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Figure 3 The action potential duration restitution (APDR) curves by S₁S₂ in each group (patients with chronic atrial fibrillation [CAF] in the left panel; patients with paroxysmal atrial fibrillation [PAF] in the middle panel; and control subjects in the right panel). In patients with CAF, action potential duration at 90% repolarization (APD₉₀) shortening became 30 ms as the diastolic interval (DI) decreased to <30 ms (APD₉₀) and the maximal slope (Slope_max) was 1.6. In patients with PAF, the change in APD₉₀ was 31 ms, and the maximal slope was 1.4. In contrast, the decrease in APD₉₀ with increasing prematurity was small in the control group, which resulted in a flat APDR curve (Slope_max = 0.8).