Analysis of autonomic activity during head-up tilt in patients with lone paroxysmal atrial fibrillation

The autonomic nervous system (ANS) has been recognized as an important modulator in the pathogenesis of paroxysmal atrial fibrillation (PAF). Changes in ANS control of heart rate (HR) and blood pressure (BP) variability occur during orthostatism to maintain cardiovascular homeostasis. The wavelet transform (WT) has been used as a tool that provides a time-frequency decomposition of the signal under investigation, allowing intermittent components to be elucidated. Aim: To study HR and BP variability with WT analysis in younger patients (P) with PAF and normal echocardiographic findings, and in healthy individuals (HI) during head-up tilt (HUT). Methods: 17P with lone PAF (age <60 years [33-59], 9 men) and 17 HI (<60years [20-59], 8 men) underwent passive HUT (70º) while on sinus rhythm. Continuous monitoring of ECG and BP was obtained without antiarrhythmic drug medication. Acute changes in RR-intervals and systolic BP were evaluated with WT, and LF (low-frequency power), HF (high-frequency power) and LF/HF calculated for 1) the last 2 minutes of the supine period; 2) the 15 seconds of tilting movement (TM); 3) 1st and 2nd minutes of HUT. Results: RR intervals were identical for the two groups in baseline and during HUT. Supine basal BP was similar for both groups. During HUT, two BP response profiles were observed: a sustained increase in PAF P, and a decrease followed by an increase and further recovery in HI. WT analysis of RR intervals for PAF P, when compared to HI, showed lower LF/HF values in the supine position (2.0±0.5 vs. 2.5±0.3, p<0.05), and a decreased LF power during TM (574±134 ms² vs. 1347±393 ms², p<0.05). In the 1st and 2nd minutes of HUT, changes were comparable in PAF P and in HI. Analysis of systolic BP for PAF P, compared to HI, showed statistically significant differences regarding lower HF values in basal (0.69±0.14 ms² vs 1.05±0.13 ms², p<0.05) and lower LF and LF/HF values during TM (6.3±2.5 ms² vs 8.2±1.6 ms², 8.4±2.9 vs 12.8±4.4; p<0.05). No differences were detected with respect to the 1st and 2nd minutes of HUT. Conclusion: P with PAF presented modified autonomic control of HR and BP in the supine position and during the initial phase of orthostatism. These findings suggest that wavelets analysis may provide a new insight into the assessment of the dynamicity of autonomic cardiovascular regulation and underscore the presence of ANS disturbances in PAF.