Ventricular fibrillation frequency from implanted cardioverter defibrillator devices

Abstract

The dominant frequency (DF) of ventricular fibrillation (VF) provides a measure of cycle length that may relate to the underlying complexity of the arrhythmia. Dominant frequency analysis may therefore provide insights into VF mechanisms, and potentially guide future therapies. Dominant frequency analysis can be undertaken on stored electrograms (EGMs) from implanted cardioverter defibrillator devices (ICDs). Demonstration of the reproducibility of the DF during separate VF events is necessary before using this tool. We identified 82 patients receiving a Medtronic ICD who had two episodes of VF induced during ICD testing. We extracted EGMs recorded during both episodes and determined DF using the fast Fourier transform. The mean DF for the population was 4.7 +/- 0.6 Hz, corresponding to a cycle length of 213 ms. First and second episodes of VF were very highly correlated (interclass correlation = 0.87, P < 0.01) demonstrating that DF was highly reproducible. The 18 patients on Class III agents had a significantly lower DF than the remaining 63 (4.4 +/- 0.4 vs. 4.8 +/- 0.6 Hz, P < 0.01, n = 18). However, the DF of patients with ischaemic heart disease (n = 34) did not differ when compared with dilated cardiomyopathy patients (n = 25) (4.7 +/- 0.6 vs. 4.6 +/- 0.4 Hz, P = 0.3). The DF of short intervals of induced VF is highly reproducible and is sensitive to pharmacological interventions that extend effective refractory period. Such estimates of DF may therefore have clinical utility and in patients with ICDs provide a means of investigating mechanisms underlying the initiation and early phases of VF.