The Anatomy and Physiology of the Sinoatrial Node-A Contemporary Review

Abstract

The sinoatrial node is the primary pacemaker of the heart. Nodal dysfunction with aging, heart failure, atrial fibrillation, and even endurance athletic training can lead to a wide variety of pathological clinical syndromes. Recent work utilizing molecular markers to map the extent of the node, along with the delineation of a novel paranodal area intermediate in characteristics between the node and the surrounding atrial muscle, has shown that pacemaker tissue is more widely spread in the right atrium than previously appreciated. This can explain the phenomenon of a "wandering pacemaker" and concomitant changes in the P-wave morphology. Extensive knowledge now exists regarding the molecular architecture of the node (in particular, the expression of ion channels) and how this relates to pacemaking. This review is an up-to-date summary of the current state of our appreciation of the above topics.

Fibrosis, Electrics and Genetics

“…7 The leading pacemaker site (site of first activation) is dynamic, a phenomenon known as pacemaker shift (Figures 1C-E). 1 Pacemaker shift may be a mechanism for mediating HR modulation and this might explain alterations in P-wave morphology on the surface ECG seen in response to variation in HR (Figures 1D,E). 1 A hierarchy of pacing rate exists within the SAN; the superior portion generhe normal pacemaker of the heart is the sinoatrial node (SAN).…”

“…1 Pacemaker shift may be a mechanism for mediating HR modulation and this might explain alterations in P-wave morphology on the surface ECG seen in response to variation in HR (Figures 1D,E). 1 A hierarchy of pacing rate exists within the SAN; the superior portion generhe normal pacemaker of the heart is the sinoatrial node (SAN). It is a highly specialized structure with distinct embryology, histology, electrophysiology and ion channel expression.…”

“…It is a highly specialized structure with distinct embryology, histology, electrophysiology and ion channel expression. 1 Sinoatrial node disease (SND) is common but poorly understood and the only treatment is palliation by implantation of an electronic pacemaker. We will review advances in the understanding of the genetics, molecular pacemaker mechanisms and structure of the SAN and discuss how these have led to a parallel evolution of concepts of heart rate (HR) adaptation, pathophysiology of SND and potential new treatments.…”

Inherited progressive cardiac conduction disorders

“…The phenotypic spectrum ranges from lethal arrhythmias to asymptomatic carriers, and includes Brugada syndrome, cardiac conduction disease and atrio-ventricular block, congenital sick sinus syndrome, atrial standstill, familial atrial fibrillation, dilated cardiomyopathy, congenital long-QT syndrome type 3 (LQT3) and sudden infant death syndrome [21]. The gene SCN5A codes for the main cardiac voltage-gated sodium channel Nav1.5 [20], which is expressed in the conduction system and in the regions surrounding the sino-atrial and the atrio-ventricular nodes [7]. Thus far, at least 16 distinct mutations in SCN5A have been found to cause conduction alterations and block in patients and their families [22].…”

Spatial Organization Types of Sinoatrial Node in Dogs with Different Body Functional Reserve Levels

“…The difficulty in localizing the sinoatrial node (SAN) in the right atrium due to the lack of an isolation capsule and an insignificant morphological difference of a node from the surrounding myocardium is also a forcible reason why the question of SAN adaptation reserves is still open. SAN regulates the intensity of heart work depending on the body state and various environmental factors it is exposed to [11][12][13][14]. The principle of structural and functional unity suggests that any alteration of heart work is accompanied by the morphological changes of a sinoauricular area.…”