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 (θ) 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 uptake (V˙O; mL·min and mL·kg·min) and θ and RCP (reported as V˙O, %V˙O, and %peak heart rate [%HR]). Patients were grouped by the presence or absence of thresholds: group 0: neither θ nor RCP; group 1: θ only; and group 2: both θ and RCP.

RESULTS

Mean V˙O was 1523 ± 627 mL·min (range: 315-3789 mL·min) or 18.0 ± 6.5 mL·kg·min (5.2-46.5 mL·kg·min) and HR 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 θ was 1240 ± 410 mL·min (580-2560 mL·min), 75% ± 8%V˙O (52%-92%V˙O), or 84% ± 6%HR (64%-96%HR). In group 2, θ was 1390 ± 360 mL·min (640-2430 mL·min), 70% ± 8%V˙O (41%-88%V˙O), or 78% ± 7%HR (52%-96%HR), and RCP was 1680 ± 440 mL·min (730-3090 mL·min), 84% ± 7%V˙O (54%-99%V˙O), or 87% ± 6%HR (59%-99%HR). Compared with group 1, θ in group 2 occurred at a higher V˙O but lower %V˙O and %HR (P < 0.05).

CONCLUSIONS

Only 32% of CPETs exhibited both θ and RCP despite flexibility in protocol options. Commonly used step-based protocols are suboptimal for "threshold-based" exercise prescription.