RELATIONSHIP BETWEEN LOCAL ATRIAL-FIBRILLATION INTERVAL AND REFRACTORY PERIOD IN THE ISOLATED CANINE ATRIUM

Background Atrial refractory periods and their spatial distribution ar e important determinants of atrial reentrant arrhythmias. The objectiv e of this study was to demonstrate a correlation between the local atr ial fibrillation interval (AFI) and local effective refractory period (ERP). Methods and Results To measure the local ERP and local AFI unde r stable conditions without hemodynamic, autonomic, or reflex influenc es, isolated perfused canine whole atria were used (n=8). The isolated atria were mounted on two endocardial electrodes. Bipolar electrogram s were simultaneously recorded from 253 endocardial sites, and 16 to 2 0 randomly distributed electrodes were used to measure the local ERP b y the extrastimulus technique. In all studies, several episodes of AF were induced by a single extrastimulus. The ERP and minimum AFI conver ged with increasing duration of AF. The convergence was more rapid if the total duration of AF analyzed came from multiple episodes of AF. T he correlation coefficient between the local ERP and minimum local AFI was .92 (n=119, P<0.01), The minimum AFI was used to construct AFI di stribution maps at all 253 sites. Activation block during premature st imulation correlated with regions of long AFI. Conclusions The minimum local AFI measured from at least 10 seconds of AF approximates the lo cal ERP. Construction of a minimum local AFI map during AF can be used to predict the distribution of refractoriness and can be used to pred ict sites of functional block. Contrary to studies done in intact anim als and patients, the AFI were longer than the ERPs, suggesting that r eflex changes may shorten ERP in the intact heart.