A 51-YEAR-OLD, 144.4-lb, 168-cm man was admitted to the authors' hospital for the treatment of bilateral breast periductal mastitis with fistulas and a right breast abscess. The patient had been homeless until very recently and did not receive routine medical care as a result. He chronically abused tobacco and alcohol, but he denied any major medical sequelae from these activities. He reported a family history of coronary artery disease, but his cardiovascular review of systems was unremarkable. The cardiac and pulmonary physical examinations were noncontributory. A laboratory analysis, including a serum potassium concentration, was normal. A preoperative electrocardiogram showed sinus bradycardia (heart rate of 58 beats/min) with a sinus arrhythmia, but no other abnormalities were present. The patient was transported to the operating room for the excision of bilateral breast subareolar ducts and fistula tracts and drainage of the right breast abscess. Anesthesia was induced using propofol (2 mg/kg), fentanyl (2 μg/kg), and rocuronium (0.6 mg/kg) and maintained using sevoflurane (end-tidal concentrations of 1.5%-2.0%) in an air-oxygen mixture. The patient remained hemodynamically stable in sinus rhythm before and after anesthetic induction. A few minutes after endotracheal intubation, an arrhythmia was observed (Fig 1). Sinus rhythm briefly returned spontaneously without medical intervention, but the arrhythmia subsequently recurred, prompting the rapid arrival of several other anesthesiologists and certified registered nurse anesthetists who had been watching the electrocardiographic (ECG) events on a remote monitor in the anesthesia service office. What is the diagnosis?