Current research indicates an imbalance in the autonomic nervous system (ANS) pathway activities in patients with congenital heart disease (CHD). The heart rate variability (HRV) is a measure to quantify activities of the parasympathetic and sympathetic branches. This study evaluated the parasympathetic activity by means of HRV in patients with CHD, regarding diagnostic subgroups and CHD severity, and the association to exercise capacity.
From July 2016 to August 2018, a total of 222 patients with different types of CHD (28.4 ± 10.1 yr; 44% female) received breathing-controlled HRV measurement in the supine position. Based on 130 adjacent heartbeats, the root mean square of successive differences (RMSSD), a parasympathetic activity surrogate was estimated and log-transformed. Additionally, all patients underwent a cardiopulmonary exercise test. For comparison, a control group (CG) of 57 (29.0 ± 7.1 yr; 61% female) healthy volunteers was recruited.
Patients with CHD exhibited reduced parasympathetic activity in comparison to the CG (lnRMSSD CHD: 3.55 ± 0.57 ms vs CG: 3.93 ± 0.55 ms; P < .001), with the lowest parasympathetic activity in patients with Fontan circulation (3.07 ± 0.54 ms; P < .001). Complex CHD (3.40 ± 0.54 ms) had worse values compared with patients with simple (3.87 ± 0.55 ms; P < .001) and moderate severity (3.74 ± 0.54 ms; P < .001). Better parasympathetic activity in CHD patients was associated with increased exercise capacity (r = 0.322; P < .001).
Impaired parasympathetic activity suggests limited function of the ANS in patients with CHD. Further studies should focus on the association of exercise capacity and ANS to possibly improve parasympathetic activity and functional outcomes.