Fig. 10.

Summary and illustration of the occurrence of short runs of action potential (APD₉₀) alternans in the human atrium at selected pacing cycle lengths. A and B: normalized values for the occurrence of APD₉₀ alternans when human atrial myocyte models were paced for 50 s under sinus rhythm (SR; A) and atrial fibrillation (AF; B) conditions. Results are shown under baseline SR and AF conditions (black traces) and after introduction of the 50% switch of Kv1.4 for Kv4.3 (red traces). C and D: initial evaluation of the duration of the pacemaker train on occurrence of APD₉₀ alternans in the same myocytes that were paced for 150 as opposed to 50 s. To construct the individual graphs, the normalized occurrence of APD₉₀ alternans was calculated as a ratio. For each chosen condition, this ratio consisted of the number of action potentials that exhibited alternans divided by the total number of action potentials that were evoked for each selected pacing cycle length and train duration.