The ankle-to-arm blood pressure index predicts risk of cardiac complications after noncardiac surgery

BACKGROUND: Peripheral arterial disease, as detected by a reduced ankle-to-arm blood pressure index (AAI), has been shown to predict future cardiac events. However, the utility of measuring the AAI to predict postoperative cardiac complications in patients undergoing noncardiac surgery is unknown. METHODS: We prospectively studied 242 consecutive patients aged 50 yr or older presenting to a university hospital preadmission clinic before elective noncardiac surgery. We performed a standardized clinical evaluation that included calculation of the revised cardiac risk index (rCRI) and measurement of the AAI using both palpation and Doppler techniques. Independent observers, blinded to preoperative assessment and AAI results, ascertained cardiac complications in the first 7 days after surgery. We assessed the ability of an abnormal AAI (<= 0.9 or absence of all four pedal pulses) to predict postoperative cardiac complications using likelihood ratios (LR), area under the ROC curves (AUC), and multivariable logistic regression in which we adjusted for the rCRI result. RESULTS: The cohort had a median age of 67 yr, 60% were male, 19% had diabetes, 14% had ischemic heart disease, and 35% underwent intraperitoneal or intrathoracic surgery. Postoperatively, 14 of 242 (6%) patients suffered cardiac complications, but no patients died. An abnormal AAI was present in 44 patients, 10 (23%) of whom had postoperative cardiac complications: positive LR 4.79 (95% Cl: 3.04-7.54), negative LR 0.34 (95% CI: 0.15-0.77), AUC = 0.80. The AAI compared favorably with the rCRI, which had positive LR 4.22 (95% CI: 2.24-7.95), negative LR 0.57 (95% CI: 0.34-0.96), and AUC = 0.74. In multivariate analysis, the adjusted odds ratio for having a cardiac complication was 10.16 (95% CI: 2.90-36.02) for those patients with an abnormal AAI, even after adjusting for rCRI results. CONCLUSIONS: An abnormally low AAI, indicative of underlying peripheral arterial disease, is an independent risk factor for postoperative cardiac complications. The accuracy of the AAI is similar to the rCRI, and it provides additional independent predictive value for preoperative cardiac risk stratification.