Discussion
In this study, we performed a comprehensive echocardiographic evaluation of cardiac remodelling in a randomised trial that focused on the effect of CPAP on patients with PAF and OSA. We hypothesised that treatment for OSA would improve structural and functional parameters. However, treatment with CPAP did not reverse cardiac remodelling in patients in spite of a significant reduction in AF burden postablation.
These results are concordant with previous results of the A3 trial; however, they are contrary to some other studies. We have previously reported that treatment with CPAP did not affect the burden of AF in these patients.14 Moreover, allocation to CPAP treatment did not affect outcomes at 12 months follow-up after PVI and did not reduce the burden of AF beyond PVI and standard care,15 despite good adherence to CPAP therapy.
The absence of significant differences in blood pressure and NT-proBNP levels between the groups (table 2) supports these findings. Pengo et al22 conducted a meta-analysis on patients with OSA, demonstrating that CPAP treatment resulted in a modest average reduction in office systolic and diastolic arterial blood pressure of approximately 2 mm Hg when compared with controls. Our results are numerically in concordance with these findings.
Echocardiography is the primary method used to evaluate the structure and function of the LA. The LA volume index (LAVI) has been the preferred measurement in the past, but it has limitations as it is based on a static volumetric measurement and does not reflect dynamic LA aspects. A novel LA strain method has been introduced to assess LA function to address these limitations. Additionally, new software has been developed (AFI LA), which is simpler, has good repeatability and has fewer image quality issues.18 20
Several studies have demonstrated that OSA is associated with atrial remodelling, suggesting a role for OSA management in AF. Thus, previous observational studies,3 4 10 as well as a randomised trial,23 have demonstrated reverse remodelling after treatment with CPAP, in contrast to our results. This can be due to several factors, including differences between the study populations regarding age, sex, obesity, duration of OSA, comorbidities, alcohol consumption, as well as the severity of OSA.7 Moreover, Colish et al24 and Kim et al23 included patients with more severe OSA (an AHI of 63/hour and 55/hour, respectively). They observed a significant improvement in remodelling indexes following 3 months of CPAP therapy. Similarly, Vural et al10 noted a correlation between OSA severity and improvement in LA function after 12 and 24 weeks of CPAP therapy. Their findings suggest that better CPAP adherence among severe OSA patients could significantly mitigate cardiovascular consequences associated with severe OSA.
The severity of OSA, as indicated by AHI, could also play a role in future research.
Our findings also contrast the CANPAP trial,25 which found improved LV EF with CPAP therapy in patients with central sleep apnoea and heart failure. However, our results concord with the substudy of the SAVE trial,26 which investigated CPAP therapy in patients with OSA and cardiovascular disease.
This substudy did not observe an improvement in EF after 6 months of CPAP treatment. Whereas our study patients did not have heart failure, all had AF, which was absent in the CANPAP as well as in the SAVE trial substudy. Although CPAP treatment effectively improves AHI in patients with OSA, its impact on cardiac remodelling may be more diverse. Where the SAVE trial included patients in secondary prevention, only a few had a previous myocardial infarction or stroke in the present study. These observations challenge the presumed cardiovascular advantages of CPAP therapy, underscoring the need for further research.
Excessive daytime sleepiness (EDS) is considered a contributing factor to the complications of OSA. In the study of Xie et al,27 patients with moderate to severe sleep-disordered breathing and EDS had a higher risk of major adverse cardiac events compared with those without EDS. Our patients did not exhibit EDS, which may partly explain the lack of effect on cardiac remodelling. More pronounced daytime sleepiness in the Xie et al study might explain why an effect was observed there.
Kim et al reported that LV function by GLS improves with CPAP treatment.23 In addition to a more severe OSA in this study, patients with arrhythmia were excluded. Moreover, this study is limited by the relatively small sample size and the short duration of follow-up, which may have influenced the results. Also, daytime sleepiness was not reported. Our larger study included patients with AF only. AF affects cardiac mechanics and could, therefore, potentially influence GLS and thus mask a positive effect of CPAP on LV function. These findings challenge the presumed cardiovascular advantages of CPAP therapy, underscoring the need for further research on this topic.
The well-known association between AF and OSA may also influence the results. OSA is a known risk factor for AF, and observational studies have found that treating OSA with CPAP can help maintain sinus rhythm. However, these studies used intermittent rhythm monitoring and only self-reported use of CPAP.28 29 The study by Eysenck et al30 in patients with persistent AF and sleep-disordered breathing with an AHI ≥15 provides valuable insight into this area, highlighting the potential for AF interventions with cardioversion or PVI to restore sinus rhythm and reduce nocturnal respiratory events with a significant reduction in the AHI. In contrast, we have previously, in a larger study, observed that PVI had no additional effect on patients with moderate to severe OSA who were randomised to CPAP compared with standard care.15
In previous studies, researchers have primarily relied on methods developed to evaluate the left ventricle to measure LA remodelling. However, these methods may be quite challenging due to the thinness of the LA wall and the complex muscle fibre pathways, the oval foramen and the pulmonary vein ostia, which can all affect the accuracy of measurements. To overcome these limitations, we used a new atrial software to evaluate LA remodelling (AFI LA, EchoPAC 204). This approach has not been used before in patients with OSA and AF.
OSA and AF are associated with obesity, hypertension, diabetes and a sedentary lifestyle. These risk factors synergistically promote cardiac remodelling and may confound the effect of a treatment that targets sleep apnoea only. Larger randomised trials of longer duration may be necessary to characterise the complex relationship between OSA and AF and to clarify the clinical relevance of CPAP treatment.
Limitations of the study
The strengths of our study are the randomised controlled design, continuous rhythm monitoring and continuous CPAP therapy monitoring, comprehensive echocardiographic assessments and the relatively homogeneous patient population with PAF and sleep apnoea. However, our study also has some limitations. The sample size was relatively small, and the study groups ended up slightly skewed in numbers between the OSA-CPAP and OSA-standard care groups due to the exclusion of more patients randomised to the CPAP group who did not proceed to PVI.
We cannot exclude the possibility that a larger study might have yielded different results. We made many comparisons, which increases the risk of finding differences by chance. The participants in our trial were exclusively of white European origin and predominantly male, limiting the generalisability of our results. The trial had an open-label design, which may have introduced bias, but all echocardiograms were analysed by an expert echocardiographer blinded to other patient data. Our results may not be representative of the entire population of AF and sleep apnoea, particularly not for those with predominantly central sleep apnoea, low LV EF, EDS or significant cardiopulmonary comorbidities.