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J Thorac Cardiovasc Surg 2006;131:1394-1395
© 2006 The American Association for Thoracic Surgery
Brief Communication |
a Department of Cardiac Surgery, Hospital General Universitario de Alicante, Alicante, Spain
b Department of Human Anatomy, School of Medicine, University of Extremadura, Badajoz, Spain.
Received for publication January 25, 2006; accepted for publication January 30, 2006. * Address for reprints: Aquilino Hurlé, MD, Servicio de Cirugía Cardiaca, Hospital General Universitario de Alicante, C/ Pintor Baeza s/n, 03010 Alicante, Spain. (Email: hurle_aqu{at}gva.es).
The normal structural disposition of the sinus node (SN) is well documented in the literature.
1
The histologic changes taking place within the atrial wall of patients with atrial fibrillation (AF) have also been described in the past.
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However, how SN histology might be affected by long-term AF is an issue that, to our knowledge, has not been previously addressed. The purpose of the present study is describing the SN microscopic features of patients with long-term permanent AF, which could be of relevance for the surgical treatment of this arrhythmia.
Methods
Sixteen patients (10 female and 6 male patients; mean age, 66 ± 9 years) undergoing operations for rheumatic heart valve disease who were in chronic AF beyond surgical treatment (ongoing AF for more than 10 years, a left atrial transverse diameter greater than 60 mm, as measured by means of transthoracic echocardiography, or both) were included in this study. Informed consent was obtained from all participants, and the study was approved by the local ethics committee. In all instances, a 4-mm transmural punch biopsy specimen was obtained from the most anterior part of the junction between the superior vena cava and the right atrium. Biopsy specimens were fixed immediately in 10% formaldehyde. They were then dehydrated and embedded in paraffin, cut into 7-µm-thick slides, and stained with Masson or Jones trichrome for histologic analysis.
Digital images (512 x 512 pixels) were taken from these histologic slides. Twenty measurements of P cell (impulse-producing cells) and SN working myocardial cell diameters (in micrometers) were randomly made on these digitalized images from each tissue block by using a linear measurement software program (SigmaScan Pro 4.0; Jandel Scientific, San Rafael, Calif). For each measurement, the widest cell cross-sectional diameter visible in the image was selected. These measurements were then averaged. The cell/connective tissue ratio in the specimens was estimated with the aid of a grid of vertical and horizontal lines, providing 121 intersections of points. The total number of points was defined as 100%, and the points overlying connective tissue were expressed as a percentage of the entire tissue within the limits of the grid. Blood vessels and perivascular interstitial tissue were excluded from the connective tissue quantification.
Five SN biopsy specimens obtained from the autopsies of 5 subjects (2 female and 3 male subjects; mean age, 52 ± 20 years) who were in sinus rhythm and died from noncardiac causes were fixed and processed in the same manner as the study biopsy specimens and served as control specimens.
Results
Five biopsy specimens of patients in AF showed fibrosis of the SN with total absence of myocardial cells as the only finding. P cells were absent in 6 further specimens. A significant increase in the proportion of connective tissue matrix could be demonstrated in the remaining 5 AF specimens when compared with the control specimens (34.5% ± 4.0% for the study group vs 46.5% ± 8.5% for the control group, P < .05).
The diameter of SN cells, when present, was significantly increased in specimens from patients in AF when compared with control specimens. Thus P cells averaged 7 ± 2 µm in diameter in the control group versus 11 ± 4 µm in the AF group (P < .05), and working myocytes averaged 15 ± 2 µm in the control group versus 24 ± 5 µm in the AF group (P < .05).
All these findings are shown in Figure 1.
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In recent years, great attention has been paid to the surgical treatment of AF by means of linear atrial ablation techniques. Different energy sources, such as radiofrequency, microwaves, cryoenergy, and others, have proved to be equally effective for atrial ablation purposes.
3
However, it is a known fact that patients with long-standing AF, giant atria, or both have a much smaller chance to revert back to sinus rhythm after these ablation procedures.
4
Our findings, herein reported, might provide an explanation to understand this fact. As we have described, the morphologic consequences of chronic AF on the normal SN can be synthesized in 3 main features: (1) progressive tissue fibrosis, (2) progressive myocardial cell loss (including P cells), and (3) myocardial cell degeneration (including P cells). These SN morphologic abnormalities must inevitably lead to an impairment of its function. Thus normal sinus rhythm is less likely to be restored in patients with long-standing AF, regardless of the atrial lesion pattern used to interrupt re-entry or the energy source used to create these lesions because their SN is morphologically and functionally abnormal. Conversely, surgical treatment of AF during its early stages, with minimal SN damage, is more likely to be successful.
References
This article has been cited by other articles:
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  A. Hurle, D. Sanchez-Quintana, S. Y. Ho, E. Bernabeu, M. Murillo, and V. Climent Capillary Supply to the Sinus Node in Subjects with Long-Term Atrial Fibrillation Ann. Thorac. Surg., January 1, 2010; 89(1): 38 - 43. [Abstract] [Full Text] [PDF]
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