Abstract 2301: Ventricular Fibrillation Initiation in MADIT II Patients With Implantable Defibrillators
OBJECTIVE: The study’s goal was to determine the most common pattern of initiation of ventricular fibrillation (VF) in Multicenter Automatic Defibrillator Implantation Trial (MADIT) II patients with ICDs and to assess whether these patterns had distinct ECG and clinical characteristics.
METHODS: Sixty episodes of VF occurred in 29 patients (mean age of 64.4 +/−2.5 years). Examination of stored electrograms enabled us to evaluate the rhythm and coupling intervals directly preceding each episode of VF and to calculate the following (intracardiac) ECG parameters: mean RR interval from the beats preceding VF, coupling interval of the initiating beat, prematurity index (coupling interval divided by the preceding RR interval), QT, QTp, and the T amplitude for the last sinus or atrial fibrillation beat preceding VF.
RESULTS: The 60 VF episodes were initiated most frequently with a ventricular premature beat (VPB) (n=46 or 77%) whereas, a short-long-short (SLS) RR interval sequence accounted for the remainder (n=14 or 23%). Of the 29 patients, 23 had only VF episodes initiated by a VPB, 2 patients with SLS only, and 4 patients with both VPB and SLS-initiated episodes. There were no significant differences between VPB and SLS-initiated episodes of VF in regards to the measured ECG parameters. Episodes of VF occurred at normal heart rates (mean RR prior to VF of 744 +/− 222 ms for VPB patients and 655+/− 104 ms for SLS patients, P=0.06). Paced beats were rare prior to the onset of VF. Clinically, VPB-type patients were on beta-blockers (83% vs. 0%; P<0.001), statins (78% vs. 0%; P<0.001), and other lipid-lowering agents (78% vs. 0%; P<0.001) at baseline in contrast to SLS-type patients. There were no significant differences in the use of other antiarrhythmics, rates of underlying heart disease, or other comorbidities.
CONCLUSIONS: Ventricular fibrillation is more commonly initiated by a VPB than by a SLS sequence among the MADIT II cohort with ICDs. A large number of patients experienced VPB-initiated episodes of VF despite beta-blocker therapy. Preceding heart rate tended to be higher for SLS initiation possibly due to absence of beta-blocker therapy. These findings may contribute to the development of algorithms for the prevention of VPB and SLS-initiated episodes of VF.