EGF and atrial fibrillation: Evidence for the following was found: (1) EGFC can be an effective marker of substrate health, and high EGFC values are tied to a higher 12-month FFAF; (2) LA EGFC is lower than but correlated with RA EGFC, suggestive of general substrate remodeling progressive from the LA to the RA; (3) EGF-identified extra-PV sources may be potent drivers of AF, whose presence decreases FFAF rates if left unablated; and (4) phenotyping patients based on EGFC and source presence may be useful in predicting patient recurrence and designing optimal mechanism-specific ablation strategies.