title: Applicability and clinical relevance of the transfer function method in the assessment of baroreflex sensitivity in heart failure patients.
abstract: OBJECTIVE
  We sought to assess applicability, clinical correlates, and prognostic value of the transfer function method for measuring baroreflex sensitivity (TF-BRS).
  
  
  BACKGROUND
  Abnormalities in autonomic reflexes play an important role in the development and progression of chronic heart failure (CHF). Simple and non-invasive techniques for clinical measurement of such reflexes are desirable.
  
  
  METHODS
  In 317 stable CHF patients in sinus rhythm (median age [interquartile range]: 54 years [48 to 59 years], New York Heart Association [NYHA] functional class II to III: 88%, left ventricular ejection fraction [LVEF]: 27% [22% to 33%]) we recorded electrocardiograms and non-invasive arterial pressure during paced breathing to measure TF-BRS.
  
  
  RESULTS
  Owing to a high number of ectopic beats, TF-BRS could be computed in 72% of the patients; TF-BRS was lower in NYHA functional class III to IV and mitral regurgitation 2 to 3 (p < 0.0005 for both). Correlation with LVEF and standard deviation of all normal-to-normal intervals was 0.18 and 0.31 (p < 0.001 for both). During a mean follow-up of 26 months, 23% of the patients experienced a cardiac event. A depressed TF-BRS (< or =3.1 ms/mm Hg) was significantly associated with the outcome (hazard ratio 3.2, 95% confidence interval [CI] 1.7 to 6.0, p = 0.0003). Patients with a missing TF-BRS had a high event rate (36%). Combining this information with available TF-BRS measurements, a new prognostic index could be computed in 97% of the patients that significantly predicted the outcome after adjustment for clinical and functional variables (hazard ratio 2.5, 95% CI 1.3 to 4.6 p = 0.004).
  
  
  CONCLUSIONS
  In CHF patients in sinus rhythm, TF-BRS conveys relevant clinical and prognostic information, but its measurability is markedly affected by ectopic activity. Nevertheless, a TF-BRS-based risk index carrying significant and independent prognostic information can be computed in almost all patients.
authors.affiliation: Department of Cardiology and Biomedical Engineering, Salvatore Maugeri Foundation, IRCCS, Scientific Institute of Montescano, Montescano, PV, Italy. gdpinna@fsm.it
authors.forename: Gian Domenico
authors.initials: GD
authors.lastname: Pinna
authors.forename: Roberto
authors.initials: R
authors.lastname: Maestri
authors.forename: Soccorso
authors.initials: S
authors.lastname: Capomolla
authors.forename: Oreste
authors.initials: O
authors.lastname: Febo
authors.forename: Elena
authors.initials: E
authors.lastname: Robbi
authors.forename: Franco
authors.initials: F
authors.lastname: Cobelli
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: La Rovere
mesh_terms: D017704:Baroreflex / Q000502:physiology*; D003943:Diagnostic Techniques, Neurological; D005260:Female; D006333:Heart Failure / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D018570:Risk Assessment