In 1 small study, intravenous verapamil converted MAT in 8 of 16 patients treated.233 Alternatively, intravenous verapamil may acutely slow the ventricular response to MAT. The major potential side effect is hypotension.233 The relatively cardioselective beta blocker metoprolol can also work by slowing the ventricular rate in MAT. Beta blockers are typically avoided in patients with severe underlying pulmonary disease, particularly those with bronchospasm; both beta blockers and verapamil are typically avoided in the presence of acute decompensated heart failure and/or hemodynamic instability. The anatomic substrate of AVNRT is dual AV nodal physiology (Table 3). AVNRT is often well tolerated and is rarely life threaten- ing. Patients will typically present with the sudden onset of palpitations and possibly with shortness of breath, dizziness, and neck pulsations. Syncope is a rare manifestation of AVNRT. AVNRT may occur spontaneously or on provocation with exertion, coffee, tea, or alcohol. 5.1. Acute Treatment: Recommendations IIa C-LD 2. Metoprolol is reasonable for ongoing management in patients with recurrent symptomatic MAT.226,229,230 See Online Data and 8. Beta blockers are typically avoided in the presence of acute decompensated heart failure or in patients with severe (particularly bronchospastic) pulmonary disease. However, metoprolol has been used in small studies in patients with serious pulmonary disease after correction of hypoxia or other signs of acute decompensation. In these studies, intravenous or oral metoprolol resulted in conversion to sinus rhythm or achieved rate control, and oral metoprolol was used for maintenance therapy.226,230 Beta blockers are generally avoided in patients with severe conduction abnormalities or sinus node dysfunction. Recommendations for Ongoing Management of Multifocal Atrial Tachycardia (Continued) COR LOE Recommendations Recommendations for Acute Treatment of AVNRT COR LOE Recommendations I B-R 1. Vagal maneuvers are recommended for acute treatment in patients with AVNRT.82 84,234,235 See Online Data Supplement 10. 