Lay summary
Atrial fibrillation (AF) is an irregular heart rhythm that is common and is associated with impaired heart function, stroke and increased risk of hospitalisation or death. Aldosterone and other substances that activate mineralocorticoid receptors usually play a role in maintaining blood pressure and blood volume, but recent evidence suggest that they may also contribute to the development of AF. The proposed study will test whether blockade of mineralocorticoid receptors with an oral medication called spironolactone that is already proven to be beneficial for subjects with heart failure, can also reduce AF in subjects who already have a cardiac pacemaker. Using the cardiac pacemaker will allow more accurate detection of the total number and duration of episodes of AF. Participants in the study will receive either daily spironolactone or placebo tablets for 12-months and the difference in number of AF episodes will be identified from pacemaker recordings