Editor-We read with interest the article by Saran and colleagues 1 describing the effect of prophylactic magnesium administration on the incidence of supraventricular arrhythmias (SVAs) in patients undergoing thoracotomy, and would like to make the following observations. Our institution undertakes oesophageal cancer surgery, and we are familiar with the occurrence of SVA after oesophageal resection and thoracotomy. Given the prognostic significance 2 3 of this complication for this group, any intervention, which would reduce its incidence, would be welcomed. Therefore, this study represented a concept of significant clinical value. However, the authors quote a range of incidence of SVA from various international centres, including comparable rates for oesophagectomy and pneumonectomy. As illustrated by the range for oesophagectomy (13 -32%), the incidence of SVA in this group varies widely from one centre to the next. Our own retrospective analysis of 5 yr of data from our unit indicates a local incidence of 5% (nine episodes in 174 cases). In their discussion, the authors describe oesophagectomy as 'greater risk of SVA' and wedge resections as 'lower risk of SVA'; our results would contest this. We would argue that such designations, based on reports from other centres, could be misleading when both conducting a study at a local level and attempting to account for the results.The intervention group in this study did not contain any patients who had undergone oesophagectomy, despite the high incidence of SVA quoted. In addition, three of those from the control group were cared for in a separate highdependency unit, which may result in non-standardized postoperative care and deviation from the study protocol. The authors claim that magnesium was effective in the 'high risk' group of pneumonectomy after subgroup analysis. We feel that the heterogeneity of the two groups would make conclusions regarding the effect of the intervention difficult to draw, particularly, as the number of pneumonectomy patients was rather low at 35.This study was further weakened by the occurrence of stinging caused by magnesium infusion in the first 100 patients, resulting in significant reduction of compliance in the intervention group and a probable negative effect on blinding. This complication resulted in an underpowered study. Because of these problems, we think it is difficult to draw any robust conclusions on the usefulness of magnesium sulphate in preventing SVA in these patients, but would agree with the authors final statement that this therapy warrants further investigation in patients undergoing thoracotomy.
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