Patients
This trial was registered at clinicalTrials.gov (NCT02139241) and adhered to CONSORT guidelines. The study complied with the Declaration of Helsinki and each patient gave his or her written consent to participate. There were no important changes to methods or outcomes after trial commencement and no interim analyses were performed. Adult patients scheduled for elective OPCAB were eligible for inclusion. Patients were excluded if they had preoperative treatment with inotropic agents or mechanical assist devices, heart failure with left ventricular ejection fraction less than 30 %, QTc interval prolongation of more than 500 ms on preoperative ECG, significant arrhythmia including atrial fibrillation or atrioventricular block, age more than 80 years, a history of hepatic failure (Child Class B or C), emergency operation, renal impairment requiring renal replacement therapy, history of allergy to 5-HT3 antagonists, recent exposure to medications known to cause QTc prolongation, or undergone concomitant major surgeries including general surgery, neurosurgery and orthopaedic surgery.
Study design and treatments
The study was double-blind, placebo-controlled, parallel-group study conducted in Seoul National University Hospital, a tertiary hospital in Seoul, Korea. Patients were randomly allocated to either ramosetron group or placebo group, using a computer-generated random number table. A randomisation sequence was created with a 1:1 allocation using random block sise of 4. An independent nurse who was not involved in the collection of data and patient care handled the random list. All patients, medical personnel, and investigators were blinded to the allocation. One researcher (D.M.H.) generated the random allocation sequence, enrolled participants and assigned participants to interventions. The independent nurse prepared 0.3 mg of ramosetron (Nasea®; Astellas, Tokyo, Japan), the manufacturer’s recommended dose or, for the control group, the same volume of normal saline.
These two medications of the same color and volume were indistinguishable to the anaesthesiologists in charge of anaesthesia. The ramosetron group received intravenous ramosetron immediately before induction of general anaesthesia, while the placebo group received intravenous normal saline according to the same schedule.
Anaesthesia
All patients received standard perioperative care. Routine monitoring included 5-lead ECG, pulse oximetry, non-invasive blood pressure, bispectral index, cerebral oximetry, continuous arterial blood pressure, pulmonary artery catheter, and transoesophageal echocardiography. A radial arterial catheter was put in place under local anaesthesia with lidocaine. Anaesthesia was induced with intravenous midazolam 0.15 mg/kg, sufentanil 1 μg/kg, and vecuronium 0.15 mg/kg, and maintained with continuous infusions of remifentanil 0.5–1.0 μg/kg/min and propofol 0.04–0.07 mg/kg/min, with targeting bispectral index values between 40 and 60. We did not use volatile anaesthetics to avoid their effects on QTc interval [12–14]. Arterial systolic, diastolic, and mean blood pressure, heart rate, and doses of inotropic or anticholinergic drugs were recorded at the time of induction and during the surgery. Anaesthesia-related hypotension (mean blood pressure < 60 mmHg) was treated with either ephedrine 0.1 mg/kg IBW (ideal body weight) (heart rate < 70 beats/min) or phenylephrine 0.5 μg/kg IBW (heart rate ≥ 70 beats/min). If blood pressure was not restored within 30 s, the regimen was repeated until the maximum dose of ephedrine 0.5 mg/kg IBW or phenylephrine 4 μg/kg IBW was reached. If the blood pressure was not restored by the maximum dose, vasopressin or epinephrine was administered at the anaesthesiologist’s discretion. Normothermia was maintained during the surgery with a heating mattress, warmed intravenous fluids, and a warm operating room temperature.
QTc interval measurement and analysis
Digital ECGs were recorded using a continuous monitoring ECG system (Solar® 8000 M, GE Medical Systems, Milwaukee, WI, USA) at the beginning of drug administration, after 1, 2, 3, 5, 10, 15, 30, 45, 60, 90, 120, and 240 min, and at the end of the operation. ECG data in lead II were extracted with an analogue-to-digital converter (DI-149; DATAQ Instruments Inc., Akron, OH, USA), which was connected to the analogue output of the patient monitor, and stored on a personal computer [15]. Lead placement was consistent in the tracing of ECG. Temporally aligned superimposed ECG leads were available as an optional display. The sampling rate was 1000 Hz. At first, the QT interval was measured using a computer-based data analysis system (LabChart7; ADI Instruments, Colorado Springs, CO, USA). ECG waves of the four consecutive cycles were averaged to acquire a more accurate representation of the ECG waveform. The QT interval was corrected according to Bazett’s formula to preclude interference from heart rate (QTc = QT/RR1/2). Additionally, QT interval was corrected using Fridericia’s formula (QTc = QT / RR1/3) and Hodges formula (QTc = QT + 1.75 (heart rate – 60)). An investigator (T.K.K.) blinded to the group allocations reviewed the ECG data and checked for possible artifacts. Noise or abnormal ECG rhythms were excluded from the QTc interval measurement. After the operation, patients were checked for arrhythmias, including atrial fibrillation, atrial flutter, ventricular tachycardia, ventricular fibrillation, bradycardia (heart rate < 50 beats/min), and tachycardia (heart rate > 100 beats/min). A postoperative ECG was performed to evaluate QTc interval on the morning of postoperative day 1.
Definition of postoperative complications
The lengths of stay in the ICU and hospital were defined as the difference in days between the date of discharge and the date of surgery. Postoperative in-hospital major adverse cardiovascular and cerebral events (MACCE) were defined as a composite of death from cardiac causes, myocardial infarction, unplanned coronary revascularisation, and stroke. Myocardial infarction was defined as elevation of troponin values (>10 × 99th percentile upper reference limit) in patients with normal baseline troponin values (<99th percentile upper reference limit). In addition, new pathological Q waves, new left bundle branch block, angiographically documented new graft or new native coronary artery occlusion, or imaging evidence of new loss of viable myocardium or new regional wall motion abnormality were required. Unplanned coronary revascularisation was defined as unplanned repeat percutaneous coronary intervention or CABG. Stroke was defined as a new ischaemic or haemorrhagic cerebrovascular accident with a neurological deficit lasting > 24 h.
Statistical analysis
The primary endpoint was maximal intraoperative change in QTc interval after administration of ramosetron or placebo. The secondary endpoints were number of patients with QTc interval > 500 ms, which is considered to increase the risk of TdP [16]; number of patients with QTc interval increase > 60 ms, which is also considered to increase the risk of TdP [17]; presence of hypotension and bradycardia during anaesthesia induction; use of vasopressors or inotropes; presence of postoperative in-hospital arrhythmia and MACCE. Our pilot study showed that maximal change in QTc interval was 15 ± 15 ms during OPCAB. Presuming that the difference of 10 ms in the QTc intervals was clinically significant, power analysis suggested that a minimum of 49 patients would be required for each group with a type 1 error of 0.05 and a power of 0.9. Considering a 15 % dropout rate, 114 patients were recruited. Comparisons of age, weight, height, body mass index, anaesthesia time, serum electrolytes, blood pressure, heart rate, preoperative and maximal change in QTc interval, and lengths of stay in the ICU and hospital were tested with Student’s t-test or Mann–Whitney U-test after testing for normality. Sex, previous medical history, use of vasopressors or inotropes, presence of prolonged QTc interval, and presence of postoperative complications were compared by the Chi-square test or Fisher’s exact test where appropriate. QTc intervals taken serially after induction, heart rate, and blood pressure were analysed using repeated measures analysis of variance for inter- and intra-group comparisons. Statistical analyses were performed using the SPSS software (ver. 21.0; SPSS Inc., Chicago, IL, USA). In all analyses, P < 0.05 was taken to indicate statistical significance.