title: Fragmentation of the paced QRS complex: a marker of antitachycardia pacing effectiveness among ICD patients.
abstract: BACKGROUND
  The presence of notches in the paced QRS complex (P-QRS) from the right ventricular apex (RVA) reflects delays in the activation of the left ventricle and may therefore be associated with longer times of stimulus conduction. Our objective was to determine prospectively the relationship between the duration of a notch ≥0.1 mV in the P-QRS (DN) and the effectiveness of antitachycardia pacing (ATP).
  
  
  RESULTS
  We followed 286 implantable cardioverter-defibrillator (ICD) patients with left ventricular dysfunction (pacing site: RVA) for 41 ± 27 months. ICD programming was standardized. P-QRS (100 bpm) was obtained at implant (50 mm/s). A total of 955 monomorphic ventricular tachycardias (VTs) with a cycle length of 335 ± 32 milliseconds occurred consecutively in 108 patients. ATP was successful in 84% of VTs. DN correlated with the probability of ineffective ATP (C = 0.67; P < 0.001), the cutoff point with the best sensitivity and specificity being 50 milliseconds. The adjusted mean ATP effectiveness per patient was 76% (95% CI: 72-85). Patients with a DN ≥ 50 milliseconds had a lower ATP efficiency: 67% (56-77) versus 92% (87-97) and a higher proportion of VTs terminated with shocks (SH): 31% (21-42) versus 8% (2-14); P < 0.001 for both. Although the occurrence of VT was similar (41% vs. 40%), the incidence of VT-related SH was higher in patients with a DN ≥ 50 (25% vs. 14%; P = 0.01) in the overall study population (n = 286).
  
  
  CONCLUSIONS
  When ATP is applied to the RVA, a DN ≥ 50 milliseconds is associated with a lower ATP effectiveness and a higher risk of SH due to VT.
authors.affiliation: Cardiology Department, IBSAL-University Hospital, Salamanca, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Jiménez-Candil
authors.forename: José L
authors.initials: JL
authors.lastname: Moríñigo
authors.forename: Jesús
authors.initials: J
authors.lastname: Hernández
authors.forename: Ana
authors.initials: A
authors.lastname: Martín
authors.forename: Olga
authors.initials: O
authors.lastname: Durán
authors.forename: Juan
authors.initials: J
authors.lastname: Carlos Rama
authors.forename: Claudio
authors.initials: C
authors.lastname: Ledesma
authors.forename: Pedro L
authors.initials: PL
authors.lastname: Sánchez
mesh_terms: D000368:Aged; D017147:Defibrillators, Implantable; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D004562:Electrocardiography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013610:Tachycardia / Q000150:complications / Q000175:diagnosis* / Q000517:prevention & control*; D016896:Treatment Outcome; D018487:Ventricular Dysfunction, Left / Q000175:diagnosis* / Q000209:etiology / Q000517:prevention & control*
keywords: ICD shock; QRS fragmentation; antitachycardia pacing; implantable cardioverter-defibrillator; ventricular tachycardia