The purpose of this study is to assess the use of the medication ondansetron (zofran) in the emergency department. There are studies of the ability of ondansetron to cause a prolongation in the QT interval (a certain measurement on an EKG) in anesthesia and cancer patients, but not on emergency department patients. This is an observational study where patients that are going to receive the anti-nausea medicine ondansetron in the emergency department will have an EKG performed every 2 minutes for 20 minutes to determine if the QT interval prolongs and returns to normal in that time period. Any serious outcomes will be reported. There is expected to be no adverse outcomes from this routinely used medication.

Intravenous ondansetron is routinely used in adult emergency department patients experiencing nausea or vomiting. The FDA has changed the drug label to warn of prolongation of the QT interval and required the manufacturer to perform additional studies. There are rare case reports of cardiac electrical toxicity to include QT prolongation, atrial fibrillation, severe bradycardia, ventricular tachycardia, supraventricular tachycardia, and the potential for Torsades de Pointes. All of the reported literature on ondansetron comes from post-operative patients, patients receiving chemotherapy, and healthy volunteers, but has never been assessed in the emergency department population. Adult emergency department patients that do not meet the exclusion criteria will be enrolled prior to receiving intravenous ondansetron. Administration of ondansetron will be at the discretion of the attending physician. A twelve-lead electrocardiogram (EKG) or 12-lead rhythm strip will be generated prior to drug administration, and every 2 minutes following drug administration for 20 minutes after administration. During the entire 20 minutes the patient will be on a cardiac monitor and if any of the defined adverse cardiac electrical events occur (non-sinus rhythm, severe bradycardia, sudden cardiac death) the patient will be treated using standard Advanced Cardiac Life Support methods and admitted for continued monitoring. The mean maximal QTc prolongation (as measured by the Bazett formula), as well as the rate of adverse cardiac events with 95% confidence intervals will be reported.

The global objective of this study is to determine if routine use of intravenous ondansetron in the emergency department is associated with cardiac risks. The primary objective is to determine the mean maximal prolongation in QTc interval from baseline as measured by the Bazett formula. The secondary objective is to determine the number of severe adverse cardiac electrical events (non-sinus rhythm, severe bradycardia, sudden cardiac death) associated with routine use of intravenous ondansetron in the adult emergency department patient.

Inclusion Criteria:

• Age >18
• Patient to receive 4mg of intravenous ondansetron

Exclusion Criteria:

• Age <18
• known long QT syndrome
• received oral or intravenous ondansetron within 4 hours of enrollment
• co-administration of any known QT prolonging agents
• QTc on baseline of >450 ms for males and >470ms for females
• allergy or known hypersensitivity to ondansetron
• altered mental status
• non-sinus rhythm on baseline EKG
• hypokalemia (as defined by the lower limit of normal for the reference laboratory)
• hypomagnesemia (as defined by the lower limit of normal for the reference laboratory)
• any presentation for chest pain with signs of ischemia on baseline EKG
• QRS duration > 120 msec
• bundle branch block (right or left)
• ventricular pre-excitation or signs of left ventricular hypertrophy with repolarization abnormalities

The target population is adult (>18 years old) emergency department patients who have been deemed appropriate to receive intravenous ondansetron.