title: Influence of cycle length variations on antitachycardia pacing effectiveness among ICD patients.
abstract: BACKGROUND
  Antitachycardia pacing (ATP) fails to terminate 5% to 25% of ventricular tachycardias (VTs) occurring in implantable cardioverter-defibrillator patients. We speculated that small fluctuations in VT cycle length (CL) may be related to the efficacy of subsequent ATP.
  
  
  OBJECTIVE
  The purpose of this study was to determine the relationship between the R-R variations of the last 12 R-R intervals before ATP and the efficacy of the first ATP attempt.
  
  
  METHODS
  We studied 551 VTs (CL 329±35 ms) occurring in 67 patients. We also analyzed the percentage of variation (P-RR), which was calculated by dividing the mean difference between each R-R interval and the next one by the CL (×100), and the acceleration index (AI), which was calculated by dividing the CL of the first 6 R-R intervals by the CL of the next 6.
  
  
  RESULTS
  The effectiveness of the first ATP therapy was 81%, being higher in VTs with AI<1 (85% vs 64%; P<.001). After classifying the events according to the tertiles of P-RR, ATP efficiency was better in higher values of P-RR (VTs with AI<1): 99% (third tertile) vs 85% (second tertile) vs 76% (first tertile), P<.001; and for VTs with AI≥1: 94% vs 68% vs 42% (P<.001). By logistic regression, P-RR (%; odds ratio 2.37; P<.001), and AI<1 (odds ratio 4.17; P<.001) were found to be independent predictors of successful first ATP attempts.
  
  
  CONCLUSIONS
  Small changes in CL increase the effectiveness of ATP significantly. VTs with lower degrees of R-R fluctuations, especially when the pattern is a progressive CL shortening, are infrequently terminated by ATP.
authors.affiliation: Arrhythmias Unit, Cardiology Department, IBSAL-University Hospital, Salamanca, Spain. jimenezcandil@secardiologia.es
authors.forename: Javier
authors.initials: J
authors.lastname: Jiménez-Candil
authors.forename: Jesús
authors.initials: J
authors.lastname: Hernández
authors.forename: Ana
authors.initials: A
authors.lastname: Martín
authors.forename: José
authors.initials: J
authors.lastname: Moríñigo
authors.forename: Rosana
authors.initials: R
authors.lastname: López
authors.forename: Claudio
authors.initials: C
authors.lastname: Ledesma
authors.forename: Cándido
authors.initials: C
authors.lastname: Martín-Luengo
mesh_terms: D000328:Adult; D000368:Aged; D002304:Cardiac Pacing, Artificial / Q000379:methods* / Q000401:mortality; D015331:Cohort Studies; D003131:Combined Modality Therapy; D017147:Defibrillators, Implantable; D004562:Electrocardiography; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D012189:Retrospective Studies; D018570:Risk Assessment; D012720:Severity of Illness Index; D015996:Survival Rate; D017180:Tachycardia, Ventricular / Q000175:diagnosis / Q000401:mortality* / Q000628:therapy*; D016896:Treatment Outcome