Under normal conditions an interatrial communication allows blood to shunt from left to right due to a higher pressure in the left atrium than the right atrium and a greater compliance of the right ventricle than the left ventricle. Right-to-left interatrial shunting (RLS) is usually associated with spontaneous or induced pulmonary hypertension. RLS may occur spontaneously during a release phase of a Valsalva manoeuvres that transiently generates a right to left pressure gradient across the interatrial septum or rarely due to a condition termed platypnea-orthodeoxia. The latter is characterized by dyspnoea and deoxygenation accompanying a change to a sitting or standing from a recumbent position. Platypnea-orthodeoxia is thought to be due to a combination of an interatrial communication and an anatomical variant e.g. a persistent Eustachian valve and/or stretching and distortion of atrial septum allowing more streaming of venous blood from inferior vena cava through the defect when in the upright position. The recommended treatment of platypnea-orthodeoxia is percutaneous closure of patent foramen ovale (PFO).
Obstructive Sleep Apnoea - Hypopnoea Syndrome (OSAHS) is characterised by repetitive upper airway obstruction during sleep causing apnoea (cessation of breathing) and oxygen desaturation. It is a significant health burden on the National Health Service (NHS) and society, affecting approximately 4% middle aged men and 2% middle-aged women. The risk of OSAHS rises with increasing body weight, active smoking and age. OSAHS is set to reach epidemic proportions as the Western population ages and the incidence of obesity rises. About 1% of men in the United Kingdom (UK) have severe OSAHS with an apnoea-hypopnoea index (AHI; the average number of episodes of apnoeas and hypopnoeas per hour of sleep) of \>20 and oxygen desaturation index (ODI; the number of desaturation episodes defined as ≥4% drop in oxygen saturations per hour during sleep) of \>20, measured by nocturnal oximetry and respiratory polygraphy (intermediate sleep study or Embletta™). Patients with untreated severe OSAHS have a higher incidence of fatal (OR 2.87) and non-fatal (OR 3.17) cardiovascular events compared to age and sex matched controls. The degree of oxygen desaturation inversely correlates with survival and the link is thought to be multifactorial; raised blood viscosity due to increased haematocrit, sympathetic activation leading to arrhythmias and systemic hypertension are thought to be important. In a Cox model a 1% decrease in average nocturnal oxygen saturation (SaO2) was associated with a 33% increase in the incident risk of fatal and nonfatal cardiovascular events. Treatment with continuous positive airways pressure (CPAP) ventilation at night reduces symptoms (snoring, mood, day time sleepiness and headache) and cardiovascular event rate, but it is poorly tolerated and refused by up to a fifth of patients. Improvement in ODI and sleepiness in OSAHS treated by CPAP is transient and when CPAP is discontinued, measurements return to baseline within 1 week.
PFO is found with a higher incidence in patients with OSAHS than controls (69% vs. 17%) and may exacerbate the oxygen desaturation in OSAHS during apnoeic/ hypopnoeic episodes observed in some patients. In OSAHS patients with greater ODI to AHI ratio (ODI/AHI\>0.67), the prevalence of large PFO was nine out of 15 (60%) versus two out of 15 (13%) in those with ODI/AHI \<0.33. OSAHS is believed to raise right heart pressures and increase RLS via the interatrial defect due to repeated nocturnal Valsalva and Muller manoeuvres. Prolonged oxygen desaturation may further exacerbate sleep apnoea by decreasing central respiratory drive. In selected populations of OSAHS patients, PFO closure may be beneficial. This has been reported in a number of case reports but has not been studied in a larger trial population.
Hypothesis:
RLS via a PFO in patients with severe OSAHS: ESS≥11 and ODI≥20 or ODI/AHI \>0.67, is deleterious and closing the PFO will improve oxygen saturation, exercise tolerance, symptoms, quality of life and will reduce CPAP requirement and, ultimately, will reduce the incidence of fatal/ non-fatal cardiovascular events.
This study will assess the improvement of symptoms of OSA (e.g. sleepiness, exercise capacity and general well-being) following PFO closure. Improving symptoms will enable patients to not be reliant on treatment for OSA. If PFO closure is beneficial the investigator aims to assess the efficacy of treatment to reduce heart disease and strokes in a larger study.
