title: Anatomical variations in the human sinuatrial nodal artery.
abstract: OBJECTIVE
  To analyze the anatomical variations of sinuatrial nodal branch(es) of the coronary artery mainly regarding their number; a recent report from Japan claims the presence of 2 branches in up to 50% of cases, an occurrence that would permit adequate flow compensation in case of occlusion or section of 1 of these branches.
  
  
  METHODS
  The sinuatrial nodal branch(es) of 50 human hearts fixed in formol solution were dissected with the aid of a Normo Health 3.0 degree visor magnifying lens, measured, and classified as to the origin, route, and number of branches.
  
  
  RESULTS
  In 94% (n = 47) of cases, a single sinuatrial nodal branch was found. classified: (A) two right side types, R1 (in 46% of cases, n = 23), situated medial to the right auricle and R2 (in 4% of cases, n = 2), situated on the posterior surface of the right atrium; (B) three left side types, L1 (in 24% of cases, n = 12), situated medial to the left auricle, L2 (in 16% of cases, n = 8), situated posterior to the left auricle, and L3 (in 4% of cases, n = 2), situated on the posterior surface of the left atrium. Except for R2, each type was subdivided into 'a' or 'b' types, according to whether the sinuatrial nodal branch(es) occurred in a clockwise or counterclockwise orientation around the base of the superior cava vena. In 4% of cases (n = 2), 2 sinuatrial nodal branch(es) were observed with 1 branch originating from each of the coronary arteries. In 1 case (2%), 3 sinuatrial nodal branch(es) were found, 2 from the right coronary artery and the third probably from the bronchial branch of the thoracic aorta. In 30% of the cases, the sinuatrial nodal branch(es) formed a ring around the base of the superior cava vena. In all cases, the sinuatrial nodal branch(es) supplied collateral branches to the atrium and/or the auricle of the same side as its origin and/or to the opposite side.
  
  
  CONCLUSIONS
  The low frequency of 2 sinuatrial nodal branch(es) in Brazilian individuals, compared to the higher frequency found among the Japanese, is probably due to a variation associated with ethnic group origin.
authors.affiliation: Centro de Ciências da Vida, Faculdade de Ciências Biológicas, Pontifícia Universidade Católica de Campinas, Campinas, SP, Brasil. ortalejr@uol.com.br
authors.forename: José Roberto
authors.initials: JR
authors.lastname: Ortale
authors.forename: Cristiane de Freitas
authors.initials: Cde F
authors.lastname: Paganoti
authors.forename: Gabriel Franceschi
authors.initials: GF
authors.lastname: Marchiori
mesh_terms: D000328:Adult; D044466:Asian People; D003326:Coronary Circulation; D003331:Coronary Vessels / Q000033:anatomy & histology*; D006352:Heart Ventricles / Q000033:anatomy & histology; D006801:Humans; D012849:Sinoatrial Node / Q000033:anatomy & histology*; D044465:White People