The role of the brain-heart connection (autonomic nervous system) in Atrial Fibrillation; a common heart rhythm disorder

AF-AF is an observational study designed to assess the contribution of atrial fibrillation (AF) and its risk factors (hypertension, sleep apnoea, obesity, diabetes mellitus) to dysfunction of the autonomic nervous system. We have previously performed (see listed parent study) a small study that demonstrates reflex deficits to autonomic testing in patients with paroxysmal (non permanent form of AF). Therefore we plan to perform simple (non-invasive) autonomic reflex tests such as lower body negative pressure, hand-grip testing, passively raising the legs and a valsalva (breath-holding manoeuvre) on a larger group of patients with intermittent AF, permanent AF and at any stage of their treatment (predefined by their heart team. We shall also use a non-invasive auricular vagus nerve stimulator (a clip attached to the tragus of the ear) in order to bypass the heart during reflex testing to see if suspected reflex deficits are corrected. The testing will take 2.5 hours to complete on one occasion. There will be no additional follow up tests. We plan to consecutively recruit up to 400 patients with AF at a single site to perform these autonomic tests. In some cases, where patients consent to re-enrolment after treatment of their AF (either by radio frequency catheter ablation, anti-arrhythmic medication) as well as after attempts made to manage their risk factors (also predetermined by the clinical team) we shall re-study their autonomic function to determine whether this improves as a result of elimination of either AF or its risk factors. This will be on an opt-in basis (as a re-consent) and our ethics board has approved of us re-contacting patients who demonstrate an interest at their first visit. The patients with AF will have varying burdens of their disease (and we shall aim to enrol 100 patients with the mildest form; paroxysmal AF or intermittent AF, 100 with persistent AF and then 100 patients in whom it is decided to leave them in chronic AF. Additional patients (anticipated n =100 will have repeat testing after their predetermined treatment strategy). Note we do not influence treatment decisions in our study. In detail; repeat testing will occur after electrical cardio version (to revert to normal rhythm), catheter ablation to treat AF and maintain normal rhythm, after treatment of risk factors that can maintain AF; obesity, blood pressure and diabetes, or any of these combinations. In general re-tests will occur within the study period of three years. The cardiologist running this study will be involved in patient care at the study site and therefore will determine with the patient when they have been booked in for their treatment and when they are likely to be retested. There will be no follow up as such. The responses of patients with AF will be compared to a control group (comprised of age and sex matched healthy adults, adults with risk factors for AF without the disease and finally a small cohort of patients with known autonomic disorders that affect the heart rate). These conditions are an abnormal reflex tachycardia to standing (postural tachycardia syndrome) and patients with an abnormally high resting heart rate (a condition called inappropriate sinus tachycardia). We anticipate enrolment of approximately 100 patients in this group.