Figure 1. Electrocardiogram (ECG) obtained from patient 1. Preoperative ECG (left column), intraoperative ECG during isoflurane (middle column, upper panel), and during halothane anesthetic (middle column, lower panel). These ECG changes were reproduced when the anesthetic was switched to isoflurane (right column, upper panel); the ECG morphology returned to normal after isoflurane was discontinued at the end of anesthesia (right column, lower panel). ECG calibration: gain 1.0 = 10 mm = 1 mV. BP = blood pressure; BPM = beats per minute; HR = heart rate.