An otherwise healthy 58-year-old presents to the ED with 2 hours of substernal pressure radiating to the left arm. ECG shows no ischemic changes. A high-sensitivity cardiac troponin T (hs‑cTnT) at presentation is below the 99th percentile for the assay. He is pain-free after aspirin. Vital signs are normal. What is the most appropriate next step to safely disposition this patient?