Measurements
HUTT
A baseline and 3-month HUTT were performed. Participants were asked to fast for no longer than 2 hours prior to the test. All drugs affecting the validity of the HUTT were stopped at least five half-lives prior to testing. Participants were prepared with continuous ECG monitoring, a non-invasive blood pressure cuff, a digital non-invasive beat-to-beat blood pressure monitor and patches for impedance monitoring using the Task Force® Monitor system (CNSystems, Graz, Austria). The tilt-testing laboratory is temperature controlled, quiet and the test was performed under low lighting levels. Participants were laid in a supine position for 10 minutes to allow haemodynamic measures to stabilise before being tilted to 70°. This was maintained for 20 minutes, when 200 μg of sub-lingual glyceryl trinitrate wa
s administered. A further 20 minutes of recording was performed. The test was terminated if syncope occurred. Time to syncope during the HUTT was recorded in seconds.
Heart Rate Variability (HRV)
The autoregressive method for HRV was used to calculate the low-frequency (LF) 0.04–0.15 Hz and high-frequency (HF) 0.15–0.4 Hz spectral densities from the continuous ECG recording for each HUTT phase. Automated software eliminated ectopic beats and artefactual recordings.
Baroreflex Sensitivity (BRS)
For each phase of HUTT the BRS was calculated using the sequence method. The slope regression was determined for increases in systolic blood pressure (SBP) accompanied by lengthening of the R-R interval (RRI) (up sequences) and decreases in SBP associated with shortening of the RRI (down sequences) for three or more consecutive R-waves. The blood pressure sequences were paired with the RRI at which the changes occurred.
Symptom and Training Diaries
Participants were asked to record their daily training regime and document reasons for failure or premature termination of training on each and every occasion. Any pre-syncopal symptoms or syncopal attacks were also documented.
Statistical Analysis
All continuous variables were reported as mean with SD for normally distributed data and median with interquartile range for non- normally distributed data. For the haemodynamic variables, LF-HRV, HF-HRV, upslope BRS, downslope BRS, the values were initially logged to ensure normal distribution. The paired student’s t-test was used for within-group comparisons of pre- and post-training logged haemodynamic data and time to syncope. For comparison of haemodynamic measures between groups, the log differences were calculated and then the elog differences were compared using the unpaired student’s t-test. Log ratios of pre- and post-haemodynamic values were recorded. A value of 1 indicated no change, <1 indicated a reduction in the haemodynamic measure and >1 indicated an improvement. A two-tailed P-value of <0.05 was considered statistically significant. PASW Statistics 18.0™ for Windows® was used for all data analysis.
Results
Overall, 106 participants with recurrent syncope underwent HUTT. Of these, 45 had a positive HUTT response and were diagnosed with VVS. The first 30 participants aged >65 years and the first 15 participants aged <65 years who met the study criteria were recruited.
Fifteen participants in the O65 group were randomised to active HOT. Two participants in the O65+ group declined the repeat tilt-table testing and their data were not used in the analysis. No reason was given. One participant in the O65− group suffered a hip fracture not related to the study. Three participants from the U65 group moved out of area and were lost to follow-up. Baseline characteristics were similar in the two O65 groups (Figure 1).
HRV
No significant difference was seen between pre- and post-training in any of the groups in any phase of HUTT (P=NS). Comparison of the elog difference of the pre- and post-training values for the U65 and O65− groups to the O65+ group showed no significant difference (see Figure 2).
BRS
No significant improvement from HOT was seen in any of the treatment groups or between any treatment group (Figure 2).
Time to syncope on HUTT
All except two participants (one in the O65+ group and one in the U65 group) had a positive HUTT on repeat testing. HOT did not significantly influence the time to syncope during HUTT (from 1473 seconds ± 336 to 1386 seconds ± 698 [P=0.67] in the U65 group; from 1574 seconds ± 278 to 1532 seconds ± 623 [P=0.80] in the O65+ group; and from 1454 seconds ± 332 to 1435 seconds ± 286 [P=0.84] in the O65− group).