I found an excellent research study that sums up what’s going on with me: Conduction Abnormality and Arrhythmia After Transcatheter Closure of Atrial Septal Defect [pdf]
Conclusion: Transcatheter closure of ASD is associated with a transient increase in supraventricular premature beats and a small risk of conduction abnormalities and paroxysmal atrial fibrillation in early follow-up. Transcatheter closure of ASD does not reduce arrhythmia that appears prior to ASD closure. Larger device size and longer procedure time are associated with increased risk of supraventricular arrhythmia on early follow-up.
Hopefully it is just transient, although I did get atrial flutter very infrequently before closure.
(PS- CT is normal- no blood clots!)