title: Predictive Power of f99 Repolarization Index for the Occurrence of Ventricular Arrhythmias.
abstract: BACKGROUND
  Defects of cardiac repolarization, noninvasively identifiable by analyzing the electrocardiographic (ECG) ST segment and T wave, are among the major causes of sudden cardiac death. Still, no repolarization-based index has so far shown sufficient sensitivity and specificity to justify preventive treatments. Thus, the aim of this work was to evaluate the predictive power of our recently proposed f99 index for the occurrence of ventricular arrhythmias.
  
  
  METHODS
  Our study populations included 170 patients with implanted cardiac defibrillator (ICD), 44 of which developed ventricular tachycardia and/or fibrillation during the 4-year follow-up (ICD_Cases) and 126 did not (ICD_Controls). The f99 index, defined as the frequency at which the repolarization normalized cumulative energy reaches 99%, was computed in each of the 15 (I to III, aVl, aVr, aVf, V1 -V6 , X, Y, Z) available ECG leads independently, and then maximized over the 6 precordial leads (f99_MaxV1 -V6 ), 12 standard leads (f99_Max12STD) and three orthogonal leads (f99_MaxXYZ) to avoid dispersion-related issues. Each index predictive power was quantified as the area under the receiving operating characteristic curve (AUC).
  
  
  RESULTS
  Median f99_MaxV1 -V6 , f99_Max12STD and f99_MaxXYZ values were significantly higher in the ICD_Cases than in the ICD_Controls (48 Hz vs. 35 Hz, P<0.05; 51 Hz vs. 43 Hz, P<0.05; 45 Hz vs. 31 Hz, P<10(-3) ; respectively), indicating a more fragmented repolarization in the former group. The AUC values were 0.62, 0.63 and 0.68, respectively.
  
  
  CONCLUSIONS
  The f99 represents a promising risk index for the occurrence of ventricular arrhythmias, especially when maximized over the three orthogonal leads.
authors.affiliation: Department of Information Engineering, Polytechnic University of Marche, Ancona, Italy.
authors.forename: Corrado
authors.initials: C
authors.lastname: Giuliani
authors.affiliation: Department of Cardiology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Cees A
authors.initials: CA
authors.lastname: Swenne
authors.affiliation: Department of Cardiology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Sumche
authors.initials: S
authors.lastname: Man
authors.affiliation: Department of Information Engineering, Polytechnic University of Marche, Ancona, Italy.
authors.forename: Angela
authors.initials: A
authors.lastname: Agostinelli
authors.affiliation: Department of Information Engineering, Polytechnic University of Marche, Ancona, Italy.|B.M.E.D. Bio-Medical Engineering Development SRL, Department of Information Engineering, Polytechnic University of Marche, Ancona, Italy.
authors.forename: Sandro
authors.initials: S
authors.lastname: Fioretti
authors.affiliation: Department of Information Engineering, Polytechnic University of Marche, Ancona, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Di Nardo
authors.affiliation: Department of Information Engineering, Polytechnic University of Marche, Ancona, Italy.|B.M.E.D. Bio-Medical Engineering Development SRL, Department of Information Engineering, Polytechnic University of Marche, Ancona, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Burattini
mesh_terms: D001145:Arrhythmias, Cardiac / Q000175:diagnosis* / Q000503:physiopathology*; D004562:Electrocardiography / Q000379:methods / Q000706:statistics & numerical data*; D005260:Female; D005500:Follow-Up Studies; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012372:ROC Curve; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: T-wave frequency content; digital electrocardiography; repolarization variability; risk assessment; sudden cardiac death