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

Vlasta Bari1, Francesca Gelpi1, Beatrice Cairo1, Noemi Cornara2, Beatrice De Maria3, Marco Ranucci2, Alberto Porta1
1Department of Biomedical Sciences for Health, University of Milan, 2Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, 3IRCCS Istituti Clinici Scientifici Maugeri, Milan


Surgical aortic valve replacement (SAVR) can have an impact on cardiovascular control as assessed via the analysis of heart period (HP) and systolic arterial pressure (SAP) variability. Frequency domain causality techniques allow the exploration of HP-SAP closed-loop relation in frequency bands typical of the cardiovascular control. A frequency-domain causality analysis was applied to HP and SAP variability acquired from 58 patients (age: 65+/-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 (K2) analysis was performed along the baroreflex pathway from SAP to HP (K2SAP->HP) and along the mechanical feedforward link from HP to SAP (K2HP->SAP) in the low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, 0.15-0.4 Hz) bands. Results showed that K2SAP->HP in LF band increased during STAND compared to REST (0.19+/-0.15 vs 0.06+/-0.15) only in POST3, thus indicating that baroreflex control reacted to orthostatic stimulus in POST3. In addition, within STAND condition K2SAP->HP in LF band was higher in POST3 compared to PRE (0.08+/-0.09) and POST (0.09+/-0.10). Remarkably, K2SAP->HP in the HF band did not vary across time and experimental conditions. Similar conclusions held for K2HP->SAP in both LF and HF bands. Findings suggested that baroreflex control was depressed just after SAVR but recovered after a three-month follow-up. Conversely, 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.