947-111 IkBlockade Selectively Eliminates Slow Antegrade Atrioventricular Nodal Conduction in the Rabbit

We studied the effects of an Ikblocker, risotilide (R) on the dynamic properties of perfused rabbit AV nodes using intermittent right atrial premature pacing and bipolar surface electrograms. R was serially perfused with 1, 3 and6× 10–6M R for 15 minutes following pre-drug measurements.ResultsTypical changes in the antegrade recovery curve produced by R are shown in the figure. There was a concentration dependent decrease in Δ.AH from the pre-drug value of 56±15 ms to 29.2±16.9 ms and 13.7±5.9 ms by 3 and6× 10-6M respectively (n = 6). A reciprocal increase in the AV node effective refractory period was observed from 91±15 ms (pre-drug) to 139±16 ms (3×10-6M) and 170±16 ms (6 × 10-6M). AH∝ was unchanged at any concentration of R.ConclusionsThese results suggest that class III antiarrhythmic agents may increase action potential duration and the refractory period of the structure(s) limiting AV conduction and thereby eliminate a majority of the “slow” AV node conduction. These findings may have important implications for a pharmacologic approach to the treatment of AV node reentry tachycardias