Non-linear regularity of arterial blood pressure variability in patient with atrial fibrillation in tilt-test procedure

Dynamics of cardiovascular series may be explored with non-linear techniques. It is unknown if the arterial pressure irregularity commonly observed in patients with atrial fibrillation (AF) might be further increased by a sympathetic stimulus such as orthostatic tilt.

Twenty patients (62 ± 14 years, 15 men) were recruited for the study. Continuous beat-to-beat non-invasive arterial pressure was acquired at rest and during a passive orthostatic stimulus (‘tilt test’). Systolic (SAP) and diastolic (DAP) arterial pressure series of 300 samples were analysed in both conditions. Approximate (ApEn) and sample entropy (SampEn) were computed, as irregularity measures. Equivalent metrics (ApEn_AR and SampEn_AR) derived from an autoregressive model of the series were also obtained through numerical simulations, to further elucidate the non-linear mechanisms present in the series. In 11 patients (Group A), SAP significantly increased during tilt (from 103 ± 13 to 114 ± 17 mmHg, P < 0.001 rest vs. tilt), whereas in 9 patients (Group B) SAP remained almost unchanged (SAP: 110 ± 18 vs. 106 ± 19 mmHg, rest vs. tilt). No clinical differences were found between Groups A and B. When analysing Group A, all irregularity measures significantly increased in SAP (ApEn: 1.75 ± 0.20 vs. 1.88 ± 0.16, P < 0.05; SampEn: 1.71 ± 0.30 vs. 1.88 ± 0.27, P < 0.05; ApEn_AR: 1.87 ± 0.20 vs. 1.96 ± 0.18, P < 0.05; SampEn_AR: 1.94 ± 0.27 vs. 2.06 ± 0.18, P < 0.05; rest vs. tilt), whereas no differences were found in DAP series. No significant differences were found in Group B for either SAP or DAP.

The alterations of SAP during tilt in AF patients are not uniform and seem associated with different regularity patterns. The pressor response to sympathetic stimulation was also associated with an increase of SAP series irregularity.