An EP study is useful in symptomatic patients with pre-excitation to risk-stratify for life-threatening arrhythmic events.254,256,298 300 See Online Data Supplements 11 15. Most symptomatic patients with accessory pathways undergo catheter ablation, but in some instances, EP studies are performed to identify whether the patient is at increased risk of rapid conduction down the accessory pathway during AF and development of life-threatening ventricular arrhythmias. The most useful findings for risk stratification are an R-R interval <250 ms between 2 pre-excited complexes during induced AF; the presence of multiple accessory pathways; the finding of AVRT precipitating pre-excited AF; and an accessory pathway refractory period <240 ms.254,256,298 300 recommendations for anticoagulation mirror those for patients Similarly, the recommendations for anticoag- ulation with regard to either pharmacological or electrical car- dioversion of patients with atrial flutter are the same as those for patients with AF, as discussed in the 2014 AF guideline 7.2. Non Isthmus-Dependent Atrial Flutters Non isthmus-dependent atrial flutter or atypical flutter describes macroreentrant ATs that are not dependent on conduction through the CTI. A variety of circuits have been described, including a path around the mitral annulus (perimi- tral flutter), re-entry involving the left atrial roof, and re-entry around regions of scarring in the right or left atrium. 