Inducing AF Induction will be performed systematically first with programmed premature atrial contractions (PACs) using single extrastimuli at shortening coupling intervals after an 8-beat drive of cycle length (CL) 500ms (120 bpm). Next, burst pacing will be done at CL 500ms, reducing in 50ms steps to 300ms, then in 10ms steps to AF from the proximal coronary sinus as a stable reference point. If AF still does not initiate, isoproterenol (≤ 10mcg/min)10 will be infused. Each patient's induction threshold will be documented.