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Response to letter by Wang et al.: Comparing cardioprotection by remote ischaemic preconditioning in patients with and without diabetics

Sir, We thank Wang et al. for their kind comments and appreciate their interest in our recent work. They specifically acknowledge that we have controlled for most known risk factors that may affect perioperative myocardial injury and/or troponin concentrations in patients undergoing coronary artery bypass graft (CABG) surgery, such as age, medications, cardiopulmonary bypass time, aortic cross clamp time, and dosages of vasoactive drugs. Nevertheless, Wang et al. still speculate that there might have been some unrecognised and hence unaccounted factors of intraoperative and post-operative management explaining our results. Specifically, beyond all the various factors accounted for in our present and former papers, they mention intraoperative defibrillation, the use of intraoperative or post-operative mechanical cardiac assist systems, episodes of intraoperative mean arterial pressure less than 55 mmHg, minimum haematocrit, and blood transfusions that might be associated with increased cardiac troponin concentrations after CABG surgery. However, intraoperative defibrillation was not used more than once, and in our manuscript, we had described the exclusion criteria explicitly including ‘any kind of mechanical assist device’. Furthermore, in our recent parent study that appears to have escaped Dr. Wang et al.’s attention, we already demonstrated that remote ischaemic preconditioning (RIPC) provided perioperative myocardial protection and improved the prognosis of patients undergoing elective CABG surgery independent of many factors. We agree, in general, that at times, it may be worthwhile to examine also very rare or remote issues, in particular in data derived from multicenter studies where protocols and clinical patterns might differ among centres and to try to assess whether there is a specific effect of such factors not only on cardioprotection but also on RIPC. Indeed, one symbol denoting statistical significance in table 3 was incorrect and should have been a ‘#’ instead of the ‘†’ in the legend. Unfortunately, that was an error occurring only in the proofs during the publishing process that had escaped our attention, too. However, this is not a relevant issue with regard to the conclusions drawn from the data or the interpretation. Wang et al. also remark that a sample size calculation was not performed. As already specifically outlined in our original manuscript, we did not present a sample size calculation because (1) a prospective sample size calculation had been presented for the main study and (2) the present analysis was part of this large ongoing study with multiple subanalyses addressing the effects and mechanisms of RIPC and anaesthesia on serial cardiac troponin I concentrations in CABG patients. Furthermore, with respect to the potential interference of sulfonylurea drugs with RIPC, which was our primary hypothesis, any speculation about a potential effect size would have been arbitrary as there were no previous data in humans on the RIPC effects of sulfonylurea drugs and/or diabetes. Fortunately, exploratory studies still make good sense even without sample size exercises. Conflicts of interest: The authors have no conflicts of interest.