue plane that marks the atrioventricular junction at the mitral orifice. The walls …