title: Morphological and mechanical examination of the atrial 'intima'.
abstract: OBJECTIVE
  To examine morphology and mechanical properties of the atrial 'intima', which we defined as the tissue interposed between atrial endocardium and myocardium, in patients without known cardiovascular disease.
  
  
  RESULTS
  Post-mortem right and left atrial tissue was obtained from male infants (<1 year, n = 4), children (10-19 years, n = 4), and adults (58-69 years, n = 7). Using light microscopy and an ocular micrometer, atrial intimal (AIT) thickness was measured. Intimal collagen bundle thickness was measured using electron microscopy. Passive atrial wall stiffness was measured using a planar biaxial testing device. Among infants, left AIT (0.2 ± 0.2 mm) and right (0.2 ± 0.1 mm) AIT were not significantly different (P = 0.84). Among children, left AIT (0.6 ± 0.2 mm) was significantly greater than right (0.2 ± 0.1 mm) AIT (P = 0.03), and left AIT was marginally greater than in infants (P = 0.07). Among adults, with the exception of the appendage region, left AIT (1.0 ± 0.2 mm) was markedly greater than right AIT (0.3 ± 0.1 mm; P < 0.05), and left AIT was significantly greater than that in other age groups (P < 0.05). There were no differences in right AIT among age groups. Left intimal collagen bundle thickness was greater in adults (0.0512 ± 0.0056 µm) than infants (0.0432 ± 0.0071 µm) or children (0.0435 ± 0.0013 µm), and bundles were less organized. Wall stiffness was attributable primarily to the intima (1245 ± 132, vs. 260 ± 45 N/m(2) for the remaining atrial wall).
  
  
  CONCLUSIONS
  The left atrial intima, but not the right, thickens with age, becomes more disorganized ultrastructurally, and is responsible for the majority of atrial wall stiffness.
authors.affiliation: Heart and Vascular Institute, University of Pittsburgh, UPMC Presbyterian, B535, Pittsburgh, PA 15213 2582, USA.
authors.forename: David
authors.initials: D
authors.lastname: Schwartzman
authors.forename: Karen
authors.initials: K
authors.lastname: Schoedel
authors.forename: Donna Beer
authors.initials: DB
authors.lastname: Stolz
authors.forename: Elena
authors.initials: E
authors.lastname: Di Martino
mesh_terms: D000293:Adolescent; D000367:Age Factors; D000368:Aged; D001344:Autopsy; D002648:Child; D003094:Collagen / Q000648:ultrastructure; D004699:Endocardium / Q000473:pathology / Q000648:ultrastructure*; D006325:Heart Atria / Q000473:pathology / Q000648:ultrastructure*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008853:Microscopy; D008854:Microscopy, Electron; D008875:Middle Aged; D009206:Myocardium / Q000473:pathology / Q000648:ultrastructure*; D055815:Young Adult
chemical_list: D003094:Collagen
keywords: Ablation; Ageing; Artery; Atrial fibrillation; Atrium; Intima; Vascular