Heart Care Info - Heart Disease Prevention & Treatment

Association of echocardiography before major elective non-cardiac surgery with postoperative survival and length of hospital stay: population based cohort study

DN Wijeysundera, WS Beattie, K Karkouti... - BMJ, 2011 - ... Association of echocardiography before major elective non-cardiac surgery with postoperative survival and length of hospital stay: population based cohort study. ... Participants Patients aged over 40 years who had elective intermediate to high risk non-cardiac surgery. ... [PDF]

Using previously described methods,6 7 8 14 we identified all Ontario residents aged 40 years or older who had the following elective non-cardiac surgeries between 1 April 1999 and 31 March 2008: abdominal aortic aneurysm repair, carotid endarterectomy, peripheral vascular bypass, total hip replacement, total knee replacement, large bowel resection, partial liver resection, Whipple procedure, pneumonectomy, pulmonary lobectomy, gastrectomy, oesophagectomy, nephrectomy, or cystectomy. We selected these procedures because they carry intermediate to high risk,4 are applicable to both sexes, and are previously described in the Discharge Abstract Database.15 16 Procedural information in this database is very accurate.11 13 For people who had more than one eligible procedure during the study period, we included only the first procedure.

Using previously described methods,17 we used the Ontario Health Insurance Plan database to identify the principal exposure: outpatient preoperative echocardiography (transthoracic or transoesophageal) within 180 days before surgery. Although our data sources could not accurately identify inpatient preoperative echocardiography, this limitation would tend to conservatively bias the results towards the null. The 180 day time window has been previously used for research purposes and allowed for inclusion of cases in which echocardiography may have led to preoperative coronary revascularisation.6 18

We followed patients for one year after surgery for the outcomes of interest—mortality and length of hospital stay. We used the Discharge Abstract Database (in-hospital death, hospital stay) and Registered Persons Database (deaths out of hospital) to ascertain these outcomes. We used a one year follow-up period to ascertain mortality because postoperative cardiac complications are not well captured by administrative databases but are closely associated with increased long term mortality.19 20

Demographic information came from the Registered Persons Database, and we used validated algorithms to identify diabetes mellitus, hypertension, and preoperative medical consultations.10 12 21 We used the Ontario Health Insurance Plan database to identify any patient who needed dialysis before the index surgery. Using the Discharge Abstract Database, we used previously described methods to identify other comorbidities on the basis of ICD-9 or ICD-10 (international classification of diseases, 9th or 10th revision) codes from hospital admissions within three years before surgery: coronary artery disease, congestive heart failure, atrial fibrillation, cardiac valvular disease (aortic or mitral stenosis), cerebrovascular disease, peripheral vascular disease, pulmonary disease, chronic renal insufficiency, previous venous thromboembolism, liver disease, peptic ulcer disease, rheumatological disease, hemiplegia or paraplegia, malignancy, and dementia.22 23 24 We also used the Discharge Abstract Database to identify previous mechanical aortic or mitral valve replacement procedures within 10 years before surgery. When assessing for comorbidities, we used only information from hospital admissions before the index surgery to ascertain coronary artery disease, congestive heart failure, atrial fibrillation, cerebrovascular disease, renal insufficiency, and venous thromboembolism. Our purpose was to ensure that postoperative complications were not misclassified as comorbidities.25

We used the Ontario Health Insurance Plan database to identify preoperative cardiac stress testing (within 180 days before surgery),6 17 preoperative outpatient anaesthesia consultations,7 perioperative epidural anaesthesia or analgesia (hereafter referred to as “anaesthesia”),14 and intraoperative invasive monitoring. We estimated patients’ socioeconomic status on the basis of their neighbourhood median income in the Canadian census and determined their residence (rural versus urban) by using Statistics Canada’s definitions.26

To understand how echocardiography might influence outcomes, we used the Discharge Abstract Database to identify preoperative cardiac interventions, and we used the Ontario Drug Benefit database to identify outpatient prescriptions for β blockers, statins, angiotensin converting enzyme inhibitors, and angiotensin receptor blockers in patients aged 65 years or older.