Figure 5.

APD₅₀ restitution in contracting vs. contraction-inhibited isolated rabbit heart (N = 1, representative example) uncoupled with Blebbistatin (at 2.8μM concentration), optical measurement on left ventricular surface. (A) APD₅₀ restitution before (black/gray) and after (yellow/orange) administration of Blebbistatin with APD₅₀ measured from 2 × 15 = 30 (even and odd) consecutive action potentials at each cycle length CL (black/gray or yellow/orange = measured separately to detect alternans). Error bars indicate standard deviation of all APD₅₀ in APD-maps (C), or all APD₅₀ measured in each pixel on heart surface. Right: Close-up of region with cardiac alternans (CL ≤ 160ms). With Blebbistatin, pacing with CL ≤ 140ms induced (non-sustained) VF. (B) Motion decreases with increasing pacing frequencies. Strong motion (10–20% of heart size) at CL = 250 − 350ms. (C) APD₅₀ maps from the same heart with and without Blebbistatin for cycle lengths CL = 200ms and CL = 350ms (different heart than in A).