Histologic And Electrophysiologic Study Of Crista Terminalis

Atrial tachycardia (AT) is a common tachyarrythmia originating from atrium, and is typically seen in patients with or without organic heart diseases. AT can occur as nonsustained, paroxysmal, incessant and chronic tachycardia. In the Bronx Longitudinal Aging Study, the occurrence rate of paroxysmal atrial tachycardia is 13% at aged 75 to 85 years old. Lesh classified AT by arrhythmogenic site and mechanism as focal AT, macroreentrant AT, inappropriate sinus tachycardia and atrial fibrillation(AF).Crista terminalis (CT) is endocardial hunches in the right atrium, which arising from the right appendage, reaching to the lateral and inferior walls and connected with Eustachian ridge. Pectinate muscles (PM) originate from the crest in varying angles and extend along the wall of the appendage. CT marks the junction of the venous part and rough zones. With the development of radiofrenquency ablation of focal atrial tachycardia especially focal atrial fibrillation, the implications of CT in the initiation and maintenance of AT arose widespread attention. The predominant foci of focal atrial fibrillation originated from the pulmonary vein and vena cava. The morphological and electrophysiological characteristics of the myocardial sleeves have been studied widely. Yang Yan-zong named this kind of AT as myocardial sleeve mediated atrial tachyarrhythmias. CT is the rare site of focal AF and most common site of focal AT. It is the anatomic basis of atrial flutter and inappropriate sinus tachycardia. Kalman named it as "Cristal tachycardias". Knowledge about the reason why CT become arrhythmogenic and their implications for the atrial tachycardiais is limited. The underlying anatomic and electrophysiologic properties remain unclear.Our study contained three parts of investigation. The purpose of this study was to investigate the morphological and electrophysiological characteristics of the crista terminalis and their implications for the atrial tachycardia especially atrial fibrillation.Part one aims to investigate the anatomy and histology of the crista terminalis in the aging process and its implications in the generation of arrhythmia. Method The anatomical architecture of the CT and its junctional area were studied in 68 rabbits right atrium. Paraffin sections of CT tissue of rabbits at the infant group (20-30 days old), adult group( 6~8 months old), aged group (26-28 months old) were stained by Masson trichrome, HE and immunohistology to investigate cellular form, collagen volume fraction (CVF), expression of connexin 43. Ultrastructure of the CT at adult and agedgroup were studied by electron microscope. Results (1) In 38.3% of the specimens, the middle and/or inferior segments of CT were so flat that there were no endocardial hunches at all. The pectinate muscles (PM) originate from the crest in varying angles and extend along the wall of the appendage toward the vestibule of tricuspid valve. They formed "ridge-like" or " bridge-like" structure. 26% PM have a uniform parallel alignpment and 74% have non-uniform arrangement with abundant interlacing trabeculations between them. (2)The perimysium enveloped groups of paralled myocardium of the crest. P-like cells were found in the CT which distributed in either separate or congregate manner. (3) The myocyte diameter and CVF of CT in the aged group was significantly increased compared with adult and infant group. Interstitial fibrosis were seen occasionally too. (4) There were no changes of the percentage of Cx43-positive area in the three groups. However, marked non-uniformities emerged in the sarcolemmal distribution of Cx43. In the aged group, Cx43-positive puncta were prominently localized at myocyte termini with an apparent reduction at myocyte sides (5) Under the electron microscope, gap junction at myocyte termini were easily seen and parts of the mitochondrion crest become blured or dissolution. Conclusion The anatomic and histological properties of CT and its junctional area may provide the morphologic basis which may be the origin of arrhythmia under the s...