Could well be related to pregnancy.
When I was pregnant I had major EKG changes. My T waves were inverted in 6 leads. This was discovered at 30 weeks and I have no idea at what stage it started. At 32 weeks the waves were all flat and at 34 weeks they were completely back to normal. Had the full cardiac workup due to frequent PVCs. No explanation for the EKG changes other than pregnancy hormones. Both cardiologists I saw said EKG changes in pregnancy are common.
The others have given you great advice. I just wanted to say CONGRATULATIONS. (I'm gonna focus on the WONDERFUL for a change :-)
First of all, CONGRATULATIONS!!
My son had an EKG come back abnormal and after a cardio consult and echocardiogram, he found out there was no problem. Try not to worry. Sometimes the machines spit out inaccurate diagnoses.
In the meantime, please get in touch with your OB about the Effexor. He/she can let you know how best to keep you on, or off, of the medication. The doctor(s) will decide if the benefits outweigh the risks, etc.
First of all STOP WORRYING! There are lots of missing pieces to an ST interpretation and the liklihood is you will have no lasting problems. Under no circumstances permit a dye contrast study while you are pregnant, nor a radiological study. As a matter of fact refuse all x-rays until your baby is delivered. Ever MRI's and CAT scans have the potential to affect the fetus. Also get off the Effexor, now that you know you are pregnant. Stop working out at the gym until you have your baby.