When a cardiologist sees a patient with high blood pressure that will not come down despite three medications, or a patient returning with a second episode of atrial fibrillation after a technically successful ablation, they are often looking at a problem whose origin is not in the heart itself but in what is happening to the airway during sleep. This is not a niche concern. Sleep apnoea is found in 40 to 80 per cent of patients attending cardiology clinics. Most of it has never been diagnosed.
I want to explain why OSA is so damaging to the cardiovascular system, go through each major condition with the evidence behind it explained clearly, and be honest about what treatment does and does not achieve.
Why Sleep Apnoea Stresses the Heart
Each apnoea event sets off a sequence of cardiovascular stressors that, taken in isolation, would be entirely survivable. But in severe sleep apnoea this sequence repeats more than thirty times per hour. The airway collapses. Oxygen levels fall. The brain detects hypoxia and triggers an emergency arousal response. The sympathetic nervous system fires — think of this as the body's fight-or-flight alarm system. Adrenaline and noradrenaline surge through the circulation. Heart rate accelerates. Blood pressure spikes. The heart pumps against dramatically increased pressure as the person struggles to breathe against the obstructed airway.
Over time this creates endothelial dysfunction — the cells lining blood vessels lose their ability to regulate their own behaviour — as well as arterial stiffness, systemic inflammation, and structural remodelling of the heart muscle. The result is accelerated atherosclerosis (furring of the arteries), a tendency toward clotting, and a myocardium that has been chronically overworked. None of these changes are dramatic on any single night. But they accumulate across years of undiagnosed disease.
OSA is found in 40 to 80 per cent of patients already attending cardiology clinics with hypertension, heart failure, coronary artery disease, or atrial fibrillation. Yet most of them have never been tested for it.
Overall Cardiovascular Disease Risk
When researchers pool results from multiple individual studies together — a process called a meta-analysis, which gives a more reliable overall answer than any single piece of research can — the picture for OSA and heart disease is clear. A meta-analysis drawing on 24 separate studies found that OSA raises the risk of cardiovascular disease overall by 71 per cent. To express that as a real-world number: cardiovascular disease affects roughly 1 in 7 adults over 50 over a ten-year period. With severe untreated OSA, that rises to closer to 1 in 4.
For cardiac death specifically, severe OSA is associated with nearly triple the risk compared with those without it. For all-cause mortality — the risk of dying from any cause — severe OSA raises it by 54 per cent compared with those without the condition. These are not marginal statistics. They represent the kind of risk elevation that, if it were caused by a known toxin or food contaminant, would prompt immediate public health action.
Hypertension: The Blood Pressure Connection
The relationship between OSA and high blood pressure is one of the most firmly established causal links in sleep medicine. The mechanism is direct: repeated overnight spikes in blood pressure from sympathetic activation — the same emergency alarm system described above — gradually shift the body's blood pressure set-point upward. The stress response carries over into waking hours. The result is hypertension that is driven by a structural problem in the airway, not just by lifestyle or genetics.
The most striking clinical finding is this: around 70 to 85 per cent of people with resistant hypertension — blood pressure that fails to come down despite taking three antihypertensive medications at appropriate doses — have obstructive sleep apnoea. If you are one of those patients sitting in a cardiology clinic with blood pressure still not controlled on three drugs, there is a very high probability that an airway problem is contributing to your situation.
A meta-analysis specifically in hypertensive OSA patients found CPAP reduces 24-hour systolic blood pressure by an average of 5 millimetres of mercury. For context, a 5 mmHg reduction in systolic blood pressure, sustained over time, is enough to meaningfully reduce stroke and heart attack risk at a population level. In resistant hypertension specifically, some trials have reported reductions of up to 10 mmHg — equivalent to adding another medication. Furthermore, each additional hour of CPAP use per night is associated with an extra 1.5 mmHg reduction. The treatment is dose-dependent: the more you use it, the greater the blood pressure benefit.
Atrial Fibrillation
Atrial fibrillation is an irregular heartbeat that significantly raises stroke risk. OSA patients are 88 per cent more likely to develop it compared with those without OSA — roughly doubling the risk. To make that concrete: atrial fibrillation has a lifetime risk of about 1 in 6 in adults over 60. With OSA, that rises to closer to 1 in 3. When AF patients are systematically tested for sleep-disordered breathing — rather than relying on symptoms to prompt investigation — around 78 per cent are found to have it. This is a majority of the AF population, most of them unknown to sleep medicine.
The mechanism involves the intermittent hypoxia and large negative pressure swings of OSA creating mechanical stress on the left atrium — the heart chamber most directly involved in AF. This stress promotes atrial enlargement and electrical remodelling: changes in how the heart conducts electrical signals that make arrhythmia more likely.
In patients who have had atrial fibrillation treated with catheter ablation, those with untreated OSA are 70 per cent more likely to have the AF return. CPAP in consistently adherent patients reduces that recurrence risk by 72 per cent.
For a patient who has undergone ablation for AF, this is perhaps the most actionable number in the entire OSA-cardiovascular literature. It means that getting tested for sleep apnoea after an ablation procedure is not optional background noise — it is a meaningful intervention that substantially changes the odds of the treatment working long-term. A meta-analysis of seven observational studies covering 4,572 patients confirms this finding consistently.
