Capillary supply to the sinus node in subjects with long-term atrial fibrillation

Atrial ischemia, and sinus node ischemia in particular, may be involved in the pathogenesis of atrial fibrillation. In this study we compared the sinus node blood capillary content in normal hearts in sinus rhythm and in pathologic hearts with chronic atrial fibrillation and we analyzed the ultrastructural features of such capillaries.

Sinus node biopsy specimens were obtained from 16 patients in chronic atrial fibrillation undergoing open heart surgery. Control sinus node specimens of normal hearts were obtained at autopsy from 7 subjects. Specimens were processed for immunohistochemical, light microscopy and transmission electron microscopy analysis and compared grossly and with morphometric techniques.

The proportion of sinus node tissue corresponding to capillaries, defined as blood vessel density (or BVD), was estimated as 1.06 +/- 1.47% for the atrial fibrillation group versus 2.12 +/- 2.0% for controls (p < 0001). Internal capillary diameter averaged 21.6 microm in the atrial fibrillation group and 24.2 microm in controls (p = 0.175), whereas external diameter averaged 32.2 microm in the atrial fibrillation group and 38.9 microm in controls (p = 0.052). Ultrastructural analysis demonstrated scarce and interrupted myoendocardial bridges and abnormal deposits of elastic fibers under the endothelial basal membrane at the level of precapillary sphincters and metaarterioles of atrial fibrillation specimens.

There is a significant reduction in the amount of capillaries in the sinus node of hearts in chronic atrial fibrillation. Our findings would support a potential association between sinus node tissue ischemia and chronic atrial fibrillation.