This is somewhat of a complex question. Anyway, Flecainide is generally used for arrythmias originating in the atria like atrial fibrillation and atrial flutter. There are generally only 3 rhythms that originate in sinus node which include the normal sinus rhythm (normal rhythm), sinus node re-entrant tachycardia, and inappropriate sinus tachycardia. There can also be atrial tachycardias that originate near the sinus node. Flecainide is not commonly used to treat these arrythmias though I would encourage you to discuss this with an electrophysiologist as your doctor may have a particular reason for using this medication. In regards to shortening the QT, Flecainide has been shown to shorten the QTc in Type 3 long QT syndrome though not in the other types of long QT. Flecainide can actually lengthen to QT some patients. I would recommend that you discuss these questions with your electrophysiologist. I hope this helps.