I had a bad experience with Rythmol (suppressed the sinus node too much and went off of it after a week) and tho I am now back on Norpace for the time being, if it fails I will not try any more anti-arrythmic drugs. My next stop will be an ablation if (when) my afib comes back.
JUst want to throw something out there for you to consider. My cardiologist stated that "messing" with various anti-arrhythmics, and experimenting with dosages carries as much risk as an electrophysiology study which could cure you so you wouldn't need the drugs. I competed for meany years with SVT while totally unmedicated. I did so mostly because there wasn't much available at the time to try for control of SVT. The upside of this was I didn't have any drug in me to slow me down. The downside was it left me wide open to SVT episodes. That said, once I got on an anti-arrhythmic, in this case 100mg./day of Metoprolol, it did literally nothing to prevent episodes. I still had my 3 to 5 episodes per month. Metoprolol did aid in converting them, but it didn't prevent them from happening. When I tried another drug, Sotalol, I had a very bad cardiac reaction to it, and immediately stopped it. Ablation was the cure for me, and I'm happy and thankful that my cardiologist gently guided me in that direction.
Forgot to mention the Atenolol worked better for me -- not so tired or dizzy.
Not sure about for running, but I was on Toprol and having a lot of dizziness and fatigue. I changed EP's and the new one put me on Atenolol, saying he believed i would have fewer symptoms because it does not pass the blood-brain barrier. It wouldn't hurt to ask. Good luck with this.