Letter Regarding Article By Koller Et Al, "Altered Dynamics Of Action Potential Restitution And Alternans In Humans With Structural Heart Disease" - Response

To the Editor: In their recent publication, Koller and colleagues1 found that the dynamic pacing protocol yielded significant differences in restitution kinetics between patients with and patients without structural heart disease, but no significant difference was observed using the S2 pacing protocol. The authors speculated that the dynamic protocol may improve the predictive value of electrophysiological testing for ventricular fibrillation (VF) (p1546). However, their dynamic pacing cycle length was not shortened to <250 ms for ethical reasons, and repolarization data were obtained from a single ventricular pacing site. Thus, the kinetics of dynamic restitution remained undetermined at diastolic intervals between 0 and approximately 50 ms, as well as at other ventricular sites. In another study in which dynamic pacing cycle length was reduced to …