Heart Failure
OSA doubles the risk of developing heart failure. Among patients undergoing cardiac surgery who have coexisting OSA, the odds of developing post-operative atrial fibrillation are more than doubled, and the odds of acute kidney injury after surgery are more than doubled. Hospital stays are significantly longer. These are consequences that matter to surgeons planning operations as well as to the patients recovering from them.
An important refinement from recent research is that the specific degree of nocturnal hypoxia — how low oxygen actually drops during apnoea events — predicts incident heart failure independently in men, over and above simply counting how many apnoea events occur per hour. This suggests that the depth of the oxygen dip matters, not just its frequency.
What Treatment Achieves — and Where It Struggles
The honest picture on CPAP and hard cardiovascular outcomes is more nuanced than is sometimes presented, and I think it is worth being clear about why.
For blood pressure, the evidence is consistent and strong: CPAP lowers it, particularly in resistant hypertension and in patients with uncontrolled blood pressure at baseline. For atrial fibrillation recurrence after ablation, the evidence strongly favours CPAP in adherent patients. For depression, quality of life, and daytime function, CPAP consistently helps.
For hard cardiovascular endpoints — heart attacks, cardiovascular death — the large randomised controlled trials (the highest standard of medical evidence, where patients are assigned by chance to treatment or control) have generally not shown a clean benefit from CPAP over medical therapy alone. The main reason, as I read the evidence, is that CPAP adherence in these trials was poor. Many participants were using it for fewer than four hours per night, which is insufficient to reverse the nightly cardiovascular stress. A meta-analysis that specifically examined patients using CPAP for more than four hours per night found a 30 per cent reduction in major adverse cardiac events. Another found a 31 per cent reduction in cardiovascular mortality in adherent patients. The treatment works; the challenge is getting people to use it enough.
For patients who cannot tolerate CPAP, surgical options can reduce OSA severity to levels where the cardiovascular burden is meaningfully reduced. The choice of treatment should be personalised. What matters most is that the condition is identified and addressed, by whatever means works for that individual.
References
[1] Salari N et al. The effect of obstructive sleep apnea on the increased risk of cardiovascular disease: a systematic review and meta-analysis. Neurological Sciences. 2021. 24 studies; OR 1.71 for cardiovascular disease, OR 1.86 for stroke, OR 1.77 for mortality.
[2] Xie C-J et al. Association of obstructive sleep apnoea with the risk of vascular outcomes and all-cause mortality: a meta-analysis. BMJ Open. 2017. 16 cohort studies, 24,308 individuals; severe OSA associated with RR 2.04 for MACE, RR 2.96 for cardiac death.
[3] Pintilie A-L et al. Sleep Apnea: The Slept-Upon Cardiovascular Risk Factor. Biomedicines. 2025. Narrative review; OSA found in 40-80% of cardiology clinic patients with hypertension, heart failure, CAD, or AF.
[4] Labarca G et al. Efficacy of continuous positive airway pressure (CPAP) in patients with obstructive sleep apnea and resistant hypertension: systematic review and meta-analysis. Sleep Medicine Reviews. 2021. 10 RCTs, 606 participants; CPAP reduced 24-hour systolic BP by 5.06 mmHg in resistant hypertension.
[5] Pengo MF et al. Effect of CPAP therapy on blood pressure in patients with obstructive sleep apnoea: a worldwide individual patient data meta-analysis. European Respiratory Journal. 2024. 36 parallel studies, 9,434 patients; greatest BP benefit in patients with uncontrolled BP at baseline.
[6] Moula AI et al. Obstructive sleep apnea and atrial fibrillation. Journal of Clinical Medicine. 2022. Meta-analysis of 54,271 patients; 88% higher incidence of AF in OSA patients.
[7] Kadhim K et al. Prevalence and assessment of sleep-disordered breathing in patients with atrial fibrillation: a systematic review and meta-analysis. Canadian Journal of Cardiology. 2021. 33 studies, 23,894 patients; pooled SDB prevalence 78% in AF patients.
[8] Congrete S et al. Effect of obstructive sleep apnea and its treatment on atrial fibrillation recurrence after radiofrequency catheter ablation: a meta-analysis. Journal of Evidence-Based Medicine. 2018. 7 observational studies, 4,572 patients; CPAP associated with OR 0.28 for AF recurrence after ablation.
[9] Manzur AR et al. Obstructive sleep apnea and outcomes in cardiac surgery: a systematic review with meta-analytic synthesis. Biomedicines. 2025. 17 primary studies; OR 2.44 for post-operative AF, OR 2.24 for acute kidney injury.
[10] Javaid SS et al. Impact of continuous positive airway pressure on cardiovascular health in patients with obstructive sleep apnea: a systematic review and meta-analysis. Cardiology in Review. 2025. 9 RCTs and 6 observational studies, 9,361 participants; CPAP significantly reduced MACE (RR 0.69) and cardiovascular mortality (RR 0.53) overall.
Contact Professor Vik Veer
If you would like to arrange a sleep assessment or discuss treatment options, please use the details below.
Private secretary: 0207 458 4584