Evidence for a Central Origin of the Low-Frequency Oscillation in RR-Interval Variability

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Abstract
Background —Short-term variability of RR interval and blood pressure occurs predominantly at low frequency (LF; ≈0.1 Hz) and high frequency (≈0.25 Hz). The arterial baroreflex is thought to be the predominant determinant of the LF component of RR variability. Patients with severe congestive heart failure (CHF) have an attenuated or absent LF oscillation in RR variability. The left ventricular assist device (LVAD) offers a unique possibility for analysis of spectral oscillations in RR interval independent of any effects of blood pressure that influence these oscillations via the baroreflex. Methods and Results —We performed spectral analysis of RR, blood pressure, and respiration in 2 patients with CHF before and after LVAD implantation. LF components of the RR-interval and blood pressure variability were absent in both CHF patients before LVAD implantation. After LVAD implantation, spectral analysis of the RR interval showed restoration of a clear and predominant LF oscillation in the native hearts of both patients, with no such oscillation evident in the blood pressure profile. Conclusions —During total circulatory support with the LVAD, the LF oscillation in RR interval of the native heart, absent in CHF, is restored. This LF oscillation in RR interval occurs in the absence of LF oscillations in blood pressure and thus is unlikely to be explained by baroreflex mechanisms. Hence, the absence of LF oscillation in the RR interval in CHF is functional and is reversible by LVAD circulation. The presence of a predominant LF oscillation in RR interval independent of any oscillation in blood pressure suggests that the LF oscillation is a fundamental property of central autonomic outflow.