Do Clinical Exercise Tests Permit Exercise Threshold Identification in Patients Referred to Cardiac Rehabilitation?

Background: To evaluate the feasibility of "threshold-based" aerobic exercise prescription in cardiovascular disease, we aimed to quantify the proportion of patients whose clinical cardiopulmonary exercise test (CPET) permit identification of estimated lactate threshold (theta(LT)) and respiratory compensation point (RCP) and to characterize the variability at which these thresholds occur.Methods: Breath-by-breath CPET data of 1102 patients (65 +/- 12 years) referred to cardiac rehabilitation were analyzed to identify peak O-2 uptake ((VO2peak)-O-center dot; mL<middle dot>min(-1) and mL<middle dot>kg(-1)<middle dot>min(-1)) and theta(LT) and RCP (reported as (VO2)-O-center dot, %(VO2peak)-O-center dot, and %peak heart rate [%HRpeak]). Patients were grouped by the presence or absence of thresholds: group 0: neither theta(LT) nor RCP; group 1: theta(LT) only; and group 2: both theta(LT) and RCP.Results: Mean (VO2peak)-O-center dot was 1523 +/- 627 mL<middle dot>min(-1) (range: 315-3789 mL<middle dot>min(-1)) or 18.0 +/- 6.5 mL<middle dot>kg(-1)<middle dot>min(-1) (5.2-46.5 mL<middle dot>kg(-1)<middle dot>min(-1)) and HRpeak was 123 +/- 24 beats per minute (bpm) (52 bpm-207 bpm). There were 556 patients (50%) in group 0, 196 (18%) in group 1, and 350 (32%) in group 2. In group 1, mean theta(LT) was 1240 +/- 410 mL<middle dot>min(-1) (580-2560 mL<middle dot>min(-1)), 75% +/- 8%(VO2peak)-O-center dot (52%-92%(VO2peak)-O-center dot), or 84% +/- 6%HRpeak (64%-96%HRpeak). In group 2, theta(LT) was 1390 +/- 360 mL<middle dot>min(-1) (640-2430 mL<middle dot>min(-1)), 70% +/- 8%(VO2peak)-O-center dot (41%-88%(VO2peak)-O-center dot), or 78% +/- 7%HRpeak (52%-96%HRpeak), and RCP was 1680 +/- 440 mL<middle dot>min(-1) (730-3090 mL<middle dot>min(-1)), 84% +/- 7%(VO2peak)-O-center dot (54%-99%(VO2peak)-O-center dot), or 87% +/- 6%HRpeak (59%-99%HRpeak). Compared with group 1, theta(LT) in group 2 occurred at a higher (VO2)-O-center dot but lower %(VO2peak)-O-center dot and %HRpeak (P < 0.05).Conclusions: Only 32% of CPETs exhibited both theta(LT) and RCP despite flexibility in protocol options. Commonly used step-based protocols are suboptimal for "threshold-based" exercise prescription.