O004 Obstructive sleep apnoea severity is associated with parasympathetic withdrawal in coronary artery disease

INTRODUCTION: Patients with Coronary Artery Disease (CAD) are exposed to myocardial ischemia and hypoxia, resulting in altered autonomic function. Obstructive sleep apnoea (OSA) is highly prevalent in CAD and is associated with increased sympathetic activity which could further exacerbate cardiovascular risk. We aimed to determine whether OSA severity is associated with altered autonomic function in CAD patients. METHODS: Patients presenting to the coronary care unit with CAD underwent level 2 portable polysomnography to assess the presence and severity of OSA. Autonomic function was calculated from continuous blood pressure and 3-lead ECG 5 minute recordings while awake. Mean spontaneous baroreceptor sensitivity (sBRS msec/mmHg); vagally mediated heart rate variability (HRV) markers (pNN50%, RMSSD, HF-HRV); and, sympathetically mediated vascular autonomic function (LF-BPV) were measured. Autonomic function was assessed in relation to OSA severity (Apnoea Hypopnea Index, AHI; oxygen desaturation index, ODI). RESULTS: OSA was present in 49/51 (96%) participants with CAD (age 54±9 years; BMI 28.9±5.4 kg/m2; male 41(77%)). No association was found between sBRS and AHI. There was a modest inverse correlation between AHI and vagally mediated HRV (RMSSD, r= -0.28 p=0.04; HF, r= -0.31 p=0.03). AHI positively correlated with LF-SBP (r=0.29, p=0.04) suggesting upregulation of sympathetic modulation. Linear regression analyses, adjusted for age, sex, and BMI, showed AHI was a determinant of parasympathetically modulated HRV measures (pNN50% -0.25(0.12), p=0.05). CONCLUSIONS: In patients with CAD, increased AHI was associated with parasympathetic withdrawal suggesting that OSA could increase poor cardiovascular prognosis in this population.