The short long short trigger of ventricular arrhythmias: Analysis of the sudden cardiac death in heart failure trial

Introduction: Rhythm disturbances prior to onset of monomorphic ventricular tachycardia (VT) or ventricular fibrillation (VF) may be important in understanding triggers of fatal arrhythmias. A short long short (SLS) cycle length initiation of ventricular arrhythmias has previously been observed. The frequency and significance however is unknown. We sought to quantitate the frequency of SLS initiating VT or VF in the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT). Methods: The trial randomized 2521 subjects with moderate heart failure and reduced left ventricular function to an ICD, amiodarone, or placebo. An ICD was implanted in 811 of 829 pts randomized to receive a device. ICDs were programmed single zone shock therapy with a detection of > 188 bpm. Pacing was programmed 50 bpm (hysteresis of 34 bpm). Electrograms were examined for sustained VT or VF episodes receiving ICD shock therapy. A SLS was defined as a sinus-ventricular premature beat (VPB)-sinus sequence with the next beat as the first in the cycle of VF/VT. The terminal beat following the long cycle was examined for native vs. paced morphology. The short cycle is defined as a sinus-VPB coupling interval 100ms shorter than the sinus rhythm cycle length (CL) and the long cycle as a VBPPO01 sinus coupling interval 100 ms longer. Comparisons between VT and VF groups were made using Pearson's chi-square test. Results: Over a 45.5 month median follow-up, 182 subjects received at least one shock for 744 episodes of VT or VF. A total of 490 episodes of VT and 254 episodes of VF were examined. A SLS preceded VT in 49 of 490 VT episodes (10%) and in 60 of 254 VF episodes (24%) [p <0.0001]. A paced beat was the terminal beat in 1 of 49 VT episodes (2%) and 10 of 60 VF episodes (17%) [p=0.014]. Conclusions: A minority of VT but nearly a quarter of VF episodes were preceded by a SLS sequence. SLS was more strongly associated with ICD shocks for VF compared to VT in patients with moderate heart failure. A paced beat as the terminal beat of the SLS sequence occurred rarely and was more likely to precede VF shocks than VT. Whether or not ICD algorithms to reduce SLS sequences will prevent sudden death from VF is unknown.