A 28-year-old female presents to urgent care complaining of a fluttering feeling in her chest. She has been ill with vomiting and diarrhea for two days, but states the GI symptoms have now stopped. She just is concerned about the heart rate. The EKG reveals multifocal PVCs. The patient's laboratory values are: serum potassium 2.6 mEq/L, serum sodium 144 mEq/L, serum chloride 90 mEq/L, and blood glucose 98 mg/dl. The nurse practitioner believes that the patient's PVCs are likely caused by which of the following: