According to Kaplan Pathology, a paradoxal embolism happens when initially there is ASD and a DVT occurs that crosses the ASD. But I think since the whole point of a paradoxal embolism is that it's a venous clot that broke off and went into the heart, then it's probably associated with both ASD and VSD. I hope this helps, it's just my take on it.
Here, found this it might help understand it better:
"The intracardiac communication between the venous and arterial circulations can be in the form of a PFO, atrial septal defect (ASD), pulmonary arteriovenous malformation, ventricular septal defect, Ebstein anomaly, and patent ductus arteriosus."
If you get a question in USMLE and you have to choose between ASD and others (VSD, AV malformation, ...etc) then choose ASD.
The reason is that the pressure difference between the atria is less and so a thrombus can easily slip into the left side.
Typical USMLE case scenario would be a patient with DVT who developed stroke. What cardiac anomaly is expected? Answer: ASD.
Note that am not saying that VSD is wrong but they want you to be smart enough to realize that ASD is more likely.