Incidence and distribution of isolated atrial amyloid: histologic and immunohistochemical studies of 100 aging hearts.

The incidence and anatomic distribution of isolated atrial amyloid (IAA) in 100 aging hearts were studied histologically and immunohistochemically using antibodies against alpha-human-atrial natriuretic peptide (alpha-ANP), human transthyretin (TTR) and human amyloid P component (AP). Ninety-one of 100 hearts (91%) had amyloid deposits in the atria. Amyloid deposits in all 91 hearts reacted with alpha-ANP and AP antisera, and in four hearts other amyloid deposits that reacted with TTR antiserum were coincidentally seen in the atria. The prevalence of IAA deposition, using a semiquantitative evaluation, was significantly higher in the hearts from patients over 80 years of age, from women, those weighing over 450 g, with a thickened left ventricular wall (> 1.4 cm) and with multiple myocardial scars. IAA deposition showed a significant distribution in the auricle and left atrium; it was located mostly in the interstitium of the subendocardial layer and the subendocardial myocardium. These results indicate that IAA occurs more frequently than previously appreciated in the elderly and in patients with certain cardiac disorders.