title: Characteristics and relevance of clustering ventricular arrhythmias in defibrillator recipients.
abstract: BACKGROUND
  Studies of recurrent ventricular tachycardia and ventricular fibrillation (VT/VF) have been limited to "electrical storms," where recurrent arrhythmias necessitate repeated external cardioversions or defibrillations. Patients with an implantable cardioverter-defibrillator (ICD) may also suffer frequently recurrent arrhythmias. The aim of this study was to analyze the temporal pattern and the clinical relevance of clustering ventricular arrhythmias in ICD recipients.
  
  
  METHODS
  The incidence and the type of arrhythmias were determined by reviewing stored electrograms. VT/VF clusters were defined as the occurrence of three or more adequate and successful ICD interventions within 2 weeks. Two hundred and fourteen consecutive ICD recipients were followed during an average of 3.3 +/- 2.2 years (698 patient-years).
  
  
  RESULTS
  Fifty-one patients (24%) suffered 98 VT/VF clusters 21 +/- 22 months after ICD implantation, 93% of these clusters consisting of recurrent regular VT. Monomorphic VT as index event leading to ICD implantation was the only factor predicting VT/VF clusters. Kaplan-Meier estimates of the combined end-point of death or heart transplantation showed a 5-year event-free survival of 67% versus 87% in patients with and without clusters, respectively (P = 0.026). Adjusted hazard ratios for death or heart transplantation in the group with arrhythmia clusters was 3.5 (95% confidence interval 1.5-7.9 P = 0.003).
  
  
  CONCLUSIONS
  VT/VF clusters are frequent late after ICD implantation particularly in patients who had VT as index-event. As arrhythmias and recurrent ICD interventions are responsible for an important morbidity, there is a possible role for a prophylactic intervention. Furthermore, VT/VF clusters are an independent marker of increased risk of death or need for heart transplantation.
authors: From the Swiss Cardiovascular Center Bern, University Hospital, Bern, Switzerland.
authors: Thomas
authors: T
authors: Stuber
authors: Christa
authors: C
authors: Eigenmann
authors: Etienne
authors: E
authors: Delacrétaz
mesh_terms: D016000:Cluster Analysis; D017147:Defibrillators, Implantable / Q000009:adverse effects; D018572:Disease-Free Survival; D004554:Electric Countershock / Q000009:adverse effects; D005260:Female; D005500:Follow-Up Studies; D016027:Heart Transplantation; D006801:Humans; D008297:Male; D008875:Middle Aged; D012008:Recurrence; D017180:Tachycardia, Ventricular / Q000209:etiology* / Q000401:mortality / Q000601:surgery; D014693:Ventricular Fibrillation / Q000209:etiology* / Q000401:mortality / Q000601:surgery