Drug options, on the other hand, are rela- tively unchanged since publication of the 2003 guideline, per- haps relating to ongoing concern about potential adverse side effects of antiarrhythmic agents. Areas of uncertainty remain, including interventions for which advanced technology is less important. For example, vagal maneuvers are recommended in many circumstances as first-line intervention in patients with SVT, but they are often ineffective. Furthermore, there is great variation in the way these maneuvers are administered. Therefore, research on the best technique of vagal maneuvers, with dis- semination of the findings, is necessary. Clinical trials on Figure 23. Ongoing management of SVT in ACHD patients. Colors correspond to Class of Recommendation in Table 1; drugs listed alpha- betically. ACHD indicates adult congenital heart disease; intra-op, intraoperative; pre-op, preopera- tive; and SVT, supraventricular tachycardia. Page et al 2015 ACC/AHA/HRS SVT Guideline e557 antiarrhythmic drugs for SVT have been limited, and data are often extrapolated from studies that primarily focused on management of patients with AF. The efficacy of a variety of drugs is likely to differ according to the tachycardia mech- anism, and therefore differentiating the best drug for each individual arrhythmia is necessary; for example, the efficacy of class III agents might be markedly different in patients with AF than in patients with atrial flutter. Limited data exist on the optimal management of less common types of SVTs, such as junctional tachycardia and multifocal AT. Therefore, in view of significant gaps that remain with regard to opti- mal management of patients with SVT, we must consider the role of electronic medical records, registries, and national datasets to better acquire observational data when trials are not available or feasible. Multicenter registry studies would allow for expansion of our knowledge on the best pharma- cological and nonpharmacological approaches to treat these arrhythmias. 