atrial flutter posts valve replacement

My husband is 5 weeks post-op for an aortic valve replacement - he now has a mechanical valve.  Recovery has been good.  Last night however he was in the ER, where they had to 'zap' him to get his heart in rythym again - they said he had an atrial flutter.  Is this common so late post-op?  Other than possible scar tissue irritating the heart, what could be the cause?  Anyone had similiar experience?  Thanks!

[Cleveland Clinic]

This is very common in the post-op state for up to 2-3 months.  He should be started on beta blockers or amiodarone (short term) to control this to prevent any further need for cardioversions.  High catecholamine state and scar are known culprits.