Development and evaluation of a treadmill-based exercise tolerance test in cardiac rehabilitation

Cardiac rehabilitation exercise prescriptions should be based on exercise stress tests; however, limitations in performing stress tests in this setting typically force reliance on subjective measures like the Duke Activity Status Index (DASI). We developed and evaluated a treadmill-based exercise tolerance test (ETT) to provide objective physiologic measures without requiring additional equipment or insurance charges. The ETT is stopped when the patient's Borg scale rating of perceived exertion (RPE) reaches 15 or when any sign/symptom indicates risk of an adverse event. Outcomes of the study included reasons for stopping; maximum heart rate, systolic blood pressure, and rate pressure product; and adverse events. We tested equivalence to the DASI as requiring the 95% confidence interval for the mean difference between DASI and ETT metabolic equivalents (METs) to fall within the range (-1, 1). Among 502 consecutive cardiac rehabilitation patients, one suffered a panic attack; no other adverse events occurred. Most (80%) stopped because they reached an RPE of 15; the remaining 20% were stopped on indications that continuing risked an adverse event. Mean maximum systolic blood pressure, heart rate, and rate pressure product were significantly (P < 0.001) below thresholds of the American Association of Cardiovascular and Pulmonary Rehabilitation. Two patients' heart rates exceeded 150 beats per minute, but their rate pressure products remained below 36,000. The mean difference between DASI and ETT METs was -0.8 (-0.98, -0.65), indicating equivalence at our threshold. In conclusion, the ETT can be performed within cardiac rehabilitation, providing a functional capacity assessment equivalent to the DASI and objective physiologic measures for developing exercise prescriptions and measuring progress.