Objectives: No studies have compared the prognostic values of invasive (phenylephrine, Phe) and noninvasive (transfer function) assessments of baroreflex sensitivity (BRS).
Methods: Three hundred and one heart failure patients [age: 53 ± 8 years, New York Heart Association class II-III: 88%, left-ventricular ejection fraction (LVEF): 28 ± 8%] underwent an 8 min ECG and arterial pressure recording, followed by Phe administration.
Results: Phe-BRS and transfer function BRS (TF-BRS) could be measured in 89 and 72% of cases, respectively. The correlation and the 5-95th percentiles of the difference between the two methods were 0.61 (P < 0.0001), and -7.6, +7.5 ms/mmHg, respectively. During a median of 36 months, 23% of the patients experienced a cardiac event. In the common dataset of 202 patients, both BRS measurements (<3 ms/mmHg) were significantly associated with the outcome (both P < 0.001), but Phe-BRS had a better discriminatory power (area under the curve (AUC): 0.74 vs. 0.66, P = 0.03). Patients with a missing BRS (due to high grade ectopic activity) had a higher event rate (Phe-BRS: 38 vs. 24%, P = 0.23; TF-BRS: 37 vs. 19%, P = 0.002). Using this information, a prognostic index was derived for each BRS method, increasing measurability to 94 and 98%, respectively. Both indexes significantly predicted the outcome after adjustment for clinical covariates [hazard ratio (95% CI): 1.9 (1.1-3.3), P = 0.03 for Phe index and 2.0 (1.1-3.7), P = 0.02 for transfer function index].
Conclusion: Although the measurability of TF-BRS in heart failure patients is impaired, prognostic information can be extended to almost all patients, with a predictive power similar to that of Phe-BRS. The two measurements, however, convey a certain amount of independent prognostic information. Hence, TF-BRS can be integrated with but not replace Phe-BRS.