Is There A Test To Check If A Syncope Was Caused By Blood Pooling In The Leg Veins?

I had an experience of syncope on 2 occasions one in dec 2017, after wards my dr. sent me to a cardiologist and he did several tests all came back normal. Then in June 2018 I had another experience my dr was out of office so her office sent me to same-da y clinic that dr. ordered a CT scan, ultrasound of carotid arteries in my neck; both were normal, so my primary dr. referred me back to the cardiologist who did a tilt table test(done in the morning at 9 am) with no results, and implanted a LINQ monitor. But one of the things I read about syncope was the possibility of blood pooling in varicose veins causing it. The first time was at 7:30 pm after an afternoon of walking, a subway ride and a short 4 block walk to my daughter s apt. and the 1st episode happened within a minute or two of coming into the apt, The 2nd episode happened at 6:40 pm as I finished walking 8 blocks -downhill to a neighborhood store. Is there a test for this to see if it is caused by blood pooling in the leg veins? Or some way to tell if this is a possible cause? My primary dr. is sure it is a cardiac related event.