Impact of Recording Direction on the Amplitude Spectrum Area of the Ventricular Fibrillation Waveform: A Study on Limb and Precordial ECG-Leads

Introduction: Currently, “smart” automated external defibrillators (AEDs) are under investigation that use the ventricular fibrillation (VF) waveform to guide shock timing. Recent publications show that AED electrode placement varies greatly in clinical practice, which may affect the registered values of VF waveform characteristics. Therefore, we investigated whether recording direction influences the observed value of the most commonly assessed VF-waveform characteristic: the amplitude spectrum area (AMSA). Methods: Prospective cohort of patients who underwent defibrillation testing after implantation of an implantable cardioverter defibrillator (ICD) (2010-2013). Four-second segments of induced VF were selected prior to the ICD-shock. AMSA was calculated for bipolar and unipolar ECG-leads (I, II, V3 and V6) and reported as means ± standard deviations. Pairwise comparisons between leads were performed using paired samples t-tests. Results: We studied 180 patients, mean age 63 ± 13 years and 134/180 (74%) males. The mean AMSA was the highest in lead V3 (20.1 ± 9.3 mVHz) and the lowest in lead I (7.9 ± 3.5 mVHz). Significant differences in AMSA between ECG-leads were found between lead I and lead II, between lead I and leads V3,V6 (all p<.001) and between lead V3 and leads II,V6 (both p<.001) (Figure). No other differences were found. Conclusion: VF-waveform characteristics vary greatly with the recording direction of ECG electrodes. In an era where “smart” defibrillators are under investigation using specific cut-off values of the AMSA, these findings are of great importance. Future studies on VF-guided shock delivery should use standardized paddle placement.