The relationship between obstructive sleep apnea (OSA) and cardiovascular disease isn’t new. Clinicians have known for decades that people with untreated OSA have higher rates of hypertension, atrial fibrillation, heart failure, stroke, and sudden cardiac death. What’s changed in recent years is our understanding of why this happens and what treatment actually does about it.

The latest research has complicated the picture in important ways. Some findings reinforce the urgency of treating OSA. Others have forced the field to reconsider assumptions about CPAP and cardiovascular protection. Here’s where things stand.

The Mechanistic Evidence Is Strong

OSA creates a cycle of intermittent hypoxia and reoxygenation throughout the night. Every apnoea event — and in severe cases there can be 60 or more per hour — triggers a drop in blood oxygen, a surge in sympathetic nervous system activity, and a spike in blood pressure. The body essentially experiences repeated “fight or flight” responses during what should be its most restorative state.

This intermittent hypoxia drives oxidative stress and systemic inflammation. C-reactive protein, interleukin-6, TNF-alpha, and other inflammatory markers are consistently elevated in OSA patients compared with matched controls. These are the same pathways implicated in atherosclerosis, endothelial dysfunction, and plaque instability.

A 2025 study in Circulation used advanced cardiac MRI to demonstrate subclinical myocardial changes in OSA patients without known heart disease. The participants showed increased left ventricular mass, impaired diastolic function, and early fibrotic changes — even in the absence of hypertension. These findings suggest that OSA directly affects cardiac structure before clinical heart disease becomes apparent.

The sympathetic overdrive component is equally concerning. Healthy sleep is associated with a nocturnal “dip” in blood pressure — a physiological rest period for the cardiovascular system. OSA eliminates this dip. Non-dipping blood pressure patterns, consistently observed in OSA patients, are independently associated with increased cardiovascular events.

Hypertension: The Clearest Link

The association between OSA and hypertension is the most established cardiovascular connection. Approximately 50 percent of people with OSA have hypertension, and 30 to 40 percent of people with hypertension have OSA.

What’s particularly telling is the relationship with resistant hypertension — high blood pressure that doesn’t respond adequately to three or more medications. Studies show that 70 to 80 percent of patients with resistant hypertension have undiagnosed OSA. Treating the OSA with CPAP often brings blood pressure under control, sometimes allowing medication reduction.

Current Australian and international guidelines recommend screening for OSA in all patients with resistant hypertension. This isn’t optional guidance — it’s considered standard practice.

Atrial Fibrillation: A Growing Concern

The link between OSA and atrial fibrillation (AF) has gained significant attention. A 2024 meta-analysis in the European Heart Journal pooled data from 18 studies and found that OSA roughly doubles the risk of developing AF. Among patients who undergo catheter ablation for AF, those with untreated OSA have recurrence rates nearly twice as high as those without OSA or those with treated OSA.

The mechanism appears to involve both the structural changes caused by intermittent hypoxia (atrial remodelling, fibrosis) and the acute autonomic swings during apnoeic events. The intrathoracic pressure changes during obstructed breathing efforts also create mechanical stress on the atria.

Several Australian cardiac centres now include sleep assessment as part of pre-ablation workup for AF patients. It’s a practical step that can meaningfully improve outcomes.

The CPAP Cardiovascular Debate

Here’s where the research gets complicated. The SAVE trial, published in the New England Journal of Medicine in 2016, was a landmark randomised controlled trial that enrolled over 2,500 patients with moderate-to-severe OSA and existing cardiovascular disease. It found no significant reduction in major cardiovascular events with CPAP therapy compared with usual care.

This result surprised many clinicians and has been debated ever since. The nuances matter. Average CPAP adherence in the trial was only 3.3 hours per night — well below the minimum four hours typically considered therapeutic. Subgroup analyses suggested that patients who used CPAP for more than four hours per night did show cardiovascular benefit, but these were post-hoc findings.

More recent data has added context. A 2025 analysis published in The Lancet Respiratory Medicine pooled individual patient data from four major trials and found that consistent CPAP use of more than four hours per night was associated with a 28 percent reduction in major adverse cardiovascular events. Below that threshold, the benefit was negligible.

The implication is clear but frustrating: CPAP likely protects the heart, but only if patients actually use it consistently. This makes adherence — which hovers around 50 percent in real-world studies — a cardiovascular issue, not just a comfort issue.

What This Means Practically

For patients with OSA, the cardiovascular message isn’t “CPAP doesn’t help.” It’s “CPAP helps if you use it.” That distinction matters enormously for clinical conversations.

For patients who genuinely can’t tolerate CPAP, alternative treatments — mandibular advancement devices, hypoglossal nerve stimulation, positional therapy, and weight management — aren’t just about snoring and daytime sleepiness. They’re about cardiovascular risk reduction.

The other practical takeaway is screening. If you have hypertension, particularly resistant hypertension, or AF, ask your doctor about sleep apnea testing. If you’ve been diagnosed with OSA and you’re struggling with CPAP adherence, have an honest conversation with your sleep physician about alternatives. The cardiovascular stakes make treatment worth persisting with, even when it’s inconvenient.

The evidence base will continue to evolve. Several large trials are currently underway examining cardiovascular outcomes with newer OSA treatments. But the direction is consistent: sleep apnea is a cardiovascular risk factor, and addressing it matters.