Characterising Left Atrial Function and Compliance in Atrial Fibrillation

All patients recruited to the study will have symptomatic atrial fibrillation (AF) planned for AF ablation. AF ablation is an interventional treatment for AF recommended for patients with symptomatic AF refractory to at least 1 anti-arrhythmic drug. Participants will be recruited when both patient and physician have decided to proceed with AF ablation. These patients will undergo AF ablation regardless of recruitment to the study. Within 4 weeks prior to their AF ablation, enrolled participants will undergo a series of non-invasive testing including baseline echocardiogram, stress echocardiogram, cardiopulmonary exercise testing and blood sampling for NT-pro BNP. They will also complete an AF symptom questionnaire and the Minnesota Living with Heart Failure questionnaire. AF ablation will then be undertaken as per standard institutional protocols. LA pressure will be measured via trans-septal puncture, as occurs routinely during such procedures. LA dimensions will be measured by transoesopageal echocardiography (TOE). TOE is also part of the standard procedure to exclude left atrial thrombus and guide transeptal puncture. Following baseline assessment of LA dimensions and LA pressure, the LA will be directly infused with isotonic saline through the standard LA sheath. The volume to be infused will be 15 mL/kg of body weight over 8 minutes. LA volume via TTE and LA pressure will be recorded every 2 minutes during the infusion using TTE. During infusion, LA pressure and respiratory parameters will be measured and infusion will be stopped if there is any evidence of fluid overload. LA compliance will be calculated from the LA volume pressure curve provided by these measurements. Procedure duration will be variable depending on the ablation procedure itself and can last anywhere between 1-4 hours. The study protocol will add only 10 minutes to the overall procedure. Following the procedure, patients will be followed up for a period of 12 months and in addition to standard follow-up protocols, will undergo repeat stress echocardiogram and CPET and 6 and 12 months post-procedure.