Clinical Significance and Contributing Factors of Long-Term Variability in Induced Ventricular Tachyarrhythmias

Introduction: Ventricular arrhythmias induced during electrophysiologic study (EPS) may vary over time, making arrhythmia induction studies unreliable. The aim of this prospective study was to clarify the clinical significance of long‐term variability in induced arrhythmias and to elucidate factors determining this variability. Methods and Results: Three noninvasive EPSs were performed 1, 13, and 25 months after implantation of a cardioverter defibrillator in 40 patients with ventricular tachyarrhythmias, without a change in their antiarrhythmic drug regimens. The induced ventricular arrhythmias were categorized into five grades. Long‐term variability, which was defined as a variation in the grades during the three EPSs, was observed in 23 patients (group A) and not in the remaining 17 patients (group B). During the 2‐year period, spontaneous sustained ventricular arrhythmias developed in 15 patients (65%) in group A but in only 4 patients (24%) in group B (P = 0.01). Inducibility of sustained tachyarrhythmias was not associated with emergence of spontaneous arrhythmias. All patients also underwent thallium‐201 and iodine‐123‐metaiodobenzylguanidine (MIBG) scans to evaluate the extent of the regions showing normal thallium uptake with reduced MIBG uptake. Group A patients showed greater thallium/MIBG mismatched regions than did group B patients (P = 0.01). Logistic regression analysis revealed that long‐term variability (relative risk [RR] 7.55, P = 0.03), amiodarone therapy (RR 0.14, P = 0.04), and left ventricular ejection fraction