1 INTRODUCTION
An implantable cardioverter defibrillator (ICD) is currently the most
reliable therapy for preventing sudden death in patients with sustained
ventricular tachycardia (VT) associated with organic heart
disease.1-4 ICDs
can terminate life-threatening VTs by using electrical shocks, or
anti-tachycardia pacing (ATP), or both. Recent studies have shown that
electrical shocks for ventricular tachyarrhythmia may lead to a worse
prognosis, such as mortality or morbidity.5,6Therefore, it is essential to reduce the use of shock therapy to
terminate VT. Although the effectiveness of ATP therapy has been
extensively reported, 7-9 it occasionally induces VT
acceleration,10,11 or progression to
ventricular fibrillations (VFs).
Many studies on the effectiveness of ICD therapy have reported that the
cycle length defines VTs best targeted by ICD therapy. However, in
addition to cycle length, the targeted VTs are characterized by RR
interval variability (Figure 1A). Variation in the RR interval in
tachyarrhythmia distinguishes VTs from supraventricular tachycardia,
such as atrial fibrillation.12 Concerning the RR
interval variability in VT, there are few reports on the clinical
characteristics of VT or the effectiveness of ATP therapy.
This study aimed to evaluate the relationship between RR interval
variability in VTs and clinical characteristics of VT, including the
effects of ICD therapy.