In some resistant cases, a second drug bolus or higher dose of initial drug agent might prove Nevertheless, in rare instances, drugs may fail to successfully restore sinus rhythm. I B-NR 5. Synchronized cardioversion should be performed for acute treatment in hemodynamically unstable patients with pre-excited AF.75,94 See Online Data Supplement 10. Synchronized cardioversion is highly effective in terminating pre-excited AF.75 When AF occurs in patients with ventricular pre-excitation, if the accessory pathway has a short refractory period, this may allow for rapid pre-excited AV conduction; the resulting fast, often irregular, broad- complex tachycardia is often unstable and may lead to ventricular fibrillation. It is therefore important to achieve early restoration of sinus rhythm in these patients. Patients often have atrial or ventricular premature complexes immediately after cardioversion that, on occasion, may induce AVRT or recurrent pre-excited AF. I C-LD or intravenous procainamide265 is beneficial for acute treatment in patients with pre-excited AF who are hemodynamically stable. See Online Data and 12. Small observational studies support the use of ibutilide or intravenous procainamide for the treatment of pre-excited AF in patients who are not Both medications can decrease ventricular rate by slowing conduction over the accessory pathway and have the additional benefit of possibly terminating AF.264,265 IIa B-R 1. Intravenous diltiazem, verapamil42,260,266,267 (Level of Evidence: B-R ), or beta blockers268 (Level of Evidence: C-LD) can be effective for acute treatment in patients with orthodromic AVRT who do not have pre-excitation on their resting ECG during sinus rhythm. C-LD See Online Data and 12. 