It is often difficult to make decisions on surgery for patients with mitral regurgitation (MR) and aortic regurgitation (AR) because there are no accurate parameters to determine functional status^1,2). The functional status is an important prognostic factor because patients with poor pre-operative functional status often show poor post-operative prognosis. In patients with MR and/or AR, pre-operative echocardiographic findings, such as left ventricular dimension (LVD) and ejection fraction (EF), cannot exactly reflect their functional status or symptoms^3–6). Even though the cardio pulmonary exercise test is a standard tool to evaluate the patient’s functional status, there are limited reports on the effects of surgical correction of MR and AR on later exercise capacity^7–10). We, therefore, evaluated the efficacy of a cardiopulmonary exercise test as an objective parameter of functional status and as a pre-operative prognostic indicator for patients with MR and AR.

It is generally accepted that the cardiopulmonary exercise test can predict the patient’s functional status¹²⁾. However, there has been only limited study about the effects of cardiac surgery on exercise capacity^7–10). Our study shows that cardiopulmonary exercise test parameters, especially VO₂peak and exercise durations, are highly correlated with the patient’s NYHA class. VO₂peak and exercise durations improved in most patients in one year of valve surgery for significant MR and AR. Patients who had high VO₂peak values before their operation were categorized as a better post-operative NYHA class, even in those with NYHA class III. This means that the initial NYHA class is not enough to predict post-operative results in some patients. Because NYHA class is a subjective parameter, objective cardiopulmonary testing has an advantage for estimating the patient’s status more accurately. Our results therefore suggest that the cardiopulmonary exercise test is an excellent modality to determine the point of operation, and that a pre-operative cut-off value of the VO₂peak of ≥19.0 mL/kg per min may be used to predict the better post-operative status in patients.

In one study carried out seven months after mitral valve surgery for severe chronic MR, although the patients’ NYHA functional class improved, exercise performance parameters, such as VO₂peak and exercise duration, did not improve¹³⁾. To explain this difference from our study, some points should be considered. The cardiopulmonary exercise test can be affected by many factors other than cardiac function, such as pulmonary and peripheral factors, skeletal muscle changes and alterations in blood flow distribution^14–17). Improvement in these factors needs an adequate time of recovery to show significant changes in VO₂peak and exercise duration. Thus, seven months may be too short to reveal any change in a patient’s exercise capacity. Because the patients in our study repeated their cardiopulmonary exercise tests one year after their operation, there may have been enough time to demonstrate improvements.

Although echocardiographic ejection fraction, end-systolic diameter and dP/dt are important parameters used to make a decision to perform cardiac surgery in patients with MR or AR^3–6,18), such findings taken in the resting state do not always correlate with the patient’s functional status. To reveal the exact functional status of patients, it is important to consider both the resting state of the patients and their exercise status^18–21). The cardiopulmonary exercise test demonstrates integrated cardiopulmonary functional potential, so it has advantages to reflect the real functional status of patients^22–24).

In cases of left ventricular volume overload due to valvular regurgitation, patients with left ventricular systolic dysfunction have poorer prognosis after valvular operations^1,2,25), so it is reasonable to perform such operations before the dysfunction develops^26,27). However it is very difficult to predict the timing of left ventricular systolic dysfunction and the timing of the operation. In such a situation, it is thought that the cardiopulmonary exercise testing can be used to predict the timing of the operation. We found that patients who had lower pre-operative VO₂peak had poorer functional status than those with higher pre-operative VO₂peak when evaluated one year after surgery.

However, our study population was too small to calculate the exact cut-off value of VO₂peak, so a large prospective study would be needed to define the correct relationship between pre-operative VO₂peak and post-operative functional status. Another limitation is that we included both MR and AR in terms of left ventricular volume overload in spite of some differences in the hemodynamics of these two diseases²⁶⁾. In a further study, it is required to evaluate the effects of cardiopulmonary test in MR or AR alone. And the difference between operative methods of MR patients, such as mitral valve repair and mitral valve replacement, is an important parameter to affect the prognosis of post-operative prognosis, so it also should be considered in the next study.

Functional capacities, such as VO₂peak and exercise duration, are excellent parameters to evaluate the subjective functional class and estimate the post-operative functional class of the patients with MR and/or AR. We found that patients who had pre-operative VO₂peak of 19.0 mL/kg per min or greater showed better functional status one year after surgery. So, a large prospective trial will be necessary to determine an accurate cut-off value of the VO₂peak for adequate timing of surgery.