Could the lower heart beat after ablation lead to reduced oxygen flow to lungs and cause atelectasis? pericardial calcification also present.

Ablation.: If we’re talking about ablation for atrial fibrillation, then the restoration of a normal heart rhythm would be expected to actually improve blood flow, and thereby the delivery of oxygen. A reduction in respiratory effort from anesthesia could lead to atelectasis, but I wouldn’t think you’d be anesthetized long enough for an ablation to make this relevant.