Clinical and electrophysiological characteristics of electrical storm of monomorphic ventricular tachycardia refractory to intravenous amiodarone

Purpose: Efficacy of intravenous amiodarone (IV-AMD) is established in preventive treatment for repetitive form of monomorphic ventricular tachycardia (VT). Few reports are available on clinical characteristics of VT refractory to IV-AMD. The purpose of this study was to evaluate the incidence, clinical features, and treatment of VT refractory to IV-AMD. Methods: IV-AMD was administrated in consecutive 60 patients with VT between 2007 and 2012. Electrical storm (ES) of VT, defined as 3 or more episodes of VT within 24 hours, occurred in 30 patients (mean age, 69±11; 10 female) with 6 prior-myocardial infarction (MI), 6 acute-MI, 9 dilated cardiomyopathy, 5 hypertrophic cardiomyopathy, 2 aortic valve stenosis, and 2 post-resuscitative state. We evaluated the efficacy of IV-AMD in suppressing the ES. The clinical and electrophysiological characteristics were compared between patients with ES suppressed by IV-AMD (Effective group) and those with refractory ES (Refractory group). Results: IV-AMD controlled recurrences of VT in 22 patients (73%; Effective group). Clinical characteristics, such as underlying disease, ejection fraction, and medications were not different between in Effective group and in Refractory group. In all 8 patients of Refractory group, a QRS morphology of VT was a right bundle branch block pattern. Although there was no difference in a cycle length of VT, QRS duration of VT and QRS duration of premature ventricular contraction (PVC) followed by VT in Refractory group were narrower than in Effective group (151±32 vs. 182±33 ms; P = 0.05, 130±10 vs. 185±27 ms; P < 0.01). In a MI patient of Refractory group, an additional coronary revascularization suppressed the ES. In the remaining patients of Refractory group, an additional administration of IV-mexiletine and/or an endocardial LV catheter ablation were effective. Conclusions: ES of VT refractory to IV-AMD shows a relatively narrow QRS tachycardia originating from an LV. The narrow trigger PVC, suggesting a Purkinje fiber origin, may be treated by IV-mexiletine and catheter ablation.