The results of our study demonstrate that clinicians working with the rTOF patient population frequently rely on CPET results to guide clinical decision-making. However, there was considerable variability in the frequency of testing. There was also variability in how the clinicians used the test results to inform what clinical intervention to use. The majority of clinicians use the test results to determine timing for percutaneous or surgical intervention, despite no known guidelines on thresholds or specific parameters to follow to guide such decisions. These results highlight the need for clinical guidelines or possibly more research to determine how exercise test results should be used in the clinical care of the rTOF population.
While recent recommendations support the use of exercise testing in pediatric congenital heart disease patients, guidance is generally non-specific without substantial details on recommended practices, such as patient selection or frequency [12]. In one recent study, Goldmuntz et al. demonstrated variation in practice patterns concerning the general management of Tetralogy of Fallot patients in the ambulatory setting [13]. To our knowledge, this is the first multi-institutional study characterizing the use of exercise testing in rTOF patients. These data are important in justifying the need for expanded clinical guidelines, or potentially further research, in how exercise testing relates to clinical outcomes in the rTOF patient population.
Our study demonstrates that nearly all surveyed clinicians routinely perform exercise testing in symptomatic rTOF patients. There is considerably more variation in the use and frequency of exercise testing of surveillance of disease progression of asymptomatic patients. Despite the evidence-based utility of exercise testing in the objective assessment of exercise capacity in asymptomatic patients [14], only 59% of clinicians regularly exercise test their asymptomatic patients. Existing guidelines generally do not specify recommended practices based on symptom burden, yet our survey identified this as a key point of divergence among pediatric cardiologists.
There are several possible explanations for the observed variation in clinical practice, including personal, patient, institutional, and/or financial reasons. Interestingly, pediatric cardiologists that reported higher levels of comfort with CPET interpretation were significantly more likely to routinely test asymptomatic patients. This suggests that training and post-fellowship practice can influence attitudes and use of exercise data. Further, the degree of perceived helpfulness of exercise data was related to provider comfort with interpretation of exercise data, again supporting that training plays a major role in how the test results are used. Survey respondents with a higher level of comfort with CPET interpretation were significantly more likely to find exercise testing helpful. While these results may not be surprising, they do highlight the need for increased education on exercise testing modalities, including CPET, during cardiology training. While we hypothesized that there would be differences based on experience level, we did not find any statistically significant differences in routine testing practices, perceived helpfulness, or CPET comfort level based on number of years in practice. Until recently, exercise testing has made up a relatively small component of pediatric cardiology fellowship curricula despite the growing recognition of the importance of the field. In 2022 the Pediatric Cardiology Exercise Medicine Curriculum Committee (PCEMCC) was created to set forth exercise physiology training recommendations [15]. This is the first significant attempt to boost training in exercise testing, which may account for the absence of observable differences based on experience level in our survey. Nevertheless, the renewed focus on exercise testing in pediatric cardiology fellowship should lead to increased comfort among providers with interpretation of exercise data and can help guide standardization of exercise testing practices in the future.
Another key finding of this survey was that almost all survey respondents indicated that they have altered management based on exercise testing results. Although management decisions must consider the complete clinical picture including history, physical exam, and additional diagnostic workup, exercise testing appears to play an important role in clinical decision-making. In particular, these results may be helpful when deciding on the timing of interventions, the need for additional imaging, or the initiation of exercise interventions. The most frequent type of management change cited among pediatric cardiologists was referral for surgical or percutaneous interventions. Following repair, Tetralogy of Fallot patients generally have an incompetent pulmonary valve with varying degrees of residual pulmonary stenosis with resultant hemodynamic consequences [16]. These residual lesions often require surgical or percutaneous intervention; however, the ideal timing for reintervention remains challenging [6]. While there is recognized prognostic value of CPET, there remains significant uncertainty surrounding the use of CPET to determine the timing of PVR [7, 17]. As demonstrated by these survey results, exercise testing may serve as a valuable adjunct to current risk stratification strategies when assessing the need for surgical or percutaneous interventions. However, further research is needed to further define the optimal role of exercise testing in management decisions, particularly those involving surgical/percutaneous interventions. Additionally, in future survey studies, it would be helpful to delineate the specific types of surgical/percutaneous interventions that providers are referring patients to in response to exercise testing findings. Interestingly, survey respondents also indicated that exercise testing plays a role in the decision to delay referrals for surgery/percutaneous interventions. An encouraging exercise test in the setting of an otherwise unremarkable workup may provide additional reassurance to providers and potentially reduce unnecessary testing and/or interventions.
The survey also sought to determine how specific CPET abnormalities might impact the likelihood of the provider making certain management decisions. There was considerable variation in the likelihood of management decisions based on the specified parameters: mildly decreased VO2 max, moderately decreased VO2 max, severely decreased VO2 max, decreased minute ventilation/carbon dioxide production ratio (VE/VCO2) slope, and early plateau or drop in oxygen pulse. Surveyed pediatric cardiologists appeared to be most likely to intervene in the case of a severely decreased VO2 max in contrast to the other parameters tested. A possible explanation for these findings is that VO2 max is more well-established than other CPET parameters, and providers may not be as familiar or comfortable with other parameters and would therefore not make management decisions based on them.
There are several important limitations to the current study. As with any survey-based study, results only reflect the opinions and practices of those who return responses, creating potential for selection bias. It is possible that respondents who do not routinely use exercise testing chose not to participate in the study, given that it was the topic of interest for the survey; however, there was still a considerable percentage of respondents who indicated they did not routinely perform exercise testing. Recall bias is also inherent to any survey-based research though only a small percentage of the survey items required recall. Finally, though we collected data about access to testing modalities, we did not critically assess the various barriers to testing that may be present. We also did not specifically ask about makeup of lab personnel; however, the presence of an exercise physiologist likely impacts the utility of CPET. Future studies that further characterize barriers to testing access, such as structural, financial, and patient-specific factors, would be beneficial.
In conclusion, this study provides an overview of the current landscape of exercise testing in rTOF patients and highlights the current variations in practice patterns among pediatric cardiologists, particularly in asymptomatic patients. Exercise testing plays an important role in managing rTOF patients; however, there remains considerable uncertainty surrounding optimal testing practices. These findings emphasize the need for evidence-based, consensus guidelines detailing the use of exercise testing in the management of rTOF patients and support the current efforts of fellowship program directors to increase exposure to exercise testing during training.