Value of the Bruce protocol to determine peak exercise oxygen consumption in patients evaluated for cardiac transplantation.

BACKGROUND: Peak exercise oxygen consumption (peak VO2) is an important discriminator of survival in patients with systolic heart failure and is used to select ambulatory patients for transplantation. The major trials assessing the relationship between peak VO2 and survival have used a variety of low-level exercise protocols. It is unknown how peak VO2 measured in this patient population by the more vigorous Bruce treadmill protocol compares with that obtained on less intense protocols. METHODS: We studied 15 patients (50 +/- 12 years old) with severe heart failure (left ventricular ejection fraction 23.5% +/- 8.6%). Patients randomly performed 3 exercise tests with the Bruce treadmill, modified Naughton treadmill, and modified bicycle protocols within 14 days. To determine the ability of this patient population to perform the Bruce protocol, we also retrospectively analyzed the ability of 84 patients to perform this test on their initial evaluations at our center. RESULTS: All patients reached the anaerobic threshold (AT) on all 3 protocols. The Bruce and modified Naughton treadmill protocols resulted in similar peak VO2 percent predicted peak VO2, and VO2 at AT values (17.7 +/- 3.8 mL/kg/min, 57.2% +/- 21.1% and 15.4 +/- 4.1 mL/kg/min vs 18.0 +/- 4.7 mL/kg/min, 58.1% +/- 22.5% and 15.6 +/- 4.4 mL/kg/min, respectively). Peak VO2 and VO2 at AT on both treadmill protocols were higher than those obtained with bicycle testing (15.3 +/- 3.1 and 11.8 +/- 3.0 mL/kg/min, P <.05). Exercise duration was shorter with the Bruce and bicycle protocols (6.2 +/- 2.2 and 6.7 +/- 2.4 minutes, respectively) compared with the modified Naughton protocol (9.7 +/- 4.3 minutes, both P <.005). In addition, 79 of the 84 patients (94%) evaluated were able to complete the Bruce protocol and reach AT. CONCLUSIONS: The Bruce protocol was more time efficient than the modified Naughton protocol and yielded similar peak VO2, percent predicted peak VO2, and VO2 at AT values. Bicycle exercise may underestimate peak VO2 values. The form of exercise should be considered when assessing peak VO2 criteria for transplant listing.

Accuracy of estimating exercise prescription intensity in patients with left ventricular systolic dysfunction.

PURPOSE: Exercise prescription in patients with left ventricular systolic dysfunction (LVSD) is difficult. Exercising beyond ventilatory threshold (VT) can have negative physiologic effects; therefore, exercise prescribed above VT may be detrimental. A majority of cardiac rehabilitation programs use the Karvonen/heart rate reserve (HRR) method, rating of perceived exertion (RPE), and/or a percentage of oxygen consumption to prescribe exercise intensity. The purpose of this study was to determine if these methods correlate with an exercise intensity below VT in LVSD patients. METHODS: The authors studied 52 patients (37 males, 15 females; age 52 +/- 13 years; left ventricular ejection fraction 27% +/- 8%) who underwent a symptom-limited cardiopulmonary exercise test and reached VT to determine functional capacity and exercise prescription. RESULTS: Peak heart rate (HR) as well as HRR derived minimum (60%), midpoint (70%), and maximum (80%) HR were highly correlated (P < 0.001) with HR at VT. Using these three different HR cutoff formulas from HRR, 15% to 62% of patients were prescribed exercise outside the range of VT-HR +/- 10%. The midpoint (70% HRR) best predicted exercise HR in the VT-HR +/- 10% range (73% of patients). Mean oxygen consumption at VT was 83 +/- 9% of peak oxygen consumption. There was no correlation (P < 0.16) between RPE and VT. CONCLUSIONS: The Karvonen/HRR method failed to estimate HR-VT +/- 10% in a large percentage of patients with LVSD. There was no correlation between RPE and VT. Based on these data, exercise training intensity should ideally be prescribed based on the HR identified at VT using cardiopulmonary exercise testing in patients with LVSD.