Frequency Domain Causal Analysis Allows the Detection of Baroreflex Control Recovery in Patients Undergoing Surgical Aortic Valve Replacement After a Three-Months Follow-up

Surgical aortic valve replacement (SAVR) can impact on cardiovascular control as assessed via the analysis of heart period (HP) and systolic arterial pressure (SAP) variability. Frequency domain causality techniques allow to explore HP-SAP closed-loop relation in the typical frequency bands of the cardiovascular control. A frequency-domain causality analysis was applied to HP and SAP variability acquired from 58 patients (age: $65\pm 13\ yrs, 39$ males) before SAVR (PRE), within one-week post-surgery (POST) and after a three-month follow-up (POST3). Analyses were carried out at rest in supine position (REST) and during an active standing test (STAND). Causal squared coherence $(K^{2})$ analysis was performed along the baroreflex pathway from SAP to HP $(K^{2}_{SAP\rightarrow HP})$ and along the mechanical feedforward link from HP to SAP $(K^{2}_{HP\rightarrow SAP})$ in the low frequency (LF, 0.04-0.15 Hz) and high frequency $(HF,\ 0.15- 0.4\ Hz)$ bands. Findings suggested that baroreflex control was depressed just after SAVR but recovered after a three-month follow-up while mechanical feedforward link was not affected. Future studies will be aimed to investigate a longer follow-up and to link results on the occurrence of post-surgery adverse outcomes.