Evidence for the effectiveness of beta blockers in terminating SVT is limited. In a trial that compared esmolol with diltiazem, diltiazem was more effective in terminating SVT.96 Nonetheless, beta blockers have an excellent safety profile, so it is reasonable to use intravenous beta blockers to attempt to terminate SVT in hemodynamically stable patients. Recommendations for Acute Treatment of SVT of Unknown Mechanism (Continued) COR LOE Recommendations 2.5. Basic Principles of Electrophysiological Study, Mapping, and Ablation 2.5.1. Mapping With Multiple and Roving Electrodes An invasive EP study permits the precise diagnosis of the underlying arrhythmia mechanism and localization of the site of origin and provides definitive treatment if coupled with catheter ablation. There are standards that define the equip- ment and training of personnel for optimal performance of EP studies involve placement of multielectrode catheters in the heart at 1 sites in the atria, ventricles, or coronary sinus. Pacing and programmed electrical stimulation may be performed with or without pharmacological provoca- tion. Making a precise and correct diagnosis of the mechanism of SVT is the key to successful outcome, particularly when multiple arrhythmia mechanisms are possible; as such, appro- priate diagnostic maneuvers should be performed before pro- ceeding with ablation. By using diagnostic maneuvers during the EP study, the mechanism of SVT can be defined in most Complications of diagnostic EP studies are rare but can be life threatening.143 Cardiac mapping is performed during EP studies to iden- tify the site of origin of an arrhythmia or areas of critical conduction to allow targeting of ablation. Multiple techniques have been developed to characterize the temporal and spatial distribution of electrical activation.144 The simplest technique uses several multipole catheters plus a roving catheter that is sequentially positioned in different regions of interest and measures local activation time. 