Significance of the automaticity recovery phase following tachycardic overdrive

The usefulness of automaticity recover time (ART) and automaticity recovery phase (ARP; the time requiring P-P cycles to return to the original P-P cycles following the termination of tachyarrhythmias) for evaluating the sinus node function was studied in 24 patients with tachyarrhythmias by recordings of 24-hour continuous electrocardiograms. Automaticity recovery time was not so valuable in evaluating sinus node function because the overlap of ART was observed between patients of normal sinus node function and patients with sick sinus syndrome. The pattern of ARP was classified into 4 types (I--IV). Type I showed qUick return to the original P-P after overdrive suppression, type II was characterized by first suppression and secondary acceleration, type III was the pattern characterized by repeated suppression after tachycardiac overdrive, and type IV was characterized by repetitive appearance of tachyarrhythmia and bradycardia. The period of each ARP was measured and the period of type II (42.2 +/- 16.6 sec) or III ARP (48.4 +/- 21.4 sec) was significantly longer than type I (22.1 +/- 11.1 sec). Type III ARP was considered to suggest sinus node dysfunction. In conclusion, it was suggested that not only the observation of ART but also ARP were valuable for evaluating more precise sinus node function. The observation of ARP is easily obtained from 24-hour continuous recordings of electrocardiograms.