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 (≤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.
Abbreviations and Acronyms
AUC
area under the curve
BRS
baroreceptor-heart rate reflex sensitivity
CHF
chronic heart failure
ICD
implantable cardioverter-defibrillator
LF
low frequency
LVEF
left ventricular ejection fraction
NYHA
New York Heart Association
ROC
receiver-operating characteristic
SAP
systolic arterial pressure
SDNN
standard deviation of all normal-to-normal intervals