What would be the best beta blocker to use for ventricular arrhythmia not caused by structural heart disease?

Complicated question. Depends on the arrhythmia - premature beats could be treated with almost any beta blocker. Non sustained V tach might be better served with a calcium channel blocker or an anti arrhythmic agent ( which has beta block like qualities) such as amiodarone or sotalol. You should discuss your particular case with your doc. Ablation may be a possibility.