2.7 Arrhythmia induction protocol
Stimuli were generated by an isolated constant voltage/current
stimulator (VCS3001, MappingLab Ltd., UK). They were delivered with a
platinum electrode onto the epicardial apex at an amplitude 1.5 × the
diastolic voltage threshold and a 2 ms pulse width. The optical mapping
was performed in conjunction with an “alternans mapping” protocol. The
heart was consecutively paced at basic cycle lengths (BCL) from 210 with
10 ms decrement until 170 ms. The heart was paced 50 times with 2 ms
duration pulses and the optical mapping recording was performed at the
last 2 second in each episode. This protocol was performed both before
and after drugs were delivered.