Changes of arsenic and electrocardiographic parameters during As₂O₃-ON and As₂O₃-OFF. (A) Plasma elemental arsenic level. The cellular arsenic level was consistently higher than the plasma arsenic level. At steady state during As₂O₃-ON, an oral dose of As₂O₃ (10 mg) did not cause a change in cellular arsenic level. At 4 weeks after cessation of treatment (As₂O₃-OFF), there was near-complete clearance of arsenic. (B) Circadian variations of heart rate. The heart rate was consistently elevated duringAs₂O₃-ON. bpm indicates beats per minute. (C) Circadian variations of mean QT intervals. Random samplings of at least 20 templates of 30-second interval recordings (each with > 80% eligible QRS complex) every hour from 24-hour recordings were selected. For each template, mean QT intervals were measured automatically from onset of Q-wave to end of T-wave. Both the pattern and the mean QT intervals were comparable during As₂O₃-ON and As₂O₃-OFF. msec indicates milliseconds. (D) Circadian variations of mean QTc. QT intervals were corrected with the mean cycle length of the 30-second interval to calculate QTc. The mean QTc intervals were significantly increased during As₂O₃-ON. However, the longest mean QTc at 16:00 (2 hours after oral As₂O₃) was still less than 500 milliseconds. (E) Circadian variation in mean QTc prolongation. The mean QTc prolongation only exceeded 30 milliseconds at one time point (16:00, 2 hours after oral As₂O₃).