The location of the circuit determines ablation approach and risks. The substrate for macroreentrant atrial arrhythmias after cardiac surgery is atrial scarring from atriotomy inci- sions and cannulation sites and from the underlying myo- pathic process of the valve disease itself; this is sometimes referred to as incisional atrial reentrant tachycardia. The location of the reentrant circuit depends on the type of surgi- cal approach, and common populations include patients who have undergone mitral valve surgery or have a repaired atrial These arrhythmias are also common after surgical or catheter ablation for AF.331,332 Both single- and dual-loop circuits, as well as focal ATs, can be present. It is useful to review the procedural notes to identify the location of atrial incisions or prior ablation that can assist with future mapping and ablation. The development of a microreentrant or macroreentrant left AT after AF ablation occurs in approximately 5% of This is less frequent if ablation is limited to pulmonary vein isolation. On the other hand, these arrhythmias Figure 13. Ongoing management of AVNRT. Colors correspond to Class of Recommendation in Table 1; drugs listed alphabetically. AVNRT indi- cates atrioventricular nodal reentrant tachycardia; pt, patient; and SHD, structural heart disease (including ischemic heart disease). Page et al 2015 ACC/AHA/HRS SVT Guideline e541 are more common in patients with longer-duration persistent AF or more dilated left atria or when linear ablation lesions Non reentrant focal arrhythmias often origi- nate at lesion edges or reconnected segments of prior isolated Reisolation of the pulmonary vein and ablation of any nonpulmonary vein foci are often effective in treating these arrhythmias. 