Oxygen Uptake Efficiency Slope is Strongly Correlated to VO2peak Long-Term After Arterial Switch Operation

Oxygen Uptake Efficiency Slope is Strongly Correlated to VO2peak Long-Term After Arterial Switch Operation.

Terol Espinosa de Los Monteros C, Van der Palin RLF, Hazekamp MG, Rammeloo L, Jongbloed MRM, Blom NA, Harkel ADJT.

Pediatr Cardiol. 2021 Feb 1. doi: 10.1007/s00246-021-02554-9. Online ahead of print.

PMID: 33527171


Take Home Points:

  • In children and young adults post arterial switch operation in this single centre, unblinded study of cardiopulmonary exercise (CPEX) and echocardiography in 48 patients discovered:
    • Left and right longitudinal peak strain on echo was reduced.
    • Peak oxygen uptake (VO2peak) was reduced compared to age/sex matched healthy controls.
    • Mean oxygen uptake efficiency slope (OUES) was reduced compared to age/sex matched healthy controls.
    • There was a positive correlation between VO2peak and OUES.
    • There was no correlation between CPEX variables and left ventricular echo parameters.
  • The authors conclude that OUES may be a valuable tool in assessing post arterial switch patients, particularly those who cannot obtain maximal effort.

Dr. Simon MacDonald


Commentary by Dr. Simon MacDonald (London, UK), section editor of ACHD Journal Watch:

Impaired exercise tolerance is described in patients post arterial switch. This may be due to chronotropic incompetence, pulmonary artery narrowing, coronary abnormalities and ventricular dysfunction, and other sequalae post surgery. In assessing exercise capacity, CPEX with measurement of maximal oxygen consumption (VO2peak) is taken to be the gold standard.


However, not all patient groups can reach maximal exercise due to such things as motivational aspects, learning disability or physical disability. Submaximal exercise parameters could thus be useful in this setting and inform practice. It is known that ventilatory efficiency (VE/VCO2slope) and oxygen uptake efficiency slope (OUES) can be useful, with OUES already been shown in healthy people and some congenital heart patients over a wide age range to correlate with VO2peak. This was the first description of the correlation in patients post arterial switch.


The authors examined 48 patients with TGA with both intact ventricular septum and ventricular septal defect post arterial switch operation (ASO). They performed CPEX testing, a physical activity score and a transthoracic echocardiogram. CPEXs were performed on a cycle ergometer on a continuous incremental protocol, only including tests with a peak RER of ≥1.00. Tests were compared to a reference range for normal children. Weekly exercise behaviour was converted into a MET score.


The study group was predominantly male (75%), with ASO performed in the first week of life and median age at follow-up 16 years (interquartile range 13-18).


All of the patients exercised to exhaustion with RER>1.0, with results showed below (Table 2 in article)


Female patients had lower VO2peak and OUES compared to males. No correlation was found between CPEX results and echo ventricular function findings.



The authors examined relationship between VO2peak and OUES, in a combined data set of all the patients, with a positive correlation found (Figure 4 from paper below):



Patients were young, predominantly male, with the ASO procedure being performed around a particular surgical era, echo rather than MRI was used to assess ventricular function and it was a single centre study.


The authors conclude that patients post arterial switch have diminished exercise capacity and there is a correlation between VO2peak and OUES. This correlation may be helpful in some patients who fail to reach maximal exercise during CPEX testing, giving an exercise capacity assessment to guide management.