Attenuation of Cardiovagal Baroreflex Gain Resetting During Isometric Handgrip Exercise in Patients With Fontan Circulation

Exercise intolerance is hallmark in patients with Fontan (FTN) circulation and may be attributed to low baroreflex sensitivity and thus, a low heart rate response for a given exercise intensity. Whether resetting of the cardiovagal baroreflex gain during exercise in FTN is attenuated remains unknown. Accordingly, we tested the hypothesis that the increase in heart rate from rest to exercise would be lower and cardiovagal baroreflex gain resetting attenuated in FTN. 23 patients with FTN (F = 11, M = 12; 14(4) yrs; BMI = 20(6)) were age- and sex-matched to 20 healthy controls (CTL; F = 7, M = 13; 14(4) yrs; BMI = 20(4)) who performed 2-min of isometric handgrip (IHG) exercise at 30-40% maximal voluntary contraction following 2-min of rest. Heart rate (electrocardiogram) and blood pressure (finger cuff photoplethysmography) were measured throughout. Cardiovagal baroreflex gain was determined using the spontaneous sequence method at rest and during IHG exercise. Sequences of 3 or more successive increases or decreases in SBP and heart rate (R-R interval) using a lag of 0, 1, or 2 cardiac cycles when r ≥ 0.7 were included. Comparisons were made using mixed-designs ANOVA or unpaired t-tests and the threshold for significance was set to P < 0.05. In FTN, 36(21) sequences/participant at rest and 35(12) sequences/participant during IHG exercise were analyzed. In CTL, 26(9) sequences/participant at rest and 39(13) sequences/participant during IHG exercise were analyzed. Resting heart rate (FTN = 76(13) vs CTL = 70(8) bpm , P = 0.2208) and SBP (FTN = 109(13) vs CTL = 106(14) mmHg, P = 0.7188) did not differ between groups. Despite similar increase of SBP from rest to IHG exercise (FTN = 5(6) vs. CTL = 8(8) ∆, P = 0.2014), the heart rate increase was attenuated in FTN relative to CTL (3(5) vs 15(10) ∆, P < 0.0001). At rest, cardiovagal baroreflex gain was lower in FTN relative to CTL (14.0(9.8) vs 24.4(6.3) ms/mmHg, P = 0.0001). Further, the baroreflex gain from rest to IHG exercise was attenuated in FTN compared to CTL (-0.2±5 vs. -9±8 ∆, P = 0.0001). The cardiovagal baroreflex gain and heart rate responses were negatively correlated in FTN (r = -0.68, P = 0.0003). Attenuated resetting of the cardiovagal baroreflex gain during exercise contributes to a blunted exercise heart rate in FTN. Heart and Stroke Foundation This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.