Power spectral analysis of heart rate variability as a predictive test in choosing the most effective length for...

In patients with refractory neurally mediated syncope, tilt training--standing motionless against a wall for increased periods of time per day over one month--can often eliminate recurrent episodes and reduce presyncopal symptoms. We designed dual retrospective and prospective studies to assess cardiovascular autonomic function in subjects with recurrent syncope and identify the most effective length of tilt training between one and three months.

In the retrospective study, before tilt training, and in the prospective study, before and after training, all subjects underwent a recording for short-term spectral analysis of heart rate and systolic blood pressure variability. Before tilt-training, autonomic nervous system function differs in patients with recurrent neurally mediated syncope who respond to tilt training for one month and those who do not. "Responders", patients experiencing no episodes of syncope during the 12-month follow-up, had higher low-frequency power of RR (LF(RR)) (p < 0.05) and LF(RR) in normalized units (NU) (p < 0.001) and lower high-frequency power (HF(RR)) (p < 0.05) and HF(RR)NU (p < 0.001) than "non-responders", patients reporting at least one syncopal episode during the 12-month follow-up. In the retrospective study, no difference was found between spectral data for "non-responders" with positive responses to tilt test with and without nitro derivatives. Prolonging tilt-training to three months increased the number of responders (late-responders) by 80% (p < 0.001) and power spectral analysis of heart rate variability (HRV) before tilt training can identify late-responders by their low LF(RR)NUs (<40) and high HF(RR)Nus (>60). Furthermore in late-responders, tilt training brings about a change in cardiovascular autonomic function: at 3 months, LF(RR)NUs increase and HF(RR)NU diminish.

Power spectral analysis of HRV seems to be a useful tool to preselect patients who are most likely to benefit from prolonged therapy, thus increasing compliance.