Abnormal EKG during pregnancy.?

On Monday I went into preterm labor and was given meds to stop the contractions. While I was there I had another fainting spell (I've had several in the past 7 weeks). They did an EKG and it came back abnormal. I was referred to a cardiologist and went yesterday. They did another EKG and also abnormal. she is recommending that I have an Echo done on Wednesday and be connected to one of those 24 hour monitors. I am really short of breath. I feel like I am not getting enough oxygen, I was also give oxygen at the hospital. Blood pressure is also fairly low. Has anyone else had a cardiac experience during pregnancy? What could this mean? I don't know much about cardiology and I've been excusing the shortness of breath for a baby shrinking my lungs (I am having twins). I am 30 weeks and hope that whatever this is doesn't mean the babies will come earlier. Any advice would be helpful. Thanks.