In the evolving world of cardiology, a new study published in “Cardiology in the Young” highlights a promising submaximal exercise testing method for assessing cardiorespiratory function in adults with congenital heart disease (CHD). The study, DOI: 10.1017/S1047951123004365, points to the oxygen uptake efficiency slope (OUES) as a reliable indicator of cardiorespiratory reserve in this patient population.

With CHD being a lifelong condition that affects the structure and function of the heart, it presents unique challenges in clinical assessments and management. Maximal oxygen uptake (V02 max), a traditional measure requiring patients to perform to their maximum capacity during a cardiopulmonary exercise test (CPET), often serves as the gold standard. However, many patients with CHD are unable to perform maximal exercise tests due to their condition, which has led clinicians to seek alternative assessment measures.

The oxygen uptake efficiency slope is one such measure that has emerged as a potentially valuable tool. OUES indicates the efficiency with which oxygen is taken up from the lungs and delivered to the body during exercise. It is derived from submaximal exercise data, which is more accessible for patients who cannot exercise to their full potential.

Conducted by Redfern et al., this study involved a retrospective analysis of CPET data from 238 consecutive adult patients with CHD who completed a CPET at a tertiary cardiology center. Its findings show a strong correlation between the peak V02 and various OUES metrics, including OUES75 and OUES90, in adult patients with CHD.

The study’s implications are significant. The results suggest that OUES can provide reliable insights into the cardiorespiratory function of adults with CHD without requiring a maximal effort. This makes it an attractive alternative for patient populations unable to complete maximal exercise testing and may influence future decision-making in clinical cardiology.

This news opens new avenues in the ongoing quest for better diagnostic tools for adult patients with CHD. Here, we delve into the details of the study, its methodology, and its potential impact on cardiac care moving forward.


Redfern JM and colleagues undertook a detailed analysis of existing CPET data sets of adult patients with CHD. By evaluating the correlation between OUES and V02 max, the team sought to determine the validity of the former as a predictor of cardiorespiratory reserve.

The researchers calculated OUES using data from submaximal stages of the CPET and compared its predictive power against the peak V02, a measure historically utilized as an indicator of functional capacity and long-term outcomes in CHD patients.

The authors highlighted that OUES presents several advantages over V02 max. OUES does not depend on a patient’s subjective effort to reach maximal exercise capacity and is less affected by external factors such as motivation or the skill level of the test administrator.

Significance of the Study

For clinicians, the potential to use OUES as a dependable substitute for V02 max is a step forward in refining the assessment and management of adult CHD patients. This is particularly important given the rising prevalence of adults living with CHD due to advances in pediatric cardiology and cardiac surgery.

Moreover, the study aligns with the pursuit of patient-centered care, reducing the physical strain on patients during testing and providing a safer alternative to maximal exertion tests.

Implications for Clinical Practice

The use of OUES could revolutionize how clinicians monitor and manage adult CHD patients, particularly those who are older or have complications that limit exercise capacity. This tool opens the door to more frequent and accessible evaluations of these patients’ health status, potentially leading to earlier interventions and better outcomes.

Additionally, the research conducted by Redfern and colleagues provides a basis for further studies to explore OUES and other submaximal exercise testing methods. These findings may well lead to the development of new guidelines in cardiac assessment and rehabilitative protocols.

Patient Perspectives

From a patient’s standpoint, this study represents a less strenuous diagnostic pathway for evaluating heart health. It emphasizes patient safety and comfort while still providing essential information for their care providers. It may, in time, reduce the psychological barriers that some patients face when undergoing exhaustive tests, leading to more consistent and proactive health monitoring.

Future Directions

While the study provides a compelling case for OUES in clinical practice, the cardiology community may look forward to additional research that will explore its application in various scenarios. Longitudinal studies to determine how OUES correlates with long-term outcomes in the CHD population would also be invaluable.

The study by Redfern et al. marks a pivotal step towards personalized and safe testing for adults with CHD. As the knowledge base around OUES grows, it will solidify its place in clinical cardiology and perhaps serve as a model for other conditions where exercise capacity is compromised.


1. Redfern J. M., Hawkes S., Bryan A., Cullington D., Ashrafi R. (2024). The oxygen uptake efficiency slope in adults with CHD: group validity. Cardiol Young, 1-10. DOI: 10.1017/S1047951123004365


1. Oxygen Uptake Efficiency Slope
2. Congenital Heart Disease in Adults
3. Cardiopulmonary Exercise Testing
4. V02 Max in Cardiology
5. Submaximal Exercise Testing Method