title: Failure to deliver a shock in a dual-chamber implantable cardioverter-defibrillator: a case report.
abstract: BACKGROUND
  Inappropriate implantable cardioverter-defibrillator (ICD) therapies due to supraventricular tachyarrhythmia (SVT) are a common problem. The authors report this case to warn of a possible detection problem and subsequent failure of deliver appropriate therapy in patients with atrial fibrillation (AF) and a dual-chamber ICD using the PARAD+ algorithm. To our knowledge this is the first reported case of failure to deliver a shock in a dual-chamber ICD due to the PARAD+ algorithm.
  
  
  METHODS
  The authors present a case of a 68-year-old Caucasian man with permanent AF and a dual-chamber Sorin Paradym ICD with the PARAD+ algorithm, who presented an episode of sustained ventricular tachycardia (VT). The ICD did not store the event and did not delivery a therapy, although the heart rate curve was consistent with an episode of VT. No evidence of system dysfunction was found.
  
  
  CONCLUSIONS
  Due to simultaneous occurrence of VT and AF rhythms and alternation in rhythm classification by the PARAD+ algorithm the number of cycles needed to diagnose VT was not achieved and no therapy was delivered. In patients with permanent or long-term persistent AF with a dual-chamber ICD using the PARAD+ algorithm, discrimination should be based only on the ventricular channel. In patients with paroxysmal or persistent recurrent AF the risk of not delivering VT therapy must be weighed against the risk of inappropriate therapy.
authors.affiliation: Cardiology Department, Faro Hospital, Portugal. Electronic address: peter_senado2002@yahoo.com.
authors.forename: Pedro A
authors.initials: PA
authors.lastname: Sousa
authors.affiliation: Cardiology Department, Faro Hospital, Portugal.
authors.forename: Rui
authors.initials: R
authors.lastname: Candeias
authors.affiliation: Cardiology Department, Faro Hospital, Portugal.
authors.forename: Ilídio
authors.initials: I
authors.lastname: Jesus
mesh_terms: D000368:Aged; D000465:Algorithms; D017147:Defibrillators, Implantable; D004868:Equipment Failure; D006801:Humans; D008297:Male; D017180:Tachycardia, Ventricular / Q000628:therapy*
keywords: Algoritmo PARAD+; Appropriate therapy; Atrial fibrillation; Cardioversor-desfibrilhador implantável; Dual-chamber; Dupla-camara; Fibrilhação auricular; Implantable cardioverter-defibrillator; PARAD+ algorithm; Taquicardia ventricular; Terapia apropriada; Ventricular tachycardia