Elevated plasma levels of troponin I in surgical patients: analysis of risk factors and outcomes

Abstract

A retrospective study of the application of troponin I assays in postoperative patients admitted to the intensive care and high dependency units in a busy district hospital was performed. Preoperative patient demographics and cardiac risk factors, prior medical history and type and urgency of surgery were correlated with the results of troponin assays: only patient gender was significantly associated, with more females having elevated serum troponin I. Outcomes were worse when troponin I was raised, with a significantly higher mortality and trend to more organ systems failed. The study was limited by small size (47 patients) and non-standardisation of the timing of troponin assay after admission. A larger prospective study needs to be performed with assays at agreed time or trigger points. The patient cohort was derived from admissions to the ICU or high dependency units (HDU) in a busy district general hospital during a 9-month period from January to September 2003. Data were collected retrospectively from the biochemistry laboratory database in order to identify those patients whose troponin I levels were assayed during this period. Serum troponin I was measured in 61 patients in the ICU or HDU setting. Of these, 14 were medical patients with myocardial infarction and were excluded from the study. The other 47 patients were surgical and they form the cohort for this study. Patients whose serum troponin was measured comprised 31 males and 16 females. Their mean age was 74 years (range 49–93, standard deviation [SD] 10 years). Among the 47 patients in whom a suspicion of myocardial dysfunction had precipitated the laboratory test, 36 had abnormally high serum levels of troponin I (troponin I > 0.05 units in our laboratory). In none of these cases had there been any demonstration of myocardial infarction on electrocardiography nor echocardiography. The remaining 11 patients were classified as having normal troponin I levels and no biochemical evidence of myocardial injury. All the patients in the normal troponin group were male, but the other cohort comprised 16 females and 20 males. This was a significant difference in sex distribution (P = 0.006, chi-squared test) (Table ​(Table11). Table 1 Analysing the outcomes of patients with raised troponin levels compared with those with normal values (summarised in Table ​Table2),2), the presence of an elevated serum troponin I was associated with a shorter duration of stay although this did not reach statistical significance (P = 0.12, unpaired t test). This contrasts with their having more organ failure as already defined: cases with abnormal serum troponin I levels had a mean of 2.0 organ systems fail during their stay in ICU/HDU, compared with 1.5 organ systems in the normal troponin I group. However, the apparent difference between the groups in numbers of organs failed did not achieve significance (P = 0.35, t test). Table 2 Among those with normal troponin tests, two of 11 patients died. This was a lower proportion than in the group with elevated serum troponin levels, in whom 13 of 36 patients died. This was statistically a highly significant difference (P < 0.001, chi-squared analysis).