Dr Zack said that Flecainide is a bit controversial in Afib. What was meant by that?

Can be effective . Flecainide should be avoided if there are certain additional cardiac abnormalities accompanying the atrial fibrillation - such as left ventricular hypertrophy or a weakened heart muscle (cardiomyopathy), and in some cases more serious rhythm abnormalities can occur. But it is very effective in certain patients.