Role of Baroreflex Sensitivity in Predicting Tilt Training Response in Patients with Neurally Mediated Syncope

Abstract

Purpose: An association between baroreflex sensitivity (BRS) and the response to tilt training has not been reported in patients with neurally mediated syncope (NMS). This study sought to investigate the role of BRS in predicting the response to tilt training in patients with NMS.

Materials and methods: We analyzed 57 patients who underwent tilt training at our hospital. A responder to tilt training was defined as a patient with three consecutive negative responses to the head-up tilt test (HUT) during tilt training.

Results: After tilt training, 52 patients (91.2%) achieved three consecutive negative responses to the HUT. In the supine position before upright posture during the first session of tilt training for responders and non-responders, the mean BRS was 18.17 ± 10.09 ms/mm Hg and 7.99 ± 5.84 ms/mm Hg (p=0.008), respectively, and the frequency of BRS ≥ 8.945 ms/mm Hg was 45 (86.5%) and 1 (20.0%; p=0.004), respectively. Age, male gender, frequency of syncopal events before HUT, type of NMS, phase of positive HUT, total number of tilt training sessions, and mean time of tilt training did not differ between the study groups. In the multivariate analysis, BRS <8.945 ms/mm Hg in the supine position (odds ratio 23.10; 95% CI 1.20-443.59; p=0.037) was significantly and independently associated with non-response to tilt training.

Conclusion: The BRS value in the supine position could be a predictor for determining the response to tilt training in patients with NMS who are being considered for inpatient tilt training.

Keywords: Baroreflex sensitivity; neurally mediated syncope; tilt training.

Fig. 1. Enrollment of patients in the study and response to tilt training. A plus sign indicates a positive response to the tilt test.

Fig. 2. BRS and hemodynamic parameters during head-up tilt test. Recordings during 5 min in the supine position immediately before upright posture (A) and during 5 min in a standing position immediately after an upright posture (B) are shown. SBP, systolic blood pressure; DBP, diastolic blood pressure; HR, heart rate; xBRS, cross-correlation baroreflex sensitivity.

Fig. 3. Methods used to compute cross-correlation BRS. (A and B) Beat to beat SBP and IBI data were fitted with cubic spline functions and resampled at 1-s intervals. (C) In 10-s windows, the correlation and regression slopes between SBP and IBI were computed. Delays of 0- to 5-s increments in IBI were computed, and the delay with the highest positive coefficient of correlation was selected; this optimal delay (Tau) was stored. (D) The slope between SBP and IBI was recorded as an xBRS estimate if the correlations was significant at p=0.01. SBP, systolic blood pressure; IBI, interbeat interval; xBRS, cross-correlation baroreflex sensitivity.

Fig. 4. Changes in responses to the tilt test before and after tilt training. This graph describes the BRS and hemodynamic parameters during the head-up tilt test in one patient (tilt training no. 134). A (first session of tilt training): Heart rate and systolic blood pressure decreased in the passive phase, and the patient lost consciousness transiently (mixed type). B (fifth session of tilt training): The patient felt mild chest discomfort; however, heat rate and blood pressure did not decrease in the passive and isoproterenol phases. HR, heart rate; xBRS, cross-correlation baroreflex sensitivity.