Applicability and Clinical Relevance of the Transfer Function Method in the Assessment of Baroreflex Sensitivity in Heart Failure Patients
Gian Domenico Pinna, MS*,
Roberto Maestri, MS,
Soccorso Capomolla, MD,
Oreste Febo, MD,
Elena Robbi, BS,
Franco Cobelli, MD and
Maria Teresa La Rovere, MD
Department of Cardiology and Biomedical Engineering, Salvatore Maugeri Foundation, IRCCS, Scientific Institute of Montescano, Montescano (PV), Italy
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Figure 1 Representative example of the dramatic effect that a single isolated ectopic beat and its correction might have in the measurement of baroreflex sensitivity by the transfer function method (TF-BRS). Tracings (A) show systolic arterial pressure (SAP) and RR interval time series with a ventricular premature complex at the beginning of the recording. Measurement of TF-BRS on these signals gives 1.2 ms/mm Hg, whereas excluding the ectopic beat from the computation (i.e., starting the analysis window from the dashed bar) gives 6.2 ms/mm Hg. Tracings (B) show the same signals after correction of the ectopic beat by linear interpolation. Despite the apparent negligible effect on the fluctuation pattern of the two signals, TF-BRS becomes 4.7 ms/mm Hg, that is, –24% compared with the measurement obtained without the ectopic beat. Although the effect of the correction is not always so dramatic, this example highlights the need to perform a careful check every time a correction is made.
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Figure 2 Receiver-operating characteristic curves for the prediction of a two-year outcome according to baroreflex sensitivity by the transfer function method (TF-BRS) (solid line) and left ventricular ejection fraction (LVEF) (dotted line). The identity line indicates no predictive discrimination. The area under the curve was 0.68 ± 0.06 for TF-BRS and 0.61 ± 0.05 for LVEF.
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Figure 3 Kaplan-Meier survival curves according to dichotomized of baroreflex sensitivity by the transfer function method (TF-BRS) (n = 228). Estimated survival probabilities (95% confidence interval) at 12, 24, and 36 months are: 0.97 (0.94 to 1.00), 0.92 (0.87 to 0.97), 0.87 (0.80 to 0.93), respectively, for TF-BRS >3.1 ms/mm Hg; and 0.88 (0.82 to 0.95), 0.73 (0.63 to 0.82), 0.65 (0.55 to 0.76), respectively, for TF-BRS  3.1 ms/mm Hg.
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Figure 4 Kaplan-Meier survival curves according to the transfer function (TF)-index (n = 309). Subjects at high risk are those with depressed baroreflex sensitivity (BRS) (i.e., TF-BRS 3.1 ms/mm Hg) or having a missing BRS due to high ectopic activity, whereas subjects at low risk are those with more preserved BRS (i.e., TF-BRS >3.1 ms/mm Hg). Estimated survival probabilities (95% confidence interval) at 12, 24, and 36 months are: 0.97 (0.94 to 1.00), 0.92 (0.87 to 0.97), and 0.87 (0.80 to 0.93), respectively, for low risk; and 0.87 (0.82 to 0.92), 0.71 (0.64 to 0.78), 0.62 (0.54 to 0.70), respectively, for high risk.
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