Background: The occurrence of paroxysmal atrial fibrillation is related to changes in autonomic tone. Vagally mediated atrial fibrillation predominantly occurs at night in young male patients without history of structural heart disease. In contrast, sympathetically mediated atrial fibrillation is typically triggered by stress.
Analysis of heart rate variability: Heart rate variability usually measured by Holter monitoring can determine changes in autonomic tone immediately preceding the onset of atrial fibrillation. Studies on this topic found divergent results on the incidence of atrial fibrillation mediated by changes in autonomic tone. Dependent on the results of different studies, night-time episodes of idiopathic atrial fibrillation either are vagally or sympathetically mediated. A sympathetic predominance is found in patients after coronary bypass surgery, concordantly. The inconsistency of these findings points to the fact that not only one mechanism, but more complex changes in autonomic tone are responsible for the occurrence of atrial fibrillation in many cases. In modern pacemakers and implantable cardioverter-defibrillators, PP or RR intervals can be stored automatically before the onset of an arrhythmia. By use of these stored intervals, time-domain parameters of heart rate variability can be calculated. We determined changes in short-term heart rate variability (10-second intervals) by analyzing 26 episodes of PP intervals sampled over the last 2 minutes before onset of atrial fibrillation by a modern dual chamber pacemaker. We observed a significant increase of the standard deviation of PP intervals (SDNN10s) as well as of the mean square route of the squared PP intervals (rMSSD10s) within the last 10-second interval before onset of atrial fibrillation (p < 0.05). This finding points to changes in autonomic tone-immediately preceding the onset of atrial fibrillation.
Conclusion: The preliminarity of these findings and the use of yet not validated short intervals for determination of heart rate variability does not allow to draw pathogenetic or even therapeutic conclusions from these findings.