A 64-year-old man with hypertension and hyperlipidemia presented with palpitations. He reported intermittent symptoms over the previous three days with dyspnea on exertion but no chest pain, dizziness, or syncope. His vital signs were notable for tachycardia (heart rate, 129 bpm) without hypotension or hypoxia. An ECG showed atrial fibrillation with rapid ventricular response.
The patient's tachyarrhythmia was not yet associated with hypotension or evidence of malperfusion, but preparation is key and includes continuous telemetry and vital sign monitoring, establishing intravenous access, and applying cardioversion pads. (Ann Emerg Med. 2015;65:532; http://bit.ly/2tLgJzF.)
This patient's atrial fibrillation was new, and the rapid ventricular response (RVR) may be symptomatic of more serious and potentially reversible pathology. A thorough history and physical examination may elucidate a precipitant and should precede attempts at rate or rhythm control. RVR may be provoked by any of the processes that would otherwise induce a sinus tachycardia, including bleeding, infection, toxic and metabolic etiologies, and endocrinopathies. (Circulation. 2014;130:2071, http://bit.ly/35I1IMl; Ann Emerg Med. 2015;65:511.)
Candidacy for Cardioversion
Hemodynamically stable patients with new-onset atrial fibrillation are candidates for cardioversion if they:
- Are stable without ischemia, hypotension, or acute CHF.
- Have clear onset of less than 48 hours.
- Have symptoms that are not severe.
- Experience few prior episodes/treatments.
- Have existing anticoagulation with warfarin and therapeutic INR (at least three weeks).
- Don't have high-risk features: rheumatic/valvular disease, severe left-ventricular dysfunction, prosthetic valves, or history of thromboembolism. (CJEM. 2010;12:181; Ann Emerg Med. 2011;58:517; J Emerg Med. 2013;45:117.)
Cardioversion may be pharmacologic (with procainamide or amiodarone) or electrical (synchronized at 100-200 J). Electrical cardioversion for acute atrial fibrillation is more effective and results in shorter stays in the emergency department, though stable patients should participate in shared decision-making. (Emerg Med J. 2012;29:188.)
Another important consideration when using cardioversion is preventing systemic embolization. Atrial fibrillation of less than 48 hours is rarely associated with systemic embolization, but certain populations are at higher risk. (Ann Intern Med. 1997;126:615.) One retrospective study of 3143 patients with atrial fibrillation for less than 48 hours demonstrated an overall risk of 0.7 percent for thromboembolic events, though the rate was significantly higher in patients over 60 or with other comorbidities (heart failure, diabetes). (J Am Coll Cardiol. 2013;62:1187; http://bit.ly/2t5dsv8.) The risk of embolic events should be weighed against the risk of bleeding.
Rate control should be pursued for patients who are not candidates for cardioversion. Options include AV nodal blocking agents such as calcium channel blockers and beta-blockers. (Emerg Med Clin North Am. 2015;33:597.) The most frequently studied agents of each category are metoprolol and diltiazem. Both classes show comparable efficacy and safety profiles with trends favoring diltiazem. (Emerg Med J. 2005;22:411, http://bit.ly/2R4dwTR; J Emerg Med. 2015;49:175.)