Discussion
This study describes a real-world cohort of patients using ASV therapy and the characteristics associated with benefit from therapy. The patients that were prescribed and started ASV therapy most often had a significant degree of obstructive component to sleep-disordered breathing, whether primary OSA with TECSA or comorbid OSA and CSA. Moreover, we found that a higher obstructive AHI on the baseline PSG was associated with adherence to ASV therapy. Another important finding was that a lower residual AHI on ASV as a proportion of the baseline was associated with PAP adherence. Adherent patients had similar clinical characteristics as the nonadherent patients, including comorbidities, severity of sleep-disordered breathing, and obesity.
Though the results of the SERVE-HF trial have dampened the enthusiasm somewhat, ASV therapy has long been considered an effective and well-tolerated treatment for many types of CSA.13 In fact, treatments that can eliminate the central AHI are fairly limited.4,14 Our data suggest that ASV is also effective and tolerated in OSA with TECSA and/or comorbid CSA. Recent studies suggest that CSA resolves spontaneously in a majority of TECSA patients within 2 to 3 months of regular CPAP use.15 Other estimates suggest that persistent TESCA may be present in 2% of patients with OSA on treatment.16
Given the high and rising prevalence of OSA, many people are at risk for clinically significant TESCA. Another retrospective case series found that 72% of patients that failed treatment with CPAP or BPAP during PSG, met diagnostic criteria (at the time) for CSA; ASV was objectively beneficial in these patients.17 ASV can be an especially useful modality to treat OSA in patients with CSA that either prevents tolerance of standard therapies or causes clinical consequences, presuming the patient does not also have HFrEF.18 The long-term outcomes of treatment with ASV therapy remain a matter of debate.
The SERVE-HF trial remains among the only studies that have assessed the mortality effects of CSA treatments, with unfavorable findings. Treatment of OSA has been associated with favorable chronic health benefits, though recent studies have questioned the degree of benefit attributable to OSA treatment.19-24 Similar studies have not been done for comorbidities represented by our study cohort (ie, OSA with TECSA and/or comorbid CSA).
The lack of CSA diagnosis alone in our cohort may be partially attributable to changing practice patterns following the SERVE-HF trial, though it is not clear from these data why a higher baseline obstructive AHI was associated with adherence to ASV therapy. Our data in this regard are somewhat at odds with the preliminary results of the ADVENT-HF trial. In that study, adherence to ASV therapy in patients with predominantly OSA declined significantly more than in patients with predominantly CSA.25 Most of our patients were diagnosed with predominantly OSA, so a direct comparison with the CSA group is problematic; additionally, the primary brand and the pressure adjustments algorithm used in our study differed from the ADVENT-HF trial.
OSA and CSA may present with similar clinical symptoms, including sleep fragmentation, insomnia, and excessive daytime sleepiness; however, the degree of symptomatology, especially daytime sleepiness, and the response to treatment, may be less in CSA.2,26 Both the subjective report of symptoms (ESS) and PSG measures of sleep fragmentation were similar in our patients, again likely explained by the predominance of obstructive events.
The pathophysiology of CSA is more varied than OSA, which is probably relevant in this case. ASV was originally designed for the management of CSA with CSR, accomplishing this goal by stabilizing the periods of central apnea and hyperpnea characteristic of CSR.27 Although other forms of CSA demonstrate breathing patterns distinct from CSR, ASV has become an accepted treatment for most of these. It is plausible that the long-term subjective benefit and tolerance of ASV in CSA without CSR is less than for CSA with CSR or OSA. None of the patients in our study had CSA with CSR.
Ultimately, it may be the objective treatment effect that lends to adherence, as has been shown previously in OSA patients; our group of adherent patients showed a greater improvement in AHI, relative to baseline, than the nonadherent patients did.28 The technology behind ASV therapy can greatly reduce the frequencies of central apneas, yet this same treatment effectively splints the upper airway and even more effectively eliminates obstructive apneas and hypopneas. Variable adjusting EPAP devices would plausibly provide even more benefit in these patients, as has been shown in prior studies.29 To the contrary, our small sample of patients with TESCA showed a nonsignificant trend toward adherence with fixed EPAP ASV.
Opioid use was substantial in our population, without significant differences between the groups. CPAP therapy is ineffective in improving opioid-associated CSA. In a recent study, 20 patients on opioid therapy with CSA were treated with CPAP therapy; after several weeks, the average therapeutic use was 4 to 5 hours per night and CPAP was abandoned in favor of ASV therapy due to persistent central apnea. ASV treatment was associated with a considerable reduction in central apnea index, AHI, arousal index, and oxygen desaturations in a remarkable improvement over CPAP.30