Aerobic exercise capacity is 1 of the strongest predictors of outcomes in apparently healthy subjects as well as virtually all patient populations. A large amount of the data supporting this premise estimate aerobic capacity from treadmill time. Patients who undergo cardiac stress testing frequently undergo exercise tests using the Bruce treadmill protocol, with American College of Sports Medicine equations used to estimate the peak MET level achieved. We have recently demonstrated that this practice is flawed, leading to a significant overestimation of peak METs in most patients with suspected myocardial ischemia who undergo cardiac stress tests. We posited that a significant contributor to this discrepancy was that subjects were allowed to use handrail support during testing, which is commonplace in current clinical practice. There are a number of equations available for the estimation of peak MET level based primarily on treadmill time. Moreover, a number of these equations have attempted to account for handrail use and the characteristics of a patient’s health. The purpose of the investigation described in this research letter was to assess several treadmill equations used to estimate peak MET level in patients with suspected myocardial ischemia who undergo cardiac stress testing compared to measurement using peak oxygen consumption.
We prospectively assessed 303 patients (157 men, mean age 50 ± 12 years) presenting to the Virginia Commonwealth University Medical Center Stress Laboratory from May 2009 to February 2010 with signs and symptoms suggestive of myocardial ischemia. Common indications included chest pain (65%), dyspnea (8%), history of heart disease (5%), syncope (1.3%), palpitations (3%), and/or abnormal electrocardiographic findings (2.4%). Institutional board approval for this study was obtained, and all subjects provided written informed consent. All subjects underwent exercise stress tests using the Bruce treadmill protocol. Peak oxygen consumption was measured through ventilatory expired gas analysis and converted to a MET value (Vmax Encore; SensorMedics, Yorba Linda, California). Peak METs achieved were also estimated using the 8 equations listed in Table 1 . Differences between measured and estimated peak MET level were determined.
| Protocol | Equation |
|---|---|
| Bruce CVD | 2.33(TT) + 9.5 |
| Bruce sedentary | 3.29(TT) + 4.1 |
| Bruce active | 3.78(TT) + 0.2 |
| Foster generalized cubic | 14.8 − 1.379(TT) + 0.451(TT ) − 0.12(TT ) |
| Handrail: TT | 2.282(TT) + 8.545 |
| Handrail: TT + age | 2.082(TT) − 0.124(age) + 16.698 |
| Handrail: TT for CVD | 1.907(TT) + 11.367 |
| Handrail: TT for healthy | 2.587(TT) + 6.004 |
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