Metoprolol weaning

Hi all I am a 23 year old female with a history of palpitations and rapid heart rate. I also have a mild mitral valve prolapse.  I was placed on metoprolol 25mg twice a day for this issue.  I only take 25mg in the morning however, my cardiologist is aware and is fine with it.  I have been contemplating pregnancy for a while now and wanted to try to wean myself off of the metoprolol so my cardiologist just said that the dose was so small I could just stop taking it.  I also have very bad panic disorder.  I didn't take it fot the past 3 days and I felt really tired and my heart would race when I would get up just to walk across the room.  I woke up today and because I had to come to work I went ahead and took it this morning. Still feeling a little panicky which had subsided up until I stopped taking it 3 days ago, I also take Effexor XR. Just wondering if anyone else had any experience with this med. or could reccommed if they took anything else as far as an antiarrythmic during pregnancy?  Help Please