Cardiac parasympathetic denervation reduces hypoxic tachycardia, baroreflex sensitivity and heart rate variability in...

The autonomic regulation of heart rate (HR) reactivity to acute hypoxia remains unclear. Parasympathetic cardioneuroablation (PCNA) may serve as a novel model for the analysis of physiological consequences of reduced vagal influence over sinus node in humans. We studied 11 adult patients scheduled for PCNA for the treatment of vasovagal syncope. HR reactivity to hypoxia was studied before and after PCNA with brief nitrogen gas administrations. Each test was followed by an atropine challenge to evaluate the contribution of parasympathetic tone to the resting HR. Additionally, we assessed changes in cardiac baroreflex sensitivity and HR variability following the procedure. PCNA led to partial parasympathetic denervation of sinus node at rest (67.0 ± 20.1%). This translated into a significant change in HR reactivity to hypoxia (0.58 ± 0.21 vs. 0.22 ± 0.13 beats min^- 1%SpO₂ ^- 1, p = 0.0001) which was proportional to the degree of cardiac vagal denervation (R = 0.76, p = 0.01). There was no change in peak HR on atropine following PCNA implying unchanged sympathetic input to sinus node. This suggests that HR reactivity to acute hypoxia is significantly influenced by parasympathetic system. Additionally, despite incomplete vagal denervation PCNA resulted in profoundly depressed HR variability and cardiac baroreflex sensitivity. The clinical meaning of the latter should be explored in further studies.