Class I antiarrhythmic medica- tions can be effective, but those are generally avoided due to concerns for adverse effects. For patients who require arrhythmia suppression for whom antiarrhythmic medications are ineffective, not tolerated, or undesired, catheter ablation can be a highly effective treatment (see Section 9). The ablation strategy is to identify the site of origin manifested by the earliest site of electrical activa- tion or, when this is not feasible, by pace-mapping. The most common site of origin for idiopathic VA is from the right ventricular outflow tract (RVOT) or the ostium of the LV, which is comprised of the oval opening of the LV to which the aorta is attached anteriorly and the left atrium is attached posteriorly. The likely origin can be reasonably predicted from the QRS morphology of the VA, which provides a good indication of the type of ap- proach required and the likelihood of success and risks. Ablation failure is often related to the absence of the VA for mapping at the time of the procedure, or origin of the VA in an inaccessible region of the heart. These foci occasionally produce sustained monomorphic VT.S8-5 S8-7 Recommendation-Specific Supportive Text 1. In a randomized, double-blinded, placebo-con- trolled study of 52 patients with symptomatic VA and a mean PVC count of 21407 1740 beats per 24 hours, atenolol significantly decreased symptom frequency (P=0.03) and PVC count (P=0.001), whereas placebo had no effect on PVC count (P=0.78) or average heart rate (P=0.44).S8-8 A prospective randomized comparison of antiar- rhythmic medications versus catheter ablation, metoprolol or propafenone had modest efficacy to suppress RVOT VA although with a far higher rate of recurrence than catheter ablation.S8-9 2. 