rick,
thanks for the post.
The heart definitely has the ability to remodel and change shape sepending on the stressors placed on it over time. For instance, ejection fraction can often increase in those with heart failue after treatment with appropriate medications. One thing to remember is that an echo does not take into account the pressures and conditions inside the heart at the time the pictures are taken. Changing those conditions can change the pictures obtained. I've seen people with out of control blood pressure, or who are critically ill have dramatically different pictures in a short amount of time.
You will not lose your underlying rhythm from excessive pacing. I dont know alot of the details of your fibrillation, but before considering AV ablation, I would alos consider different antiarrythmics, AV node remodelling, or atrial fibrillation ablation with pulmonary vein isolation to potentially avoid a permanentpacemaker.
At the Cleveland Clinic we have a center that deals solely with tratment options for atrial fibrillation. You might consider a visit, or an econsult as a second opinion.
good luck