'Paradox' of troponin elevations after non-cardiac surgery.

Dr Noordzij and colleagues report in this issue of BJA that after major abdominal surgery, elevations in troponin, measured with a high-sensitivity assay, predict non-cardiac complications. This may seem to be an apparently paradoxical result. How can a very sensitive and specific diagnostic assay for myocardial injury and infarction predict postoperative non-cardiac rather than cardiac complications? However, those who carefully follow the literature on postoperative troponin elevations should not find this surprising at all. In a study published in 2003 froma cohort of 447 patients who underwentmajor vascular surgery,we showed that even low-level troponin elevations, measured with earlier cardiac troponin (cTn) assays during the first 3 days after surgery, presaged mortality at 5 yr, while more marked elevations predicted higher mortality. The vast majority of postoperative troponin elevations were asymptomatic. In fact, among patients with low-level troponin elevations, who were the majority, only 18% had signs or symptoms that could be attributable to myocardial infarction and only 32% had ST-segment depression lasting longer than 15 min on continuous 12-lead ECGmonitoring. Even fewer ischaemic events would have been detected if only daily samples of ECGs had been used,which is the commonpractice ofmost clinicians. Among the fewer patients with higher postoperative troponin elevations, the incidence of signs or symptoms possibly related to myocardial infarction increased incrementally to 40–60%, and the chance of finding even short (15 min) episodes of ischaemia on continuous 12-lead ECG monitoring increased to 80–90%. The recent VISION study has rediscovered this phenomenon. In VISION, evenminor cTnT elevations detected with the fourthgeneration assay for cTnT during the first 3 days in 15 065 patients predicted 30 day postoperative mortality, and more marked elevations were incrementally associated with higher mortality. In that study, as in ours, out of 115 patients with troponin elevations who died, only 22 (19%) had cardiac symptoms and only 31 (27%) had ischaemic ECG findings (ST-elevation/depression, new Q-waves or left bundle branch block) on daily ECGs. Similar results were reported by Beattie and colleagues, who studied 51 701 patients retrospectively and found that 20.4% had postoperative troponin I elevations. These elevations incrementally predicted 30 day postoperative all-cause mortality. Importantly, only 34% of postoperative deaths in low-risk patients were cardiac deaths, although the proportion of cardiac deaths increased to 42 and 60% in higher-risk patients. Finally, Van Waes and colleagues recently studied 2216 consecutive patients after major non-cardiac surgery using highsensitivity troponin I measurements during the first 3 days after surgery. They too confirmed that postoperative troponin elevations strongly and incrementally predicted 30 daymortality. Of the 315 (19%) patients with troponin elevations, 27 (8.6%) died but only 10 (3.2%) had typical chest pain and only 30 (9.5%) had new ischaemic ECG changes. It is clear from the above summary that while postoperative troponin elevations in the first days after surgery are common and strongly predict both 30 day and long-term mortality, they are not strongly associated with cardiac signs or symptoms. Higher postoperative troponin concentrations are better associated with cardiac signs or symptoms, but low-level troponin elevations, although prognostically important, are rarely associated with overt signs of cardiac abnormalities.