I tried lots of meds before- verapamil, cardizem, flecainide,
Toprol XL ( hated it- had headaches, bad nausea). So far the
atenolol has worked the best with the least side effects for me. The bad effects I feel are fatigue, and a heaviness in my chest laying down or with exercise. But prior to taking my resting heart rate is 110- 120... and then the SVT attack it would go up to 150 - 175 for an hour or two. I am sure you are "worn out" with it at 155.
I too am only a low dose.