Objective assessment
CPET: Pre-operative CPET was conducted using an
electromagnetically braked cycle ergometer (Lode, Gronigen, The
Netherlands) and a Medgraphics Ultima metabolic cart
(MedGraphicsTM, Gloucester, UK) as previously outlined
by our group7, 12, 13. Briefly, calibration was
undertaken in accordance with the manufacturer’s guidelines using a 3-L
volume syringe (Hans Rudolph, Kansas City, USA) and reference
calibration gases. During data collection, the middle five of seven
breaths were averaged. An exercise protocol was employed requiring
patients to cycle at 60 revolutions per minute for three minutes in an
unloaded freewheeling state followed by a progressively ramped period of
exercise (5 to 15 W/min based on mass, stature, age, and sex) to
volitional or symptom limited termination, followed by three minutes
recovery14. Medgraphics BreezeTMsoftware automatically determined peak oxygen uptake
(V̇ O2PEAK) (defined as the highestV̇ O2 during the final 30 seconds of exercise
reported), the slope of the relationship between pulmonary ventilation
and carbon dioxide output
(V̇ E/V̇ CO2) and oxygen
uptake efficiency slope (OUES). Pulmonary oxygen uptake at the anaerobic
threshold (V̇ O2-AT) was manually interpreted by an
experienced clinician using the V-slope method15,
supported by V̇ E/V̇ CO2-AT,
and V̇ E/V̇ O2-AT.
Risk classification: Each patient was classified with aV̇ O2-AT below (<) or above
(>) 11mL O2/kg/min) based on the seminal
works of Weber and Janicki16 and Older et
al.17 We further differentiated between low,
intermediate and high risk according to the following criteria:Low risk : V̇ O2-AT ≥11 mL/kg/min;Intermediate risk : One of: V̇ O2-AT 8-10.9
mL/kg/min, V̇ E/V̇ CO2-AT
>34, history of ischaemic heart disease (IHD); High
risk : V̇ O2-AT <8 mL/kg/min or ≥two of:V̇ E/V̇ CO2-AT
>34, V̇ O2-AT <11 mL/kg/min,
history of IHD.