Measuring Success in Central Sleep Apnea Treatment
A growing number of sleep physicians and researchers argue that the apnea-hypopnea index (AHI) may not be the best measure of success in treating central sleep apnea (CSA). They suggest that patient-centered metrics, such as quality of life and daytime symptoms, should also be considered.
A post-hoc analysis of patients with central sleep apnea (CSA) and atrial fibrillation has added to the case for tracking how patients feel and function, not just how often they stop breathing.
A narrow focus on the apnea-hypopnea index (AHI) may overlook the outcomes that matter most to people with central sleep apnea: how these patients feel and function during the day. This shift toward patient-centered metrics is particularly relevant for patients with atrial fibrillation, a population in which CSA is highly prevalent but often underdiagnosed.
Overlooked Prevalence
The association between atrial fibrillation and CSA is well-documented, particularly in patients with heart failure. In this latest analysis of 151 patients with CSA, researchers found that nearly half also had a medical history of atrial fibrillation.
Despite this high prevalence, many patients with atrial fibrillation are not routinely screened for sleep-disordered breathing. Muhammad Qasim, a specialist in pulmonology and respiratory medicine, notes that the symptoms of CSA-such as fatigue and breathlessness-often overlap with those of cardiac disease.
| Condition | Atrial Fibrillation | CSA |
|---|---|---|
| Prevalence | High | High |
| Screening | Limited | Limited |
Moving Beyond the AHI
The retrospective assessment of the remēde System pivotal trial focused on 64 participants with both CSA and atrial fibrillation. While the physiological results were significant-the AHI decreased from a median of 49 to 21 events per hour, and the central apnea index dropped from 20 to 1 event per hour-the researchers were more interested in the parallel improvements in sleep quality and daytime symptoms.
Scott McKane, director of biostatistics and data management at ZOLL Respicardia, points out that physiological metrics are often invisible to the patient. “Patients can’t necessarily observe or feel the AHI has improved outside of a sleep study, so how a patient feels is top of mind for them, especially when choosing an implantable device,” McKane says.
The analysis utilized the Patient Global Assessment and the Epworth Sleepiness Scale to track these subjective improvements. Key findings included:
| Metric | Baseline | After 6 Months |
|---|---|---|
| Daytime Sleepiness | 12.5 | 4.5 |
| Global Improvement | 11% | 54% |
| Sleep Architecture | 48 | 25 |
Role of Sympathetic Activity
One of the proposed mechanisms for why TPNS improves quality of life so effectively is its impact on the sympathetic nervous system. CSA is associated with increased sympathetic activity, largely driven by frequent arousals and intermittent hypoxemia. By stabilizing the breathing pattern, TPNS may diminish this overactivity.
“During normal sleep, there is an orchestrated decrease in sympathetic activity which could be altered when sleep architecture is impaired,” Javaheri says. He notes that while this specific study did not measure sympathetic activity directly, previous research has shown that TPNS improves heart rate variability in patients with heart failure and reduced ejection fraction.
Central Versus Obstructive Hypopneas
The study also underscores a critical diagnostic challenge: the accurate subtyping of respiratory events. Javaheri emphasizes that many hypopneas are classified as obstructive by default, which can lead to a misdiagnosis of obstructive sleep apnea (OSA) when the underlying issue is actually central.
“It is increasingly important to confirm that the patient has CSA rather than OSA,” Javaheri says. “This is particularly important when the AHI is composed primarily of hypopneas, which are often not classified and may be assumed to be obstructive by default.”
Integrating TPNS
For many clinicians, the question remains where TPNS fits into a standard treatment algorithm.
“I would first confirm the diagnosis, identify the cause, and optimize contributing conditions such as heart failure or medication effects,” Qasim says. “TPNS is generally considered for selected adults with persistent moderate to severe CSA, especially when noninvasive treatments are ineffective, inappropriate, or poorly tolerated.”
Addressing Evidence Gaps
While the quality of life data is encouraging, more research is needed to link these improvements to long-term cardiovascular outcomes. A major unanswered question is whether treating CSA with TPNS can actually reduce atrial fibrillation burden or the incidence of new-onset atrial fibrillation.
“We need adequately powered trials examining [atrial fibrillation] burden, recurrence after ablation, stroke, heart failure hospitalization, cardiovascular mortality, and overall healthcare use,” Qasim says.
Patient’s Perspective on Success
Ultimately, the study reinforces the idea that the patient’s goals should be at the center of the treatment plan. If a patient’s primary complaint is that they are too tired to play with their grandchildren or attend social functions, a reduction in AHI from 40 to 5 is only a partial success if the fatigue remains.
“Success in CSA treatment should be measured across several domains, including breathing events, oxygen burden, sleep disruption, daytime symptoms, cardiovascular status, and the patient’s own goals,” Qasim says.
Javaheri agrees that measuring success requires a more holistic approach. “We need to consider the patient’s overall quality of life, not just their AHI,” he says.
