title: Temporal patterns of ventricular tachyarrhythmia recurrences follow a Weibull distribution.
abstract: Temporal patterns of ventricular tachyarrhythmias.
  
  
  BACKGROUND
  The objective of this study was to test whether the temporal patterns of ventricular tachyarrhythmia recurrences in patients with implantable cardioverter-defibrillator (ICD) follow a random or a clustered distribution.
  
  
  METHODS
  Data analysis was conducted using the Medtronic (Minneapolis, MN) Gem DR database of 521 ICD patients. Patients with >or=3 sustained ventricular tachyarrhythmia detections that resulted in shock or antitachycardia pacing therapies were studied. The times between consecutively treated ICD detections for each patient were compared to an exponential model of random recurrences and a Weibull model for clustered recurrences.
  
  
  RESULTS
  Seventy-one patients had >or=3VT episodes during follow-up of 131+/-86 days. A total of 2347 VT episodes were recorded (33+/-65 episodes/patient, median 10 episodes/patient). Patient age was 66+/-13 years, 78% male, 83% coronary artery disease, ejection fraction 31+/-11%, and 63% were taking antiarrhythmic drugs. By the Kolmogorov-Smirnov goodness-of-fit test, 38 of 71 patients (53.5%) showed that the pattern of detections differed from an exponential model (P<0.01 for each patient and the proportion of patients was similar to chance at P=0.65). In contrast, only 11 out of 71 patients (15.5%) showed that the pattern differed from the Weibull model (P<0.01 for each patient). The proportion of patients fitting the Weibull model was significantly greater than chance and was greater that the proportion fitting the exponential model (both P<0.001). The time interval between consecutive detections was less than 1 hour for 78% of all 2347 detections. The proportion of all 521 patients with >or=2, >or=3, >or= 4, >or=6, >or=8, and >or=10 ICD detections in a 24-hour period was 10.5%, 9.5%, 8.1%, 7.0%, 6.3%, and 5.2%, respectively.
  
  
  CONCLUSIONS
  In most patients with >or=3 ICD detections, the recurrence pattern of treated ventricular tachyarrhythmia detections are clustered and can be described by a Weibull distribution. The proportion of patients with multiple detections in a 24-hour period declines in a linear fashion as the number of events in 24 hours increases from 2 to 10 events.
authors.affiliation: Virginia Commonwealth University Health Systems, Richmond, Virginia 23298-0053, USA. mwoodmd@pol.net
authors.forename: Mark A
authors.initials: MA
authors.lastname: Wood
authors.forename: Bruce
authors.initials: B
authors.lastname: Gunderson
authors.forename: Amy
authors.initials: A
authors.lastname: Xia
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Zhou
authors.forename: Vasant
authors.initials: V
authors.lastname: Padmanabhan
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Ellenbogen
mesh_terms: D000368:Aged; D016000:Cluster Analysis; D017147:Defibrillators, Implantable; D005260:Female; D006801:Humans; D008297:Male; D015233:Models, Statistical; D012008:Recurrence; D016008:Statistical Distributions; D017180:Tachycardia, Ventricular / Q000503:physiopathology* / Q000628:therapy; D013997:Time Factors