Myocardial injury and anaemia in patients undergoing surgery for fractured neck of femur

Editor, Patients undergoing surgery for fractured neck of femur (NOF) are often frail with multiple comorbidities,1 particularly pre-existing cardiovascular disease (CVD) including heart failure) and also peri-operative anaemia from chronic illness, fracture or surgery-induced bleeding.2,3 It is uncertain if troponin release in this context represents new cardiac ischaemic events, existing cardiac disease, the severity of traumatic insult or other complications such as thromboembolic disease or renal failure.4 Understanding the mechanism of troponin release and its prognostic significance in this group is of importance as it may inform research aimed at increasing myocardial oxygen supply, such as the use of higher transfusion thresholds in patients with CVD undergoing surgery.5 Previous studies have used troponin release to quantify cardiac injury in surgical patients undergoing therapy to increase peri-operative oxygen delivery.6 We conducted a small observational study to investigate rates of peri-operative myocardial injury and anaemia in patients undergoing surgery for fractured NOF to evaluate the use of troponin as a study endpoint for future studies investigating peri-operative anaemia and transfusion practice. Our aims were to measure the rate of troponin release in this group and to investigate its association with blood loss and anaemia. This was an exploratory study and not based on a formal power calculation. The study protocol was approved by the Scotland A Research Ethics Committee (Edinburgh, Scotland, United Kingdom. Reference: 16/SS/0139) and registered with Clinical Trials.gov (NCT02969811). Written consent was obtained from all study participants or their nearest relative or welfare attorney. NHS Lothian and the University of Edinburgh acted as cosponsors of the study (www.accord.scot). Patients aged 50 years or greater, with a fractured NOF, within 48 h of hospital admission but whom had not yet undergone surgery were eligible for enrolment in this study. The primary outcome was myocardial injury, defined as a delta high-sensitivity troponin I [delta high-sensitivity troponin I (hsTnI) positive] above the upper reference limit as set out by Thygesen et al.7 At enrolment baseline demographic data were recorded along with baseline haemoglobin (Hb) measurement, hsTnI concentrations (ARCHITECTSTAT, Abbott Laboratories, Abbott Park, Illinois, USA) and an ECG. Peri-operative data were collected, including Hb concentration which was assessed immediately after surgery in the recovery room using the HemoCue Hb 201+ system (HaemoCue AB, Angelholm, Sweden). Further Hb and hsTnI sampling were taken on postoperative days (POD) 1 and 3 and a further ECG was performed on POD 3. Patients were followed up for blood transfusion, cardiac complications (myocardial infarction according to universal definition, cardiac arrest, cardiogenic pulmonary oedema, pulmonary embolus, arrthymia), all complications (assessed using the Clavien Dindo system) and death within 30 days following surgery or before acute hospital discharge (whichever was sooner). Patients were divided into two groups according to whether they had peri-operative cardiac injury (delta hsTnI) or not.7 Descriptive statistics were reported for each group, including demographic data, rate of anaemia and transfusion and outcomes using parametric and nonparametric tests where appropriate. Significance was set at a P value of 0.05. All analyses were performed using STATA12 SE (Statacorp, College Station, Texas, USA). The size of the study precluded the use of multivariate analysis. Of the 240 patients screened for eligibility, 156 patients were excluded. A total of 84 patients were subsequently screened for consent. Forty-three patients consented to participate in the study, in 18 (41.8%) a positive delta hsTnI was observed. Patients with the primary outcome were older but with a similar rate of cardiovascular risk factors and comorbidities (Table 1). In common with other studies, dynamic ECG changes were not related to a positive delta hsTnI in the majority of these patients. Mean ± SD values demonstrated that admission Hb (117.2 ± 17.7 g l−1 vs. 139.2 ± 16.5 g l−1; P = 0.02) and lowest Hb (91.3 ± 17.5 g l−1 vs. 102.8 ± 17.9 g l−1; P = 0.043) were both lower in the group with the primary outcome (Table 1). Maximum Hb decrease (from admission to lowest Hb) was not different between groups. Transfusion rate was greater in the group with the primary outcome. Total complications, length of stay and mortality were not increased in the group with the primary outcome.Table 1: Patient demographic and outcome dataOur findings suggest that myocardial injury, anaemia and transfusion are frequently encountered in patients undergoing surgery for fractured NOF. In this study, patients with biochemical evidence of cardiac injury had lower pre-operative Hb and postoperative nadir Hb, although the absolute Hb decrease over the peri-operative period was similar in both groups. This potential association may reflect either a higher incidence of chronic disease and severity of injury in the group with a positive delta hsTnI, or may be a consequence of reduced myocardial oxygen supply associated with anaemia. Limitations of this study include the small sample size which precluded the use of multivariate analysis to identify other associations, and the unselected nature of the inclusion criteria, with all patients presenting with fractured NOF, rather than those with pre-existing CVD being eligible. Cardiac injury in patients undergoing surgery for fractured NOF and its association with anaemia and other risk factors requires further investigation. Acknowledgements relating to this article Assistance with the letter: none. Financial support and sponsorship: NLM is supported by the Butler Senior Clinical Research Fellowship (FS/16/14/32023) from the British Heart Foundation. MAG is a Chief Scientist's Office Scotland NHS Research Scheme Clinician. The work was supported by the Department of Anaesthesia, Critical Care and Pain Medicine, University of Edinburgh. Conflict of interest: NLM has received consultancy, research grants and speaker fees from manufacturers of cardiac troponin testing including Abbott Diagnostics, Roche and Singulex.