title: Twins with implanted pacemakers: Is there an increased mortality risk for the co-twin? A follow-up study based on the Danish Twin Registry and the Danish Pacemaker Register.
abstract: BACKGROUND
  The main indications for implanting a cardiac pacemaker are either acquired atrio-ventricular block (AVB) or sick sinus syndrome (SSS). In general, the exact aetiology of these conditions is unknown. Genetic factors may play a role. Untreated AVB is associated with increased mortality but SSS seems to have a good prognosis. The present study was designed to assess whether first-degree relatives of these patients have an increased mortality risk.
  
  
  METHODS
  We investigated the survival pattern of the co-twins of twins who have had a cardiac pacemaker implanted, by linking two nationwide registries in Denmark: the Danish Pacemaker Register and the Danish Twin Registry. For each "pacemaker-twin" four control-twins matched with respect to age, sex, and zygosity were selected among the twins who were alive at the time of the pacemaker implantation. A total of 159 twins with a pacemaker treated bradycardia of unknown aetiology were identified of which 73 had AVB and 64 had SSS. A total of 622 matched control-twins could be identified. The survival from age six of the co-twins of the "pacemaker-twins" was compared with that of the co-twins of the control-twins. The follow-up period ended January 1st, 2000.
  
  
  RESULTS
  The survival curves for the co-twins of the "pacemaker-twins" were virtually identical to those of the co-twins of the control-twins. This finding was consistent for both AVB and SSS and for monozygotic as well as dizygotic twins.
  
  
  CONCLUSIONS
  No increased mortality risk could be demonstrated for first-degree relatives--including monozygotic twins--of patients with a cardiac pacemaker implanted due to either acquired AVB or SSS.
authors.affiliation: The Danish Pacemaker Register, Department of Cardiology, Odense University Hospital, DK-5000 Odense C, Denmark. tveskov@dadlnet.dk
authors.forename: Claus
authors.initials: C
authors.lastname: Tveskov
authors.forename: Axel
authors.initials: A
authors.lastname: Skytthe
authors.forename: Per
authors.initials: P
authors.lastname: Arnsbo
authors.forename: James W
authors.initials: JW
authors.lastname: Vaupel
authors.forename: Mogens
authors.initials: M
authors.lastname: Møller
authors.forename: Kaare
authors.initials: K
authors.lastname: Christensen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001919:Bradycardia / Q000235:genetics / Q000401:mortality* / Q000628:therapy*; D003718:Denmark; D004200:Diseases in Twins; D005260:Female; D006327:Heart Block / Q000235:genetics / Q000401:mortality / Q000628:therapy; D006801:Humans; D008297:Male; D008875:Middle Aged; D010138:Pacemaker, Artificial; D012042:Registries; D012804:Sick Sinus Syndrome / Q000235:genetics / Q000401:mortality / Q000628:therapy; D015996:Survival Rate; D014427:Twins