Blood pressure variability in patients with atrial fibrillation

The highly irregular ventricular rate during atrial fibrillation (AF) represents a unique and physiological experimental model to eliminate the influence of rhythmical components of RR variability on arterial pressure variability for investigating the origin of low frequency (LF) component in arterial pressure. Surface ECG, blood pressure and respiratory signals were recorded in thirty patients with persistent AF, at rest and during a passive orthostatic stimulus ("tilt test"). Short-term systolic (SAP) and diastolic arterial pressure (DAP) variability was estimated by autoregressive method. In 15 patients (group A), SAP significantly increased during tilt (from 98±16 to 114±18mmHg, p<0.001 rest vs. tilt), whereas in the remaining patients (group B) SAP remained almost unchanged (from 108±16 to 104±17mmHg, p=0.05, rest vs. tilt). No clinical differences were found between group A and B. When analyzing group A, a significant increase in the LF power in SAP and DAP variability was observed during tilt (SAP: 2.24±2.75 vs. 6.60±5.11mmHg(2), p<0.05, rest vs. tilt; DAP: 3.54±1.95 vs. 4.38±3.21mmHg(2), p<0.05, rest vs. tilt). No significant differences were found in group B. In AF patients, changes of arterial pressure variability during tilt were not uniform. Vascular regulatory mechanisms appeared to be still efficient only in the subgroup of patients who responded to a sympathetic stimulus with an increased SAP. In these subjects tilt increased the LF component in arterial pressure variability, thus mimicking the physiological response observed in subjects with sinus rhythm.