Heart rate variability and the onset of tachyarrhythmias.

The autonomic nervous system plays an important role in the genesis of cardiac arrhythmias but the precise definition of this role is quite complex. The fluctuations of the heart rate may provide useful information about the balance of the autonomic nervous system. However, one obvious limitation is represented by extrapolating to the ventricle events which occur at the sinus node level. It has been clearly documented that atrial fibrillation of vagal origin is preceded by a progressive decrease in heart rate. On the other hand, ventricular arrhythmias of adrenergic origin are preceded by progressive heart rate acceleration and by diminution of vagally mediated short term changes. The absolute value in heart rate is less important than the actual trend in allowing inferences on the relative sympathetic or vagal predominance. A better understanding of the changes in the autonomic balance will provide a key for the mechanisms underlying several clinical events.