Continued Drug Initial Dose Subsequent or Maintenance Dose Potential Adverse Effects Precautions (Exclude or Use With Caution) and Interactions whereas microreentrant ATs from other locations generally will not be terminated by these drugs. Sinus node reentrant tachycardia is an uncommon type of focal AT that involves a microreentrant circuit in the region of the sinoatrial node, causing a P-wave morphology that is identical to that of sinus tachycardia (although this is not sinus tachycardia). Characteristics that distinguish sinus node reen- try from sinus tachycardia are an abrupt onset and termination and often a longer RP interval than that observed during nor- mal sinus rhythm. Sinus node reentry is characterized by par- oxysmal episodes of tachycardia, generally 100 bpm to 150 Confirmation of the reentrant mechanism requires an EP study. Induction of sinus node reentrant tachycardia during programmed stimulation, demonstration of entrain- ment, and localization of the tachycardia origin in the region of the sinus node are necessary to confirm the diagnosis. 4.1.1. Acute Treatment: Recommendations RCTs of drug therapy for comparative effectiveness in patients with focal AT in the acute setting are not avail- able. Many of the clinical outcomes are reported from small observational studies that included infants or pediatric The design or execution of these studies is frequently suboptimal because of the poorly defined inclu- sion criteria or variable clinical settings. Several studies included a mix of patients with congenital or postoperative AT, and some of these patients likely had macroreentrant AT. In many reports, the response to intravenous drug therapy was evaluated by EP study rather than in the clinical envi- In the clinical setting, if the diagnosis is uncertain, vagal maneuvers may be attempted to better iden- tify the mechanism of SVT. Digoxin has not been well studied for focalAT. 