Atrial fibrillation (AF) is an epidemic with spiraling costs and health care burden,1 yet it is a complex disease that consistently frustrates attempts to better understand the basic pathophysiological mechanism of perpetuation. The complex interplay between triggers and electrophysiological substrate is dynamic and subject to change over time.2 The surface electrocardiogram (ECG) has long been used to inform atrial substrate in patients with a diagnosis or at risk of developing AF. Clinicians have used the P wave to inform risk since the introduction of the modern 12-lead ECG. (Read More)