Emerging Doubt About Amiodarone
Intravenous amiodarone was introduced to mainstream acute care providers in the resuscitation guidelines released in 2000. It was touted as the drug of choice for treating wide complex tachycardia (WCT) of various types, especially for monomorphic ventricular tachycardia (VT). Because it suppresses ventricular conduction and also has atrioventricular nodal blocking effects, it was presumed effective for other types of WCT as well, and it quickly became the preferred therapy for all undifferentiated WCT. However, in recent years, studies have cast some doubt on the effectiveness of this drug. The most recent study of amiodarone vs the older drug procainamide has perhaps added one more nail in amiodarone's coffin.
Amiodarone vs Procainamide
Ortiz and colleagues sought to compare the efficacy of amiodarone vs procainamide in patients with hemodynamically stable, regular WCT. The exact diagnosis (eg, VT vs supraventricular tachycardia with aberrant conduction) was not the focus of the study, given that in real-world scenarios the real diagnosis is typically uncertain, and no ECG criteria have been found to be reliable in this distinction. The authors performed a multicenter, randomized, open-label study in which a total of 29 patients received amiodarone (5 mg/kg over 20 minutes) and 33 patients received procainamide (10 mg/kg over 20 minutes). The primary endpoint was the incidence of major cardiac adverse events (clinical signs of peripheral hypoperfusion, signs of acute heart failure, development of severe hypotension, tachycardia acceleration of >20 beats/min, or appearance of fast polymorphic VT) within 40 minutes after beginning the infusion. Response to treatment was defined by conversion of the WCT to the patient's known or presumed usual heart rhythm within the study period.
The primary endpoint occurred in 12/29 (41%) in the amiodarone group vs 3/33 (9%) in the procainamide group. Tachycardia termination occurred in 11 (38%) in the amiodarone group and 22 (67%) in the procainamide group. In the following 24 hours, adverse events occurred in 31% of the amiodarone group vs 18% of the procainamide group. Among 49 patients with structural heart disease, adverse events occurred more commonly in the amiodarone group as well (43% vs 11%).
This study demonstrated that procainamide was more effective and safer than amiodarone for patients with WCT, including those with structural heart disease. Although this is the first controlled prospective trial comparing procainamide vs amiodarone, this is not the first study that has cast doubt on the effectiveness of amiodarone in WCTs. Previous studies by Marill and colleagues and Tomlinson and colleagues demonstrated that amiodarone was only effective in 29% of cases of stable VT. In 2006, the American College of Cardiology, the American Heart Association, and the European Society of Cardiology endorsed procainamide as the preferred drug for stable monomorphic ventricular tachycardia; and in 2010, the American Heart Association resuscitation guidelines followed suit. With respect to irregular WCT, amiodarone is contraindicated when there is concern for atrial fibrillation with pre-excitation. For treatment and conversion of stable narrow complex atrial fibrillation as well, procainamide has received strong support and is commonly used in Canada.
Admittedly, procainamide is not a perfect drug either. Rapid administration can induce hypotension or prolongation of the QRS or QT intervals, leading to (rarely) torsades de pointes. However, the habitual use of amiodarone in patients with undifferentiated WCTs is not well-supported by the literature. Amiodarone is poorly effective in VT; and it is dangerous in pregnancy (class D), in prolonged QT conditions, and in patients with atrial fibrillation plus pre-excitation. Safer drugs are available; and, when in doubt, acute care providers should not hesitate to sedate and cardiovert patients with WCTs. It's time to let amiodarone rest in peace and, if available to you, get reacquainted with an old friend, procainamide.
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Cite this article: IV Amiodarone for WCT: Time to Say Goodbye?. Medscape. Oct 05, 2016.