Dallas, TX

November 8-11, 1998

QT/T alternans (A) frequently precedes the onset of ventricular arrhythmias (VA) in congenital long QT syndrome (LQTS). We investigated this phenomenon in the canine anthopleurin-A model of LQTS, a surrogate of LQT3. Tridimensional activation and repolarization (R) patterns were analyzed from 256-384 electrograms and local R was calculated from activation-recovery intervals (ARI). A was induced by abrupt or stepwise pacing (P) at shorter cycle length (CL). In 4 of 7 experiments, VA developed during a A following only odd-paced beats (P3, P5, P7). R patterns showed that even-paced beats (P2, P4, P6) were associated with significant increase of dispersion of R between epicardial (Epi) and mid myocardial (Mid) zones compared to baseline dispersion at longer CL not associated with A (p<0.02). The odd P encroached on the dispersion of R of preceding even P resulting in functional conduction block and reentrant VA. (Fig).

The increased dispersion of R was due to differences in restitution kinetics of Mid versus Epi (larger Mid D ARI, p<0.0001). The present mechanism may underlie the association between overt or subclinical A and VA at large.