This was a single-center, prospective, double-blind, randomized and controlled trial. This study was registered on Chinese Clinical Trial Registry (http://www.chictr.org.cn) with registration number ChiCTR-INR-16010234. The study was conducted in accordance with the principles of the Declaration of Helsinki and approved by the Medical Ethics Committee of Fuwai Hospital. Written informed consents were obtained from all participants prior to enrollment.
Patients aged 18 to 70 years with end-stage heart diseases scheduled for primary orthotopic heart transplantation between January 2017 and August 2018 at Fuwai Hospital, Beijing, China were screened and considered for random allocation. Exclusion criteria were preoperative mechanical circulatory support, peripheral vascular disease affecting the upper limbs, redo heart transplantation. Moreover, patients taking the antidiabetic sulphonylurea or glibenclamide were also excluded because these agents have been shown to abolish preconditioning induced by ischemic preconditioning [12].
On the day of surgery, eligible patients were randomly allocated to receive either RIPC+RIPostC or sham RIPC+RIPostC (control) before heart transplantation. Randomization was performed with opaque envelopes that concealed the group allocation. A research fellow, not involved in medical treatment or data analysis performed the enrollment, group assignment, and intervention. Patients, cardiac surgeons, and postoperative intensive care staffs were all blinded to treatment.
Remote ischemic conditioning was applied after anesthesia induction (RIPC) and 20 minutes after aortic declamping (RIPostC), which consisted of four 5-min cycles of right upper limb ischemia induced by a cuff inflated to 200 mmHg with an intervening 5 min of reperfusion during which the cuff was deflated. Patients in the control group underwent the sham placement of the cuff around the right upper arm without inflation. Blood samples were collected for measurement of serum cardiac troponin I (cTnI) levels before surgery and at 3, 6, 12, 24h after removal of the aortic cross clamp.
Premedication, anesthesia, perfusion, cardioplegia, and surgical techniques were standardized. Electrocardiography (ECG), pulse oximetry, nasopharyngeal and bladder temperature, arterial blood pressure, central venous pressure, and pulmonary artery pressure were monitored continuously. Anesthesia was induced with intravenous etomidate (0.2-0.3 mg/kg), cisatracurium (0.2-0.3 mg/kg) or rocuronium (0.6-1.5 mg/kg), sufentanyl (1-2 μg /kg), and midazolam (0.2-1mg/kg), and maintained with propofol (0.05–0.08 mg/kg/min), sufentanyl(300μg-500μg) and muscle relaxants(10mg/h). Low concentration of sevoflurane (0.5-1%) was used if necessary (during central lines implantation).
Orthotopic heart transplantation was conducted through median sternotomy. Standard non-pulsatile cardiopulmonary bypass (CPB) with a membrane oxygenator was used. During CPB, moderate systemic hypothermia (nasopharyngeal temperature 28°C) was maintained. The recipient’s heart was removed. Orthotopic heart transplantation was performed using a double-venous technique. All patients received basiliximab (20mg) before incision for immune induction. Methylprednisolone (500mg) was used twice before incision and after aortic declamping.
The primary endpoint was to compare serum cTnI levels at 6 h after aortic declamping between two groups. Secondary endpoints were comparison of serum cTnI levels at 3, 12, 24 h after aortic declamping and postoperative clinical outcomes including in-hospital death, new onset stroke, renal failure requiring dialysis, mechanical circulatory support, arrhythmia requiring treatment, re-operation for any cause, gastrointestinal bleeding, mechanical ventilation time, ICU length of stay, postoperative hospital length of stay.
The clinical outcomes were derived from the Society of Thoracic Surgeons (STS) database registry [13]. New onset stroke was defined as a new ischemic or hemorrhagic cerebrovascular accident with focal neurological deficit persisting >24 h and confirmed by brain computed tomography imaging. Re-operation for any cause included re-exploration for bleeding and surgical reintervention. Mechanical circulatory support was defined as postoperative use of an intra-aortic balloon pump (IABP) or extracorporeal membrane oxygenation (ECMO). Arrhythmia requiring treatment included ventricular fibrillation, ventricular tachycardia, and atrial fibrillation requiring intervention. Data were obtained from medical records and reviewed by two cardiologists who did not participate in the study.
Statistical analysis of data
Sample size was calculated according to our pilot study, serum cTnI level was 66±23 ng/ml at 6 h after aortic decamping in the control group. We hypothesized RIPC with RIPostC significantly reduced serum cTnI levels by 30% and assuming a 5% dropout rate. To achieve 80% power at a two-sided significance level of 5%, a total of 120 patients was needed.
All statistical analyses were performed using SPSS version 20.0 (IBM Corp, Armonk, NY). The Shapiro-Wilk test was used to assess the normality of the distribution. For normally distributed data, all data were described as mean ± SD. Nonparametric data were described as median and interquartile ranges, and categorical data were described as the number of patients and relative frequency of the patient. Normally distributed variables were compared between groups with independent-sample T test. Continuous variables that were not normally distributed were analyzed with nonparametric test (Mann-Whitney U). Categorical variables were compared between groups with Chi-square test or Fisher exact test if the resulting matrixes contained cells with expected count <5. All tests were two-sided and a p value of P<0.05 was regarded as significant. The analysis was by intention to treat.