This prospective, randomized, single blind study was conducted after our Institutional Review Board approved the study protocol, consent form and the randomization form. 70 consecutive ASA I-III patients (age18 to 60 years) undergoing breast surgery for carcinoma breast were included in the study after obtaining written informed consent. Patients refusing consent, with prolonged QTc interval, with arrhythmias or conduction defects and those with abnormal serum levels of potassium, calcium, magnesium were excluded. There was no standardized anaesthesia technique. The technique of induction of anaesthesia, maintenance and reversal of anaesthesia was left to the discretion of the staff anaesthetist in the operating theatre. The data on comorbidities, preoperative medications for the comorbidities, premedication, induction agents, analgesics, muscle relaxants and inhalation agents was collected.

Sample size calculation: A sample size calculation was performed \[according to mean changes (difference of means) in QTc interval\] to find out the number of patients needed to find a significant difference between the two drugs. To detect a QTc change from baseline of greater than 5 ms with α and β error of 0.05 and 0.20, respectively, and assuming an SD of QTc change of 10 ms using a one-sided test, a minimum of 35 subjects were needed in each antiemetic group.

Randomization: The patients (n= 70) were divided randomly in two groups by computer generated random numbers by the statisticians in the Clinical Research Secretariat (CRS) in our institute. Block randomization was done with blocks of 10, to allow stratification of the patients depending on whether they had received anthracycline based neoadjuvant chemotherapy. The list of randomization numbers and clinical details were maintained in the CRS.

Intervention: Once the patients arrived postoperatively in the recovery room, one of the investigators called the Clinical Research Secretariat (CRS) on phone, after completing the randomization form and gave the patient details. The Statistician allocated the drug the patient should receive which was prepared by the investigator which was either ondansetron 8 mg (Group O) or granisetron 1mg (Group G). A baseline 12 lead electrocardiogram was obtained before the drug was administered. After baseline ECG, patients in Group O were given intravenous 8 mg ondansetron and patients in group G were given 1 mg granisetron over 30 seconds. Subsequently serial 12 lead ECGs were done at 2 mins, 5 mins, 15mins, 1 hour and 2 hours. Pulse, blood pressure and SpO2 were also monitored at those intervals. Unfiltered Electrocardiograms were recorded at paper speed of 25mm/sec and at normal amplitude with a HP Vigilent Pagewriter 100TM device which automatically calculates and prints the heart rate and the duration of various ECG intervals. The investigators independently read and analyzed the ECG to confirm that the intervals obtained with the ECG machine were indeed accurate. QT and R-R intervals were measured for calculation of corrected QT (QTc) interval. The corrected QT (QTc) interval was calculated by using the formula described by Bezzet. \[QTc = QT interval/√ (RR interval)\]