Calcium cycling as mechanism of
repolarization alternans onset in the intact heart
Etienne Pruvot
Authors: Kenneth R Laurita; David S Rosenbaum; Rodolphe P Katra; Etienne Pruvot
8:00 - 6:00
T-wave alternans (T-ALT),
a powerful marker of arrhythmic events, results from alternation in cellular
repolarization. The underlying cellular mechanism is unknown, but has been
attributed to either: 1. membrane ionic currents, manifested by steep slope
of action potential duration (APD) restitution in cells exhibiting ALT, or 2.
intracellular calcium (Ca) cycling. High resolution optical mapping techniques
were used to measure action potentials and Ca transients simultaneously from
128 epicardial sites in the guinea pig model of pacing induced T-ALT (n=5). ALT
of APD (APD-ALT) and Ca amplitude (Ca-ALT) were measured over a broad range
of cycle lengths (CL). The CL (i.e. ALT threshold) at which T-ALT (162?4 ms), APD-ALT (160?0 ms), and Ca-ALT (156?5 ms) first appeared were similar (p=ns). Likewise, the site of origin
of APD-ALT and Ca-ALT was nearly identical in all experiments and always
occurred near the base of the left ventricle. However, the site of Ca-ALT and
APD-ALT onset was not located where APD restitution was steepest. Conclusion:
The onset of APD-ALT was closely related to Ca-ALT but not APD restitution,
suggesting that the mechanism underlying the initiation of T-ALT is more
closely associated with intracellular Ca cycling rather than membrane
repolarization currents. |