Value of Biomarkers in Preoperative Risk Stratification
Abstract & Commentary
By Michael H. Crawford, MD, Editor
Sources: Weber M, et al. Incremental value of high-sensitive troponin T in addition to the revised cardiac index for perioperative risk stratification in non-cardiac surgery. Eur Heart J 2013;34:853-862. Karakas M, Koenig W. Improved perioperative risk stratification in non-cardiac surgery: Going beyond established clinical scores. Eur Heart J 2013;34:796-798.
Newer biomarkers such as B-type natriuretic peptide (BNP) and high-sensitive troponins have been shown to be of prognostic value in patients with cardiovascular disease. These investigators from central Europe sought to determine if they were of value in risk stratification for non-cardiac surgery. Thus, they studied 979 patients from eight hospitals who were undergoing major noncardiac surgery, were > 55 years of age, and had at least one risk factor for cardiovascular disease. The primary endpoints were all-cause mortality and the combination of mortality with acute myocardial infarction, cardiac arrest, or acute decompensated heart failure. The revised cardiac index was compared to high-sensitivity troponin T (hsTnT) and NT proBNP measured 1 week before surgery. The majority of patients had two or more risk factors or known coronary artery disease (CAD). During hospitalization for surgery, 2.6% of the patients died and 3.7% experienced the combined endpoint. The cardiac biomarkers were elevated in those who died vs the survivors (hsTnT 21 ng/L vs 7 ng/L, P < 0.001; NT proBNP 576 pg/mL vs 166 pg/mL, P < 0.001). Those with a hsTnT > 14 (99th percentile for normals) had a mortality of 6.9 vs 1.2% for those below this value (P < 0.001) and those with a NT proBNP > 300 had a mortality of 4.8 vs 1.4% for those below this value (P = 0.002). hsTnT had the highest ROC curve AUC at 0.81 and in a multivariate analysis, hsTnT was the strongest independent predictor of the combined endpoint (HR, 2.6; 95% confidence interval, 1.3-5.3; P = 0.01). The predictive ability of NT proBNP was similar to the revised cardiac index for the combined endpoint. The authors concluded that hsTnT is additive to the revised cardiac index for risk stratification prior to major noncardiac surgery in higher-risk patients.
Advances in surgical procedures and anesthesia have markedly reduced the risk of major non-cardiac surgery, even in higher-risk patients. This is evident in this study of older patients undergoing major surgery (> 50% vascular and abdominal) who are clinically at higher risk (72% RCRI of 1 or more). Their hospital mortality was 2.6% and major cardiac events occurred in 3.7%. This is similar to prior contemporary studies that have shown a 2-4% risk of major cardiac events in higher-risk patients. Thus, identifying the truly high-risk patient preoperatively has been likened to finding a needle in a haystack. This paper suggests that hsTnT may aide in this quest because it predicted cardiac events better than the RCRI. In this higher-risk group, 25% had hsTnT values greater than the 99th percentile in normal (usual definition of the upper limit of normal) and 67% of those who died had abnormal values. The authors suggest using it with your favorite clinical index, not as a standalone test.
The major limitation of this study is that they studied a select group of relatively high-risk patients undergoing higher-risk surgery. It may not apply more broadly and the authors don’t recommend indiscriminant use. Also, the median follow-up period was 11 days, which represented the hospital stay in most. Typically, surgical complications are defined as those that occur in 30 days. Finally, the number of endpoints is small. Clearly, a larger study is in order before widely applying this approach to risk stratification.
The study implies that once the high-risk patient has been identified, he/she should be treated more aggressively to prevent cardiac events. This could mean drugs such as beta-blockers or coronary angiography and revascularization. We are told that about half the patients were on beta-blockers and one-quarter had known CAD, so they may have had coronary revascularization. The impact of these and other therapies on the results of this study are unknown. At this point, I may use troponin levels when I am unsure about the patient’s risk, but I don’t plan wide use at this time.