Nonetheless, symptoms commonly recur after several months, with IST recurrence in up to 27% and overall symptomatic recurrence (IST or non- IST AT) in 45% of patients.177,179,180,182 Complications can be significant and may include symptomatic sinus or junctional bradycardia necessitating pacemaker placement, phrenic nerve injury with paralysis of the right hemidiaphragm, and significant facial and upper-extremity swelling caused by narrowing of the superior vena cava/RA junction, which may rarely result in superior vena cava syndrome. In view of the modest benefit of this procedure and its potential for sig- nificant harm, sinus node modification should be considered only for patients who are highly symptomatic and cannot be adequately treated by medication, and then only after inform- ing the patient that the risks may outweigh the benefits of ablation. Even more aggressive surgical methods to ablate or denervate the sinus node have been described, further high- lighting the risks that highly symptomatic patients are willing to accept to find relief.184 Effective patient communication is key for these patients. Figure 9. Ongoing management of SVT of unknown mechanism. Colors correspond to Class of Recommendation in Table 1; drugs listed alpha- betically. *Clinical follow-up without treatment is also an option. EP indicates electrophysiological; pt, patient; SHD, structural heart disease (includ- ing ischemic heart disease); and SVT, supraven- tricular tachycardia. Page et al 2015 ACC/AHA/HRS SVT Guideline e523 4. Nonsinus Focal Atrial Tachycardia and MAT See Figure 10 for the algorithm for acute treatment of sus- pected focal atrial tachycardia (AT) and Figure 11 for the algorithm for ongoing management of focal AT. 4.1. Focal Atrial Tachycardia Focal AT is characterized as a fast rhythm from a discrete ori- gin, discharging at a rate that is generally regular, and con- ducting in a centrifugal manner throughout the atrial tissue. 